Spike Decay Masking the QRS
Report:
Ventricular pacemaker rhythm 65/min 1
Possible battery depletion 2
Intermittent retrograde conduction 4
Sinus rhythm 75/min 1
Probable third degree AV block 2
Comment:
The faster sinus rhythm is almost certainly subject to 3o AV block, but the paced rhythm is not slow enough to know this for certain. It is slow enough, however, to raise the suspicion of battery failure unless it can be confirmed that 65/min is its programmed rate.
After the 5th and the 6th spike there is a biphasic down-up atrial deflection, either a retrograde P wave or, more likely, atrial fusion between sinus and retrograde waves. Retrograde waves can be biphasic44 or even positive45 in the inferior leads, but this is reportably rare.
The spike artefact is followed by an exponential voltage decay curve that distorts and almost masks the paced QRS in most of the frontal leads. This is not abnormal per se; it is occasionally seen when the spikes are – as in this case – very large.
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