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Interpretation of the ECG in a patient with a pacemaker

Raja Selvaraj
Cardiac Electrophysiologist
Professor of Cardiology
JIPMER

Learning Objectives

  • Understand basics of pacemaker function
  • ECG evaluation of pacemaker function
  • Interpretation of paced ECGs

General principles of pacemaker function

Pacing

  • Delivers a rectangular electrical stimulus at timed intervals
  • Seen as a high frequency pacing spike
  • Followed by capture of the respective chamber

Pacemaker pulse

rectangular_pulse.jpg

Pacing

pacing.jpg

Unipolar / bipolar pacing

uni_bi.jpg

Pacing

pace_animation.gif

Asynchronous pacing - VOO

voo.jpg

The pacemaker codes

pacemaker_code.png

Sensing

  • Watches for intrinsic activity
  • Generally inhibits pacing (resets timer)
  • For dual chamber pacemaker, sensing in atrium initiates pacing in ventricle after delay

Sensing

pace_sense_animation.gif

Sensing - VVI

sensing.png

Event markers

sensing_markers.png

Timing

sensing_markers_timings.png

A Systematic Approach to Pacemaker ECG

Step by step

  • What is the rate and rhythm ?
  • What is the underlying rhythm (sinus rate / AV conduction) ?
  • What pacemaker ?
  • Pacing function at each location ?
  • Sensing function at each location ?

Pacing function

  • Pacing - Delivery of pacing spike on time
  • Capture - Myocardial capture by pacing spike

Sensing function

  • Correctly identify only true intrinsic activity
  • Oversensing - Not pacing when it should
  • Undersensing - Pacing when it should not

Lets look at some ECGs

Pacemaker implanted 2 years back - Referred as "pacemaker not working"

no_pacing.jpg

Patient with a pacemaker - Routine FU

pacemaker_fn_teaching.jpg

Myth: Pacing spikes not seen = Pacemaker not functioning

  • Not pacing because intrinsic rate is faster than set lower rate
  • Bipolar pacing - small spikes
  • Lead malfunction
  • Battery depletion
  • Concern if rate is slow and patient is symptomatic

Middle aged female with pacemaker

aai.jpg

Elderly male with a pacemaker

rva.jpg

Paced morphology with apical pacing

  • LBBB pattern with left axis deviation
  • Usually qS in V1, sometimes R wave seen
  • Can happen with LV pacing / septal perforation
  • But more often occurs in presence of normal location

Pacemaker implanted for complete heart block

ddd3.jpg

Regular follow up

undersense2.jpg

Irregular rhythm

twos.jpg

Irregular rhythm explained

twos_explained.jpg

Pacemaker implanted 2 weeks back, recurrent syncope

v_non_capture.jpg

Magnet

magnet_vvi.png

Summary

  • Understanding basic functioning of pacemaker helps interpret ECGs
  • Stepwise approach
    • Rate and rhythm
    • Identify device
    • For each location - Pacing, sensing
  • Evaluate rhythm as if there is no pacemaker
  • As in other situations, interpret in context of overall clinical findings