Hemodynamic effect of the ventricular pacing site in fetal lambs with complete atrioventricular block

Complete atrioventricular (AV) block in hydrops fetalis is associated with high mortality. Fetal ventricular pacing to restore ventricular rate can be an effective procedure, however, no fetal data has shown an appropriate epicardial ventricular pacing site. To evaluate the hemodynamic effect of right and left ventricular pacing in fetal lambs with complete AV block, a fetal complete AV block model was created. Aortic pressure, central venous pressure, and QRS duration were measured, and right and left ventricular output was estimated in seven fetal lambs. The uterus was opened under maternal anesthesia, and under local anesthesia, catheters were inserted into the fetal superior vena cava and ascending aorta through a neck incision. Pacing leads were then sutured onto the fetal right and left ventricular epicardium via a midline thoracotomy. Complete AV block was created by cryoablation of the AV node. Ventricular output was estimated using echocardiography by a transuterine approach. Fetal hemodynamics were observed before AV block creation (control), and after complete AV block creation with the right and left ventricular pacing set at 150/min. The right ventricular output was 320 +/- 66 mL/kg per minute at control, decreased to 243 +/- 65 mL/kg per minute during right ventricular pacing (P < 0.05), and was 254 +/- 61 mL/kg per minute during left ventricular pacing. The left ventricular output was 224 +/- 98 mL/kg per minute at control, 176 +/- 77 mL/kg minute during right ventricular pacing, and 178 +/- 67 mL/kg per minute during left ventricular pacing. Biventricular (combined ventricular) output was 544 +/- 134 mL/kg per minute at control, 419 +/- 114 mL/kg per minute during right ventricular pacing, and 432 +/- 100 mL/kg minute during left ventricular pacing. Systolic aortic pressure was 62.2 +/- 8.7 mmHg at control, 55.2 +/- 9.5 mmHg during right ventricular pacing, and 53.4 +/- 9.1 mmHg during left ventricular pacing. Central venous pressure (CVP) was 2.6 +/- 0.5 mmHg at control, 4.0 +/- 2.7 mmHg during right ventricular pacing, and 4.4 +/- 2.5 mmHg during left ventricular pacing. The QRS duration was 51 +/- 54 ms at control, but lengthened to 87 +/- 19 ms during right ventricular pacing and to 78 +/- 21 ms during left ventricular pacing (P < 0.05). In conclusion, the right ventricular output decreased during right ventricular pacing in fetal lambs with complete AV block, while it was preserved during the left ventricular pacing. Left ventricular pacing might be superior for treating hydropic fetuses with complete AV block.