The waveform index of the ophthalmic artery predicts impaired coronary flow reserve

Coronary flow reserve (CFR) can decrease with impairment in coronary microcirculation, even in the absence of epicardial conduit obstruction. Recently, the ophthalmic artery (OA), which is the first major branch of the internal carotid artery and is representative of microarterioles, has been identified using color Doppler sonography. However, the features of ultrasound waveform indices suggestive of impaired OA microcirculation and the relationships between these indices and CFR have not been elucidated. The present study aimed to assess the features of ultrasound waveform indices suggestive of impaired OA microcirculation and the relationships between these indices and CFR.

A total of 30 consecutive patients with a normal coronary angiogram and normal left ventricular function were studied. Patients with ≥ 25% stenosis of the right common or internal carotid artery were excluded. The CFR was defined as the ratio of adenosine-induced hyperemic to baseline blood flow velocity with an intracoronary Doppler guidewire. Color Doppler imaging was used to determine the blood flow velocity of the right OA, and the indices of peripheral resistance (resistance index [RI], pulsatility index [PI], and systolic mean velocity to diastolic mean velocity [Sm/Dm] ratio) were calculated. The ultrasound form showed a distinctive biphasic wave during systole followed by a monophasic wave during diastole. The velocity component in the early-systolic wave was higher than that in the mid-systolic wave or the diastolic wave (31.4 ± 5.1 vs. 26.1 ± 5.4 vs. 15.9 ± 4.0 cm/s, P<0.0001). The RI and PI were not related to the CFR, and the Sm/Dm ratio was negatively correlated with the CFR (β=-0.415, P=0.022). However, the relationship was attenuated by clinical variables closely associated with the Sm/Dm ratio or CFR, and hemoglobin A1c was a common mediator. The best Sm/Dm ratio cutoff for predicting an impaired CFR was 2.5 based on a receiver operating characteristic curve analysis.

An increase in the Sm/Dm ratio, which reflects a characteristic waveform, indicates impaired OA microcirculation. The ratio is negatively correlated with CFR, and therefore, it may be applied for the noninvasive evaluation of coronary physiology. Furthermore, hemoglobin A1c may be a common mediator for the OA and coronary microcirculation.