Intramural Myocardial Shear During the Cardiac Cycle

Instantaneous and continuous shearing strains at various sites in the wall of the left ventricle were measured in 19 dogs with a specially designed transducer. Relatively large shearing strains occurred during the "isovolumic" and immediately prediastolic portions of systole. Shearing strain during diastole was small. Under control conditions the average shearing strain during the ejection period of systole was 0.0218 radians (1.25°) at a 6 mm depth into the myocardium. Intravenous infusion of norepinephrine (approximately 0.001 mg/kg per minute) increased myocardial shear from 0.0177 radians (1.01°) to 0.0274 radians (1.57°) during the ejection period. It is concluded that shearing strain in the myocardium during the ejection period is relatively small.