Modes of Pacing Seoul National University Hospital Department of Thoracic & Cardiovascular Surgery

Electrophysiology of Pacing Stimulation & depolarization of myocardial tissue Sensing of intramyocardial electrical activity Current pacemaker technology Pulse generator

Stimulation & Depolarization of Myocardial Tissue The myocardium must be excitable The stimulus current density (current per unit cross-sectional area) must be sufficiently high & of sufficient duration to depolarize a group of cells that is large enough to initiate impulse propagation in the myocardium The pacemaker-generated impulse then relies on the intrinsic properties of cardiac specialized conduction & myocardial tissue for depolarization of the entire heart

Factors affecting Sensing Sensing is the detection of real or spontaneous cardiac depolarization Electrode size Configuration of electrode (unipolar, bipolar) Position of the lead tip within the heart

Pacing Lead Technology Attachment of electrode Active fixation Passive fixation 1. Chronic ventricular pacing thresholds tend to be lower with passive lead, in part because of tissue injury with active fixation 2. Sensing characteristics are similar between active & passive leads 3. Epicardial electrodes historically have poorer performance over long term than endocardial lead

Pulse Generator Power source Time circuitry Sensing circuitry Output circuitry for channels connected to the electrodes Transceiver for telemetric communication with programming device

Single Chamber Pacemaker AOO AAI AAT VOO VVI VVT

Single Chamber Pacemaker AAIR VVIR

Single Chamber Pacemaker VVI I *

Intrinsic P and R waves

Atrial Sensing / Inhibition

Ventricular Sensing / Inhibition

Pacing Interval / Pacing Rate The rate at which the pacemaker will pace if the patient does not have their own rhythm Expressed in either PPM or ms

Rate Conversion Conversion Pacing rate in PPM divided into 60,000 = ms 60,000 / 60 PPM = 1000 ms Interval in ms divided into 60,000 = PPM 60,000 / 1000 ms = 60 PPM

Ventricular Sensing / Inhibition pacing interval

Capture Definition The depolarization and resultant contraction of the atria or ventricles in response to a pacemaker stimulus.

Threshold Stimulation Threshold Definition : The minimum amount of electrical energy that consistently produces a cardiac depolarization

Atrial Capture Pacemaker Stimulus Atrial Capture

Ventricular Capture Ventricular Capture (paced ventricular beats look like PVC’s or LBBB)

Refractory Period Refractory Period

Alert Period Definition The portion of timing cycle where the device senses electrical activity (e.g. cardiac) & responds in a preset or programmed manner

Alert Period Refractory Period Alert Period

Dual Chamber Pacemaker VAT VDD DOO DVI DDI DDD

Dual Chamber Pacemaker DDD T / I * I

Atrial & Ventricular Pacing

Sense in Atrium & Pace in Ventricle

Pace & Sense in Atrium & Pace in Ventricle

Pace Atrium & Sense Ventricle

Pace and Sense in Atrium Sense in Ventricle

AV / PV Delay AV Delay PV Delay

Post Ventricular Atrial Refractory Period (PVARP) Definition Timeframe the atrial channel is refractory, initiated when there is either a ventricular pacer spike or sensed R-wave. PVARP

Atrial Alert Period Definition Timeframe after PVARP when the sense amplifier is open and can see P-waves

Atrial Alert Period Alert Period PVARP AV Delay PV Delay

Ventricular Refractory Period

Ventricular Alert Period Definition Timeframe after the ventricular refractory period that the sense amplifier is open looking for R-waves

Ventricular Alert Period Ventricular Refractory Period Ventricular Alert Period

Dual Chamber Pacing Minimum Rate or Base Rate Lowest rate that the pacemaker will pace in the Atrium Maximum length of time the Pacemaker will wait for intrinsic activity

Dual Chamber Pacing Minimum Rate

Dual Chamber Pacing Maximum Rate / Maximum Tracking Rate The fastest rate that the Ventricular channel can track intrinsic P-waves

Maximum Tracking Rate

Pacemaker Follow-up Aim Interval Verify appropriate pacemaker operation Optimize pacemaker functions Interval Immediate and POD # 1 day Postoperative 3, 6, 12 months

Pediatric Aspects of Cardiac Pacing Ventricular epicardial leads Thoracotomy approach Transdiaphragmatic approach Subcostal or subxiphoid incision Atrial epicardial leads Base of left atrial appendage Transvenous leads All the leads have the problem with child growth and results in high threshold, exit block, lead fracture. Even when a loop of lead was left in the pericardium, adhesions frequently formed that prevented unwinding of the loop.

Interrogation

Assess Current Pacemaker Function Compare the surface ECG to markers to determine appropriate pacing (capture) & sensing

Measured Data Provides information on: -Magnet Information, -Lead Status, -Battery Status

Diagnostics

Pacemaker Testing Sensing and Capture testing should be performed to insure adequate safety margins are programmed

Ventricular Threshold Test Sensing and Capture testing should be performed to insure adequate safety margins are programmed

Loss of Capture Definition: The emitted pacemaker stimulus does not cause depolarization and resultant cardiac contraction

Ventricular Loss of Capture Programmed Rate Programmed Rate

Problem Solving Loss of Capture Causes Dislodged Lead Insulation Break Program Voltage higher Program Pulse Width higher Reposition pacing electrode

Sensing Threshold The sensitivity number is increased until loss of sensing is seen Then the sensitivity number is decreased until sensing is regained This is the Sensing Threshold

Ventricular Sensitivity Test

Oversensing Definition : The sensing of events other than P or R-waves by the pacemaker circuitry

Ventricular Oversensing Pacing interval Pacing interval Pacing interval Pacing interval Pacing interval

Causes of Oversensing Insulation Break Intermittent Lead Fracture Myopotentials EMI Problem Solving Program sensitivity to a higher number Program the refractory period longer

Undersensing Definition : Failure of the pacemaker circuitry to sense intrinsic P- or R-waves

Ventricular Undersensing non-sensed R-waves

Causes of Undersensing Dislodged Lead Insulation Break Problem Solving Program the sensitivity to a lower number

Testing of Chronic Pacing System Current Voltage Resistance Threshold Threshold Dislodgement of electrode from endocardium H H N Perforation H H N Exit block (fibrosis around electrode tip) H H N Pulse generator malfunction N N N Lead/connector abnormality N N N Battery depletion N N N Partial lead fracture L to N H H F F Complete lead fracture N H H Lead insulation fracture H H L H; high, N; normal, L; low. F; fluctuating

Follow-up Check Interrogate Measure Impedance Check Diagnostics Check Sensing Measure Threshold