In vivo validation of intra-coronary absolute flow measurements and comparison of reliability between different microvascular indices and the microvascular resistance reserve

Background Coronary microvascular dysfunction plays a major role in patients with cardiac ischemia without flow limiting epicardial coronary stenosis, takotsubo cardiomyopathy, aortic valve stenosis and heart failure with preserved ejection fraction. In clinical practice, the index of microvascular resistance (IMR) and coronary flow reserve (CFR), and more recently the absolute coronary blood flow (ABF), absolute coronary resistance (ACR) and the microvascular resistance reserve (MRR) are used as parameters to measure resistance and flow using continuous coronary thermodilution. Purpose Firstly, to validate ABF measured with continuous coronary thermodilution in vivo against epicardial doppler-measured flow. Secondly, to assess reliability and reproducibility in-vivo of different microvascular indices. Methods For the purpose of this study coronary measurements were conducted in two large animal models and in patients, all with the appropriate ethical committee approval. For the first part of the study, fourteen sheep underwent repeated paired measurements of ABF and ACR (with use of continuous thermodilution) with different saline infusion speeds, as well as IMR, CFR and MRR in multiple coronary vessels. Seven additional sheep underwent these measurements while having simultaneous measurements with epicardial coronary flow probes (gold standard) in an open-chest model. The epicardial flow probes were placed on the proximal left anterior descending and circumflex artery. Maximal hyperemia was induced with adenosine (CFR and IMR) or infusion of saline at a rate of 30ml/min (ABF, ACR and MRR). For the second part of the study, in 41 patients receiving routine microvascular assessment, IMR and CFR measurements were duplicated by a single operator, after re-calibration, to assess the reproducibility of the measurement. The combined animal and human data resulted in the analysis of 408 coronary measurements made in 88 coronary vessels during 65 heart catheterizations. Results In sheep, ABF measured with ...