Microvascular Resistance In Patients Research Articles

Non-hyperaemic coronary flow velocity acceleration indices correlate with hyperaemic microvascular resistance in patients with INOCA

Abstract Background Coronary microvascular dysfunction (CMD) is associated with an overall worse prognosis. While the diagnosis and endo-typing of CMD currently rely on hyperaemic physiological indices, the search for accurate non-hyperaemic techniques continues. Flow velocity acceleration pattern is mechanistically associated with changes in shear stress, endothelial function, arterial stiffness and pressure in pulsatile flow systems (1-3). Purpose We aim to interrogate whether resting flow velocity acceleration indices correlate with hyperaemic microvascular resistance (HMR) in patients with Ischemia and no obstructive coronary artery disease (INOCA). Methods In 21 Patients with INOCA (all of whom had presented with typical angina pectoris, had no significant epicardial stenoses but positive myocardial perfusion scan test for ischemia) invasive physiological assessment was performed by means of intracoronary Doppler. Hyperaemia was induced with intracoronary adenosine administration. Coronary flow reserve (CFR) and HMR were calculated per their definitions. Flow velocity acceleration indices were derived from the first derivative of the averaged resting flow velocity waveforms with respect to time. We have defined 6 wave peaks of interest in all patients (peak diastolic acceleration (initial prominent peak with ventricular relaxation, referred as A), early diastolic deceleration (B), early re-acceleration wave (C), peak presystolic deceleration (seen just before initial systolic acceleration peak, J), initial systolic acceleration peak (X) and pre-diastolic deceleration nadir (Z)) and calculated the ratios between them as well as adjusted them with respect to resting mean flow velocity (Figure 1). Results The mean age was 59 ± 8 years and the majority of the study group was female (%81). Cardiovascular risk factors were common amongst the study group.All patients had CFR < 2.5. Mean CFR and HMR were 2.05 ± 0.32 and 2.20 ± 0.60 mmHg.cm.sec-1 respectively. Raw C peak magnitude was significantly correlated with APVh (rho:-0.457 p:0.037) and HMR (rho:0.612 p:0.004). Adjusting the C magnitudes with APVb at patient level yielded better correlations (APVh rho:-0.496 p:0.022 ; HMR:0.642 p:0.002). The ratio between diastolic reacceleration peak (C) and presystolic peak deceleration (J), C/J , adjusted with the APVb ((C/J)/APVb) showed the most pronounced correlation with HMR (rho: 0.758 p < 0.001) (unadjusted C/J – HMR rho: 0.718 p<0.001)(Figure 2). Conclusion(s) Acceleration characteristics of resting coronary flow velocity correlate with hyperaemic microvascular resistance indicating structurally impaired coronary microcirculation, hence their utilisation may aid developing non-hyperaemic physiological markers for coronary microvascular dysfunction in patients with INOCA.Derived Acceleration WaveformsCorrelations between HMR and C/J Ratio

Gender-related differences in absolute coronary flow and microvascular resistance in patients with angina and non-obstructed coronary arteries (ANOCA)

Abstract Background Women with angina more often have non-obstructive coronary artery disease (ANOCA) compared to males. Coronary microvascular dysfunction (CMD) is responsible for angina in a sizable proportion of ANOCA patients. Intracoronary continuous thermodilution allows direct quantification of absolute coronary flow (Q) and microvascular resistance (Rµ). Purpose To evaluate gender-related differences in the prevalence and pattern of CMD assessed with intracoronary continuous thermodilution in ANOCA patients. Specifically, we assessed resting and hyperemic Q (Qrest and Qhyper), R (Rµ,rest and Rµ,hyper), coronary flow reverse (CFR), and microvascular resistance reserve (MRR) in ANOCA patients stratified by gender. Methods Single-center, prospective study of patients with ANOCA. CMD was invasively assessed by intracoronary continuous thermodilution in the left anterior descending artery (LAD) and defined as CFR<2.5. Results A total of 118 patients (n=49 females and n= 69 males) were enrolled. The mean patient age was 65 years. The mean fractional flow reserve (FFR) was 0.85±0.04, with no difference between the 2 genders. There was no difference in Rµ,rest, Qrest and Qhyper between the two genders. However, Rµ,hyper were higher in females compared to males (p=0.003). Among patients with ANOCA, CMD was more prevalent in females (28% vs 22%, p=0.014). Yet, in both females and males with CMD, a higher Qrest was observed compared to patients without CMD. In male patients, also Qhyper was lower in CMD patients versus those without CMD. Conclusion Among patients with ANOCA and investigated with intracoronary continuous thermodilution, CMD appeared more prevalent in females compared to males. Females had higher microvascular Rµ,hyper compared to males. In both genders, CMD was characterized by higher Qrest, suggestive of functional rather than structural CMD.

TCT-675 Core Laboratory Comparative Assessment of Angiography-Derived Index of Microvascular Resistance in Patients With Wire-Based IMR

TCT-675 Core Laboratory Comparative Assessment of Angiography-Derived Index of Microvascular Resistance in Patients With Wire-Based IMR

Coronary Microcirculatory Function Indicated by Coronary Angiography-Derived Index of Microvascular Resistance in Patients Undergoing Rotational Atherectomy

Background: There are scarce published data reporting the effect of rotational atherectomy (RA) on coronary microcirculation function. Objectives: We aimed to evaluate coronary microcirculation function indicated by the coronary angiography-derived index of microvascular resistance (caIMR) in patients undergoing RA. Methods: RA procedures between January 2013 and December 2021 were retrospectively analyzed. We investigated coronary microcirculation function indicated by caIMR as well as peri-procedural adverse events among the study population. All caIMR measurements were performed using a FlashAngio system. The primary outcome was a composite of post-RA thrombolysis in myocardial infarction (TIMI) flow grade <3 in the target vessel, myocardial injury, procedure-related myocardial infarction, and cardiac death during hospitalization. Results: A total of 155 RA procedures were analyzed. The post-RA caIMRs were significantly higher than pre-RA caIMRs in the target vessels (16.0 ± 7.0 vs. 14.5 ± 7.5, p = 0.029). Patients with post-RA caIMR ≥25 accounted for nearly 12% of those with pre-RA caIMR <25. Patients with post-RA thrombolysis in myocardial infarction (TIMI) flow grade <3 had a significantly higher pre-RA caIMR (23.5 ± 10.2 vs. 13.7 ± 6.6, p = 0.005), and the proportion of patients with pre-RA caIMR ≥25 in the group with TIMI flow grade <3 was greater (61.5% vs. 38.5%, p < 0.001) than that in the group with TIMI flow grade of 3. Maximum RA time of each pass (odds ratio: 1.127, 95% confidence interval: 1.025–1.239, p = 0.014) and pre-RA caIMR ≥25 (odds ratio: 3.254, 95% confidence interval: 1.054–10.048, p = 0.040) were identified to be the independent predictors of the primary outcome for patients who underwent RA. Conclusions: There were significant changes in the coronary microcirculation function of the target vessels after receiving RA as indicated by increased post-RA caIMR compared to pre-RA caIMR. Patients with baseline coronary microcirculatory dysfunction were more likely to have post-RA TIMI flow grade <3, whereas those with pre-RA caIMR ≥25 experienced worse outcomes.

TCT-295 Periprocedural Angiography-Derived Index of Microvascular Resistance in Patients With Multivessel Disease: Perspective From Multivessel TALENT Trial

TCT-295 Periprocedural Angiography-Derived Index of Microvascular Resistance in Patients With Multivessel Disease: Perspective From Multivessel TALENT Trial

Aortic Stiffness Is Associated with Coronary Microvascular Dysfunction in Patients with Non-obstructive Coronary Artery Disease.

ObjectiveAssociations between aortic stiffness and cardiovascular disease events are mediated in part by pathways that include coronary microvascular dysfunction (CMD) and remodeling. However, the relationship between aortic stiffness and CMD remains unclear.The present study aimed to determine whether aortic stiffness causes CMD as evaluated by the hyperemic microvascular resistance index (hMVRI) in patients with non-obstructive coronary artery disease (CAD).MethodsThe intracoronary physiological variables in 209 coronary arteries were evaluated in 121 patients with non-obstructive CAD (fractional flow reserve >0.80) or reference vessels. The cardio-ankle vascular index (CAVI) as a measure of aortic stiffness and atherosclerotic risk factors were also measured.ResultsUnivariate analyses showed that hMVRI correlated with age (β=0.24, p=0.007), eicosapentaenoic acid (EPA; β=-0.18, p=0.048), EPA/arachidonic acid (AA) (EPA/AA) ratio (β=-0.22, p=0.014) and CAVI (β=0.30, p=0.001). A multivariate regression analysis identified CAVI (β=0.25, p=0.007) and EPA/AA ratio (β=-0.26, SE=0.211, p=0.003) as independent determinants of hMVRI.ConclusionAortic stiffness may cause CMD in patients with non-obstructive CAD via increased coronary microvascular resistance. Aortic stiffness is associated with CMD which is evaluated as hyperemic microvascular resistance in patients with non-obstructive CAD.

A novel method for measuring absolute coronary blood flow and microvascular resistance in patients with ischaemic heart disease.

AimsIschaemic heart disease is the reduction of myocardial blood flow, caused by epicardial and/or microvascular disease. Both are common and prognostically important conditions, with distinct guideline-indicated management. Fractional flow reserve (FFR) is the current gold-standard assessment of epicardial coronary disease but is only a surrogate of flow and only predicts percentage flow changes. It cannot assess absolute (volumetric) flow or microvascular disease. The aim of this study was to develop and validate a novel method that predicts absolute coronary blood flow and microvascular resistance (MVR) in the catheter laboratory.Methods and resultsA computational fluid dynamics (CFD) model was used to predict absolute coronary flow (QCFD) and coronary MVR using data from routine invasive angiography and pressure-wire assessment. QCFD was validated in an in vitro flow circuit which incorporated patient-specific, three-dimensional printed coronary arteries; and then in vivo, in patients with coronary disease. In vitro, QCFD agreed closely with the experimental flow over all flow rates [bias +2.08 mL/min; 95% confidence interval (error range) −4.7 to +8.8 mL/min; R2 = 0.999, P < 0.001; variability coefficient <1%]. In vivo, QCFD and MVR were successfully computed in all 40 patients under baseline and hyperaemic conditions, from which coronary flow reserve (CFR) was also calculated. QCFD-derived CFR correlated closely with pressure-derived CFR (R2 = 0.92, P < 0.001). This novel method was significantly more accurate than Doppler-wire-derived flow both in vitro (±6.7 vs. ±34 mL/min) and in vivo (±0.9 vs. ±24.4 mmHg).ConclusionsAbsolute coronary flow and MVR can be determined alongside FFR, in absolute units, during routine catheter laboratory assessment, without the need for additional catheters, wires or drug infusions. Using this novel method, epicardial and microvascular disease can be discriminated and quantified. This comprehensive coronary physiological assessment may enable a new level of patient stratification and management.

Investigating the Utility of Remote Index of Microvascular Resistance in Patients With Chronic Total Occlusion

Investigating the Utility of Remote Index of Microvascular Resistance in Patients With Chronic Total Occlusion

Lower Circulating Omega-3 Polyunsaturated Fatty Acids Are Associated with Coronary Microvascular Dysfunction Evaluated by Hyperemic Microvascular Resistance in Patients with Stable Coronary Artery Disease.

The consumption of omega-3 polyunsaturated fatty acids (PUFAs) reduces the incidence of cardiovascular events and sudden cardiac death. Coronary microvascular dysfunction (CMD) is a predictor of cardiac mortality, but little information is known on the relationship between CMD and omega-3 PUFAs. This study aimed to identify the relationship between the serum levels of omega-3 PUFAs and the CMD evaluated by the hyperemic microvascular resistance index (hMVRI) to assess coronary microvascular function in patients with stable coronary artery disease (CAD).Intracoronary physiological variables (fractional flow reserve (FFR), hMVRI, mean distal coronary pressure (Pd), and average peak velocity (APV)) were measured in 108 patients. These parameters were evaluated in 150 coronary arteries with stenosis of intermediate severity and without significant ischemia (FFR > 0.80). The PUFA levels and atherosclerotic risk factors were also measured. Univariate analysis shows that hMVRI was negatively correlated with eicosapentaenoic acid (EPA)/arachidonic acid (AA) ratio (β = -0.31, P = 0.001) and EPA (β = -0.25, P = 0.009) and was positively correlated with dihomo-γ-linolenic acid (β = 0.26, P = 0.006). Multivariate regression analysis shows that the EPA/AA ratio was the only independent determinant of hMVRI (β = -0.234, SE = 0.231, P = 0.024). Furthermore, hMVRI decreased significantly from the lowest to highest tertiles of the EPA/AA ratio (P = 0.007). The EPA/AA ratio was positively correlated with APV at hyperemia (β = 0.26, P = 0.008) but not with Pd at hyperemia.A lower serum EPA/AA ratio may cause CMD in patients with stable CAD.

1 Why is cold air associated with increased susceptibility to myocardial ischaemia?

Introduction Cold air inhalation (CAI) during exercise increases cardiac mortality. The pathophysiology remains unclear, but may reflect adverse changes in microvascular resistance (MVR). We compared the accuracy of two novel intra-coronary measures of MVR to predict microvascular dysfunction (MVD). We then used the best MVR measure to quantify changes during CAI, exercise alone and exercise with CAI. Methods 56 patients (74 arteries: post PCI or FFR >0.8) had hyperaemic microvascular resistance (hMR) and index of microcirculatory resistance (IMR) compared against: Coronary flow reserve (CFR) CMR perfusion CMR microvascular obstruction (MVO). In a further 55 patients (45 with coronary artery disease (CAD), baseline and peak MVR was measured after 5 min of either: CAI (-15 o C) Cycling CAI during cycling. Results hMR had better diagnostic accuracy than IMR to predict CFR (AUC 0.82 vs. 0.58), CMR perfusion (AUC 0.85 vs. 0.72) and MVO (AUC 0.83 vs. 0.72) (Figure 1, Study 1). CAI at rest decreased MVR in patients with normal coronaries but increased MVR in CAD patients (p Conclusions hMR is a better predictor of MVD than IMR. CAI causes adverse changes in MVR in CAD patients both at rest and during exercise, rendering the heart more susceptible to ischaemia.

Abstract 17658: The Impact of Elective Percutaneous Coronary Intervention on Coronary Microvascular Resistance

Background: The influence of elective percutaneous coronary intervention (PCI) in patients with stable angina pectoris on coronary microvascular function has not been fully elucidated. We performed a prospective study to investigate serial changes of microvascular function in patients undergoing elective PCI. Methods and Results: The index of microcirculatory resistance (IMR) and fractional flow reserve (FFR) was measured before, after PCI, and at follow-up (10 months) in 52 patients treated with single vessel uncomplicated elective PCI (male 80.8%, age 66.5 ± 8.3). IMR was calculated by taking collateral flow into account. The median IMR values before, after PCI, and at follow-up were 24.2 (interquartile range (IQR) 13.1-31.3), 15.8 (IQR 11.8-21.6), and 14.7 (IQR 11.3-20.9), respectively. IMR values significantly decreased after PCI (P=0.006), and showed no further significant change at follow-up. There was no significant relationship between delta IMR (post-pre IMR) values and PCI-related cardiac troponin elevations that distributed in the range of (median: 0.50 ng/dL, IQR 0.22-1.02 ng/dL). Pre-PCI IMR was not correlated with pre-PCI FFR values. Post-PCI IMR was significantly correlated with pre-PCI IMR values (P=0.005). Periprocedural IMR decrease (Pre-Post) was inversely associated with pre-PCI FFR (P=0.008) and greater improvement of FFR values by PCI was significantly associated with greater reduction of IMR values at follow-up (P=0.03). Decrease in FFR values from immediately after PCI to follow-up was greater in patients with DM (P=0.01). Furthermore, IMR at follow-up was worse in patients with DM than those without (P=0.009). Conclusions: Removal of physiologically significant epicardial stenosis leads to a decrease in microvascular resistance in patients with stable angina undergoing electively performed uncomplicated PCI. The periprocedural decrease in microvascular resistance was influenced by the hemodynamic significance of the epicardial stenosis before PCI. The baseline status of microvascular function is a significant determinant of post-PCI and follow-up microvascular function in these patients, and diabetes has an impact on the serial changes in microvascular function after successful PCI.

Fractional flow reserve and the index of microvascular resistance in patients with acute coronary syndromes.

The aim of this article is to review what is currently known about fractional flow reserve (FFR) and related coronary physiological indices in patients with acute coronary syndrome (ACS) including non-ST-elevation (NSTEMI) and ST-elevation myocardial infarction (STEMI) with a view to making recommendations for daily practice. We explored all relevant publications to date including literature reviews, clinical trials and registries. We identified sufficient data on FFR in the setting of NSTEMI to confirm it to be a reliable and useful tool for lesion-level decision making with certain pitfalls as outlined below. There was limited published literature on FFR in STEMI. However, there is some evidence that, in patients who are stable after culprit lesion intervention, FFR may be of value for assessing the functional significance of non-culprit lesions. When measured in the culprit artery of patients with STEMI, the index of myocardial resistance (IMR) predicts long-term clinical outcomes. In patients with ACS, there is an increasing evidence base to support the role of FFR to guide revascularisation and of IMR to predict outcome.

Thermodilution-Derived Coronary Microvascular Resistance and Flow Reserve in Patients With Cardiac Syndrome X

Although increased coronary microvascular resistance (CMR), resulting in coronary microvascular dysfunction, is speculated to be responsible for myocardial ischemia in patients with cardiac syndrome X (CSX), it has never been directly demonstrated, and the correlation between CMR and severity of myocardial ischemia has not been elucidated in this setting. This study aimed to ascertain the increased CMR directly and to explore the relationship between CMR and severity of ischemia in patients with CSX. We studied 18 patients with CSX and 18 age- and sex-matched control subjects. Thermodilution-derived coronary flow reserve and index of microvascular resistance were measured using a pressure-temperature sensor-tipped coronary wire. Exercise treadmill test was performed by the Bruce protocol for calculating Duke treadmill score. Coronary flow reserve was significantly lower (2.37±0.81 versus 3.68±0.72; P<0.001) and index of microvascular resistance was higher (33.1±7.9 versus 18.8±5.6 U; P<0.001) in patients with CSX compared with those in control subjects. The Duke treadmill score was correlated positively to coronary flow reserve (r=0.539; P=0.021) and negatively to index of microvascular resistance (r=-0.742; P<0.001) in patients with CSX. Using an intracoronary thermodilution method, we for the first time directly demonstrated an increased microvascular resistance in patients with CSX. Furthermore, severity of ischemia was found to be intimately associated with CMR in this setting.

Percutaneous coronary intervention increases microvascular resistance in patients with non-ST-elevation acute coronary syndrome

In the acute coronary syndrome setting, the interaction between epicardial coronary artery stenosis and microcirculation subtended by the culprit vessel is poorly understood. The purpose of the present study was to assess the immediate impact of percutaneous coronary intervention (PCI) on microvascular resistance (MR) in patients with non-ST-elevation myocardial infarction (NSTEMI). Thirty-eight patients undergoing PCI for NSTEMI were recruited consecutively. Culprit lesions were stented over a Doppler and pressure-sensor-equipped guidewire. In the presence of epicardial stenosis, MR was calculated by taking collateral flow, as measured by the coronary wedge pressure, into consideration. After removal of epicardial stenosis, MR was calculated simply as distal coronary pressure divided by average peak velocity. When collateral flow was incorporated into the calculation, MR increased significantly from 1.70 ± 0.76 to 2.05 ± 0.72 (p=0.001) after PCI in the whole population. Periprocedural changes (Δ) in absolute values of MR and troponin T correlated significantly (r=0.629, p=0.0001). In patients who developed periprocedural myocardial infarction, MR increased significantly after PCI (1.48 ± 0.73 versus 2.28 ± 0.71, p<0.001). Nevertheless, removal of the epicardial lesion did not change MR in patients without periprocedural MI (1.91±0.73 versus 1.81±0.67, p=0.1). When collateral flow is accounted for, removal of epicardial stenosis increases MR in patients with NSTEMI undergoing PCI.

Microcirculatory function and left ventricular recovery after STEMI, exploring the hidden territories

Microcirculatory function and left ventricular recovery after STEMI, exploring the hidden territories

Variability of Microcirculatory Resistance Index and Its Relationship With Fractional Flow Reserve in Patients With Intermediate Coronary Artery Lesions

The relationship between the functional significance of epicardial coronary artery stenosis and microvascular resistance remains to be determined. Furthermore, little is known regarding the determinants of microvascular resistance in patients with intermediate coronary lesions. Using a pressure-temperature sensor-tipped guidewire, thermodilution-derived index of microcirculatory resistance (IMR) was measured, along with fractional flow reserve (FFR), in 131 coronary arteries of 104 patients with intermediate stenosis, in order to determine the relationship between IMR and clinical data. IMR varied widely (median, 20.8; range, 6.3-65.2), and no significant relationship was observed between IMR and FFR after IMR was corrected for coronary wedge pressure in the territories with functionally significant stenoses. There was no significant relationship between IMR and Framingham risk score, systematic coronary risk evaluation (SCORE), ACC/AHA lesion classification, or SYNTAX score. Right coronary artery (RCA) lesion location and history of hypertension were significantly associated with increased IMR. Multivariate analysis showed that RCA lesion location (odds ratio [OR], 4.52; 95% confidence interval [CI]: 1.84-11.11, P=0.001) and hypertension (OR, 3.03; 95% CI: 1.15-7.96, P=0.025) were independent predictors of increased IMR. Functional significance of intermediate coronary stenosis was not correlated with microvascular resistance of the perfusion territory. Intermediate coronary lesions may result in increased microcirculatory resistance irrespective of functional significance of the stenosis, with significant regional difference in microvascular resistance.

Abstract 18705: Regional Variability of Microcirculatory Resistance After Successful Percutaneous Coronary Intervention

Background: The main drawback of Fractional Flow Reserve (FFR) measurements occurs in the presence of microvascular disease, as FFR does not take into consideration the contribution of abnormal microvascular resistance. Normal FFR with concomitant microcirculatory disease may be a cause of angina symptoms or myocardial ischemia. Recently, the blood flow in the myocardium has been reported to show significant spatial heterogeneity. We assessed the hypothesis that heterogeneity of regional microvascular resistance exists in patients after successful percutaneous coronary intervention (PCI). Methods and Results: FFR and the index of microcirculatory resistance (IMR) were measured after successful PCI in 20 patients with native de novo discrete coronary lesions both in the territory of the culprit vessel and in the reference territory of non-culprit vessel. Hyperemic mean transmit time (Tmn) was used for the assessment of coronary flow. FFR value after PCI was 0.89 (IQR 0.82-0.96). IMR value in the culprit vessel was 18.8 (IQR 12.1-25.7), and 19.05 (IQR 14.3-26.7) in the non-culprit vessel, respectively. There was no significant relationship between these two regional measurements (r 2 =0.0128, p=ns). Mean difference between these two measures was 17.4 ± 15.9. The coefficients of variation of IMR were 75.7% in the culprit vessel, and 59.5% in the non-culprit vessel. There was a significant relationship between IMR and Tmn both in the culprit vessels (r=0.968, p&lt;0.0001) and non-culprit vessels (r=0.913, p&lt;0.0001). Conclusion: A considerable regional heterogeneity of coronary perfusion and microvascular resistance were observed in the present study. There is a high inter-subject, intra-subject, and interregional variability of coronary flow and microvascular resistance in patients after successful PCI. These results highlight the difficulty in establishing the limits of normal microvascular resistance or vasodilating response in patients with ischemic heart disease.

When Collateral Supply is Accounted For Epicardial Stenosis Does Not Increase Microvascular Resistance

The relationship between epicardial stenosis and microvascular resistance remains controversial. Exploring the relationship is critical, as many tools used in interventional cardiology imply minimal and constant resistance. However, variable collateralization may impact well on these measures. We hypothesized that when collateral supply was accounted for, microvascular resistance would be independent of epicardial stenosis. Forty patients with stable angina were studied before and following percutaneous intervention. A temperature and pressure sensing guide wire was used to derive microvascular resistance using the index of microcirculatory resistance (IMR), defined as the hyperemic distal pressure multiplied by the hyperemic mean transit time. Lesion severity was assessed using fractional flow reserve. For comparison, evaluation of an angiographically normal reference vessel from the same subject also was undertaken. Both simple IMR (sIMR) and IMR corrected for collateral flow (cIMR) were calculated. When collateral supply was not accounted for, there was a significant difference in IMR values between the culprit, the post PCI, and nonculprit values (culprit sIMR 26.68±2.06, nonculprit sIMR 18.37±1.89, P=0.002; post percutaneous intervention sIMR 18.5±1.94 versus culprit sIMR 26.68±2.06, P<0.0001). However, when collateral supply was accounted for there was no difference observed (cIMR 16.96±1.78 versus nonculprit sIMR 18.37±1.89, P=0.52; post percutaneous intervention sIMR 18.5±1.94 versus cIMR 16.96±1.78, P=0.42). When collateral supply is accounted for, epicardial stenosis does not increase microvascular resistance in patients with stable angina.

Elective Coronary Stenting Increases Fractional Flow Reserve in Other Arteries due to an Increase in Microvascular Resistance: Clinical Implications for Assessment of Multivessel Disease

Fractional flow reserve (FFR) can guide percutaneous coronary intervention (PCI) in multivessel disease (MVD). However, the effect of target vessel (TV) stenting on subsequent FFR measurements in remote non-TVs (NTVs) is unknown. We investigated the effect of TV stenting on NTV FFR in patients with MVD. Patients with MVD (>50% stenosis, ≥2 vessels >2.5 mm diameter; n = 51) undergoing elective PCI were studied. NTV distal pressure, aortic pressure, and saline-bolus thermodilution transit time (Tmn) were measured at baseline and during maximal hyperemia to derive FFR, index of myocardial resistance (IMR), and coronary flow reserve (CFR). PCI was then performed to the TV and the measurements repeated. Collaterals were assessed by modified Rentrop score before and after TV stenting. Mean FFR increased in the NTV after stenting the TV (0.79 ± 0.02 vs. 0.81 ± 0.02; P < 0.01), particularly in patients with normal baseline IMR (0.77 ± 0.02 vs. 0.80 ± 0.02; P = 0.001; n = 41). In this group, PCI to the TV increased remote microvascular resistance (NTV IMR increased from 12.5 ± 0.7 to 16.3 ± 1.4; P = 0.007; and CFR decreased from 3.0 ± 0.2 to 2.4 ± 0.2; P = 0.008). This change was independent of angiographic loss of coronary collaterals from the NTV. Elective TV PCI increases NTV FFR due to an increase in remote coronary microvascular resistance in patients with normal microvascular function. The effect of stent deployment on subsequent FFR measurements in other arteries should be considered.

Fractional flow reserve after previous myocardial infarction

Marques and colleagues have conducted an interesting study on microvascular resistance of viable tissue within an infarcted area.1 This study is important, not only from a conceptual point of view, but also because it has several relevant implications for the applicability of MIBI spect and fractional flow reserve (FFR) measurement in patients with previous myocardial infarction and a residual or recurrent stenosis in the infarct-related coronary artery. The use of these methods, one non-invasive and the other invasive, has been supported by theoretical and empirical data, but the present study corroborates their usefulness in patients with previous myocardial infarctions. To understand the clinical implications of the study by Marques et al. , it is paramount to understand microvascular resistance, which so far has been hard to assess in conscious humans. Microvascular resistance equals the ratio of distal coronary pressure divided by myocardial blood flow. As surrogates for the numerator and denominator of that ratio, sometimes aortic pressure and coronary blood flow or flow velocity, respectively, have been used, which might be correct in healthy persons. However, in patients with coronary artery disease, the first number overestimates distal coronary pressure and the second one underestimates myocardial blood flow, and therefore use of these surrogates leads to progressive overestimation of myocardial resistance in the case of a stenotic coronary artery.2–4 As a consequence, our knowledge about microvascular resistance in patients with coronary disease, and especially after previous myocardial infarction, has remained questionable. Furthermore, from a clinical point of view, i.e. the question of whether inducible ischaemia is still present or present again, the interesting index to study is hyperaemic blood flow, corresponding to minimal resistance of the viable myocardium within the infarcted zone, not the resistance of the scar tissue. … Corresponding author. Tel: +31 (40) 239 7004; fax: +31 (40) 244 7885. E-mail address: nico.pijls{at}inter.nl.net