Impact of Coronary Microvascular Dysfunction on Functional Left Ventricular Remodeling and Diastolic Dysfunction

BACKGROUND

Coronary microvascular dysfunction (CMD) is a common complication of ST-segment-elevation myocardial infarction (STEMI) and can lead to adverse cardiovascular events. Whether CMD after STEMI is associated with functional left ventricular remodeling (FLVR) and diastolic dysfunction, has not been investigated.

METHODS AND RESULTS

This is a nonrandomized, observational, prospective study of patients with STEMI with multivessel disease. Coronary flow reserve and index of microcirculatory resistance of the culprit vessel were measured at 3 months post-STEMI. CMD was defined as index of microcirculatory resistance ≥25 or coronary flow reserve <2.0 with a normal fractional flow reserve. We examined the association between CMD, LV diastolic dysfunction, FLVR, and major adverse cardiac events at 12-month follow-up. A total of 210 patients were enrolled; 59.5% were men, with a median age of 65 (interquartile range, 58-76) years. At 3-month follow-up, 57 patients (27.14%) exhibited CMD. After 12 months, when compared with patients without CMD, patients with CMD had poorer LV systolic function recovery (-10.00% versus 8.00%; P<0.001), higher prevalence of grade 2 LV diastolic dysfunction (73.08% versus 1.32%; P<0.001), higher prevalence of group 3 or 4 FLVR (11.32% versus 7.28% and 22.64% versus 1.99%, respectively; P<0.001), and higher incidence of major adverse cardiac events (50.9% versus 9.8%; P<0.001). Index of microcirculatory resistance was independently associated with LV diastolic dysfunction and adverse FLVR.

CONCLUSIONS

CMD is present in ≈1 of 4 patients with STEMI during follow-up. Patients with CMD have a higher prevalence of LV diastolic dysfunction, adverse FLVR, and major adverse cardiac events at 12 months compared with those without CMD.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique Identifier: NCT05406297.

Assessing Coronary Microvascular Dysfunction in Ischaemic Heart Disease: Little Things Can Make a Big Difference

The role of coronary microvascular dysfunction (CMD) in the pathogenesis of ischaemic heart disease and in determining long-term prognosis is increasingly recognised. In selected patients, a comprehensive coronary assessment including an assessment of microvascular function may help refine risk stratification and improve patient outcomes. Various non-invasive and invasive techniques have been developed to assess the coronary microcirculation. Many of these tests utilise the indicator-dilution principle to determine coronary or myocardial blood flow. However, these techniques are often limited by their variability and lack of specificity for the coronary microvasculature. Consequently, there is still paucity of data on targeted therapies for CMD and their implications on long-term clinical outcomes, particularly in the setting of non-ST elevation acute coronary syndromes. Recent technical advancements, such as the index of microcirculatory resistance, have largely overcome these limitations and are able to provide novel insights into the assessment and treatment of CMD. This review summarises the currently available techniques for the assessment of CMD and provides an overview of its clinical implications.

Coronary flow reserve is related to the extension and transmurality of myocardial necrosis and predicts functional recovery after acute myocardial infarction

BACKGROUND

Few studies have examined the effect of transmurality of myocardial necrosis on coronary microcirculation. The aim of this study was to examine the influence of cardiac magnetic resonance-derived (GE-MRI) structural determinants of coronary flow reserve (CFR) after anterior myocardial infarction (STEMI), and their predictive value on regional functional recovery.

METHODS

Noninvasive CFR and GE-MRI were studied in 37 anterior STEMI patients after primary coronary angioplasty. The wall motion score index in the left descending anterior coronary artery territory (A-WMSI) was calculated at admission and follow-up (FU). Recovery of regional left ventricular (LV) function was defined as the difference in A-WMSI at admission and FU. The necrosis score index (NSI) and transmurality score index (TSI) by GE-MRI were calculated in the risk area. Baseline (BMR) and hyperemic (HMR) microvascular resistance, arteriolar resistance index (ARI), and coronary resistance reserve (CRR) were calculated at the Doppler echocardiography.

RESULTS

Bivariate analysis indicated that the CPK and troponin I peak, heart rate, NSI, TSI, BMR, the ARI, and CRR were related to CFR. Multivariable analysis revealed that TSI was the only independent determinant of CFR. The CFR value of >2.27, identified as optimal by ROC analysis, was 77% specific and 73% sensitive with accuracy of 76% in identifying patients with functional recovery.

CONCLUSIONS

Preservation of microvascular function after AMI is related to the extent of transmurality of myocardial necrosis, is an important factor influencing regional LV recovery, and can be monitored by noninvasive CFR.

Invasive Assessment of the Coronary Microvasculature

Traditionally, invasive coronary physiological assessment has focused on the epicardial coronary artery. More recently, appreciation of the importance of the coronary microvasculature in determining patient outcomes has grown. Several invasive modalities for interrogating microvascular function have been proposed. Angiographic techniques have been limited by their qualitative and subjective nature. Doppler wire-derived coronary flow reserve has been applied in research studies, but its clinical role has been limited by its lack of reproducibility, its lack of a clear normal value, and the fact that it is not specific for the microvasculature but interrogates the entire coronary circulation. The index of microcirculatory resistance—a thermodilution-derived measure of the minimum achievable microvascular resistance—is relatively easy to measure, more reproducible, has a clearer normal value, and is independent of epicardial coronary artery stenosis. The index of microcirculatory resistance has been shown to have prognostic value in patients with ST-segment–elevation myocardial infarction and cardiac allograft vasculopathy after heart transplantation. Emerging data demonstrate its role in evaluating patients with chest pain and nonobstructive coronary artery disease. Increasingly, the index of microcirculatory resistance is used as a reference standard for invasively assessing the microvasculature in clinical trials.

Hyperaemic microvascular resistance predicts clinical outcome and microvascular injury after myocardial infarction

OBJECTIVES

Early detection of microvascular dysfunction after acute myocardial infarction (AMI) could identify patients at high risk of adverse clinical outcome, who may benefit from adjunctive treatment. Our objective was to compare invasively measured coronary flow reserve (CFR) and hyperaemic microvascular resistance (HMR) for their predictive power of long-term clinical outcome and cardiac magnetic resonance (CMR)-defined microvascular injury (MVI).

METHODS

Simultaneous intracoronary Doppler flow velocity and pressure measurements acquired immediately after revascularisation for AMI from five centres were pooled. Clinical follow-up was completed for 176 patients (mean age 60±10 years; 140(80%) male; ST-elevation myocardial infarction (STEMI) 130(74%) and non-ST-segment elevation myocardial infarction 46(26%)) with median follow-up time of 3.2 years. In 110 patients with STEMI, additional CMR was performed.

RESULTS

The composite end point of death and hospitalisation for heart failure occurred in 17 patients (10%). Optimal cut-off values to predict the composite end point were 1.5 for CFR and 3.0 mm Hg cm^-1•s for HMR. CFR <1.5 was predictive for the composite end point (HR 3.5;95% CI 1.1 to 10.8), but not for its individual components. HMR ≥3.0 mm Hg cm^-1 s was predictive for the composite end point (HR 7.0;95% CI 1.5 to 33.7) as well as both individual components. HMR had significantly greater area under the receiver operating characteristic curve for MVI than CFR. HMR remained an independent predictor of adverse clinical outcome and MVI, whereas CFR did not.

CONCLUSIONS

HMR measured immediately following percutaneous coronary intervention for AMI with a cut-off value of 3.0 mm Hg cm^-1 s, identifies patients with MVI who are at high risk of adverse clinical outcome. For this purpose, HMR is superior to CFR.