Interactions between transvenous nonthoracotomy cardioverter defibrillator systems and permanent transvenous endocardial pacemakers.

Limited information is available regarding potential adverse interactions between transvenous nonthoracotomy cardioverter defibrillators and pacemakers. We describe our experience with 37 patients who have undergone successful implantation of both a transvenous defibrillator and pacemaker. The patients' mean age was 64 +/- 12.9 years. Thirty-three were male and four were female. The mean LVEF was 30.8% +/- 11.8%. The indications for pacemaker implantation included sick sinus syndrome in 13 patients, complete heart block in 15 patients, sinus bradycardia secondary to medications in 8 patients, and neurocardiogenic syncope in 1 patient. The indications for insertion of a defibrillator included medically refractory VT in 27 patients and sudden cardiac death in 10 patients. Twenty-three patients received an Endotak lead and 14 patients received a Transvene lead. Eighteen patients had a pacemaker prior to an ICD, 14 patients had an ICD prior to a pacemaker, and 4 patients had both devices placed simultaneously. Interaction was evaluated at implant of the second device and 1-3 days after both devices were placed. Detection of VF/VT was analyzed during asynchronous pacing (DOO/VOO) with maximum pacing output. In addition, in six patients, DFT was determined before and after pacemaker implantation. In 14 patients (38%), device interactions that could not always be optimally corrected were observed. In five patients, the pacemaker was reset to the "noise reversion" mode after high energy ICD discharge. Oversensing of atrial pacemaker stimuli resulted in inappropriate ICD firings in four patients. This was observed only with a specific device and could not be prevented by atrial lead repositioning in two of them, but required reprogramming of the pacemaker to the VVI mode. An increase in DFT was observed in five patients who had a pacemaker implanted after an ICD. Compared with previously published studies, a greater frequency of transvenous ICD and pacemaker interactions were observed. Considering that almost 50% of the patients already have a pacemaker at the time of ICD implant, the availability of defibrillators with dual chamber pacing capability will not eliminate the potential for this problem.