INFLUENCE OF EPICARDIAL PATCHES ON DEFIBRILLATION THRESHOLD WITH NONTHORACOTOMY LEAD CONFIGURATIONS

Background In previous studies, epicardial patch electrodes decreased transthoracic defibrillation efficacy. We studied the effects of two i nactive epicardial 14-cm(2) titanium mesh patches on defibrillation en ergy requirements with nonthoracotomy internal lead configurations. Me thods and Results A 6/6-millisecond biphasic shock wave-form was deliv ered via several electrode configurations 10 seconds after ventricular fibrillation was initiated with a 60-Hz generator. In two series, a t otal of 16 dogs (weight, 23.3+/-2.4 kg) underwent an up-down defibrill ation protocol. In the first series, the defibrillation threshold (DFT ) was determined for each electrode configuration in the presence of t wo inactive epicardial patches. In the second series, DFTs were determ ined in the presence of an inactive right ventricular (RV) or left ven tricular (LV) parch alone. For several nonthoracotomy lead configurati ons tested in the first 8 dogs, the mean+/-SD DFT energy increased 49% to 97% with two inactive patches on the heart compared with no patche s on the heart as follows: RV to superior vena caval (SVC) electrode, from 8.9+/-2.6 to 18.0+/-14.3 J; RV to SVC plus subcutaneous array ele ctrode, from 7.0+/-2.4 to 10.7+/-5.3 J; RV to subcutaneous pectoral pl ate electrode, from 6.2+/-1.3 to 11.4+/-4.0 J (P less than or equal to .05). The lowest DFT was achieved by defibrillating between the epicar dial patches (3.8+/-3.3 J). The second series showed that DFT voltage requirements increased significantly for all three non-thoracotomy lea d configurations with the inactive LV patch alone (P less than or equa l to.05) but not with the inactive RV patch alone. Conclusions Inactiv e epicardial patches can significantly increase the defibrillation ene rgy requirements for nonthoracotomy lead configurations. This negative impact may be due to an insulating effect of the patches and to a dis turbance of the potential gradient field under the patches. If the sam e holds true in patients, these results have clinical implications. Fu nctioning epicardial patch leads should be incorporated in the defibri llation lead system if already present. If the LV patch is nonfunction ing, such as because of a lead fracture, the marked increase in DFT du e to an inactive LV patch calls for thorough DFT testing during surger y and, in selected patients, may necessitate patch removal to produce an effective transvenous-based system.