[Measurement of coronary reserve by high-frequency transthoracic Doppler ultrasonography: indications and results].

Coronary flow reserve is the ability of coronary flow to increase above its basal value when the coronary vascular bed is maximally dilated. It is a global parameter of coronary flow, which is early altered in the presence of epicardial coronary artery stenosis or a coronary microcirculation disorder. Until now, clinical use of coronary flow reserve has been hampered by the lack of an easy, reliable and non-invasive method. Recently developed high-frequency transthoracic Doppler echocardiography now allows non-invasive assessment of coronary flow reserve. After an initial learning curve, it is possible to study coronary flow, essentially in the left anterior descending artery. Coronary flow reserve is expressed as the ratio of maximal hyperaemic to basal mean coronary velocity. Maximal hyperaemic flow is obtained with adenosine. Clinical applications of coronary flow reserve are numerous. Coronary flow reserve enables the assessment of hemodynamic relevance of a moderate coronary stenosis. Detection of coronary restenosis is also possible by repeated non-invasive measurement of coronary flow reserve. Moreover, evaluation of the microcirculation is of crucial importance in order to appreciate myocardial reperfusion following successful recanalisation on the infarct-related artery. Transthoracic Doppler echocardiography could allow identification of "no-reflow" by analysis of coronary flow pattern and coronary flow reserve. Furthermore, transthoracic Doppler echocardiography constitutes one of the only available and simple means to evaluate microcirculatory disorders (hypertension, diabetes,...). Finally, the possibility of non-invasive follow-up of arterial bypasses constitutes a major advantage of this technique.