ULTRASONIC TISSUE CHARACTERIZATION OF ISCHEMIC MYOCARDIUM IN RESPONSETO PHARMACOLOGICAL STRESS TEST

We investigated changes in quantitative ultrasonic parameters of ische mic myocardium in response to moderate coronary occlusion combined wit h pharmacologic stress in five open chest dogs. Baseline ischemia was induced by cuff occluders while coronary blood flow reduction was meas ured using ultrasonic flowmeters placed around the proximal LAD and ci rcumflex (LCX) coronary arteries. Pharmacologic stress was achieved by IV infusion of adenosine (75 mcg/kg/min). Fractional shortening (FS) and integrated ultrasonic backscatter (IB) were obtained on line from M-mode tracing of anterior wall segments in a short axis view, midpapi llary level at three stages: Sl: open chest control; S2: 75% LAD occlu sion and 50% LCX occlusion; S3: adenosine plus occlusions as in S2. Cy clic variation of IB (CIB) and phase of CIB (PCIB) were analyzed off-l ine by Fourier analysis. The interventions used effectively reduced LA D flow by 39% during stage 2 and 68% during stage 3. Amplitude of cycl ic variation of integrated backscatter decreased from 3.3 +/- .5 dB (m +/- SD) during stage 1 to 1.9 +/- .7 dB and .7 +/- .4 dB during stage 2 and 3 respectively (p < .05). Wall thickening measured in the same regions of interest (anterior wall) showed a trend toward a decrease b ut changes were not statistically significant. Changes in ultrasonic t issue characterization parameters occur early and are more sensitive t han wall motion abnormalities in detecting ischemic myocardium during pharmacologic stress. The combination of ultrasonic tissue characteriz ation with pharmacologic stress may be a promising technique for detec ting coronary blood flow reduction in ischemic heart disease.