LEFT-VENTRICULAR RESPONSES TO EXPERIMENTAL AORTIC COARCTATION IN GROWING PUPPIES

The haemodynamic status of 8 coarctated and 7 sham-operated beagle puppies was studied by a catheterization technique at rest and during isoproterenol and volume loading at the ages of 7 (I) and 9 (II) months (5 and 7 months after the experimental coarctation). Proximal aortic systolic and pulse pressures were constantly higher in the coarctation group than in the control group (P < 0.05), and the systolic pressure gradient across the coarctation was always significantly higher in the coarctation group [I at rest mean 45 +/- 5 (SD) vs 5 +/- 4 mmHg, P < 0.001, and after I isoproterenol infusion 56 +/- 9 vs 10 +/- 6 mmHg, P < 0.001, and after I dextran infusion 58 +/- 10 vs 8 +/- 7 mmHg, P < 0.001]. The time constant of exponential isovolumic left ventricular pressure fall after the isoproterenol tests was longer in the coarctation group (I 28 +/- 8 ms and II, 30 +/- 4 ms) than in the control group (I, 21 +/- 2, P < 0.05 and II, 19 +/- 3 ms, P < 0.005), indicating impaired relaxation. The tension time index during the volume loading tests increased in the coarctation dogs (I, 4150 +/- 660 and II, 4080 +/- 810 mmHg s min-1) to higher levels than in the control group (I, 3550 +/- 220, II, 2540 +/- 1140 mmHg s min-1, P < 0.05 both). Cardiac output, left ventricular end diastolic pressure, inotropic parameters and heart rate were similar in both groups during the infusions. The results show that the hearts of the young animals exposed to chronic pressure load by aortic coarctation maintained their pump performance well. The changes in left ventricular relaxation may be an early sign of impaired diastolic function.