ECG Quiz 46 – Discussion – Pacemaker sensing failure
Pacemaker sensing failure
Click here for a larger image
ECG shows PR interval prolongation, Q and ST elevation with T inversion in lead II, 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.