[The significance of heart rate for stress hemodynamics following heart transplantation].

Since 1985, orthotopic heart transplantation had been carried out in 20 patients. Seventeen patients are still alive. 341 +/- 156 days after cardiac transplantation hemodynamics at rest were normalized. Left ventricular ejection fraction at rest and during exercise was within normal ranges for all patients except one. During symptom-limited bicycle exercise (121 +/- 35 Watt), pulmonary capillary wedge pressure (PCP) and right atrial pressure (RAP) increased to unphysiological high levels (PCP: 8.2 +/- 2.7 mmHg at rest, 19.1 +/- 4.9 mmHg at exercise; RAP: 4.1 +/- 2.3 mmHg at rest, 12.1 +/- 3.9 mmHg at exercise), whereas cardiac index was elevated to a normal level (3.6 l/min.m2 at rest; 6.9 l/min.m2 at exercise). Increase in heart rate, however, was subnormal (from 90 +/- 13/min at rest to 122 +/- 15/min at exercise). To examine the influence of heart rate on hemodynamics, in 8 patients with normal tricuspid valve function, heart rate was gradually increased by atrial stimulation during continuous exercise; PCP maximally could be reduced from 19.1 +/- 4 mmHg to 10.8 +/- 2.7 mmHg (p less than 0.01) at an optimum heart rate of 139 +/- 9/min. Reduction of RAP was by far less pronounced and normalization could not be achieved (from 12.2 +/- 3.7 mmHg to 9.5 +/- 3.4 mmHg, p less than 0.01), suggesting an impaired right ventricular function. By atrial stimulation stroke volume was reduced from 109.8 +/- 17.7 ml to 91.8 +/- 14.2 ml (p less than 0.01). These results indicate that, at exercise, the denervated transplanted heart, to a large extent, increases cardiac output by means of the Frank-Starling mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)