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Normal Values of Thermodilution-Derived Absolute Coronary Blood Flow and Microvascular Resistance in Humans.

AIMS
Absolute hyperemic coronary blood flow (Q, in mL/min) and resistance (R, in Woods Units, WU) can be measured invasively by continuous thermodilution. The aim of this study was to assess normal reference values of Q and R.


METHODS AND RESULTS
In 177 arteries (69 patients: 25 controls i.e. without identifiable coronary atherosclerosis; 44 patients with mild, non-obstructive atherosclerosis), thermodilution-derived hyperemic Q and total, epicardial, and microvascular absolute resistances (Rtot, Repi, and Rmicro) were measured. In 20 controls and 29 patients measurements were obtained in all 3 major coronary arteries,thus allowing calculations of Q and R for the whole heart. In 15 controls (41 vessels) and 25 patients (71 vessels),vessel-specific myocardial mass was derived from coronary computed tomography angiography. Whole heart hyperemic Q tended to be higher in controls compared to patients (668±185 vs 582±138 mL/min,p=0.068). In the left anterior descending coronary artery (LAD), hyperemic Q was significantly higher (293±102 mL/min versus 228±71 mL/min,p=0.004) in controls than in patients . This was mainly driven by a difference in Repi (43±23 vs 83±41 WU, p=0.048),without significant differences in Rmicro. After adjustment for vessels-specific myocardial mass, hyperemic Q was similar in the 3 vascular territories (5.9±1.9,4.9±1.7,and 5.3±2.1 mL/min/g,p=0.44,in the LAD, left circumflex and right coronary artery,respectively).


CONCLUSIONS
The present report provides reference values of absolute coronary hyperemic Q and R. Q was homogeneously distributed in the 3 major myocardial territories but the large ranges of observed hyperemic values of flow and and of microvascular resistance preclude their clinical use for interpatient comparison.