A 41-year-old man with severe ischemic cardiomyopathy and sustained VT, recipient of an Entrust VR single chamber ICD implanted for secondary prevention, had SVT diagnosed in the device memory on a routine ambulatory visit.
Systematic oversensing of a cardiac signal results in the sensing of 2 EGMs of different morphologies in the same cardiac cycle. As illustrated in this example, alternating short and longer RR cycles are common. This occurs also in presence of ventricular bigeminy. This type of episode plot is completely different from that observed in presence of electromagnetic interference (several very fast identical signals during the same cardiac cycle) or lead failure (short non-physiological cycles of variable amplitude). The stability criterion can often prevent the delivery of inappropriate therapy when the RR intervals are variable, as the device favors the diagnosis of SVT.
The episode is diagnosed as SVT due to the irregularity of the rhythm.
