Minimal effect of collateral flow on coronary microvascular resistance in the presence of intermediate and noncritical coronary stenoses

Abstract

-Depending on stenosis severity, collateral flow can be a confounding factor in the determination of coronary hyperemic microvascular resistance (HMR). Under certain assumptions, the calculation of HMR can be corrected for collateral flow by incorporating the wedge pressure (P w) in the calculation. However, although P w Ͼ 25 mmHg is indicative of collateral flow, Pw does in part also reflect myocardial wall stress neglected in the assumptions. Therefore, the aim of this study was to establish whether adjusting HMR by P w is pertinent for a diagnostically relevant range of stenosis severities as expressed by fractional flow reserve (FFR). Accordingly, intracoronary pressure and Doppler flow velocity were measured a total of 95 times in 29 patients distal to a coronary stenosis before and after stepwise percutaneous coronary intervention. HMR was calculated without (HMR) and with Pw-based adjustment for collateral flow (HMRC). FFR ranged from 0.3 to 1. HMR varied between 1 and 5 and HMRC between 0.5 and 4.2 mmHg·cm Ϫ1 ·s. HMR was about 37% higher than HMRC for stenoses with FFR Ͻ 0.6, but for FFR Ͼ 0.8, the relative difference was reduced to 4.4 Ϯ 3.4%. In the diagnostically relevant range of FFR between 0.6 and 0.8, this difference was 16.5 Ϯ 10.4%. In conclusion, P w-based adjustment likely overestimates the effect of potential collateral flow and is not needed for the assessment of coronary HMR in the presence of a flow-limiting stenosis characterized by FFR between 0.6 and 0.8 or for nonsignificant lesions. wedge pressure; fractional flow reserve; coronary circulation CORONARY MICROVASCULAR DYSFUNCTION is increasingly being recognized as a major contributor to myocardial ischemia (3) and is likely associated with an altered coronary hyperemic microvascular resistance (HMR). Hence, a reliable assessment of microvascular resistance is needed that accurately reflects the status of the microcirculation and supports further development of diagnostic tools for microvascular disease.Resistance of a vascular compartment is defined as the ratio between the pressure drop over it and flow through it. Application of the resistance concept to the coronary circulation is challenging in the clinical setting, since volume flow cannot practically be measured directly and coronary back pressure is governed by multiple factors including microvascular conductance and extravascular compressive forces (16,17,32,37). At present, two guidewire-based systems are capable of the combined measurement of pressure and a surrogate of flow through a coronary stenosis. In the first system, flow velocity is measured by a Doppler crystal next to a pressure sensor (31, 35). The second system exploits the temperature sensitivity of the pressure sensor to determine the mean transit time of a temperature change induced by a bolus of saline (10). The corresponding indexes of HMR are respectively defined as the mean distal pressure (P d ) divided by mean distal flow velocity (35) The entrance of the microcirculation is not uniquely defined. Colla...

Low Coronary Microcirculatory Resistance Associated With Profound Hypotension During Intravenous Adenosine Infusion

“…44 However, other authors who used Doppler velocity to measure coronary flow have observed that the incorporation of wedge pressure as an estimated contribution of collateral blood flow does not substantially influence the assessment of coronary microcirculatory resistance when FFR >0.6. 45 Being aware of the current debate and to minimize a potential methodological error, we decided to correct IMR values when FFR <0.75 using the regression equation derived by Yong et al 14 for this purpose. However, a separate analysis of our data set using uncorrected values of IMR (Table 2) revealed similar results to those reported in the article, suggesting that this correction had little effects in our findings.…”

Epicardial Artery Stenosis with a High Index of Microcirculatory Resistance Is Frequently Functionally Insignificant as Estimated by Fractional Flow Reserve (FFR)

“…Vessels with severe stenosis (distal coronary pressure ! 60 mmHg) and a collateral flow were excluded from the analysis because of the effect of the collateral flow (5,12). In addition, thermodilution CFR was calculated by dividing the resting mean transit time by the hyperemic mean transit time (14).…”

“…Since the translesional pressure gradient remains relatively low in lesions with severely impaired microvascular integrity, the FFR for a given stenosis substantially increases following an increase of microvascular resistance and this is particularly prominent in the area of intermediate stenosis rather than in mild or severe stenotic lesions (4,5).…”

“…FFR is calculated from the trans-lesional pressure gradient of epicardial artery stenosis and it is therefore affected by microcirculation (1)(2)(3)(4)(5).…”

“…In the present study, we assessed microvascular integrity using the index of microcirculatory resistance (IMR), which is closely correlated with absolute microvascular resistance and is not affected by hemodynamic variation, epicardial artery stenosis, or baseline coronary flow (5,(10)(11)(12). The fol-lowing points were addressed: 1) whether microvascular integrity estimated by IMR is correlated with FFR in intermediate lesions; 2) whether the functional significance of intermediate lesions estimated by FFR is affected by microvascular integrity as estimated with IMR.…”