Sonomicrometry was used in 10 conscious dogs to measure regional segment length and dynamic wall thickness by telemetry in a zone supplied by the left circumflex coronary artery after implantation of an ameroid constrictor. When coronary obstruction was nearly complete and collaterals had developed (24-42 days), control exercise and exercise runs after oral isosorbide dinitrate were carried out. During control runs, significant increases occurred in hemodynamic parameters, and percent shortening in normal segments increased (P < 0.01). During the repeat runs after isosorbide dinitrate, there were smaller increases in left ventricular systolic and end-diastolic pressures and significantly reduced end-diastolic dimensions. In addition, percent wall thickening and percent segment shortening in the ischemic zone did not deteriorate significantly during exercise. In this animal model, which appears to mimic chronic single-vessel coronary heart disease, isosorbide dinitrate can prevent exercise-induced deterioration of regional myocardial function.
In five open-chest dogs, pairs of ultrasonic dimension gauges were implanted in the anterior papillary muscle and in a circumferential subendocardial segment of the anterior left ventricular free wall, and simultaneous recordings were made with intracardiac pressure. The average shortening of the anterior segment in isovolumetric systole was 6% of end-diastolic length (EDL), with a total shortening of 19%. In the papillary muscles, isovolumetric shortening averaged 2%, total shortening was 10%, and shortening velocity was only 0.60 length/s. With acute pressure and volume overload, or inotropic interventions, changes in EDL were relatively less in papillary muscles than in the free wall. During acute occlusion of the anterior descending coronary artery, shortening of anterior segments and papillary muscles was replaced by holosystolic lengthening, and occlussion of the circumflex artery produced augmentation of shortening in both these regions, with lengthening of the posterior papillary muscle. The present study documents shortening of the anterior left ventricular papillary muscle throughout systole that is substantially less than that of the circumferential free wall, and demonstrates severe papillary muscle dysfunction with systolic elongation during regional ischemia.
