The subcutaneous array: a new lead adjunct for the transvenous ICD to lower defibrillation thresholds.

Despite the benefits of transvenous implantable cardioverter defibrillators (ICDs), concern exists that patients with high defibrillation thresholds (DFTs) have an inadequate safety margin between the DFT and the maximum defibrillator energy. A new transvenous ICD lead adjunct, a subcutaneous lead array (SQ Array), was developed to increase safety margins by lowering DFTs. Composed of three lead elements joined in a common yoke, the SQ Array is tunneled subcutaneously in the left lateral chest. Serving as their own controls, 20 patients were studied intraoperatively comparing transvenous lead-alone DFTs with lead-SQ Array DFTs. Seventeen males and three females were randomized to receive the SQ Array through the CPI Ventak PRx/Endotak 70 series protocol. Mean patient age was 63.7 +/- 2.5 years and mean ejection fraction 0.34 +/- 0.04. DFTs were determine using a precise protocol of step-down/step-up testing commencing at 20 joules. Lead-alone DFTs were tested using the proximal coil as the anode (+). For the lead-SQ Array, the proximal coil and the array were linked as a common anode. The lead-SQ Array resulted in a statistically significant reduction in mean monophasic DFT from 23.3 +/- 2.3 joules (lead-alone) to 13.5 +/- 1.9 joules (lead-SQ Array) (P < 0.001). Six patients had lead-alone DFTs > 25 joules but did not require thoracotomy because of adequate DFT reduction with the SQ Array. We conclude that the SQ Array adjunct to the transvenous ICD lead lowers monophasic DFTs an average of 9.8 joules (40.6%) obviating the need for a thoracotomy in selected patients.