In vitro method for measurement of cardiac performance and responses to inotropic drugs after experimentally induced myocardial infarction in the rat.

In this paper, a method is described for the measurement of the performance of rat hearts with an experimentally induced myocardial infarction of the left ventricle. After ether anesthesia of the animals and left thoracotomy, the left coronary artery was ligated, and the thorax was rapidly closed. The whole procedure took no more than 2 min. Forty-eight hours after the operation, the hearts were prepared for retrograde constant pressure perfusion, according to the Langendorff technique. The effects of the betasympathomimetic drug dobutamine and of the novel phosphodiesterase inhibitor milrinone on the contractile force of the right ventricle and the infarcted left ventricle, as well as on the total coronary flow, were quantified. Sham operated animals were used as control. The maximal obtainable stimulation of the contractility of infarcted hearts by dobutamine was significantly reduced from control. Milrinone increased the contractility in control animals, although to a much lesser extent. This increase was significantly smaller in infarcted hearts. The stimulation of the coronary flow by dobutamine and milrinone was significantly reduced in hearts with an infarction. Milrinone potentiated the effect of isoprenaline significantly. The results of the present study indicate the usefulness and reproducibility of this model for the evaluation of the efficacy of positive inotropic agents on the heart in the presence of a myocardial infarction.