Leadless Epicardial Pacing at the Ventricular Apex: An Animal Study

Background: State-of-the-art pacemaker implantation technique in small children consists of pace-/sense electrodes attached to the epicardium and a pulse generator in the abdominal wall with a high rate of dysfunction during growth. Aim of the study was to investigate the feasibility to place a leadless pacemaker at the ventricular epicardium in an animal model.

Method: Ten lambs (median body weight: 24 kg) underwent epicardial implantation of a commercially available leadless pacemaker. Using a subxiphoid access, the pacemaker was placed using its proprietary delivery system at the ventricular apex. The pacemaker was introduced through a short thick-walled tube to increase tissue contact and to prevent tilting from the epicardial surface. The delivery system was firmly pressed against the heart while the pacemaker was delivered out of the sheath allowing the tines to stick into the epimyocardium. Pacemakers were programmed to VVI 30/min. Pacemaker function and integrity was followed for 4 months after implantation.

Results: After implantation, median intrinsic R amplitude was 5 (IQR: 2.8–7.5) mV, median pacing impedance was 2235 (IQR: 1,725–2,500) Ω, while the median pacing threshold was 2.125 (IQR: 1.25–2.9) V at 0.24 ms. During follow-up, 6/10 animals had a significant increase in pacing threshold with loss of capture at 0.24 ms in 2/10 animals. After 4 months, median R wave amplitude had dropped to 2.25 (IQR: 1.2–3.6) mV, median pacing impedance was 595 (IQR: 575–645) Ω and median pacing threshold increased to 3.3 (IQR: 1.8–4.5) V at 0.24 ms. Explanation of one device revealed deep penetration of the pacemaker tip into the myocardium.

Conclusion: Short-term pacing and sensing parameters of the leadless pacemaker at the epicardial aspect of the ventricular apex in lambs were satisfying. During mid-term follow-up parameters deteriorated and penetration of the electrode/pacemaker tip into the myocardium was of concern. Though the concept of epicardial leadless pacing seems very attractive, the current shape of the leadless pacemaker is not suitable yet for epicardial placement in growing organisms.

Publication History

Article published online:
28 January 2023