[Non-invasive assessment of coronary flow reserve with transthoracic echocardiography: physiopathology, methodology and clinical value]

The assessment of coronary flow reserve with transthoracic Doppler echocardiography, measured as the ratio between hyperemic and baseline coronary flow velocities, is a new tool for the evaluation of coronary artery disease and coronary microcirculation. Color-guided pulsed Doppler allows almost optimal identification of flow velocities at the middle and distal left anterior descending artery and good visualization of the right coronary artery. The development of ultrasound technology (second harmonic, contrast agents, dedicated softwares) is responsible for great feasibility (until 98% for the left anterior descending artery and 40-50% for the right coronary artery) and very good reproducibility of this tool. Doppler-derived coronary flow reserve has excellent concordance with that obtainable with intravascular Doppler flow wire. Diagnosis of stenosis and restenosis after stent implantation in the middle and/or proximal left anterior descending artery and of stenosis of the right coronary artery is very accurate. In the absence of stenosis of epicardial coronary arteries, the reduction in coronary flow reserve implies a damage of coronary microcirculation, which can be a determinant of angina pectoris and signs of myocardial ischemia in arterial hypertension, diabetes mellitus and coronary X syndrome. Further progress may be expected by using myocardial contrast agents for quantitation of regional myocardial coronary flow reserve.