Permanent cardiac pacemaker implant in the fetal lamb.

To investigate the feasibility of permanent cardiac pacing in the fetal lamb, we attempted five implants in lambs between 100 and 115 days of gestation. The lambs were approached by a left thoracotomy done through a transverse hysterotomy in the ewe. An epicardial lead was fixed to the left ventricle. Pacing parameters were measured and the lead was connected to an Enertrax implantable pulse generator. A pouch was created for the generator deep to the latissimus dorsi. Documentation of pacing was obtained electrocardiographically; pacing faster than the fetal intrinsic rate. The muscle and the fetal skin were closed. The pacemaker was programmed to a rate of 70 in the ventricular inhibited (VVI) mode and the uterine and abdominal wall incisions were then closed. One lamb was successfully delivered by Cesarean section at term. Pacing parameters were measured at birth and one month later. There were small changes in the pacing lead function parameters as the implant progressed into the chronic phase. They were within the capacity of the generator to pace with a margin of safety. Four lambs died in utero and were delivered 5 to 26 days post-implant. We conclude that permanent cardiac pacemaker implantation is feasible in the fetal lamb and with further development, it may eventually be used in humans in the treatment of fetal congestive heart failure due to bradyarrhythmias.