Coronary Flow Reserve and Myocardial Contrast Echocardiography

Abstract

Although there are several diagnostic techniques available for assessing coronary function, the quantification of coronary flow ( CF) and coronary flow reserve ( CFR) by angiography using an intracoronary Doppler flow wire is usually invasive. Recently, there have been several advances in echocardiography, not only in the direct visualization of the coronary arteries, but also in measuring CF and CFR. In this chapter, the current state of myocardial contrast echocardiography will be revisited, as well as the measurement of CF and CFR by transthoracic echocardiography {TTE) and transesophageal echocardiography (TEE), with special emphasis on recent advancements in ultrasound contrastenhanced agents. CF and CFR: Physiological AspectsCoronary resistance is determined not only by the "tone" of the arteries, but also by the extrinsic compression of the coronary arteries by myocardial muscle during systole. The coronary blood flow has the peculiarity of having a two-phase characteristic pattern and the blood supply to the myocardium takes place fundamentally during diastole (Fig. 7.1). The ratio between diastolic and systolic coronary flow velocity is higher than 1.5 in the left coronary artery and its branches. In the right coronary artery (RCA), this diastolic blood flow is less predominant, probably due to the small systolic resistance in the right coronary side [ 1].The left internal mammary artery (LIMA) without anastomosis has a pattern of systolic flow, the native coronary arteries have a twophase pattern with predominant diastolic flow, and bypass graft with LIMA has a twophase pattern, although the diastolic component is undoubtedly less intense than in the native coronary arteries. The ratio of diastolic and systolic blood flow velocity in coronary bypass grafts of the LIMA is smaller in the proximal portion than in the distal segment [2, 3]. However, the flow in coronary artery bypass grafts of the saphena vein shows a predominant diastolic component along the J. L. Zamorano et al., Contrast Echocardiography in Clinical Practice