Development and validation of a novel angiography-derived index of absolute coronary blood flow and resistance

Intracoronary continuous thermodilution has been recently proposed as an invasive method to quantify absolute coronary flow (Q_abs) and resistance (R_abs) in vivo. The aim of the present study is to develop and validate of a novel pressure-wire- and microcatheter-free surrogate of coronary flow and resistance derived from a standard coronary angiogram. Angiography derived coronary flow (Q_angio) and resistance (R_angio) was prospectively validated in a two-center cohort of patients from Oxford Heart Centre and the Essex Cardiothoracic Centre. Q_abs and R_abs were measured during resting and hyperemic conditions with continuous thermodilution using the Rayflow microcatheter. Q_angio and R_angio were computed from the diagnostic coronary angiogram in a blinded fashion in resting and hyperemic conditions. A total of 62 patients and 115 vessels were included in the present analysis. The median Q_abs at rest was 75 ml/min (53-95) and 151 ml/min (105-203) during hyperemia; Q_angio at rest was 84 ml/min (66-108) and 154 ml/min (115-195) during hyperemia. There was a strong correlation between Q_abs and Q_angio (R = 0,72; p < 0.001, R = 0,86; p < 0.001 respectively) with satisfactory interclass correlation (0.841, 95% CI 0.509-0.957; p = 0.0003). The median R_abs was 1111 mmHg/(L/min) (830-1581.4) at rest and 454 mmHg/(L/min) (348-610) during hyperemia; angiographic resistance (R_angio) was 937.4 mmHg/(L/min) (695.4-1261.9) at rest and 492.4 mmHg/(L/min) (406-697) during hyperemia. There was a strong correlation between R_abs and R_angio in both conditions (R = 0,81; p < 0.001 and R = 0,78; p < 0.001 respectively). The was a good correlation between absolute coronary flow reserve (CFR) and angiography-derived CFR (R = 0,61; p < 0.001) and between absolute microvascular resistance reserve (MRR) and angiography-derived MRR (R = 0,49; p < 0.001).