Phasic flow patterns of right versus left coronary arteries in patients undergoing clinical physiological assessment

Background: Coronary blood flow in humans is known to be predominantly diastolic. Small studies in animals and humans suggest that this is less pronounced or even reversed in the right coronary artery (RCA). Aims: This study aimed to characterise the phasic patterns of coronary flow in the left versus right coronary arteries of patients undergoing invasive physiological assessment. Methods: We analysed data from the Iberian-Dutch-English Collaborators (IDEAL) study. A total of 482 simultaneous pressure and flow measurements from 301 patients were included in our analysis. Results: On average, coronary flow was higher in diastole both at rest and during hyperaemia in both the RCA and LCA (mean diastolic-to-systolic velocity ratio [DSVR] was, respectively, 1.85 +/- 0.70, 1.76 +/- 0.58, 1.53 +/- 0.34 and 1.58 +/- 0.43 for LCA(r)(est), LCA(hyp), RCA(rest). and RCA(hyp), p<0.001 for between-vessel comparisons). Although the type of RCA dominance affected the DSVR magnitude (RCA(dom)=1.55 +/- 0.35, RCAF 1.40 +/- 0.27, RCA(non-dom)=1.35; standard deviation not reported as n=3), systolic flow was very rarely predominant (DSVR was greater than or equal to 1.00 in 472/482 cases [97.9%] overall), with equal prevalence in the LCA. Stenosis severity or microvascular dysfunction had a negligible impact on DSVR in both the RCA and LCA (DSVR x hyperaemic stenosis resistance R-2=0.018, p=0.03 and DSVR x coronary flow reserve R-2<0.001, p=0.98). Conclusions: In patients with coronary artery disease undergoing physiological assessment, diastolic flow predominance is seen in both left and right coronary arteries. Clinical interpretation of coronary physiological data should therefore not differ between the left and the right coronary systems.