Transcutaneous cardiac pacing in patients with automatic implantable cardioverter defibrillators and epicardial patch electrodes

Abstract

In patients with automatic implantable cardioverter defibrillators, insulation of the epicardial patch electrodes (patches) prevents externally applied current from passing through the electrode to the cardiac muscle so that external transthoracic and even internal defibrillation can be unsuccessful. Because emergency cardiac pacing may be required in such a case, a study was performed to evaluate whether, and at what threshold and electrode orientation, transcutaneous pacing is possible in patients with implanted patches. Thresholds for transcutaneous pacing were determined during general anesthesia in nine patients with patches sewn across the heart (anterior right and posterior left ventricles) either before or after surgery, or at both times (automatic implantable cardioverter defibrillator implantation/exchange with or without coronary artery bypass grafting). Because surgery per se can increase the pacing threshold, nine patients of similar body size and weight undergoing routine coronary artery bypass grafting also were evaluated and served as a control group. Pacing thresholds (stimulus duration: 50 ms) were determined during normothermia with a transportable transcutaneous pacer, and adult cutaneous electrodes were placed across the patients' chest in the standard anteroposterior and right- to-left orientations. In all patients with patch electrodes, anteroposterior pacing was possible at a mean threshold of 73 ± 30 mA standard deviation (range: 40-140 mA). This threshold was not significantly different (Mann- Whitney test) from that in control patients before (57 ± 20 mA; range: 30-90 mA) or after (94 ± 24 mA; range: 40-120 mA) coronary artery bypass grafting. The surgical procedure per se significantly increased the threshold (Wilcoxon test, P < 0.05). Right-to-left pacing was possible (threshold < 150 mA) in only four patients with patches and in one without patches. Thus, emergency noninvasive transcutaneous cardiac pacing is possible at normal thresholds in patients with implanted patches. In contrast, right-to-left pacing was rarely effective and therefore does not represent an acceptable alternative in patients in whom standard anteroposterior pacing landmarks are not accessible.