Abstract
Conventional measurement of wall thickening with two transit-time crystals requires considerable skill, is associated with myocardial trauma, and does not discern the function of different layers of the left ventricular (LV) wall. To overcome these limitations, we have developed a 10 MHz pulsed Doppler technique that measures thickening at any depth of the LV wall from a single crystal sutured to the epicardium. To verify its accurary, we compared measurements of thickening fraction (TF) by pulsed Doppler and transit-time methods in 25 open-chest dogs. The epicardial Doppler crystal was placed over an intramyocardial crystal positioned either in the subendocardium or midwall. The epicardial crystal acted as both the Doppler transducer and the transit-time transmitter, so that TF was measured by each technique at the same site. A wide range of regional function (transmural TF: -28-42%, epicardial TF:-20-28%) was produced by coronary occlusion followed by reperfusion, and by isoproterenol and phenylephrine infusions. There was a good correlation between the two methods, both for transmural TF (r = 0.98, 107 paired measurements) and epicardial TF (r = 0.99, 70 paired measurements). Despite marked changes in function, the two techniques yielded similar measurements under all of the conditions tested (base line, ischemia, 5, 15, 30, 60, 120, and 180 min of reperfusion, isoproterenol and phenylephrine). One-millimeter errors in selecting the depth of the Doppler sample volume did not significantly affect the accuracy of TF measurements. Thus the single pulsed Doppler crystal provides a single, atraumatic, and accurate means for measuring myocardial function, both transmurally and in selected layers of the LV wall.