Influence of malpositioned transvenous leads on defibrillation efficacy with and without a subcutaneous array electrode.

Some patients cannot receive a transvenous lead system because of high defibrillation thresholds (DFTs). We hypothesized that a right ventricular (RV) catheter electrode not extending as far as possible into the RV apex could cause high DFTs. Recently, a subcutaneous array (SQA) electrode has been shown to lower DFTs substantially. We compared the influence of a malpositioned RV catheter electrode on defibrillation efficacy for endocardial lead systems with and without a SQA. In eight anesthetized pigs, defibrillation catheters were placed in the RV apex and near the junction of the superior vena cava (SVC) and right atrium. SQA, formed by three elements, each 20 cm in length, was placed in the left thorax. DFTs were determined for a biphasic waveform using an up/down protocol with the RV catheter at the apex and with it repositioned 1-cm and 2-cm proximal to the apex. The mean DFT energies for the configurations with a SQA were less than those without a SQA for every catheter position. The placement of the RV catheter away from the apex caused an increase in defibrillation energy for the configurations without a SQA (apex: 17.1 +/- 3.8 J [mean +/- SD]; 1 cm: 20.1 +/- 4.6 J; 2 cm: 27.6 +/- 9.5 J; P < 0.05), but not for the configurations with a SQA (apex: 12.2 +/- 2.2 J; 1 cm: 12.3 +/- 2.9 J; 2 cm: 12.1 +/- 0.9 J: P = NS). These results suggest that a malpositioned RV catheter electrode, at the time of implantation or by late dislodgment, significantly elevates DFTs for a total endocardial system but not for a system that includes a SQA.