Segmental mid-wall myocardial dimensions in man recorded by sonomicrometry

Abstract

Regional myocardial function after cardiac operations has been quantitated indirectly by conventional angiography, radionuclide angiography, epicardial markers, and the intraoperative application of isometric epicardial force gauges. However, real-time assessment of regional mid-wall myocardial motion has not been possible. The purpose of this study was to assess the feasibility of using pulse transit sonomicrometry, as described by Franklin and associates in experimental animals, to measure regional mid-wall dimensions in man. To test the applicability of this system in the human heart, we implanted two miniature ultrasonic transducers at mid-wall depth into a region of myocardium supplied by a bypass graft. They were located along the minor axis of the heart, 1 cm. apart and at a depth of 7 mm. from the epicardium. A 16 gauge polyvinyl catheter was positioned into the left ventricle for measuring left ventricular pressure, left ventricular end-diastolic pressure (LVEDP), dP/dt, and timing wall motion signals. Following termination of bypass, the patients were studied prior to and 30 seconds after graft occlusion. The transducers then were removed and no complication related to their use was encountered. From the wall motion signals in 17 patients, we calculated end-systolic length (ESL), end-diastolic length (EDL), and the extent and rate of both shortening and relaxation. Ischemia, induced by graft occlusion, was associated with abnormal systolic wall bulging as well as significant changes in systolic excursion and systolic lengths. By varying left ventricular filling volumes, we were able to assess regional left ventricular mid-wall compliance as well as systolic function. Inotropic agents resulted in a decrease in ESL with a resulting increase in the systolic excursion. Further refinement of this technique should allow more accurate measurement of bypass effects in hearts with regional contraction abnormalities.