A 67-year-old woman presenting with a primary cardiomyopathy, a left ventricular ejection fraction of 25%, a QRS duration of 130 ms, and in NYHA functional class III underwent implantation of an InSync Sentry CRT-D. At the end of the procedure, VF was induced by high-frequency stimulation.
There are at least 2 techniques of VF induction available in the cardiac catheterization laboratory after implantation of the system regardless of the device manufacturer: high frequency pacing (50 Hz in this example) and low-amplitude shock delivered in the vulnerable period. The most efficient method should 1) reduce the number of induction attempts, 1) reduce frequency of induction of organized ventricular tachycardia (more VF than VT) 3) lead to physiological ventricular fibrillation (similar characteristics between spontaneous and induced-VF) 4) be simple to program. There are a few studies comparing the results and the efficacy of these different methods with a limited number of included patients. It seems that the different methods can be considered reliable with a high rate of induction. Small differences may be observed. Shock on T-wave tends to induce more organized ventricular tachycardia, the arrhythmias triggered with continuous or alternating current being more polymorphic than when triggered by T wave shocks. This may lead to more undersensing and longer times in VF. The number of attempts to induce VF may be also more important with shock on T wave. In patients with amiodarone, the success rate of DC fiber induction (available in St Jude Medical devices) seems higher than Shock on T or high frequency pacing and should probably be used first.
Induced VF followed by a successful 20 J shock, requiring a charge time of over 3 sec; shock impedance = 50 ohms. The programmed parameters correspond to a standard induction (single detection zone >188 bpm and therapy; ventricular sensing to 1.2 mV).
