Myocardial Perfusion, Coronary Flow Reserve and Kinetic Analysis During Dobutamine Stress Echocardiography

Overview

Stress echocardiography is a screening test for coronary heart disease that already has good sensitivity and specificity (both around 70%). This examination is mainly offered to stable patients, consulting externally, in order to detect ischemic heart disease in the same way as would a myocardial scintigraphy or MRI stress. This examination is an echocardiographic modality consisting in visualizing and analyzing the modifications of the contraction of the cardiac muscle during a stress constituted by an effort or by injection of certain drugs. Stress echocardiography is performed by injection of drugs to reproduce the conditions of the effort. The products used to perform this examination are initially an intravenous infusion of dobutamine, atropine whose effect is to increase the heart rate, and in a second time, an intravenous infusion of beta-blockers or a bradycardic calcium channel blocker at the end of the procedure whose effect is to slow down the heart rate. The use of echographic contrast medium, allowing a better visibility, is recommended for the realization of a stress ultrasound, since the echogenicity is judged insufficient on two segments (segmentation of the left ventricle in 17 segments). The analysis of dobutamine stress echocardiography currently relies solely on the analysis of segmental kinetics, namely the quality of the thickening of the endocardium. When segmental kinetics are abnormal, patients benefit from a coronary CT scan or coronary angiography to visualize all the coronary arteries and to check whether there is a narrowing of the arteries. Moreover, stress echocardiography performed using a contrast medium makes it possible to analyze two other indices in addition to segmental kinetics. Thus, the second parameter that can be analyzed corresponds to the Coronary Flow Reserve measurement, thanks to the easy identification of the Doppler flow in the anterior interventricular at rest and peak of dobutamine. The coronal reserve is well validated with adenosine, but much less well known under dobutamine. The third parameter that can be analyzed is myocardial perfusion. By using appropriate settings, it is possible to see the microbubbles in the thickness of the myocardium. These bubbles are then destroyed by an ultrasonic flash of high mechanical index. This results in the destruction of all intra-myocardial bubbles. The analysis of the myocardial perfusion is based on the rate of reappearance of these bubbles (through the coronary arteries) at rest and peak stress. In case of significant stenosis or coronary occlusion, there is a delay or complete absence of perfusion in the territory concerned. Joint analysis of segmental kinetics, coronary reserve and myocardial perfusion has already been described with adenosine, but not with dobutamine. Studies in the literature suggest that the analysis of coronary reserve on the one hand, and myocardial perfusion on the other hand would increase the sensitivity and specificity of the examination. In addition, other studies suggest that among the tests considered normal for segmental kinetics analysis, there are patients with myocardial perfusion abnormality and / or coronary reserve abnormality that strike (s) on prognosis (alteration of the coronary microcirculation). This is why it seems interesting to compare the results of these 3 indices obtained during stress echocardiography under dobutamine.