Background:
The right ventricular (RV) apex has been the preferred site for ventricular pacing for many years, mostly due to simple implantation technique and low risk of lead dislocation. However, single site RV pacing has been identified as an independent risk factor for left ventricular (LV) remodeling and hemodynamic changes leading to impaired LV function. On the other side, crossing the tricuspid valve (TV) is potentially associated with short and long term risk of TV malfunction, especially after biological TV replacement

In cardiac resynchronization therapy (CRT), a transvenous lead is inserted in coronary sinus (CS) for LV free wall pacing in addition to RV pacing. A single site CS only pacing has been reported as an alternative for permanent ventricular pacing in specific patient groups.

Methods:
In this retrospective study, we evaluated seven consecutive patients (3 female) with postoperative high degree AV block after TV replacement (St. Jude medical Epic 33 mm).  Five patients went to surgery due to severe tricuspidal regurgitation (TR), one of them with a transvenous pacemaker. Two patients had an urgent surgery for TV endocarditis, one associated with a pacemaker lead endocarditis. One additional patient in our study had no surgery, but an unsuccessful implantation of an endocardial pacemaker due to endocardial fibrosis, associated with total AV block.

Results:
Mean age at implantation was 67 ± 11 years. No patient had a significantly impaired LV ejection fraction (mean LVEF 62 ± 6 %). The mean duration of implantation was 55±9 Minutes with mean fluoroscopy time of 7.6 ± 4 Minutes.  All patients had a successful implantation without perioperative complications. Six bipolar leads have been implanted in an anterior vein and two in a posterolateral vein. The mean threshold was 1.1±0.5 V with a pulse duration set to 0.5 ms. The pacing impedance was 945±237 Ohm. The mean sensing was 10.5±5.9 mV. At 1 day and 40 days follow up pacing, sensing and impedance values were unchanged without lead dislocation.
One patient with a bipolar lead in a posterolateral vein reported phrenic nerve stimulation at 40 days follow up. The location was unchanged in X ray. We implanted an additional quadripolar lead in an anterior vein for stimulation leaving the previously implanted bipolar lead in posterolateral vein as a “right ventricular” sensing lead and connected both to a CRT pacemaker device.

Discussion:
In this report, we present our experience with CS single site pacing after tricuspid valve replacement associated with AV block and in one patient with endocardial fibrosis. Lead dislocation has not been identified in any patient in a short-term follow up of 40 days, pacing and sensing parameters were stable. We conclude that single site pacing through CS provides a safe approach in the need of permanent pacing after tricuspid valve replacement in order to prevent complications such as postoperative valve thrombosis and lead induced regurgitation.  Long-term safety as well as potential advantages of such approach in comparison with RV pacing or epicardial pacing with surgical implanted leads needs further evaluation.