This 34-year-old man suffering from hypertrophic cardiomyopathy underwent implantation of an Atlas dual chamber ICD for VT complicated by syncope. He was seen after he suffered a syncopal event followed by a shock while exercising.
Main programmed parameters
The device diagnosed a VF episode prompting a 25-J shock with a 46-Ohm impedance. The diagnosis of VF by the ICD was strictly based on the heart rate criterion instead of the irregular and polymorphic characteristics of the arrhythmia; a VT entering the VF zone is diagnosed as VF; similarly, the diagnosis of restoration of sinus rhythm indicates a slowing of the heart rate instead of a differentiation between sinus rhythm and AF.
Tracing
Several episodes diagnosed as VF by the ICD, based on a heart rate >200 bpm, are fast monomorphous VT. As discussed earlier, a priority of ICD programming is to lower to a maximum the number of shocks delivered without jeopardizing the safety of the patient. ATP is painless and, by lowering the energy consumption, spares the battery. Consequently, it must be given priority in the treatment of organized ventricular tachyarrhythmias, event when very rapid. In this patient, the VT was rapid, monomorphic, detected in the VF zone and treated by an outright maximum energy electrical shock. However, the programming of a burst of ATP for that arrhythmia might have been appropriate, though it cannot be offered beyond certain heart rate limits. This is another example of the divergent effects of electrical shocks delivered by ICD. On the one hand it terminated a ventricular arrhythmia (its expected function), and on the other, it induced an atrial arrhythmia. The tracing shows that the shock was synchronized with the R wave, though probably fell in the vulnerable period of the sensed atrial activity.
