59-02: Ventricular Pacing from the Substernal Space in Humans

Abstract

Introduction: Transvenous lead failure remains an important drawback of transvenous implantable cardioverter-defibrillators (ICD). The subcutaneous ICD overcomes this issue, but lacks pacing capabilities. The objective of this study was to assess feasibility of ventricular pacing and thresholds from within the substernal space to examine a new extravascular ICD configuration with pacing capabilities. Methods: Patients with midline sternotomy for coronary arterial bypass grafting (CABG) or aortic valve replacement (AVR) were enrolled. After the sternum was opened, a duodecapolar diagnostic pacing catheter was positioned in the substernal space anterior to the pericardium, and a cutaneous patch in the left midaxillary line, after which the chest was closed. Different pacing configurations were assessed: bipolar between the catheter electrodes (inter electrode spacing 2mm, 30mm, or 60mm) and unipolar between the catheter electrodes and the patch. A downwards stepwise pacing protocol was used to identify the best configuration, starting at 25mA with a pulse width (PW) of 10ms. Results: Eight patients, (6 males), with mean age 69 ± 9 years, of whom 7 underwent AVR and one CABG, were included. In five out of eight patients ventricular capture was achieved in ≥1 configuration. The mean bipolar pacing thresholds at PW 10ms, 5ms, 3ms, 1ms were 12.4 ± 3.7mA (5 pts), 13.3 ± 5.8mA (3 pts), 18.3 ± 5.7mA (3 pts) and 25 ± 0mA (2 pts) respectively. The 60mm electrode spacing was the most successful bipolar configuration. Unipolar pacing was attempted in 4 pts and successful in 3 pts with mean thresholds of 10 ± 0mA at 10ms (3 pts), 15 ± 0mA at 5ms (3 pts), 16.7 ± 2.9mA at 3ms (3 pts) and 20 ± 7.1mA at 1ms (2 pts). The optimal unipolar vector was from the catheter electrodes over the right ventricle to the patch.