PACEMAKER BASICS Frijo jose a

Electrode on the tip of a pacing lead Anode: positive Cathode: negative Electrode on the tip of a pacing lead Anode: positive The “ring” electrode on a bipolar lead The PG case on a unipolar system Anode Cathode

Implantable Pacemaker Circuit Pulse generator (PG): Battery Circuitry Connector(s) Leads Cathode Anode Body tissue Lead IPG Anode Cathode

The Pulse Generator Battery - provide energy Circuitry - controls pacemaker operations Connector- join the PG to the lead(s) Connector Block Circuitry Battery

Lead Characterization Position within the heart Endocardial/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

Endocardial Passive Fixation Leads The tines become lodged in the trabeculae, a fibrous meshwork, of the heart Tines

Transvenous Active Fixation Leads The helix, or screw, extends into the endocardial tissue Allows for lead positioning anywhere in the heart’s chamber The helix is extended using an included tool

Epicardial Leads Leads applied directly to the surface of the heart Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Applied via sternotomy or laproscopy

Lead Polarity Unipolar leads Bipolar leads Smaller diameter lead body than bipolar leads Usually larger pacing artifacts on ECG Bipolar leads Usually less susceptible to oversensing of non-cardiac signals Unipolar lead To tip (cathode) Bipolar coaxial lead

Unipolar Pacing System Lead has only one electrode –cathode – at the tip PG can - anode When pacing, the impulse: Flows through the tip electrode (cathode) Stimulates the heart Returns through body fluid and tissue to PG can (anode) Anode + more interference (myopotentials) Big spike on ECG Pectoral (pocket) stimulation possible Cathode -

Bipolar Pacing System The lead has both an anode and cathode The pacing impulse: Flows through the tip electrode located at the end of the lead wire Stimulates the heart Returns to the ring electrode, the anode, above the lead tip Anode + Cathode - Anode less interference Spike difficult to see on ECG No pectoral (pocket) stimulation Cathode

STIMULATION THRESHOLD The minimum stimulus intensity & duration necessary to reliably initiate a propagated depolarising wavefront from an electrode For a pacing stimulus to “capture”, the stimulus must exceed a critical amplitude & must be applied for a sufficient duration Stimulus amplitude & duration interact- minimal amplitude required to capture depends on the pulse duration

Strength–Duration Relation Stimulus amplitude for endocardial stimulation has an exponential relation to duration of the pulse- rapidly rising strength–duration curve at pulse durations <0.25 ms and a relatively flat curve at pulse durations > 1.0 ms

Chronaxie pulse duration ~ point of min threshold energy on strength–duration curve With pulse durations > chronaxie- relatively little ↓ in threshold V Wider pulse dur→wasting of energy without providing a substantial ↑ in safety margin When threshold determined by ↓ amplitude, stimulus V set twice the threshold value PG that determine threshold by automatically ↓pulse duration-at least 3times threshold Wedensky effect

Hyperacute phase of threshold evolution- active fixation electrodes may produce,immediately following implantation,an ↑ stimulation threshold that ↓over the next 20-30 min- transient high threshold – a/c injury at myocardial–electrode interface

Proper programming of the stimulus amplitude The strength–duration relation must be appreciated The safety margin that is chosen for a particular pt must be based on the degree of pacemaker dependency An appreciation of the effect of stimulus amplitude & duration on battery longevity The overall metabolic & pharmacologic history of the pt must be considered Pacing threshold varies inversely with surface area of the stimulating electrode

Strength–Interval Relation The stimulation threshold is influenced by the coupling interval of electrical stimuli and frequency of stimulation ICD- greater stimulus intensity during ATP than during antibradycardia pacing

(Ztotal) = Zc Ze Zp Zp - related to movmnt of charged ionmyo toward the s in cathode Zp -directly related to pulse duration & can be ↓ by use of relatively ↓ pulse durations Polarization is inversely related to SA of electrode- to ↓ Zp but ↑ Ze, SA of electrode can be made large but radius small by use of a porous coating

Afterpotential of opposite charge is induced in the myocardium at the interface of the stimulating electrode

The slope of intrinsic deflectn (dV/dt) expressed in V/s -referred to as slew rate For an EKG to be sensed, the amplitude & slew rate must exceed the sensing threshold

For a battery,the decay characteristics should be predictable For a battery,the decay characteristics should be predictable. The ideal battery should have a predictable fall in V near the end of life, yet provide sufficient service life after initial voltage decay to allow time for the elective replacement indicator to be detected and for replacement to be performed

RATE-ADAPTIVE SENSORS Activity Sensors and Accelerometers Minute Ventilation Sensors

P- Native atrial depolarization A- Atrial paced event R- Native ventricular depolarization V- Ventricular paced event AV- Sequential pacing in the atrium and ventricle AVI- Programmed AV pacing interval AR- Atrial paced event foll by intrinsic ventricular ARP- Atrial refractory period PV- Native atrial foll by paced ventricular, P-synchronous AEI- Interval from a ventricular sensed/paced to atrial paced event, the VA interval

NASPE/ BPEG Generic (NBG) Pacemaker Code I. Chamber II. Chamber III. Response to IV. Programmability V. Antitachy Paced Sensed Sensing Rate Modulation arrhythmia funct. O= none O= none O= none O= none O= none A=atrium A= atrium T= triggered P= simple P= pacing V= ventricle V= ventricle I= inhibited M= multi S= shock D= dual D= dual D= dual C= communication D= dual (A+V) (A+V) (T+I) R= Rate Modulation Manufacturers’ Designation only: S= single S= single (A or V) (A or V)

PACING MODES

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

Ventricular asynchronous (VOO) pacing Neither sensing nor mode of response Irrespective of any other events, V pacing artifacts occur at programmed rate. Timing cycle cannot be reset by any intrinsic event

Atrial asynchronous (AOO) AV sequential asynchronous (DOO) AVI & VAI or AEI are both fixed- intervals never change, as is insensitive to any atrial or ventricular activity, and timers never reset

Ventricular demand inhibited (VVI) Sensing on V channel- output inhibited by sensed V event Refractory after V/R- VRP- any V event in VRP-not sensed & doesn’t reset V timer LRL

VVI MODE If the intervals are equal: No hysteresis Automatic interval starts from a paced complex (to the next paced complex) Escape interval starts from a sensed complex (to the next paced complex) Automatic Interval If the intervals are equal: No hysteresis If the escape interval > automatic interval: Hysteresis Escape Interval

VVI MODE (with hysteresis) 1000 ms 850 ms Escape interval = 1000 ms (60 ppm) Automatic interval = 850 ms (70 ppm)

AAI Useful for SSS with N- AV conduction Should be capable of 1:1 AV to rates 120-140 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” An A activity too early may not cause depolarisation & better not sensed- ARP Caution- far-field sensing of V activity

Atrial inhibited (AAI) pacing

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 Can be used for noninvasive EPS,with already implanted PPI tracking chest wall stimuli created by a programmable stimulator

Single-Chamber Rate-Modulated Pacing

AV sequential-V Inhibited Pacing (DVI) PPI is inhibited & reset by sensed V activity but ignores all intrinsic A complexes Native R during AVI sensed – V output inhibited & AEI reset For both A&V stimuli to be inhibited, sensed R must occur during AEI

Modified or partially committed version-physiologic AVI

AV Sequential, Non–P-Synchronous Pacing with D-Chamber Sensing (DDI) AAI + VVI Difference btw DVI & DDI- DDI incorporates A sensing as well as V sensing- prevents competitive A pacing Mode of response is inhibition only- no tracking of P waves - paced V rate cannot be > programmed LRL Goes by LR for each Timing cycles- LRL, AVI, PVARP & VRP

A Synchronous (P-Tracking) Pacing (VDD) VAT + VVI Timing cycle- LRL,AVI,PVARP,VRP,& URL Concept of AV interval (AVI) A sensed atrial event initiates AVI Goes by LR If no A event occurs, PPI escapes with a V pace at LRL- VVI AV block with intact sinus node function (esp useful in congenital AV block)

DDD VAT + AAI + VVI AV interval & VA interval VA interval replaces the LR Concept of PVARP (to prevent endless loop or PMT) Indications 1. The combination of AV block and SSS 2. Patients with LV dysfunction & LV hypertrophy who need coordination of atrial & ventricular contractions to maintain adequate CO

DDD

DDD Examples The Four Faces of DDD Atrial and ventricular pacing Atrial pace re-starts the lower rate timer and triggers an AV delay timer (PAV) The PAV expires without being inhibited by a ventricular sense, resulting in a ventricular pace A P V

DDD Examples The Four Faces of DDD Atrial pacing and ventricular sensing Atrial pace restarts the lower rate timer and triggers an AV delay timer (PAV) Before the PAV can expire, it is inhibited by an intrinsic ventricular event (R-wave) A P V S

DDD Examples The Four Faces of DDD Atrial sensing, ventricular pacing The intrinsic atrial event (P-wave) inhibits the lower rate timer and triggers an AV delay timer (SAV) The SAV expires without being inhibited by an intrinsic ventricular event, resulting in a ventricular pace A S V P

DDD Examples The Four Faces of DDD Atrial and ventricular sensing The intrinsic atrial event (P-wave) inhibits the lower rate timer and triggers an AV delay timer (SAV) Before the SAV can expire, it is inhibited by an intrinsic ventricular event (R-wave) A S V

Dual Response to Sensing DDD The pacemaker can: Inhibit and trigger A P-wave inhibits atrial pacing and triggers an SAV interval An atrial pace triggers a PAV interval An R-wave inhibits ventricular pacing

Single-Chamber Timing

Single Chamber Timing Terminology Lower rate Refractory period Blanking period Upper rate

Lower Rate Interval Defines the lowest rate the pacemaker will pace VP VVI / 60

Refractory Period Interval initiated by a paced or sensed event Designed to prevent inhibition by cardiac or non-cardiac events Lower Rate Interval VP VVI / 60 Refractory Period

Blanking Period The first portion of the refractory period Pacemaker is “blind” to any activity Designed to prevent oversensing pacing stimulus Lower Rate Interval VP VVI / 60 Blanking Period Refractory Period

Upper Sensor Rate Interval Defines the shortest interval (highest rate) the pacemaker can pace as dictated by the sensor (AAIR, VVIR modes) Lower Rate Interval Upper Sensor Rate Interval 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 Interval-60 ppm Hysteresis Rate-50 ppm VP VP VS VP

Dual Chamber Timing Parameters Lower rate AV and VA intervals Upper rate intervals 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 AP AP VP VP DDD 60 / 120

AV Intervals Initiated by a paced or non-refractory sensed atrial event Separately programmable AV intervals – SAV /PAV Lower Rate Interval PAV SAV 200 ms 170 ms AP VP AS DDD 60 / 120

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 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 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 { Lower Rate Interval Upper Tracking Rate Limit SAV VA SAV VA 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 AP A-V Interval (Atrial Refractory) Post Ventricular Atrial Refractory Period (PVARP) VP Ventricular Refractory Period (VRP)

Blanking Periods First portion of the refractory period-sensing is disabled AP AP VP Atrial Blanking (Nonprogrammable) Post Ventricular Atrial Blanking (PVAB) Ventricular Blanking (Nonprogrammable) Post Atrial Ventricular Blanking

Dual Chamber Timing Atrial Pace (AP) - Ventricular Pace (VP) example DDD 60 A-A interval VRP ARP PVARP PVAB PAV V-A interval

Atrioventricular Interval

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