Abstract 1684: Invasive Assessment of the Coronary Microcirculation: Novel Thermodilution Based Measure of Absolute Microvascular Resistance
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 (Qk), saline temperature (Tk) at infusion catheter tip relative to baseline blood temperature, and distal blood temperature (T) relative to baseline blood temperature, with Q = Qk · (Tk/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.