Pacemaker sensing failure

Pacemaker sensing failure

Pacemaker sensing failure Pacemaker sensing failure

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What are the findings in this ECG and possible explanations?

ECG shows PR interval prolongation, Q and ST elevation with T inversion in lead III, small q and T inversion in aVF along with lateral ST depression and T wave inversion indicating an inferolateral myocardial infarction with first degree AV block.

The interesting part is evident in the rhythm strip. Multiple pacemaker spikes or pacing artefacts are visible. The spike marked with blue arrow has come a short while after the preceding QRS complex and has captured the ventricles causing a wide QRS complex. The premature occurrence of the pacing spike would indicate a sensing failure of the pacemaker.

The pacing artefact marked by red arrow has occurred prematurely and has failed to capture the ventricles. The premature occurrence indicates sensing failure. Though it has not captured the ventricles, it does not mean capture failure as it has occurred within the QT interval of the previous QRS complex when we expect the ventricles to be refractory.

Rhythm strip shows two additional pacing spikes with ventricular captures, also occurring fairly early after the previous QRS complex. Early occurrence again indicates sensing failure. Usually demand pacemaker waits for a pause in the basic rhythm before firing as it senses the spontaneous rhythm and works in inhibited mode. Inhibited mode means that a sensed impulse will inhibit the pacing.

In the setting of evolved inferior wall infarction, it is likely that temporary pacing was done for complete heart block, which has now resolved into first degree AV block. Possibility of lead displacement has to be considered, which is more likely with temporary pacing.

Temporary pacing (Representative image)
Temporary pacing (Representative image)

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