Microvascular Resistance Reserve for Assessment of Coronary Microvascular Function: JACC Technology Corner.

The need for a quantitative and operator-independent assessment of coronary microvascular function is increasingly recognized. We propose the theoretical framework of microvascular resistance reserve (MRR) as an index specific for the microvasculature, independent of autoregulation and myocardial mass, and based on operator-independent measurements of absolute values of coronary flow and pressure. In its general form, MRR equals coronary flow reserve (CFR) divided by fractional flow reserve (FFR) corrected for driving pressures. In 30 arteries, pressure, temperature, and flow velocity measurements were obtained simultaneously at baseline (BL), during infusion of saline at 10 mL/min (rest) and 20 mL/min (hyperemia). A strong correlation was found between continuous thermodilution-derived MRR and Doppler MRR (r = 0.88; 95% confidence interval: 0.72-0.93; P < 0.001). MRR was independent from the epicardial resistance, the lower the FFR value, the greater the difference between MRR and CFR. Therefore, MRR is proposed as a specific, quantitative, and operator-independent metric to quantify coronary microvascular dysfunction.

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Funding Support and Author Disclosures Dr De Bruyne has had a consulting relationship with Boston Scientific, Abbott Vascular, CathWorks, Siemens, and Coroventis Research; has received research grants from Abbott Vascular, Coroventis Research, Cathworks, and Boston Scientific; and holds minor equities in Philips-Volcano, Siemens, GE Healthcare, Edwards Life Sciences, HeartFlow, Opsens, and Celiad. Dr Pijls has received institutional grants from Abbott Vascular and Hexacath; has served as a consultant for Abbott Vascular, GE, and Opsens; and has minor equities in Philips, GE, ASML, and HeartFlow. Dr Collet has received research grants from Biosensor, GE Healthcare, Medis Medical Imaging, Pie Medical Imaging, Cathworks, Boston Scientific, Siemens, HeartFlow Inc, and Abbott Vascular; and has received consultancy fees from Heart Flow Inc, Opsens, Pie Medical Imaging, Abbott Vascular, and Philips-Volcano. Dr Barbato has received speaker’s fees from Abbott Vascular, Boston Scientific, and GE. Dr Fearon has received institutional research support from Abbott Vascular, Medtronic, and Edwards Lifesciences; has had a consulting relationship with CathWorks; and holds minor stock options with HeartFlow. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.