Functional coronary angiogram findings in angina with non-obstructive coronary arteries patients with coronary slow flow

Background The Coronary Slow Flow Phenomenon (CSFP) is considered a coronary microvascular disorder and has been defined as a corrected thrombolysis in myocardial infarction frame count (cTFC) ≥25 frames. Recent invasive physiology studies have reported that cTFC is not a surrogate marker for coronary microvascular dysfunction (CMD), defined by an abnormal Coronary Flow Reserve (CFR), questioning the integrity of CSFP. This study evaluates the Functional Coronary Angiography (FCA) findings of patients with and without CSFP, as well as the relationship between cTFC and invasive coronary functional measures. Methods FCA utilizing a pressure-Doppler flow wire during adenosine infusion, and acetylcholine provocation, was undertaken in 103 patients with angina and non-obstructive coronary artery disease (<50% stenosis; ANOCA). Results The FCA findings revealed CMD (i.e. CFR<2) in 43%, inducible coronary artery spasm (58%) and microvascular spasm (13%) in patients with the CSFP ( n = 69), which was similar to those without CSFP ( n = 34). However, the CSFP patients had a lower resting coronary blood flow velocity (19 ± 7 vs 23 ± 7cm/s, P = . 009) with higher resting microvascular resistance (5.8 ± 1.9 vs 4.4 ± 1.7mmHg/cm/s, P = . 006) and higher hyperemic microvascular resistance (2.35 ± 1.09 vs 1.94 ± 0.93, P = . 049), despite a similar hyperemic CFR (2.25 ± 0.84 vs 2.26 ± 0.58, P = . 971) compared to those without CSFP. Furthermore, the cTFC as a continuous measure, correlated with resting coronary blood flow, resting/hyperemic resistance but not CFR. Conclusion The conventional marker of CMD (i.e. CFR <2) was similar in patients with/without the CSFP. However alternative hemodynamic markers of impaired coronary microvascular function were abnormal in patients with the CSFP, including resting/hyperemic coronary microvascular resistance. Moreover, cTFC is a simple semi-quantitative marker correlated with coronary microvascular resistance and thus has clinical utility in the diagnosis of the CSFP.