The middle cardiac vein - A novel pathway to reduce the defibrillation threshold

Defibrillation energy requirements of epicardial implantable cardioverter defibrillator systems are generally lower than endovascular systems currently used. The former has the disadvantage of requiring a thoracotomy and so has a greater morbidity and mortality than an endovascular procedure. The middle cardiac vein (MCV) is an epicardial structure that is accessible by a non-thoracotomy approach. This study investigated the merits of ventricular defibrillation from the middle cardiac vein. Methods and Results. Defibrillation thresholds (DFT) mere measured in 10 anesthetized pigs, weighing 34.5-44.1 kg (mean 39 kg). An Angeflex electrode (1.7mm x 50mm) was introduced via the left external jugular vein to the right ventricular apex. The MCV was identified with standard angiography techniques and a 4080 (Angeion Corp.) defibrillation electrode (1.6mm x 65mm) introduced into the vein. An active can was implanted in the left subpectoral region. The defibrillation thresholds (DFT) of the following defibrillation configurations were assessed using a modified four-reversal binary search: RV --> Can, RV+MCV --> Can and MCV --> Can. The DFT's for the three configurations were 15.5+/-2.8 J, 10.8+/-3.4 J and 13.7+/-2.4 J. Analysis of variance showed that the DFT with the RV+MCV combination was significantly less than the RV alone (p < 0.05) Conclusions: Defibrillation is possible through the MCV and that incorporating an electrode in the MCV with RV-Can configuration can reduce the DFT by 30%.