Echocardiographic assessment of coronary microvascular dysfunction: Basic concepts, technical aspects, and clinical settings

FIGURE 1. Color Doppler images of the distal left anterior descending coronary artery (LAD) and interventricular posterior coronary artery (IVP). The modified apical 4‐chamber (A) and 2‐chamber (B) positions, with cranial angulation of the transducer and a Nyquist limit of 20‐67 cm/s, allow optimal identification of the diastolic coronary flow. LV = left ventricle; RV = right ventricle; LA = left atrium

FIGURE 2. an example of normal coronary flow reserve in a healthy subject. Velocity patterns are registered by pulsed‐wave Doppler. Resting laminar peak diastolic velocity in normal coronary artery is from 0.21 ± 0.08 m/s to 0.28 ± 0.09 m/s, and the velocity will not exceed 1 m/s even in case of its three‐ fourfold increase in the stenosis site. CFR is expressed as the ratio of coronary flow velocity under maximal vasodilatation to coronary flow velocity at rest. In this case, the basal peak diastolic flow velocity is normal, and it increases more than 2 times after dipyridamole, and therefore, CFR is normal. LV = left ventricle; Vp(d) = velocity peak (diastolic); CFVR = coronary flow velocity ratio

FIGURE 3. impaired CFR in an HCM patient with normal epicardial coronary arteries. Basal increased coronary flow with high peak diastolic flow velocity in distal LAD at rest; after dipyridamole, the increase of peak diastolic flow velocity is slight, and CFR is equal to 1.2. Vp(d)= velocity peak (diastolic)