Abstract 1684: Invasive Assessment of the Coronary Microcirculation: Novel Thermodilution Based Measure of Absolute Microvascular Resistance

Abstract

Background: Assessment of coronary microcirculatory function would aid in understanding the pathophysiology of various disease states. Recently Pijls and colleagues introduced a novel thermodilution based measure of absolute coronary flow. We hypothesize that this method will allow quantitation of absolute microvascular resistance during cardiac catheterization. Method: Using a coronary pressure/temperature wire and subselective coronary infusion catheter, volumetric coronary flow (Q) is derived by principle of thermodilution from saline infusion rate (Q k ), saline temperature (T k ) at infusion catheter tip relative to baseline blood temperature, and distal blood temperature (T) relative to baseline blood temperature, with Q = Q k · (T k /T) · 1.08. We hypothesize that distal coronary pressure divided by calculated flow provides a measure of microvascular resistance (MR) and will correlate with true microvascular resistance (TMR), defined as distal coronary pressure divided by hyperemic flow measured with external ultrasonic flow probe. A total of 111 measurements in the left anterior descending (LAD) distribution were made in 8 Yorkshire swine at baseline and after microcirculatory disruption with microsphere embolization, with and without epicardial LAD stenosis. Results: Thermodilution based LAD flow correlated well with ultrasound based flow ( r = 0.88, p < 0.0001, mean absolute difference 20 ml/min), in both presence ( r = 0.88, p < 0.0001) and absence ( r = 0.87, p < 0.0001) of microcirculatory disruption. Correspondingly, there was significant agreement between MR and TMR ( r = 0.66, p < 0.0001). Mean MR increased significantly after microsphere injection (0.54 ± 0.11 to 0.86 ± 0.18 mmHg · mL −1 · min −1 , p < 0.0001), in both presence (0.56 ± 0.12 to 0.82 ± 0.11 mmHg · mL −1 · min −1 , p < 0.0001) and absence (0.49 ± 0.06 to 0.91 ± 0.27 mmHg · mL −1 · min −1 , p < 0.0001) of epicardial stenosis. After microcirculatory disruption, % change in MR (164 ± 30%) was similar to % change in TMR (161 ± 36%, p = NS vs. MR % change). Conclusion: This novel thermodilution based method provides quantitative and accurate assessment of microvascular resistance in selective coronary territories and can facilitate investigation of coronary physiology during cardiac catheterization.