BASICS OF PACEMAKER DN.

BASICS OF PACEMAKER DN

First pacemaker patient
HISTORY 1958 – Senning and Elmqvist Asynchronous (VVI) pacemaker implanted by thoracotomy and functioned for 3 hours Arne Larsson First pacemaker patient Used 23 pulse generators and 5 electrode systems Died 2001 at age 86 of cancer 1960 – First atrial triggered pacemaker 1964 – First on demand pacemaker (DVI) 1977 – First atrial and ventricular demand pacing (DDD) 1981 – Rate responsive pacing by QT interval, respiration, and movement 1994 – Cardiac resynchronization pacing

A Pacemaker System consists of a Pulse Generator plus Lead (s)
What is a Pacemaker? A Pacemaker System consists of a Pulse Generator plus Lead (s)

Implantable Pacemaker Systems Contain the Following Components:
Pulse generator- power source or battery Leads Cathode (negative electrode) Anode (positive electrode) Body tissue Lead IPG In a bipolar system, body tissue is part of the circuit only in the sense that it affects impedance (at the electrode-tissue interface). In a unipolar system, contact with body tissue is essential to ground the IPG and allow pacing to occur. Anode Cathode S

The Pulse Generator Contains a battery that provides the energy for sending electrical impulses to the heart Houses the circuitry that controls pacemaker operations Lithium-iodine is the most commonly used power source for today’s pacemakers. Microprocessors (both ROM and RAM) control sensing, output, telemetry, and diagnostic circuits. Circuitry Battery

The Pulse Generator Casing (can) Connector (header) Components Battery
Titanium (biocompatible, lightweight, stronger than steel) Connector (header) Leads plug into ports in the clear epoxy header Components Diodes, resistors, oscillator, microchips Battery The largest single component inside the pulse generator Lithium iodide The casing (or can) of the pacemaker is made out of titanium, a very light metal that has two great qualities: it is biocompatible and stronger than steel. The connector block (sometimes called the lead connection or the header) is the clear epoxy top of the pulse generator. The connector will have one or more ports into which the leads plug. There are tiny “feedthroughs” or wires from the ports into the hermetically sealed interior of the casing so that electricity from within the pulse generator can travel through the leads. Every pulse generator contains numerous components; a pulse generator is really a mini-computer and contains chips, diodes, resistors, and so on. Today’s pulse generator batteries are lithium-iodine. They last a long time (10 years or more) and have a very predictable discharge curve, that is, they wear out gradually in a way that is easy to predict (rather than abruptly).

Anatomy of a Pacemaker Resistors Atrial connector Connector
Ventricular connector Defibrillation protection Output capacitors Hybrid Clock Reed (Magnet) switch Telemetry antenna Battery

General Characteristics of Pacemaker Batteries
Hermeticity, as defined by the pacing industry, is an extremely low rate of helium gas leakage from the sealed pacemaker container low rate of self-discharge lithium iodine -a long shelf life and high energy density DDD drains a battery more rapidly

Power source Longevity in single chamber pacemaker is 7 to 12 years.
For dual chamber longevity is 6 to 10 years. Most pacemakers generate 2.8 v in the beginning of life which becomes 2.1 to 2.4 v towards end of life.

halving of output voltage increases the longevity of battery by almost twice the number of years.

Simplified model of a lithium iodine battery
The open-circuit voltage of 2.8 V is characteristic of lithium iodine chemistries. The series resistance increases from 100 W at beginning of battery life (BOL) to more than 10,000 W at end of life (EOL).

Leads Deliver electrical impulses from the pulse generator to the heart Sense cardiac depolarisation Lead

Pacing Lead Components
Conductor Connector Pin Insulation Electrode This slide illustrates the essential components of a pacing lead. The following topics will be discussed for each component: · Purpose · Design factors · Performance factors Tip Electrode Conductor Insulation Connector Pin

Lead Characterization
Position within the heart Endocardial or transvenous leads Epicardial leads Fixation mechanism Active/Screw-in Passive/Tined Shape Straight J-shaped used in the atrium Polarity Unipolar Bipolar Insulator Silicone Polyurethane Student Notes We characterize and describe leads based on their: Position Fixation mechanism Polarity Insulator Shape Instructor Notes

Lead components Conductor Connector Pin Insulation Electrode

Transvenous Leads - Fixation Mechanisms

Fixation mechanisms of the Electrode
Passive fixation Wingtips Active fixation Screw Active fixation Tines

Passive fixation The tines become lodged in the trabeculae

Active Fixation The helix (or screw) extends into the endocardial tissue Allows for lead positioning anywhere in the heart’s chamber For smooth-walled hearts or those that lack trabeculation, or in patients that have had a previous CABG procedure, active fixation leads may be a better choice to prevent lead dislodgment. The lead pictured on top is a fixed screw design. Those pictured at the bottom have an extendable/retractable helix.

Myocardial and Epicardial Leads
Leads applied directly to the heart Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Epicardial or myocardial leads are implanted to the outside of the heart. These implants represent less than 5% of leads implanted, and are used primarily in pediatric cases or for patients in whom transvenous lead implant is contraindicated.

Active Fixation Passive Fixation Advantages Easy fixation
Easy to reposition Lower rate of dislodgement Removability Less expensive & simple Minimal trauma to patient Lower thresholds Disadvantages More expensive >Complicated implantation Higher rate of dislodgement (>a/c) Difficult to remove chronic lead

Cathode:-An electrode that is in contact with the heart
Negatively charged Anode:-receives the electrical impulse after depolarization of cardiac tissue Positively charged when electrical current is flowing Presenter Note: Explain that the system presented here is a bipolar system: the anode for a unipolar system is actually the IPG itself. Note that this topic will be covered in more detail within the next few minutes. Anode Cathode

+ - Flows through the tip electrode (cathode) Stimulates the heart
A Unipolar Pacing System Contains a lead with an electrode in the heart Flows through the tip electrode (cathode) Stimulates the heart Returns through body fluid and tissue to the PG (anode) + Anode In the unipolar system, the impulse: Travels down the lead wire to stimulate the heart at the tip electrode also referred to as the cathode (–) Returns to the metal casing of the impulse generator or the anode (+) by way of body fluids The flow of the impulse makes a complete circuit. - Cathode

A Bipolar Pacing System Contains a lead with 2 electrodes in the heart
Flows through the tip electrode located at the end of the lead wire Stimulates the heart Returns to the ring electrode above the lead tip The impulse: Travels down the lead wire to stimulate the heart at the tip electrode, which is the cathode (–) Travels to the ring electrode, which is the anode (+), located several inches above the lead tip Returns to the pulse generator by way of the lead wire Anode Cathode

Unipolar leads One electrode on the tip & one conductor coil
Conductor coil may consist of multiple strands - (multifilar leads) Unipolar leads have a smaller diameter than bipolar leads Unipolar leads exhibit larger pacing artifacts on the surface ECG Lead technology is advancing such that unipolar and bipolar leads will have smaller French sizes than those currently available. Depending on the monitoring equipment, unipolar pacing usually exhibits a larger pacing spike on some surface ECGs.1 1Ellenbogen KA, et al. Clinical Cardiac Pacing. London: WB Sanders Company; Page 71.

Bipolar leads Circuit is tip electrode to ring electrode
Two conductor coils (one inside the other) Inner layer of insulation Bipolar leads are typically thicker than unipolar leads Bipolar leads are less susceptible to oversensing noncardiac signals (myopotentials and EMI) While unipolar and bipolar leads look similar (both have the appearance of one wire), most bipolar leads have a coaxial design, meaning an inner wire is insulated and wrapped with an outer wire, giving the lead the appearance of having only one wire. Bipolar leads are less susceptible to oversensing noncardiac signals as the spacing of the two electrodes (located in close proximity to one another) accounts for a much lower incidence of sensing extra-cardiac signals. Coaxial Lead Design

Unipolar Bipolar Advantages Smaller diameter Easier to implant
Large spike No pocket stimulation Less susceptible to EMI Programming flexibility Disadvantages Pocket stimulation Far-field oversensing No programming flexibility Larger diameter Stiffer lead body Small spike Higher impedance Voltage threshold is 30% higher When it comes to unipolar versus bipolar leads, there are pros and cons to both types. Unipolar leads are smaller in diameter because they only have one coil; this makes them more reliable (or at least, that is the perception based on the fact that one coil is more robust than two) and the smaller size makes them easier to implant. Most clinicians prefer the big spike that unipolar devices make on an ECG. However, the large unipolar antenna that creates that spike can stimulate the surrounding tissue (pocket stimulation). Sometimes a unipolar lead is “picked up” by the opposite chamber, for instance a ventricular pacing spike is sensed by the atrial lead and inappropriately interpreted as an intrinsic atrial event (this phenomenon is sometimes call far-field oversensing, far-field R-wave sensing, far R, or crosstalk). Finally, a unipolar lead can only ever be a unipolar lead; it is not possible to program a unipolar lead to a bipolar pacing or sensing configuration because the lead only has one electrode to work with. Bipolar leads have a smaller antenna, which produces both a smaller pacing spike (hard to see on some ECGs) but less pocket stimulation. The small antenna makes the bipolar lead less susceptible to electromagnetic interference (EMI). The presence of two electrodes on the leads means that the clinician can reprogram a bipolar lead to a unipolar configuration, if desired. The main drawbacks to a bipolar lead are the fact that the lead is usually thicker in diameter and the dual coils can make the lead seem more rigid and harder to implant.

Best distance is 1 cm for bipolar.
Unipolar vs bipolar Size Higher impedance for bipolar Same current threshold Voltage threshold is 30% higher for bipolar Unipolar may oversense and bipolar may undersense Skeletal muscle stimulation Stimulus Artifact Amplitude – observer and ICD implications Best distance is 1 cm for bipolar. Smaller tip- lower threshold for pacing, offset later by polarisation. Ideal impedance is 400 to 1,200 ohms.

Electrodes Leads have 1/> electrically active surfaces referred to as the electrodes Deliver an electrical stimulus, detect intrinsic cardiac electrical activity, or both Electrode performance can be affected by Materials Polarization Impedance Pacing thresholds Steroids It is also important to understand the design and nature of the electrodes themselves since this has a powerful impact on device system performance.

Electrode Materials The ideal material for an electrode
Porous (allows tissue ingrowth) Should not corrode or degrade Small in size but have large surface area Common materials Platinum and alloys (titanium-coated platinum iridium) Vitreous carbon (pyrolytic carbon) Stainless steel alloys such as Elgiloy An electrode should be made of a porous material, since this will allow tissue ingrowth, which secures the lead in place. The metal in the electrode should conduct electricity well but should not corrode or degrade. An ideal lead is relatively small in size but has a large surface area. These seemingly contradictory conditions are met by electrodes with a highly textured surface (see picture). Today, St. Jude Medical makes electrodes using titanium-coated platinum iridium which is a platinum alloy. Other electrode materials include vitreous carbon, that is, heat-treated carbon, and alloys of stainless steel such as Elgiloy (which is actually made of cobalt, iron, chromium, molybdenum, nickel and manganese).

Voltage Voltage is the force that causes electrons to move through a circuit In a pacing system, voltage is: Measured in volts Represented by the letter “V” Provided by the pacemaker battery Referred to as amplitude The terms “amplitude” and “voltage” are often used interchangeably, undoubtedly to express “Voltage Amplitude” which refers to the voltage output.

Current The flow of electrons in a completed circuit
In a pacing system, current is: Measured in mA (milliamps) Represented by the letter “I” Determined by the amount of electrons that move through a circuit Current: Measured in amperes (I) 1 Ampere =1000 milliamps Movement of electricity or free electrons through a circuit One ampere is a unit of electrical current produced by 1 volt acting through a resistance of 1 ohm

Constant-Voltage and Constant-Current Pacing
Most permanent pacemakers are constant-voltage pacemakers Voltage and Current Threshold Voltage threshold is the most commonly used measurement of pacing threshold

“Consistently” refers to at least ‘5’ consecutive beats
Defined as the minimum amount of electrical energy required to consistently cause a cardiac depolarization “Consistently” refers to at least ‘5’ consecutive beats Low thresholds require less battery energy Pacing Thresholds Capture Non-Capture

The Strength-Duration Curve
The strength-duration curve illustrates the relationship of amplitude and pulse width Values on or above the curve will result in capture .50 1.0 1.5 2.0 .25 Stimulation Threshold (Volts) Capture The strength-duration curve illustrates the tradeoff of amplitude (intensity of stimulation, measured in volts) and duration (the length of time the stimulation is applied, measured in milliseconds). Capture occurs when the stimulus causes the tissue to react. On the graph, capture occurs on or above the curve. Anything below the curve will not capture. The lowest voltage on a stimulation curve which still results in capture at an infinitely long pulse duration is called rheobase. A voltage programmed below is inefficient and will lead to non-capture. The pulse duration at twice the rheobase value is defined as the chronaxie. Chronaxie time is typically considered most efficient in terms of battery consumption. 0.5 1.0 1.5 Duration Pulse Width (ms)

Strength-Duration Curve

Rheobase- (the lowest point on the curve) by definition is the lowest voltage that results in myocardial depolarization at infinitely long pulse duration Chronaxie(pulse duration time ) by definition, the chronaxie is the threshold pulse duration at twice the rheobase voltage

typical pulse width setting is 0.5 msec
chronaxie point is two times the rheobase a moderately high impedance with a good threshold leads to an ideal situation in which the heart is easily paced with a minimum number of electrons (i.e., less battery drain). anxiety related to pacemaker insertion can increase levels of circulating catecholamines, causing lower thresholds lowest threshold (acute threshold) at the time of implantation 2 to 6 weeks, the threshold rises to its highest level -edema and inflammation Then falls- fibrous tissue- electric charge is now less dispersed- impedance remains unchanged. Very low impedance leads to a high current for every paced beat and more electrons are expended per paced beat because of the low impedance. An extremely high impedance would make it impossible to pace

Lessons from SDC The ideal pulse duration should be greater than the chronaxie time Cannot overcome high threshold exit block by increasing the pulse duration, If the voltage output remains less than the rheobase Energy (μJ) = Voltage (V) × Current (mA) × Pulse Duration (PD in ms). Charge (μC) = Current (mA) × Pulse Duration (ms).

At very low pulse width thresholds, the charge is low, but the energy requirements are high because of elevated current and voltage stimulation thresholds. At pulse durations of 0.4–0.6 ms, all threshold parameters - ideal At high pulse durations, the voltage and current requirements may be low, but the energy and charge values are unacceptable

-Safety margins -When a threshold is determined by decrementing the pulse width at a fixed voltage At a given voltage where the pulse width value is < .30 ms: Tripling the pulse width will provide a two-time voltage safety margin. Daily fluctuations in threshold that can occur due to eating, sleeping, exercise, or other factors - a/c pacing system - higher safety margin, due to the lead maturation process- occur within the first 6-8 weeks following implant. (Pulse widths at a given voltage value which are >.30 ms are not typically selected, because they are less efficient (expend more energy), while not providing further safety. In this case, the voltage should be doubled to provide a two-time safety margin.)

Changes in stimulation threshold (voltage or current) following implantation
of a standard nonsteroid-eluting electrode

Impedance The opposition to current flow
In a pacing system, impedance is Measured in ohms Represented by the letter “R” (W for numerical values) The measurement of the sum of all resistance to the flow of current Resistance is a term used to refer to simple electric circuits without capacitors and with constant voltage and current Impedance is a term used to describe more complex circuits with capacitors and with varying voltage and current Impedance is the sum of all resistance to the flow of current. The resistive factors to a pacing system include: Lead conductor resistance The resistance to current flow from the electrode to the myocardium Polarization impedance, which is the accumulation of charges of opposite polarity in the myocardium at the electrode-tissue interface. Resistance is a term used to refer to simple electric circuits without capacitors and with constant voltage and current. Impedance is a term used to describe more complex circuits with capacitors and with varying voltage and current. Therefore, the use of the term impedance is more appropriate than resistance when discussing pacing circuits.

Impedance Pacing lead impedance typically stated in broad ranges, i.e. 300 to 1500 Ω Factors that can influence impedance Resistance of the conductor coils Tissue between anode and cathode The electrode/myocardial interface Size of the electrode’s surface area Size and shape of the tip electrode Impedance in pacing is defined as everything that opposes the flow of current through a circuit. Although in strict engineering terminology, resistance and impedance are different things, in pacing the terms are used interchangeably. It is important to know a pacing lead’s impedance because it can be an early indicator of possible lead problems. Lead impedance is a measured value; you cannot adjust it. Lead manufacturers state acceptable impedance values in broad ranges rather than as specific values because many things can impact lead impedance.

Ohm’s Law is a Fundamental Principle of Pacing That:
Describes the relationship between voltage, current, and resistance V I R V = I X R I = V / R R = V / I Can be expressed in three ways: V = I x R R = V ÷ I I = V÷ R If any two values are known, the third may be calculated (cover the value you are seeking and the others appear in the appropriate format to calculate the unknown value). x

When Using Ohm’s Law You Will Find That:
If you reduce the voltage by half, the current is also cut in half If you reduce the impedance by half, the current doubles If the impedance increases, the current decreases

Resistance and Current Flow
“Normal” resistance “Low” resistance Resistance affects current flow. Leads with an insulation breach, such as the garden hose pictured in the middle, will measure a low resistance reading with a resultant high current flow, and possible premature battery depletion. Conversely, if there is a high resistance, such as a lead conductor break, the current flow will be low or non-existent. High current flow “High” resistance Low current flow

Voltage and Current Flow
Spigot (voltage) turned up (high current drain) Using the garden hose as an analogy, the higher the voltage, the greater the push, or “flow” of electrons (and the greater the current drain). Spigot (voltage) turned low (low current drain)

Impedance and Electrodes
Large electrode tip Threshold ↑ Impedance ↓ Polarization ↓ Small electrode tip Threshold ↓ Impedance ↑ Polarization ↑ One thing that affects impedance is the size of the tip electrode. Impedance will typically decrease with a small electrode but increase with a larger one.

Polarization After an output pulse, positively charged particles gather near the electrode. The amount of positive charge is Directly proportional to pulse duration Inversely proportional to the functional electrode size (i.e. smaller electrodes offer higher polarization) Polarization effect can represent 30–40% of the total pacing impedance As high as 70% for smooth surface, small surface area electrodes

Within the electrode, current flow is due to movement of electrons (e−).
At the electrode–tissue interface, the current flow becomes ionic & (-) vely charged ions (Cl−, OH−) flow into the tissues toward the anode leaving behind oppositely charged particles attracted by the emerging electrons. It is this capacitance effect at the electrode tissue interface, that is the basis of polarization

Lead Maturation Process
Fibrotic “capsule” develops around the electrode following lead implantation 3 phases A/c phase, where thresholds immediately following implant are low Peaking phase- thresholds rise and reach their highest point(1wk) ,followed by a ↓ in the threshold over the next 6 to 8 wks as the tissue reaction subsides C/c phase- thresholds at a level higher than that at implantation but less than the peak threshold Trauma to cells surrounding the electrode→ edema and subsequent development of a fibrotic capsule. Inexcitable capsule ↓ the current at the electrode interface, requiring more energy to capture the heart. There are three phases that make up the lead maturation process: The acute phase, where thresholds immediately following implant are low The peaking phase, where thresholds rise and reach their highest point, usually around one week post-implant; followed by a decline in the threshold over the next 6 to 8 weeks1 as the tissue reaction subsides. The chronic phase, where thresholds assume a stable reading to a level somewhat higher than that at implantation but less than the peak threshold.1 The lead maturation process occurs due to the trauma to cells surrounding the electrode, which causes edema and subsequent development of a fibrotic capsule. The inexcitable capsule reduces the current at the electrode interface, requiring more energy to capture the heart. 1Hayes DH et al. Cardiac Pacing and Defibrillation: A Clinical Approach. Armonk, NY: Futura Publishing Company; Page 7.

Steroid Eluting Leads Steroid eluting leads reduce the inflammatory process and thus exhibit little to no acute stimulation threshold peaking and low chronic thresholds Porous, platinized tip for steroid elution Steroid eluting leads reduce inflammation by employing a capsule of dexamethasone sodium phosphate, which gradually emits steroid over time, nearly eliminating the peaking phenomenon of the lead maturation process. Tines for stable fixation Silicone rubber plug containing steroid

Lead Maturation Process
Effect of Steroid on Stimulation Thresholds Implant Time (Weeks) Textured Metal Electrode Smooth Metal Electrode 1 2 3 4 5 Steroid-Eluting Electrode 7 8 9 10 11 12 Volts This graph compares the stimulation thresholds of contemporary pacing leads. Older electrodes exhibited higher threshold peaking than that of steroid leads shown on the slide. The different types of electrodes exhibit a wide range of threshold peaking. Steroid-eluting electrodes continue to show lower chronic stimulation thresholds and no significant peaking. Threshold changes are shown here over a 12-week period post-implant, where a comparison is made between: • smooth metal electrode • textured metal electrode • steroid-eluting electrode Traditionally, implant stimulation thresholds are relatively low. Non-steroid-eluting electrodes exhibit a peaking phase from week 1 to approximately week 6, due to the maturation process at the electrode-tissue interface. Steroid-eluting electrodes exhibit virtually no peaking. The chronic phase of stimulation threshold occurs 8-12 weeks post-implant which is characterized by a plateau. This plateau is higher than the acute phase, due to fibrotic encapsulation of the electrode. Steroid-eluting lead chronic thresholds remain close to implant values. 3 6 Pulse Width = 0.5 msec

Sensing Sensing is the ability of the pacemaker to detect an intrinsic depolarization Pacemakers sense cardiac depolarization by measuring changes in electrical potential of myocardial cells between the anode and cathode

An Electrogram (EGM) is the Recording of Cardiac Waveforms Taken From Within the Heart
Intrinsic deflection on an EGM occurs when a depolarization wave passes directly under the electrodes Two characteristics of the EGM are: Signal amplitude(mv) Slew rate(v/sec) Electrograms are generated by the difference in electrical potential between the two electrodes. The intracardiac EGM is characterized in clinical practice in terms of its amplitude (measured in millivolts), and slew rate (measured in volts per second).1 1Ellenbogen, KA, et al. Clinical Cardiac Pacing London: WB Saunders Company; Page 41.

Intrinsic R wave Amplitude
Typical intrinsic R wave amplitude measured from pacing leads in the Right Ventricle are more than 5 mV in amplitude Intrinsic R wave in EGM Amplitude The Intrinsic R wave amplitude is usually much greater than the T wave amplitude

Slew Rate of the EGM Signal Measures the Change in Voltage with Respect to the Change in Time
The longer the signal takes to move from peak to peak: The lower the slew rate The flatter the signal Higher slew rates translate to greater sensing Measured in volts per second Change in voltage Slew rate= Time duration of voltage change Voltage Slope Typically, slew rate measurements at implant should exceed .5 volts per second for P waves; .75 volts per second for R wave measurements. Time Slew rate measurements at implant should exceed .5 volts per second for P waves; .75 volts per second for R wave measurements

Factors That May Affect Sensing Are:
Lead polarity (unipolar vs. bipolar) Lead integrity Insulation break Wire fracture EMI – Electromagnetic Interference

Scheduled pace delivered Intrinsic beat not sensed
Undersensing . . . Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately Scheduled pace delivered Intrinsic beat not sensed VVI / 60

Oversensing VVI / 60 ...though no activity is present Marker channel shows intrinsic activity... An electrical signal other than the intended P or R wave is detected Oversensing will exhibit pauses in single chamber systems. In dual chamber systems, atrial oversensing may cause fast ventricular pacing without P waves preceding the paced ventricular events.

Signal Amplitude / Slew Rate
Pacemaker Implantation Signal Amplitude / Slew Rate Signal

Rate Programmability The pacemaker function most commonly programmed is rate

Pulse-Width Programmability

Voltage Programmability

Refractory Period Programmability

Hysteresis Programmability

NASPE/ BPEG Generic (NBG) Pacemaker Code
Chamber Paced II Sensed III Response to Sensing IV Programmable Functions/Rate Modulation V Antitachy Function(s) P: Simple programmable V: Ventricle V: Ventricle T: Triggered P: Pace M: Multi- programmable A: Atrium A: Atrium I: Inhibited S: Shock D: Dual (A+V) D: Dual (A+V) D: Dual (T+I) C: Communicating D: Dual (P+S) The first letter refers to the chamber(s) being paced The second letter refers to the chamber(s) being sensed The third letter refers to the pacemaker’s response to a sensed event: T = Triggered D = Dual (inhibited and triggered*) I = Inhibited O = No response *In a single chamber mode, “triggered” means that when an intrinsic event is sensed, a pace is triggered immediately thereafter. In a dual chamber mode, “triggered” means that a sensed atrial event will initiate (trigger) an A-V delay. The fourth letter denotes the pacemaker’s programmability and whether it is capable of rate response: P = Simple Programmable (rate and/or output) M = Multiprogrammable (rate, output, sensitivity, etc.) C = Communicating (pacemaker can send/receive information to/from the programmer) R = Rate Modulation O = None Note that this sequence is hierarchical. In other words, it is assumed that if a pacemaker has rate modulation capabilities, “R”, that it also can communicate, “C”. The fifth letter represents the pacemaker’s antitachycardia functions: P = Pace D = Dual (pace and shock available) S = Shock O = None You may want to test the audience by having them describe different pacing modes. More modes and ECG strips are found in Module 2. O: None O: None O: None R: Rate modulating O: None S: Single (A or V) S: Single (A or V) O: None

Pacemaker Timing Pacing Cycle : Time between two consecutive events in the ventricles (ventricular only pacing) or the atria (dual chamber pacing) Timing Interval : Any portion of the Pacing Cycle that is significant to pacemaker operation e.g. AV Interval, Ventricular Refractory period

Single-Chamber Timing

Single Chamber Timing Terminology
Lower rate Refractory period Blanking period Upper rate Single chamber timing has three components: Lower rate interval Refractory period Blanking period Single chamber devices that are programmed to a rate responsive mode add a fourth component, the upper rate interval.

Lower Rate Interval Defines the lowest rate the pacemaker will pace
The lower rate defines the lowest rate that the pacemaker will pace. For example, if the lower rate is programmed to 60 ppm in the VVI mode, the pacemaker is required to pace at a rate of 60 ppm if the patient's intrinsic ventricular rate is less than 60 bpm. A paced or non-refractory sensed event restarts the rate timer at the programmed rate. VP VVI / 60

Refractory Period Interval initiated by a paced or sensed event
Designed to prevent inhibition by cardiac or non-cardiac events Events sensed in the refractory period do not affect the Lower Rate Interval but start their own Refractory Periods Lower Rate Interval During refractory periods, the pacemaker “sees” but is unresponsive to any signals. This is designed to avoid restarting the lower rate interval in the event of oversensing. T-wave oversensing in VVI and AAI modes will occur if refractory periods are too short. In the AAI mode, the pacemaker may even sense the QRS complex (“far-field R wave”) if the refractory period is not long enough. Events that fall into the refractory period are sensed by the pacemaker (the marker channel will display a “SR” denoting ventricular refractory or atrial refractory in single chamber systems) but the timing interval will remain unaffected by the sensed event. A refractory period is started by a paced, non-refractory, or refractory sensed event. VP VVI / 60 Refractory Period

Blanking Period The first portion of the refractory period
Pacemaker is “blind” to any activity Designed to prevent oversensing of pacing stimulus/depolarisation Lower Rate Interval A paced or sensed event will initiate a blanking period. Blanking is a method to prevent multiple detection of a single paced or sensed event by the sense amplifier (e.g., the pacemaker detecting its own pacing stimuli or depolarization, either intrinsic or as a result of capture). During this period, the pacemaker is "blind" to any electrical activity. A typical blanking period duration in a single-chamber mode is 100 msec*. Note: In Thera and Kappa devices, nonprogrammable blanking parameters are dynamic (ranging from ms) depending on the strength/duration of the paced or sensed signal. VP VVI / 60 Blanking Period Refractory Period

Physiologic Classification of Sensors- rate adaptive
Primary Physiologic factors that modulate sinus function Catecholamine level, Autonomic nervous system activity Secondary Physiologic parameters that are the consequence of exercise QT, respiratory rate Minute ventilation,temperature pH, stroke volume, Preejection interval, SVO2 Peak endocardial acceleration Tertiary External changes that result from exercise Vibration Acceleration

Upper Sensor Rate Interval
Defines the shortest interval (highest rate) the pacemaker can pace as dictated by the sensor (AAIR, VVIR modes) Limit at which sensor-driven pacing can occur Lower Rate Interval Upper Sensor Rate Interval The upper sensor rate interval in single chamber pacing is available only in rate-responsive modes. The upper rate defines the limit at which sensor-driven pacing can occur. VP VVIR / 60 / 120 Blanking Period Refractory Period

Lower Rate Interval-60 ppm
Hysteresis Allows the rate to fall below the programmed lower rate following an intrinsic beat lower rate limit is initiated by a paced event, while the hysteresis rate is initiated by a non-refractory sensed event. Lower Rate Interval-60 ppm Hysteresis Rate-50 ppm Hysteresis allows the sensed intrinsic rate to decrease to a value below the programmed lower rate before pacing resumes. Hysteresis provides the capability to maintain the patient's own heart rhythm as long as possible, while pacing at a faster rate if the intrinsic rhythm falls below the hysteresis rate. The hysteresis rate is always < the lower rate limit. The lower rate limit is initiated by a paced event, while the hysteresis rate is initiated by a non-refractory sensed event. In the example above, the lower rate limit is 60 ppm (1000 ms), while the hysteresis rate is 50 ppm (1200 ms). The patient is paced at 60 ppm until an intrinsic event occurs, and an interval of 1200 ms is started. This patient did not have another sensed event, so a ventricular pace was delivered. However, if another sensed event had occurred, the pacemaker would again have extended the interval to 1200 ms. VP VP VS VP

Noise Reversion Continuous refractory sensing will cause pacing at the lower rate Lower Rate Interval Noise Sensed The portion of the refractory period after the blanking period ends is commonly called the "noise sampling period." This is because a sensed event in the noise sampling period will initiate a new refractory period and blanking period. If events continue to be sensed within the noise sampling period causing a new refractory period each time, the pacemaker will asynchronously pace at the lower rate since the lower rate timer is not reset by events sensed during the refractory period. This behavior is known as "noise reversion." Note: In rate-responsive modes, noise reversion will cause pacing to occur at the sensor-driven rate. SR SR SR SR VP VP VVI/60

Modes-SINGLE CHAMBER

AOO & VOO-asynchronous modes
By application of magnet Useful in diagnosing pacemaker dysfunction During surgery to prevent interference from electrocautery

VOO Mode Asynchronous pacing delivers output regardless of intrinsic activity Lower Rate Interval VOO mode paces in the ventricle but will not sense and, therefore, has no response to cardiac events. Pacemakers programmed to the VVI, VVIR, and VDD modes will revert to VOO mode upon magnet application. In this example, an intrinsic beat occurs, but it has no effect on the timing interval and another ventricular pace is delivered at the programmed rate. No sensing occurs, thus, the entire lower rate interval is unresponsive to intrinsic activity. VP Blanking Period VOO / 60

VOO TIMING V VP VP VP VP VP

VVI Mode { Pacing inhibited with intrinsic activity
Lower Rate Interval In inhibited modes (VVI/AAI), intrinsic events that occur before the lower rate interval expires will reset the lower rate interval, as shown in the example above. As with paced events, sensed events will also initiate blanking and refractory periods. VP VS VP Blanking/Refractory VVI / 60

VVI TIMING V VP VP VP VS VP

VVIR Pacing at the sensor-indicated rate Lower Rate
Upper Rate Interval (Maximum Sensor Rate) Single chamber rate-responsive pacing is identical to non-rate responsive pacing operation, with the exception that the pacing rate is driven by a sensor. The sensor determines whether or not a rate increase is indicated, and adjusts the rate accordingly. The highest rate that the pacemaker is allowed to pace is the upper rate limit or interval. In this example, the pacemaker is pacing at the maximum sensor indicated rate of 120 ppm. VP Refractory/Blanking VVIR / 60/120 Rate Responsive Pacing at the Upper Sensor Rate

AAI Useful for SSS with N- AV conduction
Should be capable of 1:1 AV to rates b/m Atrial tachyarrhythmias should not be present Atria should not be “silent” If no A activity, atria paced at LOWER RATE limit (LR) If A activity occurs before LR,- “resetting” Caution- far-field sensing of V activity

AAIR Atrial-based pacing allows the normal A-V activation sequence to occur Lower Rate Interval Upper Rate Interval (maximum sensor rate) Although this mode is seldom used (particularly in the USA) , AAI/R pacing is a mode which, unlike VVI/R, allows for normal AV conduction to occur. Single-chamber, atrial inhibited pacing is selected only for those patients in whom the bradyarrhythmia is a sinus mechanism and AV block is not a problem.1 In this example, the patient received a single chamber device programmed to the AAIR pacemaker mode due to sick sinus syndrome and chronotropic incompetence. Presently the patient is at rest, so the sensor is at the programmed lower rate. An atrial event (paced or sensed) will initiate a refractory period including a blanking period. As previously stated, in AAI/R, the refractory period must be long enough so that the far-field R and T waves are ignored. Therefore, the refractory period must be longer in the AAI/R mode than in the VVI/R mode—typically 400 msec. Atrial events sensed during the refractory period in AAI/R are marked with an "SR" on the marker channel. Moses HW et al. A Practical Guide to Cardiac Pacing. 4th ed. Boston: Little, Brown and Company, Page 91. AP Refractory/Blanking AAIR / 60 / 120 (No Activity)

Single-Chamber Triggered-Mode
Output pulse every time a native event sensed ↑current drain Deforms native signal Prevent inappropriate inhibition from oversensing when pt does not have a stable native escape rhythm

Benefits of Dual Chamber Pacing
Provides AV synchrony Lower incidence of atrial fibrillation Lower risk of systemic embolism and stroke Lower incidence of new congestive heart failure Lower mortality and higher survival rates Studies have been done that demonstrate the differences in outcome, hemodynamic improvement, and quality of life assessment by using AV synchronous, or "atrial-based," pacing modes instead of VVI/R. Some of the benefits of using an atrial-based pacing mode include: AV synchrony–Clinical benefits such as increased cardiac output, augmentation of ventricular filling (especially important for the majority of the pacing population with LVD and reduced compliance from effects of aging). Providing AV synchrony minimizes valvular regurgitation, and preserves atrial electrical stability. In the Framingham Study, the development of chronic AF was associated with a doubling of overall mortality and of mortality from cardiovascular disease (Kannel, 1982) The following emphasize the importance of preventing atrial fibrillation: Patients with AF unrelated to rheumatic or prosthetic valvular disease have a risk of ischemic stroke about five times higher than those with normal sinus rhythm. AF is associated with over 75,000 cases of stroke per year. See bibliography for listing of studies cited.

Dual Chamber Timing Parameters
Lower rate AV and VA intervals Upper rate intervals Refractory periods Blanking periods Dual-chamber pacing requires attention to these parameters: Lower rate AV and V-A intervals Upper rates Refractory periods Blanking periods

Lower Rate The lowest rate the pacemaker will pace the atrium in the absence of intrinsic atrial events Lower Rate Interval In order to provide optimal hemodynamic benefit to the patient, dual-chamber pacemakers strive to mimic the normal heart rhythm. In dual-chamber pacemakers, the lower rate is the rate at which the pacemaker will pace the atrium in the absence of intrinsic atrial activity. Similar to single-chamber timing, the lower rate can be converted to a lower rate interval (A-A interval), or the longest period of time allowed between atrial events. AP AP VP VP DDD 60 / 120

AV Delay The AV delay in the pacemaker timing cycle is designed to simulate that natural pause between the atrial and ventricular events by mimicking the PR interval Benefits of a properly timed AV delay Allows optimal time for ventricular filling, which may contribute to improved cardiac output Allows sufficient time for proper mitral valve closure- minimize MR Note to instructors: some pacing experts feel that an optimized or ideally timed AV delay may have benefits that clinicians do not yet fully appreciate.

AV Intervals Initiated by a paced or non-refractory sensed atrial event Separately programmable AV intervals – SAV /PAV Two things can happen with the AV delay AV delay times out (and ventricular pacing spike is delivered) AV delay is interrupted by a sensed ventricular event (and ventricular pacing spike is inhibited) Lower Rate Interval PAV SAV 200 ms 170 ms The SAV is usually programmed to a shorter duration than the PAV to allow for the difference in interatrial conduction time between intrinsic and paced atrial events. Think of the difference in the activation sequence between a cycle initiated with an intrinsic atrial event versus a paced atrial event. The cycle starting with the intrinsic atrial event will use the normal conduction pathways between the right atrium and the left atrium. The cycle starting with the paced atrial beat will not use the normal interatrial conduction pathways but will instead use muscle tissue, which takes a little longer to reach the left atrium and causing it to contract. If the AV interval is timed to allow the appropriate amount of time for left ventricular filling when the cycle is initiated with a sensed atrial event, the same duration for the PAV may not be the appropriate amount of time to allow for left ventricular filling when the cycle is initiated by a paced atrial event. Proper LA-LV timing promotes left ventricular filling ("atrial kick") and prevents regurgitant flow through an open mitral valve. Therefore, it is beneficial to have separately programmable PAV and SAV intervals. In this example, the lower rate interval is terminated by a sensed atrial event, which initiates a SAV interval (and restarts the the lower rate interval). AP VP AS DDD 60 / 120

The pacemaker spike initiates the paced AV delay timing cycle
Sensed AV Delay The time period between the paced atrial event and the next paced ventricular event The pacemaker spike initiates the paced AV delay timing cycle Programmable value The time period between the sensed atrial event and the next paced ventricular event The pacemaker has to sense the atrial event before the timing cycle is initiated—there is usually a slight time lag Program the sensed AV delay to a value slightly shorter than the paced AV delay (~ 25 ms) cycle starting with the intrinsic atrial event will use the normal conduction pathways between the right atrium and the left atrium. The cycle starting with the paced atrial beat will not use the normal interatrial conduction pathways but will instead use muscle tissue, which takes a little longer to reach the left atrium and causing it to contract

Atrial Escape Interval (V-A Interval)
Lower rate interval- AV interval =V-A interval The A-V interval is employed to allow the appropriate amount of time to optimize ventricular filling and mimic the activation sequence of the normal heart. Knowing the lower rate interval and the PAV interval (A-V interval after a paced atrial event), the V-A interval can be found: V-A interval = lower rate interval minus PAV interval. The V-A interval is the longest period that may elapse after a ventricular event before the atrium must be paced in the absence of atrial activity. The V-A interval is also commonly referred to as the atrial escape interval. The V-A interval is the longest period that may elapse after a ventricular event before the atrium must be paced in the absence of atrial activity. The V-A interval is also commonly referred to as the atrial escape interval

Atrial Escape Interval (V-A Interval)
The interval initiated by a paced or sensed ventricular event to the next atrial event Lower Rate Interval 200 ms 800 ms AV Interval VA Interval Knowing the lower rate interval and the PAV interval (A-V interval after a paced atrial event), the V-A interval can be found: V-A interval = lower rate interval minus the AV interval. The V-A interval is the longest period that may elapse after a ventricular event before the atrium must be paced in the absence of atrial activity. The V-A interval is also commonly referred to as the atrial escape interval. AP VP DDD 60 / 120 PAV 200 ms; V-A 800 ms

Upper Activity (Sensor) Rate
In rate responsive modes, the Upper Activity Rate provides the limit for sensor-indicated pacing Lower Rate Limit Upper Activity Rate Limit PAV V-A PAV V-A This upper rate is defined as the upper activity rate, also known as the upper sensor rate or maximum sensor rate. Before mode switching was available, pacemakers utilized a separate activity/sensor rate and upper tracking rate to limit the rate to which the patient could track (e.g., in the presence of SVTs), but allow the patient to pace to higher rates if they were exercising. DDDR 60 / 120 A-A = 500 ms AP VP

DDDR 60 / 100 (upper tracking rate)
The maximum rate the ventricle can be paced in response to sensed atrial events Prevents rapid ventricular pacing rates in response to rapid atrial rates { Lower Rate Interval Upper Tracking Rate Limit SAV VA SAV VA The sequence of an atrial intrinsic event being sensed, starting an SAV interval, timing out the SAV interval, and pacing in the ventricle can be referred to as "tracking." If the atrial rate begins to increase and continues to increase, is it desirable to let the ventricle "track" to extremely high rates? No. It is desirable to limit the rate at which the ventricle can pace in the presence of high atrial rates. This limit is called the upper tracking rate. AS VP DDDR 60 / 100 (upper tracking rate) Sinus rate: 100 bpm

Refractory Periods VRP and PVARP are initiated by sensed or paced ventricular events The VRP is intended to prevent self-inhibition such as sensing of T-waves The PVARP is intended primarily to prevent sensing of retrograde P waves The Post-Ventricular Atrial Refractory Period (PVARP) is the period of time after a ventricular pace or sense when the atrial channel is in refractory. In other words, atrial senses outside of blanking that occur during this period are "seen" (and marked “AR) on the marker channel), but do not initiate an AV interval. The purpose of PVARP is to avoid allowing retrograde P waves, far-field R waves, or premature atrial contractions to start an AV interval which would cause the pacemaker to pace in the ventricle at a high rate. The refractory period after a ventricular event (paced or sensed) is designed to avoid restarting of the V-A interval due to a T wave. Ventricular sensed events occurring in the noise sampling portion of the ventricular refractory period are "seen" (and marked “VR” on the marker channel) but will not restart the V-A interval. The atrial channel is refractory following a paced or sensed event during the AV interval. This allows atrial senses occurring in the AV interval to be "seen" but not restart another AV interval . AP A-V Interval (Atrial Refractory) Post Ventricular Atrial Refractory Period (PVARP) VP Ventricular Refractory Period (VRP)

Post-Ventricular Atrial Refractory Period
PVARP is initiated by a ventricular event(sensed/paced), but it makes the atrial channel refractory PVARP is programmable (typical settings around ms) Benefits of PVARP Prevents atrial channel from responding to premature atrial contractions, retrograde P-waves, and far-field ventricular signals Can be programmed to help minimize risk of pacemaker-mediated tachycardias

PVARP and PVAB The PVAB is the post-ventricular atrial blanking period during which time no signals are “seen” by the pacemaker’s atrial channel It is followed by the PVARP, during which time the pacemaker might “see” and even count atrial events but will not respond to them PVAB-independently programmable Typical value around 100 ms

PVAB and PVARP Point out:
The pacemaker’s atrial channel will not respond to anything that occurs in the blue or red bars This is useful because the pacemaker’s atrial channel might otherwise pick up the T-wave or other far-field signals Events that occur in the blue bar are not even “seen” but events in the red bar are detected (may even get counted) but will not provoke a response

Blanking Periods First portion of the refractory period-sensing is disabled AP AP VP Atrial Blanking (Nonprogrammable) Post Ventricular Atrial Blanking (PVAB) DDD/R modes have four types of blanking periods: A non-programmable atrial blanking period (varies from msec) is initiated each time the atrium paces or senses. This is to avoid the atrial lead sensing its own pacing pulse or P wave (intrinsic or captured). In Thera and Kappa devices, this blanking period is dynamic, depending on the strength of the paced/sensed signal. The PVAB-(Post-Ventricular Atrial Blanking Period) is initiated by a ventricular pace or sensed event (nominally set at 220 msec) to avoid the atrial lead sensing the far-field ventricular output pulse or R wave. In dual-chamber timing, a non-programmable ventricular blanking period occurs after a ventricular paced or sensed event to avoid sensing the ventricular pacing pulse or the R wave (intrinsic or captured). This period is msec in duration and is dynamic, based on signal strength. There also is a ventricular blanking period after an atrial pacing pulse in order to avoid sensing the far-field atrial stimulus (crosstalk). This period is programmable (nominally set at 28 msec). This blanking period is relatively short because it is important not to miss ventricular events (e.g., PVCs) that occur early in the AV interval. Ventricular blanking does not occur coincident with an atrial sensed event. This is because the intrinsic P wave is relatively small and will not be far-field sensed by the ventricular lead. The issue of ventricular safety pacing and cross-talk will be addressed later on in the presentation. A note of caution in programming long ventricular blanking periods after an atrial pace should be mentioned. If the ventricular blanking period after an atrial pace is excessively long, conducted ventricular events may go unsensed and cause the pacemaker to pace in the ventricle after the AV interval expires. This pace could occur before the ventricle has recovered from depolarization and may induce a ventricular arrhythmia (R on T phenomena). Ventricular Blanking (Nonprogrammable) Post Atrial Ventricular Blanking

Total Atrial Refractory Period (TARP)
TARP is the timing cycle on the atrial channel during which the pacemaker will not respond to incoming signals TARP consists of the AV delay plus the PVARP TARP = AV delay + PVARP TARP is not programmable directly -can program the AV delay and PVARP and thus indirectly control TARP TARP is important for controlling upper-rate behavior of the pacemaker

Total Atrial Refractory Period (TARP)
Sum of the AV Interval and PVARP defines the highest rate that the pacemaker will track atrial events before 2:1 block occurs Lower Rate Interval Upper Tracking Rate SAV = 200 ms PVARP = 300 ms Thus TARP = 500 ms (120 ppm) DDD LR = 60 ppm (1000 ms) UTR = 100 bpm (600 ms) AS AS The total time that the atrial chamber of the pacemaker is in refractory is during the AV interval and during the PVARP. The Total Atrial Refractory Period (TARP) is equal to the SAV interval plus the PVARP. The TARP is important to understand as it defines the highest rate that the pacemaker will track atrial events before 2:1 block occurs. VP VP SAV PVARP SAV PVARP { TARP No SAV started for events sensed in the TARP

Wenckebach Occurs when the intrinsic atrial rate lies between the UTR and the TARP rate Results in gradual prolonging of the AV interval until one atrial intrinsic event occurs during the TARP and is not tracked

P Wave Blocked (unsensed or unused)
Wenckebach Operation Prolongs the SAV until upper rate limit expires Produces gradual change in tracking rate ratio { Lower Rate Interval Upper Tracking Rate P Wave Blocked (unsensed or unused) AS AS AR AP VP VP VP Pacemaker Wenckebach has the characteristic Wenckebach pattern of the PR (AV) interval gradually extending beat-to-beat until an atrial event falls into the PVARP and cannot restart an AV interval. In effect, a ventricular beat is “dropped”. In this graphic, starting from the left side of the ECG, the pacemaker senses an atrial beat and starts an SAV. Because no ventricular event occurs by the end of the SAV, a ventricular pace is delivered. Now the pacemaker is looking for a sensed atrial beat. An atrial beat is sensed outside of the PVARP and starts an SAV. This time, when the SAV times out, the upper rate interval has not yet expired. Since the pacemaker can never violate the upper tracking rate, the ventricular pace has to be delayed until the end of the upper rate interval, at which time a ventricular pace is delivered. This pattern of sensing a P wave, starting an SAV, waiting for the upper rate interval to time out, and pacing in the ventricle repeats until a P wave falls into the PVARP and does not start an SAV. The amount of delay created by the time from the sensed P wave until the upper rate interval expires is a little longer each time, producing the gradually lengthening of the P wave to ventricular pace intervals. Once a P wave falls into the PVARP and does not initiate an SAV, the pacemaker looks for the next sensed P wave and the pattern starts all over again. This is how the classic Wenckebach pattern develops. The rate at which the pacemaker will exhibit Wenckebach behavior is at the upper tracking rate (or upper rate if the pacemaker does not have a separate upper tracking rate and upper activity rate). SAV PVARP SAV PVARP PAV PVARP TARP TARP TARP

Wenckebach Operation DDD / 60 / 120 / 310
This ECG depicts Wenckebach operation. DDD / 60 / 120 / 310

Fixed Block or 2:1 Block Occurs whenever the intrinsic atrial rate exceeds the TARP rate Every other atrial event falls in the TARP when the atrial rate exceeds the TARP rate Results in block of atrial intrinsic events in fixed ratios

2:1 Block Every other P wave falls into refractory and does not restart the timing interval { Lower Rate Interval Upper Tracking Limit AS VP AR Pacemaker 2:1 block is characterized by two sensed P waves per paced QRS complex. This pattern develops because every other P wave falls into PVARP. Starting on the left side of this ECG, the sequence begins with a sensed P wave. This P wave initiates a SAV, followed by a paced ventricular event. The next P wave falls into the PVARP, started by the ventricular pace, so no SAV is initiated. The following P wave is sensed outside of the PVARP, so a SAV is started. Again, no ventricular event occurs during the SAV, so the pacemaker paces in the ventricle. In this manner, a 2:1 block pattern is created. The rate at which the pacemaker will exhibit a 2:1 block pattern is determined by the SAV and the PVARP (or the TARP). Atrial rates with a P-P coupling interval shorter than the TARP will result in 2:1 block. To determine at what rate the pacemaker will go into 2:1 block, the TARP is simply converted from an interval to a rate. Therefore, the rate the pacemaker will go into 2:1 block is: 60,000/TARP. AV PVARP AV PVARP { Sinus rate = 133 bpm (450 ms) PVARP = 300 ms SAV = 200 ms TARP=500 ms TARP TARP P Wave Blocked

2:1 Block DDD / 60 / 120 / 310

Summary-upper rate behaviours
1:1 tracking occurs whenever the patient’s atrial rate is below the upper tracking rate limit Wenckebach will occur when the atrial rate exceeds the upper tracking rate limit Atrial rates greater than TARP cause 2:1 block

Ventricular Safety Pacing
Crosstalk is the sensing of a pacing stimulus delivered in the opposite chamber, which results in undesirable pacemaker response, e.g., false inhibition Following an atrial paced event, a ventricular safety pace interval is initiated If a ventricular sense occurs during the safety pace window, a pacing pulse is delivered at an abbreviated interval (110 ms) One method to manage crosstalk is to program Ventricular Safety Pacing (VSP) ON. If VSP is programmed ON, a ventricular safety pace window opens up for 110 msec after an atrial pace. The first portion of this window (about 28 msec) is blanked. After the blanking period ends, if a ventricular event is sensed within 110 msec after the atrial pace, the pacemaker will pace at the end of the 110 msec window. The logic here is that it is assumed that if a sensed event happens within 110 msec of an atrial pace, it may not have happened as a result of conduction to the ventricle (i.e., it is not physiologic), and it may be crosstalk or noise. Rather than inhibit the ventricular pace and risk having no ventricular support, the pacemaker will pace. By pacing at the end of 110 msec, if the event was truly physiologic, the pace will fall into the absolute refractory period of the ventricular muscle tissue. Ventricular Safety Pacing is characterized by short (110 msec) AV intervals. On the marker channel, the VSP will be marked by two downward spikes–one for the ventricular sense and one for the ventricular pace. Ventricular Safety Pacing is designed to minimize the effects of cross-talk, but it can also occur under other circumstances. If a ventricular sensed event (e.g., a PVC or a conducted ventricular event) falls within the first 110 msec after an atrial pace, the pacemaker may Ventricular Safety Pace. Also, if there is an atrial undersensing problem, ventricular safety pacing may be seen. This happens if a scheduled atrial pace is delivered shortly after this unsensed P wave. The scheduled atrial pace initiates a PAV. If the unsensed P wave conducts to the ventricle within the Ventricular Safety Pace window, a Ventricular Safety Pace will occur. Other names for Ventricular Safety Pacing are "non-physiologic AV delay" or "110-msec phenomenon". When in effect, the AV interval will always be shortened. PAV Interval Post Atrial Ventricular Blanking Ventricular Safety Pace Window

Ventricular Safety Pace
Programmed parameters for this strip are: DDD; lower rate 60; upper rate 120; PAV 150ms; SAV 150 ms. Ventricular Safety Pace (VSP) ON. VSP occurred due to a PVC falling in the AV interval. DDD 60 / 120

Ventricular Safety Pace
AP AP AP VP VS VP VP AV PVARP PVARP AV PVARP 110 ms

VDD Mode Atrial Synchronous pacing or Atrial Tracking Mode
A sensed intrinsic atrial event starts an SAV The Lower Rate Interval is measured between Vs to Vp or Vp to Vp If no atrial event occurs at the end of the Lower Rate Interval a Ventricular pace occurs Paces in the VVI mode in the absence of atrial sensing AV block with intact sinus node function (esp useful in congenital AV block)

VDD { Provides atrial synchronous pacing System utilizes a single lead
Lower Rate Interval Upper Tracking Limit This is an example of normal VDD operation. In the VDD mode, the pacemaker will pace only in the ventricle and will sense in both chambers. In response to sensing in the ventricle, the pacemaker will inhibit. If a P wave is sensed, an SAV will be triggered. There is no PAV in the VDD mode because the pacemaker will not pace in the atrium. Since the VDD mode does not have the capability to pace in the atrium, the pacemaker will operate as if in the VVI mode in the absence of atrial activity faster than the programmed lower rate. Therefore, this mode is only appropriate for patients with a normally functioning, chronotropically competent sinus node and second- or third-degree heart block. In this example, a P wave is sensed and initiates an SAV. Since no ventricular activity is sensed during the SAV, the pacemaker paces in the ventricle. The V-A interval is then initiated, followed by another sensed atrial and paced ventricular event. Following this VA interval, no atrial activity is sensed, and a ventricular pace is delivered at the end of the V-A interval (lower rate interval). It should be noted that in the VDD mode, the ventricular rate is permitted to dip below the lower rate to promote AV synchrony, since atrial sensed events are accepted up to the end of the lower rate interval. Thus, it will pace as low as the lower rate interval plus the SAV. AS AS VP VP VP VDD LR = 60 ppm UTR = 120 ppm Spontaneous A activity = 700 ms (85 ppm)

DDD Mode Chamber paced: Atrium & ventricle
Chamber sensed: Atrium & ventricle Response to sensing: Triggered & inhibited An atrial sense: Inhibits the next scheduled atrial pace Re-starts the lower rate timer Triggers an AV interval (called a Sensed AV Interval or SAV) An atrial pace: Triggers an AV delay timer (the Paced AV or PAV) A ventricular sense: Inhibits the next scheduled ventricular pace Student Notes In dual chamber pacing, as the name implies, both the atrium and ventricle are used and affected by the pacemaker. One of the most common dual chamber modes is DDD. In DDD the atrium can be paced and sensed, as can the ventricles. So the pacemaker must be able to “see” P- and R- waves, but what is the response to sensing? The final D in DDD indicates a dual response to sensing – we mean the pacemaker can inhibit AND trigger. Let’s look at some examples. Instructor Notes Ask for questions before proceeding into Dual Chamber timing. If learners are unsure of the meaning of VVI pacing, stop now and take a couple of minutes to review.

Dual chamber timing PVARP Atrial Channel Ventricular Channel VRP VAI
AVI + PVARP = TARP PVARP Atrial Channel Ventricular Channel VRP VAI URI Atrial Escape Timing AVI NOTES: LRI = VAI + AVI A spontaneous ventricular contraction has shortened the AVI and therefore the TARP PVARP extension after a PVC BL

The Four States of DDD Pacing

Four “Faces” of Dual Chamber Pacing
Atrial Sense, Ventricular Sense (AS/VS) V-A AV AS VS In this example, the patient has adequate sinus node function and intact AV conduction, but may experience little to no increase in sinus rate with activity and/or AV block that occurs at increased rates. At appropriate rates, it is best to try and utilize the patient’s intrinsic rhythm when possible. Rate (sinus driven) = 70 bpm / 857 ms Spontaneous conduction at 150 ms A-A = 857 ms

Atrial Pace, Ventricular Pace (AP/VP) AV V-A AV V-A Knowing the basic A-V and V-A intervals will help in understanding the four modes or “faces” of dual chamber pacing. In the first example, the pacemaker is pacing in both the atrium and the ventricle–most likely a patient with sinus node dysfunction and AV block. AP VP Rate = 60 bpm / 1000 ms A-A = 1000 ms

Atrial Pace, Ventricular Sense (AP/VS) AP VS V-A AV In this example, the atrium is being paced, but AV conduction is intact, so the ventricular output is inhibited by a sensed ventricular event. Rate = 60 ppm / 1000 ms A-A = 1000 ms

Atrial Sense, Ventricular Pace (AS/ VP) V-A AV In this example, the atrial rate is driving the ventricular rate–also called atrial tracking. This patient has adequate sinus node function with AV block. AS AS VP VP Rate (sinus driven) = 70 bpm / 857 ms A-A = 857 ms

Is AV conduction intact? Are atrial tachyarrhythmias present?
Mode Selection DDIR DDDR N VVI VVIR Are they chronic? Y DDD, VDD Is AV conduction intact? Is SA node function presently adequate? Symptomatic bradycardia Are atrial tachyarrhythmias present? AAIR DDDR, DDIR (SSS) This is the decision tree that we will be using to (practice) determine the optimal pacing mode for five example patients. When evaluating which pacing mode would provide optimal pacing therapy for each patient, we must ask ourselves three questions: Are atrial tachyarrhythmias present? (Can the atrium be paced and sensed reliably?) Is AV conduction intact? Is SA node function presently adequate?

Optimal Pacing Mode (BPEG)
Sinus Node Disease - AAI (R) AVB - DDD SND + AVB - DDDR + DDIR Chronic AF + AVB - VVI

Alternative Pacing Mode
Sinus Node Disease - AAI AVB - VDD SND + AVB - DDD + DDI Chronic AF + AVB - VVI CSS DDD / VVI MVVS - DDD

Thank u

Mode Selection Decision Tree
DDIR with SV PVARP DDDR with MS N VVI VVIR Are they chronic? Y DDD, VDD DDDR Is AV conduction intact? Is SA node function presently adequate? Symptomatic bradycardia Are atrial tachyarrhythmias present? AAIR DDD, DDI with RDR (SSS) (CSS, VVS) This is the decision tree that we will be using to (practice) determine the optimal pacing mode for five example patients. When evaluating which pacing mode would provide optimal pacing therapy for each patient, we must ask ourselves three questions: Are atrial tachyarrhythmias present? (Can the atrium be paced and sensed reliably?) Is AV conduction intact? Is SA node function presently adequate?

Pacing Modes Stuart Allen 06

VVI Ventricular Demand VVI Output circuit AMP Programmed lower rate
50 mm/s VVI

Pacing Modesp VVIR Ventricular Demand Sensor indicated rate
Output circuit VVIR AMP Sensor Ventricular Demand Pacing Modesp Programmed lower rate 50 mm/s Sensor indicated rate Stuart Allen 06 9

AAI Atrial Demand AAI Output circuit AMP Programmed lower rate 50 mm/s
Stuart Allen 06 13

Pacing Modes - Summary Ventricular Demand VVI AAI Atrial Demand VAT
Output circuit AAI AMP Atrial Demand AMP Output circuit Output circuit VAT AMP Atrial Synchronised Output circuit VDD AMP Atrial synchronised Ventricular Inhibited Output circuit DVI AMP A-V Sequential Output circuit DDD AMP A-V Universal Timing & Control Stuart Allen 06 6

BASICS OF PACEMAKER DN.

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