DO HEART-TRANSPLANT RECIPIENTS BENEFIT FR OM RATE-ADAPTIVE PACING

Exercise capacity of heart transplant recipients is limited in compari son to normals and, due to cardiac denervation, exercise-induced heart -rate response is blunted in these patients. In order to evaluate the effect of rate-responsive atrial pacing on exercise capacity, 13 patie nts (three female, 10 male; age: 53 +/- 7 years) were studied 2-35 mon ths after orthotopic heart transplantation. Spiroergometry with breath -to-breath gas analysis was performed during a progressive supine bicy cle test with a starting workload of 25 watts and increments of 15 wat ts every minute. In comparison to 1 0 normals (two female, eight male; age: 51 +/- 7 years) maximal heart rate (127 +/- 17 vs. 146 +/- 12 mi n-1), maximal work load (107 +/- 27 vs. 208 +/- 42 watts) and oxygen c onsumption at the anaerobic threshold (9 +/- 2 vs. 18 +/- 4 ml/kg/min) were significantly reduced in heart transplant recipients (p < 0.05). During the exercise test the p-waves of the remaining part of the rec ipients' atria were registered via a transoesophageal catheter. The ma ximal rate of the innervated recipients sinus node (146 +/- 15 min-1) was equal to the maximal heart rate of the control group. The exercise protocol was repeated during atrial stimulation of the transplanted h earts. To achieve a physiological adaptation of the heart rate, the pa cing rates were adjusted to the rates of the recipients sinus node. In comparison to the previous tests an improvement of cardiopulmonary ex ercise capacity was not observed during rate adaptive pacing. Thus, in heart transplant recipients without bradycardias requiring pacing, th e implantation of rate-adaptive pacemacers for normalization of the he art-rate response during exercise cannot be recommended.