Low-dose aspirin improves in vivo hemodynamics in conscious, chronically infarcted rats

The equivalent of the clinically used low (= antiplatelet)-dose aspirin, inhibited collagen deposition in the non-infarcted myocardium in rats with myocardial infarction. In the present study, the in vivo hemodynamic consequences of this daily low-dose aspirin were investigated in conscious, chronically instrumented, infarcted rats. Rats, treated with 25 mg/kg aspirin daily from 2 days before to 3 weeks after coronary artery ligation, were chronically instrumented with an electromagnetic flow-probe and arterial and venous catheters, to record cardiac output, and arterial and venous blood pressure, respectively, in the conscious freely moving animal. In parallel, isolated hearts were studied with regard to left ventricular stiffness (pressure/volume relationships), maximal cardiac perfusion (adenosine), and in vitro heart rate and beta-adrenergic responsiveness. Plasma catecholamine levels were measured. Aspirin normalized the increased heart rate after infarction, at a preserved cardiac output. This was accompanied by a (non-significant) increase in stroke volume, at unchanged cardiac loading conditions. The lower heart rate after aspirin was due to reduced intrinsic heart rate rather than to lower sympathetic activation of the heart, since similar effects were observed in isolated perfused hearts, while circulating levels of catecholamines and beta-adrenergic responsiveness were not influenced. The improved stroke volume was not explained by reduced left ventricular stiffness or increased maximal perfusion after aspirin. In addition to the antithrombotic action, effects of low-dose aspirin on cardiac remodeling could be associated with favorable hemodynamic effects, as reflected by a lower heart rate for the same cardiac output. Although the underlying mechanisms are still unknown, it suggests a clinically relevant beneficial effect which deserves further investigation.