Left ventricular dynamics and plasma catecholamines during isometric exercise in patients following cardiac transplantation.

Haemodynamics and plasma catecholamine responses to isometric exercise were evaluated invasively in 11 orthotopic heart transplant recipients and seven control subjects. Differences in haemodynamic responses between the two groups were already apparent after one min of handgrip at 30% of maximal voluntary contraction, and very pronounced at the end of the fourth minute. At this point transplanted patients showed smaller increments in heart rate (4.8 +/- 3.2 vs 20.4 +/- 14.1 beats.min-1, P less than 0.001), mean arterial pressure (13.7 +/- 7.2 vs 31.5 +/- 12.2 mmHg, P less than 0.001) and cardiac index (0.51 +/- 0.22 vs 1.02 +/- 0.53 L.min-1.m-2, P less than 0.01), whereas left ventricular end-diastolic pressure increased to a greater extent (8.8 +/- 4.9 vs 2.2 +/- 1.8 mmHg, P less than 0.01). Stroke volume index increased similarly (3.8 +/- 1.8 vs 2.0 +/- 3.5 ml beat-1.m-2, NS) and systemic vascular resistance remained unchanged in both groups. The slopes of the left ventricular function curves (ratio of change in left ventricular work to change in left ventricular end-diastolic pressure) indicated depressed left ventricular function in the transplanted patients. The two groups showed similar increments in mixed venous plasma norepinephrine and epinephrine indicating normal sympathoadrenal activation in the transplanted patients. In conclusion, transplanted hearts respond to handgrip with attenuated increases in heart rate, cardiac output and arterial pressure and by increasing left ventricular filling pressure, suggesting a poor contractile reserve probably due to denervation. Circulating catecholamines, especially epinephrine, probably contribute to the cardiac responses to isometric exercise.