Persistence of myocardial failure following removal of chronic volume overload

Length-contractile force curves and dose-response curves of heart rate, blood pressure, and contractile force were recorded from the left ventricle of six anesthetized dogs in a control state. These measurements were repeated at an average of 56 days following creation of an atrioventricular fistula when signs of heart failure were present. The fistula was then closed and the dogs restudied after an additional 57 days. Heart failure was associated with a shift up the ascending limb of a depressed length-contractile force curve and a depressed contractile response to isoproterenol. For instance, 0.1 micrograms/kg of isoproterenol produced a 173 +/- 8% increase in contractile force in control and 42 +/- 7% in failure. The contractile response to ouabain (30 micrograms/kg) was unchanged in heart failure, i.e., 36 +/- 5% in control vs. 39 +/- 4% in heart failure. When the dogs were restudied following fistula closure, the length-contractile force curve was still depressed as was the contractile response to isoproterenol, whereas the response to ouabain was again unchanged from control. Plasma norepinephrine and renin levels increased 5- and 10-fold, respectively, during heart failure and then returned to control following closure of the fistula. The data support the view that myocardial dysfunction associated with volume-overload heart failure is not reversible within the same time frame as its onset.