Orthotopic heart transplantation (OHT) is most effective method for treatment of irreversible heart failure. Patients after OHT considered for permanent pacing consist still present a challenge for the implanting physician due to distorted atrial geometry and specific electrophysiological conditions of atrium. The aim of our study was to analyse the effectiveness of permanent atrial pacing in these patients. PATIENTS AND METHODS: We implanted atrial lead in 37 SND pts., 2 months--7 years after OHT, (3 pts with coexisting AV block received ventricular lead). Only straight BP screw-in leads and manually formed stylets were used; we found satisfactory pacing/sensing conditions in 25 pts in RA appendage or anterior/lateral wall, in 10 pts--in CS ostium region and in 2--in proximal part of CS. RESULTS: All implantations were successful and no patient received VVI pacing system. One dislodged lead required revision (1/37, 3%) but this was not related to endomyocardial biopsy. In 2 pts, due to unacceptable low RA potential and/or high PTh values atrial lead was implanted to CS for sensing/pacing of left atrium. The average acute value of A wave were 2.4 mV and chronic 2.2 mV; values of pacing threshold were 0.9 V and 1.6 V respectively. Only in 13/37 pts native A waves were recorded but with amplitude < 0.6 mV. Wenckebach point was 120/min only in 2 pts., in borders 130-160 bpm in 15 pts. and exceeded 170 bpm. in remained 20 pts. Retrograde VA conduction was intact in 33/37 pts, but in 4 pts exceeded 260/min. During long term follow-up in no patient we observed AV conduction disturbances. In 6 pts. treadmill exercise (Bruce's protocol) was repeated three times during: sinus (spontaneous) rhythm, AAI pacing 70/min, AAI-R (DDD-R) pacing. AAI 70 bpm did not influence significantly attained workload, heart rate on peak exercise or duration of exercise. But atrial rate modulated pacing increased values of examined parameters significantly. CONCLUSIONS: 1. Atrial pacing (and atrial based pacing modes) are possible in majority of transplanted heart patients. 2. Frequency of atrial lead dislocation, appearance of atrial sensing problems and AV conduction disturbances (all in about 3%) are comparable to non-transplanted patients. 3. In most patients with SND after OHT AV conduction remains within normal limits; it indicates safety of rate responsive pacing modes in these patients. 4. Rate modulated atrial pacing improves exercise tolerance in heart transplanted patients with SND. 5. High ("supra-normal") values of Wenckebach's point observed in most of patients with transplanted (dennervated) heart may have clinical importance in cases of atrial arrhythmias in these patients.

Keywords: Arrhythmias, Cardiac - diagnosis, Cardiac Pacing, Artificial - methods, Electrocardiography, Exercise Test, Heart Atria, Heart Rate, Heart Transplantation - physiology, Postoperative Complications - diagnosis, Time Factors