Lead placement in extravascular ICD recipients: the first step to prevent P-wave oversensing

Abstract Background Extravascular (EV) implantable cardiac defibrillators (ICD) with substernal lead have recently proved to be a safe and effective alternative to conventional transvenous (TV) and subcutaneous defibrillators (S-ICDs) 1, owing to the possibility to deliver antitachycardia and asystole pacing while saving intravascular hardware. However, inappropriate shock delivery occurred in 9.7% of patients, and P-wave oversensing accounted for 42% of inappropriate shocks in the EV ICD Pivotal Study. Purpose to investigate the difference of lead placement in patients with and without P-wave oversensing. Method 17 patients undergoing implantation as part of the EV ICD Pivotal Study received the substernal lead placement based on computer tomography imaging (CT) and following the protocol recommendations. Lead placement beyond the left lateral sternum border was attempted whenever possible, based on CT guidance. P-wave detectability (P detected visually but non sensed by the device) on the sensing vector and P-wave oversensing by the device were investigated at each follow-up. The distance of sensing ring electrodes (R1 and R2) from the mid-spine line (line connecting the spinous processes from cervical to lumbar vertebral processes) was measured in each patient on the posterior-anterior chest radiogram. Results Mean age, BMI, NYHA class and left ventricular ejection fraction (LVEF) were respectively 53±9yrs, 25.3 ±6 kg/m2, 2 ±0.7, and 39±14%. The main aetiology was non-ischemic cardiomyopathy (12/17), including 3 arrhythmogenic cardiomyopathy patients and one with hypertrophic cardiomyopathy. The implantation was successful in 16 (6 females) out of 17 patients without any complication, with one implant failure due to inadequate sensing (0,5 mV) despite several attempts at tunnelling in different locations (rightward and leftward of the sternum). One patient with P-wave detectability had lead dislodgement after 2 weeks, and underwent repositioning to a more leftward location, where P-wave was not detectable. Only one patient had P-wave oversensing at follow-up, and received inappropriate shocks (Figure A); the remaining 15 patients neither had detectable P-wave on the sensing vector nor inappropriate shocks (Figure B). The median sensing amplitude at implantation was 2,7±1.4 mV and 2.6±1.2 mV along a 18±4 months follow-up, with R1-R2 being the final sensing vector chosen for 14/16 and R2-Can for 2/16 patients. The distance of R1 and R2 from the mid-spine line was significantly longer in patients with detectable P-wave compared to those without (37±13mm vs 18 mm and 30±15 vs 16 mm, respectively). Conclusions Placement of the EV ICD lead leftward to the left sternum border is safe, and prevents P-wave detection. The mid-spine line represents an easy landmark to guide lead placement during implantation. R1 distance ≥ 25 mm and R2 distance ≥ 20 mm from the mid-spine line provide a reliable marker of freedom from P-wave oversensing.Figure AFigure B