Successful implantation of cardiac defibrillators without induction of ventricular fibrillation using upper limit of vulnerability testing

Abstract

Introduction: Conventionally, the implantable cardioverter-defibrillator (ICD) is tested at implantation by measurement of defibrillation threshold (DFT), which involves repeated induction of ventricular fibrillation (VF). We report our data on successful ICD implantation without VF induction using a modified upper limit of vulnerability (ULV) testing method, compared to standard DFT testing.

Methods: Fourteen patients underwent ICD implantation using a modified ULV testing method by delivering a 15 J shock during the vulnerable period on the peak of the T wave, and if VF was not induced 15 J shocks were repeated at -20 and -40 msec before the peak of T wave. Failure to induce VF, indicating a ULV <15 joules (J), suggested a DFT < or =20 J based on previous studies demonstrating a close correlation (+/-5 J) between ULV and DFT. If VF was induced, a 20 J rescue shock was delivered. ICD therapy was then programmed on the basis of ULV testing. All patients underwent pre-discharge DFT testing to confirm adequate DFT.

Results: Using a modified ULV testing method, ICD implantation was completed without induction of VF in 8 patients and only a single episode of VF in 6 patients. The mean number of VF episodes (0.42 +/- 0.5) induced with ULV testing was significantly lower (p <.001) than the number induced during DFT testing (3.9 +/- 0.8). Pre-discharge DFT testing did not alter ICD programming in any patient. During follow-up of 14.85 +/- 12.31 months, three patients had seven episodes of VT/VF, six of whom were converted with the programmed first-shock strength, while one required a second high-energy shock to convert. This patient had a pre-discharge DFT of 10 joules.

Conclusions: Successful ICD implantation can be safely performed with no or fewer episodes of VF induction using a modified ULV testing method.