Musings in the life of an internist, cardiologist and cardiac electrophysiologist.
I think some of the QRS are intrinsic conduction and some are originate from the pacer.
Looks like afib. Some beats are fully paced but most are conducted with a pacing spike beforehand (fused beats). Probably a Medtronic BiV ICD with "ventricular sense response" on (forced pacing when ventricular sensing occurs). I'd pace the LV 20-40 msec earlier than the RV and tighten up that QRS!
Looks like pacing with an underlying intrinsic rhythm like flutter or fib, with intrinsic beats coming through. As for treatment, call you...
Abate this! You da man (or woman). This is an underrecognized pacing that occurs from a biventricular pacemaker or defibrillator. The patient's underlying rhythm is atrial fibrillation, and the lower rate of the pacemaker was programmed at 60 beats per minute (but rate response is on, hence why the longer RR interval pacing is just above 60). The other QRS morphology is an intrinsically-conducted QRS complex that applies a left ventricular stimulus at the time the right ventricular enocardial signal is sensed by the device, causing the change in QRS complex morphology that is seen. The pacemaker worked properly and had normal pacing thresholds, so the EKG-reading cardiologist was reassurred that all was well with the device.
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