767-6 Effect of Lead Polarity on the Defibrillation Threshold of Pectorally Implanted Cardioverter Defibrillators

The effect of the polarity of the initial phase of a biphasic shock waveform on the defibrillation threshold (DFT) of cardioverter-defibrillators (ICDs) is not known. We tested this in two investigational pectorally implanted biphasic ICDs — Medtronic Models 7219C and 7219D PCD Jewel devices — in 22 consecutive patients (Pts). The 7219C has an “active can” and requires a single right ventricular (RV) lead while the 7219D requires RV and superior vena cava leads ± subcutaneous patch(es). The 7219C was implanted in 10 Pts and the 72190 in 12 Pts. Polarities were tested in random order. The results were: RV +  * RV- * P value 7219C DFT 6.6 + 3.1J 10.8 + 5.5J 0.007  Impedance 59.3 + 8.8Ω 60.3 + 7.0Ω 0.33 7219D DFT 12.0 + 4.0J 16.3 + 7.3J 0.07  Impedance 50.5 + 67Ω 47.5 + 8.9Ω 0.23 * Refers to the polarity of the initial pulse deflection Of the 10 Pts receiving a 7219C device, 7 had lower DFT with RV + while in 3 lead polarity had no effect. Of the 12 Pts receiving a 7219D device, 7 had lower DFT with RV +, 2 had lower DFT with RV-, and in 3 lead polarity had no effect. Overall, with RV + there was a 39% reduction in DFT for Model 7219C and a 31% reduction for Model 7219D. An implant criterion of DFT ≤24J was met in 21 Pts using either RV + or RV-. In one Pt, however, the OFT for RV- was 34J and for RV + was 12J. Conclusion In this series, the lowest DFT was achieved most often using the RV + polarity. These results suggest that both RV lead polarities should be tested to achieve the lowest DFT in Pts receiving a pectorally implanted ICD.