Myocardial contrast two-dimensional echocardiography: Experimental examination at different coronary flow levels

Regional myocardial echo contrast appearance-disappearance after intracoronary contrast agent injection was examined with computerized two-dimensional contrast echocardiography in eight open chest dogs during successive variation of the coronary blood supply. A new sonication method applied to dextrose 50% produced an echo contrast agent with a microbubble size of 12 ± 6 μ (mean ± standard deviation), and 1 cc of this agent was injected into a coronary artery during the echocar-diographic study of the left ventricle. Left anterior descending or circumflex coronary artery flow, measured by electromagnetic flowmeter, was successively reduced up to 90% with an extravascular hydraulic occluder, or else increased 40 to 60% through intravenous dipyridamole infusion (7 to 10 μg/kg per min). The corresponding myocardial echo time-intensity curves were analyzed for each of 12 segments of a midventricular short-axis cross section.Several potential indexes of myocardial perfusion were derived: peak echo contrast intensity, time from echo contrast appearance to peak intensity, half-life of echo contrast decay phase (T½ and total duration of contrast appearance-disappearance. Except for peak intensity, all of these indexes provided significant (p < 0.05) differentiation between control coronary flow (66 ± 17 nil/min) and greater than 50% flow reductions (26 ± 6 nil/min) or hyperemia (115 ± 17 ml/min). Half-life values were 5.2 ± 0.3 seconds for the control state, 9 ± 2 seconds for the reduced coronary flow and 2 ± 2 seconds for dipyridamole hyperemia. Compared with an echo contrast-delineated circumferential extent of 5.6 ±1.4 myocardial segments subserved from the site of the coronary occluder, greater than 50% flow reduction significantly decreased contrast disappearance T½ in 3.7 ± 1.7 segments versus decreased systolic wall thickening in 6.6 ±1.4 segments. T½ for the central ischemic zone correlated moderately with coronary flow (r = 0.56, p < 0.05).It is concluded that myocardial contrast two-dimensional echocardiography, using small microbubbles as the agent, can identify a primary perfusion defect and may permit characterization of myocardial blood supply