Invasive Coronary Microcirculation Assessment

Yuhei Kobayashi, William F Fearon
2014 Circulation Journal  
The technological advance of the coronary pressure wire enabled simultaneous measurement of coronary artery pressure and coronary artery flow. With commercially available software, the pressure sensor of the wire acts as a distal thermistor, while the shaft of the wire serves as a proximal thermistor. In this manner, the mean transit time (Tmn) of room-temperature saline injected into a coronary artery can be determined from a thermodilution curve (Figure 1) . De Bruyne and Pijls et al applied
more » ... he thermodilution technique in an experimental model and found a strong correlation between the inverse of Tmn and absolute coronary flow. 9,10 They also showed that the thermodilution-derived coronary flow reserve (CFRthermo), defined as the resting mean transit time (TmnRest) divided by the hyperemic mean transit time (TmnHyp), correlated well with the standard CFR, both in their experimental model and in humans. Fearon et al 6,11 further elucidated the usefulness of CFRthermo in open-chest porcine models. Using an ultrasonic flow probe placed around the proximal left anterior descending coronary artery (LAD) and a vascular occluder placed distal to the flow probe, the resting and hyperemic absolute coronary flow could be measured at baseline and after creation of an epicardial stenosis. CFRthermo showed better correlation with the absolute coronary flow-derived CFR than the Doppler velocity-derived CFR, which further validated the thermodilution technique as a method of estimating coronary flow. 11 ecent studies have demonstrated the importance of the coronary microvasculature in various clinical settings and in the development of non-invasive tests for assessing it, including Doppler echocardiography, contrast echocardiography, cardiovascular magnetic resonance, and positron emission tomography. 1-4 However, conventional invasive parameters for assessing the microvasculature such as coronary flow reserve (CFR), Thrombolysis In Myocardial Infarction (TIMI) flow grade, corrected TIMI frame count, and TIMI myocardial perfusion grades 5 have important limitations, including their dependence on resting hemodynamics, semiquantitative nature, and lack of independence of the epicardial vessel. For these reasons, it became important to develop an invasive method for independently, quantitatively and reproducibly assessing the microvasculature, which is predictive of outcomes in various settings. Against this background and with the development of a thermodilution technique for estimating coronary flow while simultaneously measuring coronary pressure, the index of microcirculatory resistance (IMR) was first described just over 10 years ago. 6,7 This method enables investigation of the coronary microvasculature directly with high reproducibility and reliability in the cardiac catheterization laboratory where many patients in the USA first present for evaluation of their coronary circulation. 8 This review discusses the development of IMR, tips and tricks for its measurement, and its usefulness in various clinical settings. R Assessment of the coronary microvasculature in the clinical setting is a key issue, given that microvascular dysfunction itself has a predictive value for cardiovascular events. The index of microcirculatory resistance (IMR) is an invasive method of interrogating the microvasculature and provides further insight into the physiology of cardiovascular diseases. It is simple and readily applicable in the cardiac catheterization laboratory where many patients first present for evaluation of their coronary circulation. In contrast to other invasive and non-invasive tests, this method is known to be stable and reproducible under various hemodynamics and even in the presence of epicardial coronary artery stenosis. IMR has been shown to have prognostic value in patients with ST-segment elevation myocardial infarction; therefore it can be a surrogate marker of cardiovascular events. At the same time, it has the potential to be a therapeutic as well as an investigational tool in the physiology of cardiovascular diseases. This review summarizes the development of IMR, tips and tricks for its measurement, and its usefulness in various clinical settings. (Circ J 2014; 78: 1021 -1028
doi:10.1253/circj.cj-14-0364 pmid:24739222 fatcat:zltyicmljfa2tbynvso3iaamge