Microvascular resistance of the culprit coronary artery in acute ST-elevation myocardial infarction

Predictive value of angiographic microvascular resistance for left ventricular thrombus in anterior ST-segment elevation myocardial infarction

Angiographic microvascular resistance (AMR) serves as an effective metric for assessing coronary microvascular status. The aim of this study was to investigate the predictive value of AMR for left ventricular thrombus (LVT) in ST-segment elevation myocardial infarction. This study enrolled 401 consecutive patients with anterior STEMI who underwent primary percutaneous coronary intervention (PPCI) between May 2019 and July 2023. AMR was measured immediately after PPCI via coronary angiography. LVT was identified during hospitalization through cardiac magnetic resonance imaging (CMR) or transthoracic echocardiography (TTE). Major adverse cardiac and cerebrovascular events (MACCEs) were recorded over 36 months follow-up. The predictive value of AMR was evaluated by logistic regression and receiver operating characteristic (ROC) analysis. Kaplan-Meier analysis was performed to estimate event-free rates for MACCEs. LVT was identified in 38 out of 401 anterior STEMI patients (9.5%). After adjusting for confounders through multivariable analysis, AMR was found to be an independent predictor of LVT (odds ratio [OR] 1.240 per 0.1 mmHg·s/cm, 95% confidence interval [CI]: 1.131-1.359, P < 0.001). ROC analysis demonstrated an area under the curve (AUC) of 0.742. For LVT, AMR provided modest incremental predictive value over established risk factors (continuous net reclassification improvement, 0.826 [95% CI: 0.523-1.129]; P < 0.001). Furthermore, Kaplan-Meier analysis revealed MACCEs for anterior STEMI patients with AMR ≥ 2.82 (log-rank P < 0.001). AMR is an independent predictor of LVT in anterior STEMI, providing incremental predictive value beyond traditional risk factors, and may be utilized to identify patients at risk for LVT.

CVIT expert consensus document on primary percutaneous coronary intervention (PCI) for acute coronary syndromes (ACS) in 2024

Primary Percutaneous Coronary Intervention (PCI) has significantly contributed to reducing the mortality of patients with ST-segment elevation myocardial infarction (STEMI) even in cardiogenic shock and is now the standard of care in most of Japanese institutions. The Task Force on Primary PCI of the Japanese Association of Cardiovascular Intervention and Therapeutics (CVIT) proposed an expert consensus document for the management of acute myocardial infarction (AMI) focusing on procedural aspects of primary PCI in 2018 and updated in 2022. Recently, the European Society of Cardiology (ESC) published the guidelines for the management of acute coronary syndrome in 2023. Major new updates in the 2023 ESC guideline include: (1) intravascular imaging should be considered to guide PCI (Class IIa); (2) timing of complete revascularization; (3) antiplatelet therapy in patient with high-bleeding risk. Reflecting rapid advances in the field, the Task Force on Primary PCI of the CVIT group has now proposed an updated expert consensus document for the management of ACS focusing on procedural aspects of primary PCI in 2024 version.

Coronary microvascular dysfunction and cardiovascular disease: Pathogenesis, associations and treatment strategies

Coronary microvascular dysfunction (CMD) is a high-risk factor for a variety of cardiovascular events. Due to its complex aetiology and concealability, knowledge of the pathophysiological mechanism of CMD is still limited at present, which greatly restricts its clinical diagnosis and treatment. Studies have shown that CMD is closely related to a variety of cardiovascular diseases, can aggravate the occurrence and development of cardiovascular diseases, and is closely related to a poor prognosis in patients with cardiovascular diseases. Improving coronary microvascular remodelling and increasing myocardial perfusion might be promising strategies for the treatment of cardiovascular diseases. In this paper, the pathogenesis and functional assessment of CMD are reviewed first, along with the relationship of CMD with cardiovascular diseases. Then, the latest strategies for the treatment of CMD and cardiovascular diseases are summarized. Finally, urgent scientific problems in CMD and cardiovascular diseases are highlighted and future research directions are proposed to provide prospective insights for the prevention and treatment of CMD and cardiovascular diseases in the future.

Angiography-based index of microcirculatory resistance (AccuIMR) for the assessment of microvascular dysfunction in acute coronary syndrome and chronic coronary syndrome

Background

To assess the diagnostic accuracy of AccuIMR, a newly proposed, pressure wire-free index, in identifying coronary microvascular dysfunction (CMD) among patients with acute coronary syndrome [including ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction (NSTEMI)] and chronic coronary syndrome (CCS).

Methods

A total of 163 consecutive patients (43 with STEMI, 59 with NSTEMI, and 61 with CCS), who underwent invasive coronary angiography (ICA) and for whom the index of microcirculatory resistance (IMR) was measured, were retrospectively enrolled at a single center. IMR measurements were made in 232 vessels. The AccuIMR based on computational fluid dynamics (CFD) was calculated from coronary angiography. The diagnostic performance of AccuIMR was assessed using wire-based IMR as a reference standard.

Results

AccuIMR correlated well with IMR (overall r=0.76, P<0.001; STEMI r=0.78, P<0.001; NSTEMI r=0.78, P<0.001; CCS r=0.75, P<0.001) and had good diagnostic performance in detecting abnormal IMR [overall diagnostic accuracy, sensitivity, and specificity were 94.83% (91.14% to 97.30%), 92.11% (78.62% to 98.34%), and 95.36% (91.38% to 97.86%), respectively]. Using a cutoff value of IMR >40 U for AccuIMR in STEMI and IMR >25 U in NSTEMI and CCS, the area under the receiver operating characteristic (ROC) curve (AUC) of AccuIMR for predicting abnormal IMR value was 0.917 (0.874 to 0.949) in all patients, 1.000 (0.937 to 1.000) in patients with STEMI, 0.941 (0.867 to 0.980) in patients with NSTEMI, and 0.918 (0.841 to 0.966) in patients with CCS.

Conclusions

The use of AccuIMR in the evaluation of microvascular diseases could provide valuable information and potentially increase the application of physiological assessment for microcirculation in patients with ischemic heart disease.

Correlations between Cardiovascular Risk Factors and Ventricular Arrhythmias Following Primary Percutaneous Coronary Intervention in Patients with ST-Elevation Myocardial Infarction

Background

Ventricular arrhythmias (VAs), which result from acute myocardial infarction and revascularization, are preventable causes of sudden cardiac death. This study aimed to determine the incidence, types, and risk factors of VAs in patients with ST-elevation myocardial infarction undergoing primary percutaneous coronary intervention (PCI).

Methods

This cross-sectional study was conducted at the cardiology department of a tertiary care cardiac center in Zanjan, Iran. All the patients were monitored during hospitalization, and the incidence of cardiac arrhythmias and the outcomes were recorded.

Results

Among 315 patients, the mean age was 62.14±10.11 years, and 76.2% were male. Male gender was significantly associated with VA occurrence (P=0.038). Among the patients, 50.5% had VAs, of which 26.4% were sustained ventricular tachycardia (sustained VT) and ventricular fibrillation (VF). Sustained VT and VF, but not total arrhythmias, were more common in anterior infarctions. Most arrhythmias occurred during the first 12 hours, and frequent premature ventricular contractions (43.3%) and idioventricular rhythm (20.1%) were the most common. A history of PCI and coronary artery bypass grafting (CABG) was associated with substantially reduced arrhythmias (P=0.017 and P=0.013, respectively). However, cardiovascular risk factors exerted no statistically significant effects on the VA type.

Conclusion

Approximately half of our patients experienced reperfusion-induced VAs. Overall, gender and a history of PCI and CABG were significantly associated with VA occurrence. Therefore, males and patients without a positive history of PCI and CABG should receive antiarrhythmic drugs as a precaution.

Reference values of myocardial native T1 and T2 mapping values in normal Indian population at 1.5 Tesla scanner

T1 and T2 mapping techniques on cardiovascular magnetic resonance (CMR) provide insights into the myocardial tissue characterisation. We sought to establish the normal reference values of native T1 and T2 mapping in Indian population which can be used subsequently in clinical practice for addressing various cardiac pathologies. This prospective study included consecutive healthy volunteers (18-60 years) who underwent CMR on a 1.5 Tesla scanner using standard protocol. T1 mapping sequence was performed using MOLLI sequence with two different flip angles (FA) (35° and 50°). T2 mapping was performed using a hybrid gradient and spin-echo sequence sequence with two different FA (70° and 12°). Images were analysed with ROIs drawn in all the 16 AHA myocardial segments. 50 volunteers (average age-34 years, males-72%) were included. All the scans were normal. The mean T1 value at 35-degree FA was 946.86 + 14.16 ms and at 50-degree FA was 941.60 + 11.89 ms. The mean T2 mapping value at 70-degree FA was 45.67 + 1.39 ms and at 12-degree FA was 45.61 + 1.47 ms. The mapping values were not statistically different between males and females (all p > 0.2). The T1 and T2 mapping values did not show any significant correlation with LVEF, age, BMI or heart rate (all r < 0.33). The T1 mapping values significantly differ at 35- and 50-degree FAs (p = 0.002). The results establish the normal reference T1 and T2 mapping value for Indian population in institutes using the same protocol and parameters at 1.5 Tesla and may guide future research.

The Dynamic Relationship Between Invasive Microvascular Function and Microvascular Injury Indicators, and Their Association With Left Ventricular Function and Infarct Size at 1-Month After Reperfused ST-Segment-Elevation Myocardial Infarction

BACKGROUND

The invasive microvascular function indices, coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR), exhibit a dynamic pattern after ST-segment-elevation myocardial infarction. The effects of microvascular injury on the evolution of the microvascular function and the prognostic significance of the evolution of microvascular function are unknown. We investigated the relationship between the temporal changes of CFR and IMR, and cardiovascular magnetic resonance-derived microvascular injury characteristics in reperfused ST-segment-elevation myocardial infarction patients, and their association with 1-month left ventricular ejection fraction and infarct size (IS).

METHODS

In 109 ST-segment-elevation myocardial infarction patients who underwent angiography for primary percutaneous coronary intervention (PPCI) and at 1-month follow-up, invasive assessment of CFR and IMR were performed in the culprit artery during both procedures. Cardiovascular magnetic resonance was performed 2 to 7 days after PPCI and at 1 month and provided assessment of left ventricular ejection fraction, IS, microvascular obstruction, and intramyocardial hemorrhage.

RESULTS

CFR and IMR significantly changed over 1 month (both, P<0.001). The absolute IMR change over 1 month (ΔIMR) showed association with both microvascular obstruction and intramyocardial hemorrhage presence (both, P=0.01). ΔIMR differed between patients with/without microvascular obstruction (P=0.02) and with/without intramyocardial hemorrhage (P=0.04) but not ΔCFR for both. ΔIMR demonstrated association with both left ventricular ejection fraction and IS at 1 month (P<0.001, P=0.001, respectively), but not ΔCFR for both. Receiver-operating characteristics curve analysis of ΔIMR showed a larger area under the curve than post-PPCI CFR and IMR, and ΔCFR to be associated with both 1-month left ventricular ejection fraction >50% and extensive IS (the highest quartile).

CONCLUSIONS

In reperfused ST-segment-elevation myocardial infarction patients, CFR and IMR significantly improved 1 month after PPCI; the temporal change in IMR is closely related to the presence/absence of microvascular damage and IS. ΔIMR exhibits a stronger association for 1-month functional outcome than post-PPCI CFR, IMR, or ΔCFR.

Prediction of microvascular obstruction by coronary artery angiography score after acute ST-segment elevation myocardial infarction: a single-center retrospective observational study

Background

Some coronary artery angiography (CAG) scores are associated with the no-reflow phenomenon after percutaneous coronary intervention (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI). However, quality evidence regarding the association between the CAG scores and microvascular injury is still needed. Our study aimed to validate the ability of the CAG scores in predicting microvascular obstruction (MVO) detected by cardiac magnetic resonance (CMR) imaging.

Methods

From October 2020 to October 2021, 141 consecutive patients with acute STEMI who underwent primary PCI and CMR were retrospectively reviewed. CMR imaging was performed between 3 and 7 days after PCI. The patients were divided into MVO and non-MVO group based on the CMR results. Three CAG scores (SYNTAX score, SYNTAX II score and Gensini score) were used to assess the severity of coronary artery atherosclerotic burden.

Results

A total of 122 patients were included (mean age 60.6 ± 12.8 years). MVO occurred in 51 patients (41.8%). Patients with MVO had higher SYNTAX scores, SYNTAX II scores and Gensini scores than those without MVO (all p < 0.001). The Gensini score (r = 0.567, p < 0.001) showed the strongest correlation with infarction size than SYNTAX score (r = 0.521, p < 0.001) and SYNTAX II score (r = 0.509, p < 0.001). The areas under the receiver operator characteristic curves of SYNTAX score, SYNTAX II score and Gensini score for predicting MVO patients were 0.726, 0.774 and 0.807. In multivariable regression analysis, peak troponin I (odd ratio [OR] = 1.236, p = 0.001) and SYNTAX II score (OR = 11.636, p = 0.010) were identified as independent predictors of MVO.

Conclusions

In patients with acute STEMI undergoing primary PCI treatment, the peak troponin I and SYNTAX II score may be an independent predictor of MVO.

Prognostic significance of severe coronary microvascular dysfunction post-PCI in patients with STEMI: A systematic review and meta-analysis

Coronary microvascular dysfunction (CMVD) is common and associated with poorer outcomes in patients with ST Segment Elevation Myocardial Infarction (STEMI). The index of microcirculatory resistance (IMR) and the index of hyperemic microvascular resistance (HMR) are both invasive indexes of microvascular resistance proposed for the diagnosis of severe CMVD after primary percutaneous coronary intervention (pPCI). However, these indexes are not routinely assessed in STEMI patients. Our main objective was to clarify the association between IMR or HMR and long-term major adverse cardiovascular events (MACE), through a systematic review and meta-analysis of observational studies. We searched Medline, PubMed, and Google Scholar for studies published in English until December 2020. The primary outcome was a composite of cardiovascular death, non-cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, and rehospitalization for heart failure occurring after at least 6 months following CMVD assessment. We identified 6 studies, reporting outcomes in 1094 patients (mean age 59.7 ± 11.4 years; 18.2% of patients were women) followed-up from 6 months to 7 years. Severe CMVD, defined as IMR > 40 mmHg or HMR > 3mmHg/cm/sec was associated with MACE with a pooled HR of 3.42 [2.45; 4.79]. Severe CMVD is associated with an increased risk of long-term adverse cardiovascular events in patients with STEMI. Our results suggest that IMR and HMR are useful for the early identification of severe CMVD in patients with STEMI after PCI, and represent powerful prognostic assessments as well as new therapeutic targets for clinical intervention.

Coronary flow reserve and cardiovascular outcomes: a systematic review and meta-analysis

AIMS

This meta-analysis aims to quantify the association of reduced coronary flow with all-cause mortality and major adverse cardiovascular events (MACE) across a broad range of patient groups and pathologies.

METHODS AND RESULTS

We systematically identified all studies between 1 January 2000 and 1 August 2020, where coronary flow was measured and clinical outcomes were reported. The endpoints were all-cause mortality and MACE. Estimates of effect were calculated from published hazard ratios (HRs) using a random-effects model. Seventy-nine studies with a total of 59 740 subjects were included. Abnormal coronary flow reserve (CFR) was associated with a higher incidence of all-cause mortality [HR: 3.78, 95% confidence interval (CI): 2.39-5.97] and a higher incidence of MACE (HR 3.42, 95% CI: 2.92-3.99). Each 0.1 unit reduction in CFR was associated with a proportional increase in mortality (per 0.1 CFR unit HR: 1.16, 95% CI: 1.04-1.29) and MACE (per 0.1 CFR unit HR: 1.08, 95% CI: 1.04-1.11). In patients with isolated coronary microvascular dysfunction, an abnormal CFR was associated with a higher incidence of mortality (HR: 5.44, 95% CI: 3.78-7.83) and MACE (HR: 3.56, 95% CI: 2.14-5.90). Abnormal CFR was also associated with a higher incidence of MACE in patients with acute coronary syndromes (HR: 3.76, 95% CI: 2.35-6.00), heart failure (HR: 6.38, 95% CI: 1.95-20.90), heart transplant (HR: 3.32, 95% CI: 2.34-4.71), and diabetes mellitus (HR: 7.47, 95% CI: 3.37-16.55).

CONCLUSION

Reduced coronary flow is strongly associated with increased risk of all-cause mortality and MACE across a wide range of pathological processes. This finding supports recent recommendations that coronary flow should be measured more routinely in clinical practice, to target aggressive vascular risk modification for individuals at higher risk.

Presence of Microvascular Dysfunction and CHA2DS2-VASc Score in Patients with ST-Segment Myocardial Infarction after Primary Percutaneous Coronary Intervention

Objective

We aimed to investigate the relation between CHA₂DS₂-VASc score and microvascular dysfunction (MVD) assessed by the index of microvascular resistance (IMR) immediately after primary percutaneous intervention (PPCI) for patients with ST-segment elevation myocardial infarction (STEMI).

Subjects and Methods

The study included 115 consecutive patients with STEMI who underwent successful PPCI. Angiographic results of reperfusion were inspected to evaluate the association of high CHA₂DS₂-VASc score and IMR. Also, we assessed echocardiographic changes with respect to CHA₂DS₂-VASc score.

Results

Subjects were stratified into 2 groups based on IMR </≥ 40 U; 72 patients (62.6) with IMR <40 U and 43 patients (37.4) with IMR ≥40 U. Patients with IMR ≥40 U had higher CHA₂DS₂-VASc score (p < 0.001). CHA₂DS₂-VASc score was significantly correlated with increased left atrial volume index, diastolic dysfunction, wall motion score index, and inversely correlated left ventricular ejection. Moreover, CHA₂DS₂-VASc score was strongly correlated with IMR (p < 0.001). At multivariate analysis, low systolic blood pressure, stent diameter, and CHA₂DS₂-VASc score were associated with MVD. Besides, CHA₂DS₂-VASc score ≥4 was the optimal value in predicting MVD (IMR ≥40) in STEMI patients.

Conclusions

The data of the current study point out that increased CHA₂DS₂-VASc score, lower systolic blood pressure <90 mm Hg, and stent diameter are associated with increased incidence of MVD (increased IMR) after PPCI of STEMI. We suggest that the CHA₂DS₂-VASc score may be a simple, inexpensive useful risk score for the prediction of MVD risk after PPCI for STEMI patients.

The role of myocardial work in evaluating coronary microcirculation of STEMI patients after percutaneous coronary intervention

BACKGROUND

Despite of restoring epicardial infarct-related artery(IRA) patency after myocardial infarction, microvascular reperfusion were not achieved sometimes, and the deterioration of myocardial perfusion persists in a considerable number of patients. This phenomenon is known as microvascular obstruction (MVO). MVO is often observed in ST-Segment Elevation Myocardial Infarction(STEMI) patients, even if percutaneous coronary intervention (PCI) was successful. In addition, some evidence has indicated that the presence of MVO predicted poor clinical outcomes independent of myocardial infarct size. Noninvasive as well as invasive modes for assessing microvascular perfusion(MVP) are complex, time consuming, and expensive have, there is yet no simple method available at present to assess coronary microcirculation. In this research, we attempt to evaluate the usefulness of left ventricular myocardial work (LVMW), a new index of myocardial performance, for the assessment of MVP in STEMI patients after PCI.

METHODS

Forty-seven patients with STEMI treated by PCI were enrolled and underwent a transthoracic doppler echocardiography (TTE) within 24-72 hours after PCI. IRA were left anterior descending (LAD) artery (29,62%), left circumflex (LCX) artery(9,19%), right coronary artery (RCA) (9,19%) respectively. Myocardial contrast echocardiography (MCE) was used to evaluate MVP after PCI, then perfusion score index (PSI) was calculated referring to whether the ultrasonic enhancing agents was replenishment or not. Patients were divided into normal MVP and impaired MVP group according to PSI. Left ventricular global longitudinal strain (GLS) was generated by speckle tracking echocardiography(STE) and pressure-strain loops (PSLs) was used to generate global work index (GWI), global constructive work (GCW), global wasted work (GWW), and global work efficiency (GWE). GLS and the MW parameters (GWI, GCW, GWW, GWE) were compared between groups. Receiver operating characteristic (ROC) curves were calculated by plotting sensitivity versus (1-specificity), allowing calculation of the area under the curve (AUC) and the identification of LVMW parameters and GLS cutoff thresholds that best identify STEMI patients with impaired MVP after PCI.

RESULTS

In this study, a statistically significant difference was observed in GWI (1163±405 mm Hg% vs 1617±363 mm Hg%), GCW (1296±430 mm Hg% vs 1789±406 mm Hg%), GWE (83±8.52% vs 90±5.58%) and GLS (11.56±3.29 vs 16.65±3.59) between impaired MVP group and normal MVP group. However, there is no statistical significance difference in left ventricular ejection fraction (LVEF), and GWW. ROC analysis revealed that GCW (cut-off value: 1326 mm Hg%, AUC: .80, sensitivity: 95% and specificity: 56%), GWI (cut-off value: 1281 mm Hg%, AUC: .81, sensitivity: 90% and specificity: 70%), GWE (cut-off value: 90%, AUC: .77, sensitivity: 65% and specificity: 78%) and GLS (cut-off value: 12.5, AUC: .86, sensitivity: 90% and specificity: 67%) have appreciable AUC, sensitivity, and specificity to identify STEMI patients with impaired MVP after PCI.

CONCLUSION

Measuring LVMW indices of STEMI patients after PCI may add adjuvant value for the assessment of MVP.

ST-segment resolution as a marker for severe myocardial fibrosis in ST-segment elevation myocardial infarction

Objective

To investigate the relationship between ST-segment resolution (STR) and myocardial scar thickness after percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI).

Methods

Forty-two STEMI patients with single-branch coronary artery stenosis or occlusion were enrolled. ST-segment elevations were measured at emergency admission and at 24 h after PCI. Late gadolinium-enhanced cardiac magnetic resonance imaging (CMR-LGE) was performed 7 days after PCI to evaluate myocardial scars. Statistical analyses were performed to assess the utility of STR to predict the development of transmural (> 75%) or non-transmural (< 75%) myocardial scars, according to previous study.

Results

The sensitivity and specificity of STR for predicting transmural scars were 96% and 88%, respectively, at an STR cut-off value of 40.15%. The area under the curve was 0.925. Multivariate logistic proportional hazards regression analysis disclosed that patients with STR < 40.15% had a 170.90-fold higher probability of developing transmural scars compared with patients with STR ≥ 40.15%. Pearson correlation and linear regression analyses showed STR percentage was significantly associated with myocardial scar thickness and size.

Conclusion

STR < 40.15% at 24 h after PCI may provide meaningful diagnostic information regarding the extent of myocardial scarification in STEMI patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-021-02269-y.

Acute Coronary Syndromes (ACS)-Unravelling Biology to Identify New Therapies-The Microcirculation as a Frontier for New Therapies in ACS

In acute coronary syndrome (ACS) patients, restoring epicardial culprit vessel patency and flow with percutaneous coronary intervention or coronary artery bypass grafting has been the mainstay of treatment for decades. However, there is an emerging understanding of the crucial role of coronary microcirculation in predicting infarct burden and subsequent left ventricular remodelling, and the prognostic significance of coronary microvascular obstruction (MVO) in mortality and morbidity. This review will elucidate the multifaceted and interconnected pathophysiological processes which underpin MVO in ACS, and the various diagnostic modalities as well as challenges, with a particular focus on the invasive but specific and reproducible index of microcirculatory resistance (IMR). Unfortunately, a multitude of purported therapeutic strategies to address this unmet need in cardiovascular care, outlined in this review, have so far been disappointing with conflicting results and a lack of hard clinical end-point benefit. There are however a number of exciting and novel future prospects in this field that will be evaluated over the coming years in large adequately powered clinical trials, and this review will briefly appraise these.

Adjunctive Intracoronary Fibrinolytic Therapy During Primary Percutaneous Coronary Intervention

Despite routinely restoring epicardial coronary patency, with primary percutaneous coronary intervention (PCI), microvascular obstruction affects approximately half of patients and confers an adverse prognosis. There are no evidence-based treatments for microvascular obstruction. A key contributor to microvascular obstruction is distal embolisation and microvascular thrombi. Adjunctive intracoronary fibrinolytic therapy may reduce thrombotic burden, potentially reducing distal embolisation of atherothrombotic debris to the microcirculation. In this review, the evidence from published randomised trials on the effects of adjunctive intracoronary fibrinolytic therapy during primary PCI is critically appraised, the ongoing randomised trials are described, and conclusions are made from the available evidence. Clinical uncertainties, to be addressed by future research, are highlighted.

Predictors of Microvascular Reperfusion After Myocardial Infarction

Purpose of Review

In acute ST-segment elevation myocardial infarction (STEMI), successful restoration of blood flow in the infarct-related coronary artery may not secure effective myocardial reperfusion. The mortality and morbidity associated with acute MI remain significant. Microvascular obstruction (MVO) represents failed microvascular reperfusion. MVO is under-recognized, independently associated with adverse cardiac prognosis and represents an unmet therapeutic need.

Recent Findings

Multiple factors including clinical presentation, patient characteristics, biochemical markers, and imaging parameters are associated with MVO after MI.

Summary

Impaired microvascular reperfusion is common following percutaneous coronary intervention (PCI). New knowledge about disease mechanisms underpins precision medicine with individualized risk assessment, investigation, and stratified therapy. To date, there are no evidence-based therapies to prevent or treat MVO post-MI. Identifying novel therapy for MVO is the next frontier.

Effect of coronary flow on intracoronary alteplase: a prespecified analysis from a randomised trial

OBJECTIVES

Persistently impaired culprit artery flow (

METHODS

In T-TIME (trial of low-dose adjunctive alTeplase during primary PCI), patients ≤6 hours from onset of ST-elevation myocardial infarction (STEMI) were randomised to placebo, alteplase 10 mg or alteplase 20 mg, administered by infusion into the culprit artery, pre-stenting. In this prespecified, secondary analysis, coronary flow was assessed angiographically at the point immediately before drug administration. Microvascular obstruction, myocardial haemorrhage and infarct size were assessed by cardiovascular magnetic resonance (CMR) at 2-7 days and 3 months.

RESULTS

TIMI flow was assessed after first treatment (balloon angioplasty/aspiration thrombectomy), immediately pre-drug administration, in 421 participants (mean age 61±10 years, 85% male) and was 3, 2 or 1 in 267, 134 and 19 participants respectively. In patients with TIMI flow ≤2 pre-drug, there was higher incidence of microvascular obstruction with alteplase (alteplase 20 mg (53.1%) and 10 mg (59.5%) combined versus placebo (34.1%); OR=2.47 (95% CI 1.16 to 5.22, p=0.018) interaction p=0.005) and higher incidence of myocardial haemorrhage (alteplase 20 mg (53.1%) and 10 mg (57.9%) combined vs placebo (27.5%); OR=3.26 (95% CI 1.44 to 7.36, p=0.004) interaction p=0.001). These effects were not observed in participants with TIMI 3 flow pre-drug. There were no interactions between TIMI flow pre-drug, alteplase and 3-month CMR findings.

CONCLUSION

In patients with impaired culprit artery flow (

TRIAL REGISTRATION NUMBER

NCT02257294.

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Key Words

• acute myocardial infarction

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MESH Headings Collapse

Grants

• FS/16/74/32573 British Heart Foundation
• MC_PC_12037 Medical Research Council
• MC_PC_15113 Medical Research Council

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Affiliation(s)

Annette Marie Maznyczka Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
Peter McCartney Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK
Patrycja Duklas Robertson Centre for Biostatistics, Institute of Health and Wellbeing, University of Glasgow, Glasgow, UK
Margaret McEntegart Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK
Keith G Oldroyd Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
John P Greenwood Department of Cardiology, Leeds General Infirmary, Leeds, UK Leeds Institute of Cardiovascular and Metabolic Medicine, University of Leeds, Leeds, UK
Douglas Muir James Cook University Hospital, Middlesbrough, UK
Saqib Chowdhary Manchester University NHS Foundation Trust, Manchester, UK
Anthony H Gershlick Division of Cardiology, University of Leicester, Leicester, UK
Clare Appleby Liverpool Heart and Chest Hospital NHS Foundation Trust, Liverpool, UK
Hany Eteiba Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK
James Cotton Department of Cardiology, Royal Wolverhampton Hospitals NHS Trust, Wolverhampton, Wolverhampton, UK
Andrew Wragg Barts and The London Hospital, London, UK
Nick Curzen Wessex Cardiac Unit, University Hospital Southampton NHS Foundation Trust, Southampton, UK
R Campbell Tait Department of Haematology, Glasgow Royal Infirmary, Glasgow, UK
Peter MacFarlane Electrocardiology Group, Royal Infirmary, Glasgow, UK
Paul Welsh British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
Naveed Sattar British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
Mark C Petrie British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK
Ian Ford Robertson Centre for Biostatistics, Institute of Health and Wellbeing, University of Glasgow, Glasgow, UK
Keith A A Fox Department of Cardiology, University of Edinburgh and Royal Infirmary of Edinburgh, Edinburgh, UK
Alex McConnachie Robertson Centre for Biostatistics, Institute of Health and Wellbeing, University of Glasgow, Glasgow, UK
Colin Berry Department of Cardiology, Golden Jubilee National Hospital, Glasgow, UK British Heart Foundation Glasgow Cardiovascular Research Centre, Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK

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Kinetics Analysis of Circulating MicroRNAs Unveils Markers of Failed Myocardial Reperfusion

BACKGROUND

Failed myocardial reperfusion occurs in approximately 50% of patients with ST-elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PPCI). It manifests as microvascular obstruction (MVO) on cardiac magnetic resonance (CMR) imaging. Although prognostically important, MVO is not routinely screened for. Our aim was to investigate the kinetics of circulating short noncoding ribonucleic acids [microRNAs (miRNAs)] following PPCI and their association with MVO in STEMI patients.

METHODS

Screening of 2083 miRNAs in plasma from STEMI patients with (n = 6) and without (n = 6) MVO was performed by next-generation sequencing. Two candidate miRNAs were selected and quantified at 13 time points within 3 h postreperfusion in 20 STEMI patients by reverse transcription and quantitative PCR. Subsequently, these 2 miRNAs were measured in a "validation" STEMI cohort (n = 50) that had CMR imaging performed at baseline and 3 months post-PPCI to evaluate their association with MVO.

RESULTS

miR-1 and miR-133b were rapidly released following PPCI in a monophasic or biphasic pattern. Both miRNAs were enriched in circulating microparticles. A second miR-1 peak (90-180 min postreperfusion) seemed to be associated with a higher index of microvascular resistance. In addition, miR-1 and miR-133b levels at 90 min post-PPCI were approximately 3-fold (P = 0.001) and 4.4-fold (P = 0.008) higher in patients with MVO, respectively. Finally, miR-1 was significantly increased in a subgroup of patients with worse left ventricular (LV) functional recovery 3 months post-PPCI.

CONCLUSIONS

miR-1 and miR-133b levels increase within 3 h of PPCI. They are positively associated with MVO and worse LV functional recovery post-PPCI.

The Potential Use of the Index of Microcirculatory Resistance to Guide Stratification of Patients for Adjunctive Therapy in Acute Myocardial Infarction

The goal of reperfusion therapies in ST-segment elevation myocardial infarction has evolved to include effective reperfusion of the microcirculation subtended by the culprit epicardial coronary artery. The index of microcirculatory resistance is measured using a pressure- and temperature-sensing coronary guidewire and quantifies microvascular dysfunction. The index of microcirculatory resistance is an independent predictor of microvascular obstruction, infarct size, and adverse clinical outcomes. It has the advantage of being immediately measurable in the catheterization laboratory, before the results of blood biomarkers or noninvasive imaging become available. This provides an opportunity for additional intervention that may alter outcomes. In this review, the authors provide a critical appraisal of the published research on the emerging role of the index of microcirculatory resistance as a tool to guide the stratification of patients for adjunctive therapeutic strategies in acute ST-segment elevation myocardial infarction.

Comparative Significance of Invasive Measures of Microvascular Injury in Acute Myocardial Infarction

BACKGROUND

The resistive reserve ratio (RRR) expresses the ratio between basal and hyperemic microvascular resistance. RRR measures the vasodilatory capacity of the microcirculation. We compared RRR, index of microcirculatory resistance (IMR), and coronary flow reserve (CFR) for predicting microvascular obstruction (MVO), myocardial hemorrhage, infarct size, and clinical outcomes, after ST-segment-elevation myocardial infarction.

METHODS

In the T-TIME trial (Trial of Low-Dose Adjunctive Alteplase During Primary PCI), 440 patients with acute ST-segment-elevation myocardial infarction from 11 UK hospitals were prospectively enrolled. In a subset of 144 patients, IMR, CFR, and RRR were measured post-primary percutaneous coronary intervention. MVO extent (% left ventricular mass) was determined by cardiovascular magnetic resonance imaging at 2 to 7 days. Infarct size was determined at 3 months. One-year major adverse cardiac events, heart failure hospitalizations, and all-cause death/heart failure hospitalizations were assessed.

RESULTS

In these 144 patients (mean age, 59±11 years, 80% male), median IMR was 29.5 (interquartile range: 17.0-55.0), CFR was 1.4 (1.1-2.0), and RRR was 1.7 (1.3-2.3). MVO occurred in 41% of patients. IMR>40 was multivariably associated with more MVO (coefficient, 0.53 [95% CI, 0.05-1.02]; P=0.031), myocardial hemorrhage presence (odds ratio [OR], 3.20 [95% CI, 1.25-8.24]; P=0.016), and infarct size (coefficient, 5.05 [95% CI, 0.84-9.26]; P=0.019), independently of CFR≤2.0, RRR≤1.7, myocardial perfusion grade≤1, and Thrombolysis in Myocardial Infarction frame count. RRR was multivariably associated with MVO extent (coefficient, -0.60 [95% CI, -0.97 to -0.23]; P=0.002), myocardial hemorrhage presence (OR, 0.34 [95% CI, 0.15-0.75]; P=0.008), and infarct size (coefficient, -3.41 [95% CI, -6.76 to -0.06]; P=0.046). IMR>40 was associated with heart failure hospitalization (OR, 5.34 [95% CI, 1.80-15.81] P=0.002), major adverse cardiac events (OR, 4.46 [95% CI, 1.70-11.70] P=0.002), and all-cause death/ heart failure hospitalization (OR, 4.08 [95% CI, 1.55-10.79] P=0.005). RRR was associated with heart failure hospitalization (OR, 0.44 [95% CI, 0.19-0.99] P=0.047). CFR was not associated with infarct characteristics or clinical outcomes.

CONCLUSIONS

In acute ST-segment-elevationl infarction, IMR and RRR, but not CFR, were associated with MVO, myocardial hemorrhage, infarct size, and clinical outcomes. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02257294.

Pathophysiology and diagnosis of coronary microvascular dysfunction in ST-elevation myocardial infarction

Early mechanical reperfusion of the epicardial coronary artery by primary percutaneous coronary intervention (PCI) is the guideline-recommended treatment for ST-elevation myocardial infarction (STEMI). Successful restoration of epicardial coronary blood flow can be achieved in over 95% of PCI procedures. However, despite angiographically complete epicardial coronary artery patency, in about half of the patients perfusion to the distal coronary microvasculature is not fully restored, which is associated with increased morbidity and mortality. The exact pathophysiological mechanism of post-ischaemic coronary microvascular dysfunction (CMD) is still debated. Therefore, the current review discusses invasive and non-invasive techniques for the diagnosis and quantification of CMD in STEMI in the clinical setting as well as results from experimental in vitro and in vivo models focusing on ischaemic-, reperfusion-, and inflammatory damage to the coronary microvascular endothelial cells. Finally, we discuss future opportunities to prevent or treat CMD in STEMI patients.

Effects of Intracoronary Alteplase on Microvascular Function in Acute Myocardial Infarction

Background

Impaired microcirculatory reperfusion worsens prognosis following acute ST‐segment–elevation myocardial infarction. In the T‐TIME (A Trial of Low‐Dose Adjunctive Alteplase During Primary PCI) trial, microvascular obstruction on cardiovascular magnetic resonance imaging did not differ with adjunctive, low‐dose, intracoronary alteplase (10 or 20 mg) versus placebo during primary percutaneous coronary intervention. We evaluated the effects of intracoronary alteplase, during primary percutaneous coronary intervention, on the index of microcirculatory resistance, coronary flow reserve, and resistive reserve ratio.

Methods and Results

A prespecified physiology substudy of the T‐TIME trial. From 2016 to 2017, patients with ST‐segment–elevation myocardial infarction ≤6 hours from symptom onset were randomized in a double‐blind study to receive alteplase 20 mg, alteplase 10 mg, or placebo infused into the culprit artery postreperfusion, but prestenting. Index of microcirculatory resistance, coronary flow reserve, and resistive reserve ratio were measured after percutaneous coronary intervention. Cardiovascular magnetic resonance was performed at 2 to 7 days and 3 months. Analyses in relation to ischemic time (<2, 2–4, and ≥4 hours) were prespecified. One hundred forty‐four patients (mean age, 59±11 years; 80% male) were prospectively enrolled, representing 33% of the overall population (n=440). Overall, index of microcirculatory resistance (median, 29.5; interquartile range, 17.0–55.0), coronary flow reserve(1.4 [1.1–2.0]), and resistive reserve ratio (1.7 [1.3–2.3]) at the end of percutaneous coronary intervention did not differ between treatment groups. Interactions were observed between ischemic time and alteplase for coronary flow reserve (P=0.013), resistive reserve ratio (P=0.026), and microvascular obstruction (P=0.022), but not index of microcirculatory resistance.

Conclusions

In ST‐segment–elevation myocardial infarction with ischemic time ≤6 hours, there was overall no difference in microvascular function with alteplase versus placebo.

Clinical Trial Registration

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02257294.

Relationship between the ST-Segment Resolution and Microvascular Dysfunction in Patients Who Underwent Primary Percutaneous Coronary Intervention

Objectives

Incomplete ST-segment elevation resolution (STR) occasionally occurs despite successful revascularization of epicardial coronary artery after primary percutaneous coronary intervention (PPCI). The aim of this study was to evaluate the relationship between the degree of STR and the severity of microvascular dysfunction.

Methods

A total of 73 consecutive patients with ST-segment elevation myocardial infarction (STEMI) who underwent successful PPCI were evaluated. Serial 12-lead electrocardiography was performed at baseline and at 90 minutes after PPCI. Microvascular dysfunction was assessed by index of microvascular resistance (IMR) immediately after PPCI.

Results

Patients were classified into 2 groups: 50 patients with complete STR (STR ≥50%) and 23 patients with incomplete STR (STR <50%). The incomplete STR group had a higher IMR value and lower left ventricular ejection fraction (LVEF), compared with the complete STR group. The degree of STR was significantly correlated with IMR (r = −0.416, P=0.002) and LVEF (r = 0.300, P=0.011). These correlations were only observed in patients with left anterior descending artery (LAD) infarction but not observed in patients with non-LAD infarction. A cutoff IMR value was 27.3 for predicting incomplete STR after PPCI.

Conclusion

Incomplete STR after PPCI in patients with STEMI reflects the presence of microvascular and left ventricular dysfunction, especially in patients with LAD infarction.

Microvascular obstruction in acute myocardial infarction: an old and unsolved mystery

In the setting of acute myocardial infarction, flow restoration in the culprit epicardial coronary artery is not synonymous with efficient reperfusion. Microvascular obstruction occurs in 50% of cases and represents a predictor of a long-term unfavorable outcome. Its prevalence has remained constant in recent years despite various treatment attempts. However, the success of targeted therapies could be mainly a problem of timing. Recent data bring evidence with regard to the role of pre-procedural distal embolization and highlight the relation between distal embolism, microvascular obstruction and intramyocardial inflammation. As a result, early detection of microvascular injury represents the first step in the development of targeted, individualized therapeutic approaches. In this context, the identification of new invasive surrogate parameters for the timely assessment and quantification of microvascular obstruction in the catheterization laboratory has become an important subject of current research. Among these, coronary wedge pressure is the most practical and revealing in the setting of primary percutaneous coronary intervention. It may offer comprehensive details on the mechanisms of microvascular injury and may therefore offer guidance for appropriate treatment selection.

Index of Microcirculatory Resistance as a Tool to Characterize Microvascular Obstruction and to Predict Infarct Size Regression in Patients With STEMI Undergoing Primary PCI

OBJECTIVES

This study aimed to compare the value of the index of microcirculatory resistance (IMR) and microvascular obstruction (MVO) measured by cardiac magnetic resonance (CMR) in patients treated for and recovering from ST-segment elevation myocardial infarction.

BACKGROUND

IMR can identify patients with microvascular dysfunction acutely after primary percutaneous coronary intervention (pPCI), and a threshold of >40 has been shown to be associated with an adverse clinical outcome. Similarly, MVO is recognized as an adverse feature in patients with ST-segment elevation myocardial infarction. Even though both IMR and MVO reflect coronary microvascular status, the interaction between these 2 parameters is uncertain.

METHODS

A total of 110 patients treated with pPCI were included, and IMR was measured immediately at completion of pPCI. Infarct size (IS) as a percentage of left ventricular mass was quantified at 48 h (38.4 ± 12.0 h) and 6 months (194.0 ± 20.0 days) using CMR. MVO was identified and quantified at 48 h by CMR.

RESULTS

Overall, a discordance between IMR and MVO was observed in 36.7% of cases, with 31 patients having MVO and IMR ≤40. Compared with patients with MVO and IMR ≤40, patients with both MVO and IMR >40 had an 11.9-fold increased risk of final IS >25% at 6 months (p = 0.001). Patients with MVO and IMR ≤40 had a significantly smaller IS at 6 months (p = 0.001), with significant regression in IS over time (34.4% [interquartile range (IQR): 27.3% to 41.0%] vs. 22.3% [IQR: 16.0% to 30.0%]; p = 0.001).

CONCLUSIONS

Discordant prognostic information was obtained from IMR and MVO in nearly one-third of cases; however, IMR can be helpful in grading the degree and severity of MVO.

Sex-based associations with microvascular injury and outcomes after ST-segment elevation myocardial infarction

Objectives

We aimed to assess for sex differences in invasive parameters of acute microvascular reperfusion injury and infarct characteristics on cardiac MRI after ST-segment elevation myocardial infarction (STEMI).

Methods

Patients with STEMI undergoing emergency percutaneous coronary intervention (PCI) were prospectively enrolled. Index of microcirculatory resistance (IMR) and coronary flow reserve (CFR) were measured in the culprit artery post-PCI. Contrast-enhanced MRI was used to assess infarct characteristics, microvascular obstruction and myocardial haemorrhage, 2 days and 6 months post-STEMI. Prespecified outcomes were as follows: (i) all-cause death/first heart failure hospitalisation and (ii) cardiac death/non-fatal myocardial infarction/urgent coronary revascularisation (major adverse cardiovascular event, MACE) during 5- year median follow-up.

Results

In 324 patients with STEMI (87 women, mean age: 61 ± 12.19 years; 237 men, mean age: 59 ± 11.17 years), women had anterior STEMI less often, fewer prescriptions of beta-blockers at discharge and higher baseline N-terminal pro-B-type natriuretic peptide levels (all p < 0.05). Following emergency PCI, fewer women than men had Thrombolysis in Myocardial Infarction (TIMI) myocardial perfusion grades ≤ 1 (20% vs 32%, p = 0.027) and women had lower corrected TIMI frame counts (12.94 vs 17.65, p = 0.003). However, IMR, CFR, microvascular obstruction, myocardial haemorrhage, infarct size, myocardial salvage index, left ventricular remodelling and ejection fraction did not differ significantly between sexes. Female sex was not associated with MACE or all-cause death/first heart failure hospitalisation.

Conclusion

There were no sex differences in microvascular pathology in patients with acute STEMI. Women had less anterior infarcts than men, and beta-blocker therapy at discharge was prescribed less often in women.

Trial registration number

NCT02072850.

Coronary Physiology in the Cardiac Catheterization Laboratory

Coronary angiography has been the principle modality for assessing the severity of atherosclerotic coronary artery disease for several decades. However, there is a complex relationship between angiographic coronary stenosis and the presence or absence of myocardial ischemia. Recent technological advances now allow for the assessment of coronary physiology in the catheterization laboratory at the time of diagnostic coronary angiography. Early studies focused on coronary flow reserve (CFR) but more recent work has demonstrated the physiologic accuracy and prognostic value of the fractional flow reserve (FFR) and instantaneous wave free ratio (iFR) for the assessment of coronary artery disease. These measurements have been validated in large multi-center clinical trials and have become indispensable tools for guiding revascularization in the cardiac catheterization laboratory. The physiological assessment of chest pain in the absence of epicardial coronary artery disease involves coronary thermodilution to obtain the index of microcirculatory resistance (IMR) or Doppler velocity measurement to determine the coronary flow velocity reserve (CFVR). Physiology-based coronary artery assessment brings "personalized medicine" to the catheterization laboratory and allows cardiologists and referring providers to make decisions based on objective findings and evidence-based treatment algorithms. The purpose of this review is to describe the theory, technical aspects, and relevant clinical trials related to coronary physiology assessment for an intended audience of general medical practitioners.

Assessing and managing coronary microcirculation dysfunction in acute ST-segment elevation myocardial infarction

INTRODUCTION

Microvascular dysfunction in the setting of acute ST-segment elevation myocardial infarction (STEMI) is an indicator of poor long-term prognosis. Prompt assessment and pharmacological or procedural therapy (prophylactic or post onset of dysfunction) may improve outcomes in STEMI post-primary percutaneous intervention. Areas covered: The aim of this review is to provide a comprehensive analysis of the evidence available about the assessment and management of coronary microcirculatory injury/dysfunction in STEMI. We also aim to elucidate the possible strategies that could be applied in clinical practice to support the application of already available or novel therapeutic strategies for the prevention and management of microvascular impairment. Expert commentary: There are multiple established methods in assessing microvascular dysfunction, both non-invasively and invasively. Invasive physiological measurements allow real-time assessment of microvascular dysfunction and have prognostic cut-off values. Multiple therapeutic modalities exist for both preventing and treating microvascular dysfunction. These can be either pharmacological or mechanical, and there is no algorithm to guide if, how and when to apply them. Future research into both procedural and pharmacological therapy guided by physiological measurements is needed, with the aim of recognizing high-risk patients who would benefit from therapy.

Comparison of native myocardial T1 and T2 mapping at 1.5T and 3T in healthy volunteers : Reference values and clinical implications

Background

Myocardial native T1 and T2 mapping are promising techniques for quantitative assessment of diffuse myocardial pathologies; however, due to conflicting data regarding normal values, routine clinical implementation of this method is still challenging.

Methods

To evaluate this situation during daily clinical practice the characteristics of normal values obtained in 60 healthy volunteers who underwent magnetic resonance imaging (MRI) scans on 1.5T and 3T scanners were studied. The T1 modified look-locker inversion recovery (MOLLI; 5(3)3; modified for higher heart rates) and T2 navigator gated black-blood prepared gradient-spin-echo (GraSE) sequences were used.

Results

While age and body mass index did not affect relaxation times, a gender and heart rate dependency was found showing higher T1 and T2 values in females, whereas at higher heart rates a prolongation of T1 and a shortening of T2 relaxation times was found. Particularly prone to artifacts were T2 measurements at 3T and the inferolateral wall. In the individual setting mean relaxation times for T1 were 995.8 ± 30.9 ms at 1.5T and 1183.8 ± 37.5 ms at 3T and 55.8 ± 2.8 ms at 1.5T and 51.6 ± 3 ms at 3T for T2 indicating a high dependency of reference values on MRI protocol when compared to the literature. Furthermore, as presumed mean T1 and T2 values correlated in the same individual.

Conclusions

The T1 and T2 relaxation times depend on physiological factors and especially on MRI protocols. Therefore, reference values should be validated individually in every radiological institution before implementing mapping protocols in daily clinical practice. Correlation of mean T1 and T2 values in the same proband at both field strengths indicates intraindividual reproducibility.

Current Smoking and Prognosis After Acute ST-Segment Elevation Myocardial Infarction: New Pathophysiological Insights

Objectives

The aim of this study was to mechanistically investigate associations among cigarette smoking, microvascular pathology, and longer term health outcomes in patients with acute ST-segment elevation myocardial infarction (MI).

Background

The pathophysiology of myocardial reperfusion injury and prognosis in smokers with acute ST-segment elevation MI is incompletely understood.

Methods

Patients were prospectively enrolled during emergency percutaneous coronary intervention. Microvascular function in the culprit artery was measured invasively. Contrast-enhanced magnetic resonance imaging (1.5-T) was performed 2 days and 6 months post-MI. Infarct size and microvascular obstruction were assessed using late gadolinium enhancement imaging. Myocardial hemorrhage was assessed with T2* mapping. Pre-specified endpoints included: 1) all-cause death or first heart failure hospitalization; and 2) cardiac death, nonfatal MI, or urgent coronary revascularization (major adverse cardiovascular events). Binary logistic regression (odds ratio [OR] with 95% confidence interval [CI]) with smoking status was used.

Results

In total, 324 patients with ST-segment elevation MI were enrolled (mean age 59 years, 73% men, 60% current smokers). Current smokers were younger (age 55 ± 11 years vs. 65 ± 10 years, p < 0.001), with fewer patients with hypertension (52 ± 27% vs. 53 ± 41%, p = 0.007). Smokers had better TIMI (Thrombolysis In Myocardial Infarction) flow grade (≥2 vs. ≤1, p = 0.024) and ST-segment resolution (none vs. partial vs. complete, p = 0.010) post–percutaneous coronary intervention. On day 1, smokers had higher circulating C-reactive protein, neutrophil, and monocyte levels. Two days post-MI, smoking independently predicted infarct zone hemorrhage (OR: 2.76; 95% CI: 1.42 to 5.37; p = 0.003). After a median follow-up period of 4 years, smoking independently predicted all-cause death or heart failure events (OR: 2.20; 95% CI: 1.07 to 4.54) and major adverse cardiovascular events (OR: 2.79; 95% CI: 2.30 to 5.99).

Conclusions

Smoking is associated with enhanced inflammation acutely, infarct-zone hemorrhage subsequently, and longer term adverse cardiac outcomes. Inflammation and irreversible myocardial hemorrhage post-MI represent mechanistic drivers for adverse long-term prognosis in smokers. (Detection and Significance of Heart Injury in ST Elevation Myocardial Infarction. [BHF MR-MI]; NCT02072850)

PET measurements of myocardial blood flow post myocardial infarction: Relationship to invasive and cardiac magnetic resonance studies and potential clinical applications

This review focuses on clinical studies concerning assessment of coronary microvascular and conduit vessel function primarily in the context of acute and sub acute myocardial infarction (MI). The ability of quantitative PET measurements of myocardial blood flow (MBF) to delineate underlying pathophysiology and assist in clinical decision making in this setting is discussed. Likewise, considered are physiological metrics fractional flow reserve, coronary flow reserve, index of microvascular resistance (FFR, CFR, IMR) obtained from invasive studies performed in the cardiac catheterization laboratory, typically at the time of PCI for MI. The role both of invasive studies and cardiac magnetic resonance (CMR) imaging in assessing microvascular function, a key determinant of prognosis, is reviewed. The interface between quantitative PET MBF measurements and underlying pathophysiology, as demonstrated both by invasive and CMR methodology, is discussed in the context of optimal interpretation of the quantitative PET MBF exam and its potential clinical applications.

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.

Invasive Assessment of the Coronary Microcirculation in Reperfused ST-Segment-Elevation Myocardial Infarction Patients: Where Do We Stand?

For patients presenting with an acute ST-segment-elevation myocardial infarction, the most effective therapy for reducing myocardial infarct size and preserving left ventricular systolic function is primary percutaneous coronary intervention (PPCI). However, mortality and morbidity remain significant. This is partly attributed to the development of microvascular obstruction, which occurs in around 50% of ST-segment-elevation myocardial infarction patients post-PPCI, and it is associated with adverse left ventricular remodeling and worse clinical outcomes. Although microvascular obstruction can be detected by cardiac imaging techniques several hours post-PPCI, it may be too late to intervene at that time. Therefore, being able to predict the development of microvascular obstruction at the time of PPCI may identify high-risk patients who might benefit from further adjuvant intracoronary therapies, such as thrombolysis, vasodilators, glycoprotein IIb/IIIa inhibitors, and anti-inflammatory agents that may reduce microvascular obstruction. Recent studies have shown that invasive coronary physiology measurements performed during PPCI can be used to assess the coronary microcirculation. In this article, we provide an overview of the various invasive methods currently available to assess the coronary microcirculation in the setting of ST-segment-elevation myocardial infarction, and how they could potentially be used in the future for tailoring therapies to those most at risk.

Comparative Prognostic Utility of Indexes of Microvascular Function Alone or in Combination in Patients With an Acute ST-Segment-Elevation Myocardial Infarction

BACKGROUND

Primary percutaneous coronary intervention is frequently successful at restoring coronary artery blood flow in patients with acute ST-segment-elevation myocardial infarction; however, failed myocardial reperfusion commonly passes undetected in up to half of these patients. The index of microvascular resistance (IMR) is a novel invasive measure of coronary microvascular function. We aimed to investigate the pathological and prognostic significance of an IMR>40, alone or in combination with a coronary flow reserve (CFR≤2.0), in the culprit artery after emergency percutaneous coronary intervention for acute ST-segment-elevation myocardial infarction.

METHODS

Patients with acute ST-segment-elevation myocardial infarction were prospectively enrolled during emergency percutaneous coronary intervention and categorized according to IMR (≤40 or >40) and CFR (≤2.0 or >2.0). Cardiac magnetic resonance imaging was acquired 2 days and 6 months after myocardial infarction. All-cause death or first heart failure hospitalization was a prespecified outcome (median follow-up, 845 days).

RESULTS

IMR and CFR were measured in the culprit artery at the end of percutaneous coronary intervention in 283 patients with ST-segment-elevation myocardial infarction (mean±SD age, 60±12 years; 73% male). The median IMR and CFR were 25 (interquartile range, 15-48) and 1.6 (interquartile range, 1.1-2.1), respectively. An IMR>40 was a multivariable associate of myocardial hemorrhage (odds ratio, 2.10; 95% confidence interval, 1.03-4.27; P=0.042). An IMR>40 was closely associated with microvascular obstruction. Symptom-to-reperfusion time, TIMI (Thrombolysis in Myocardial Infarction) blush grade, and no (≤30%) ST-segment resolution were not associated with these pathologies. An IMR>40 was a multivariable associate of the changes in left ventricular ejection fraction (coefficient, -2.12; 95% confidence interval, -4.02 to -0.23; P=0.028) and left ventricular end-diastolic volume (coefficient, 7.85; 95% confidence interval, 0.41-15.29; P=0.039) at 6 months independently of infarct size. An IMR>40 (odds ratio, 4.36; 95% confidence interval, 2.10-9.06; P<0.001) was a multivariable associate of all-cause death or heart failure. Compared with an IMR>40, the combination of IMR>40 and CFR≤2.0 did not have incremental prognostic value.

CONCLUSIONS

An IMR>40 is a multivariable associate of left ventricular and clinical outcomes after ST-segment-elevation myocardial infarction independently of the infarction size. Compared with standard clinical measures of the efficacy of myocardial reperfusion, including the ischemic time, ST-segment elevation, angiographic blush grade, and CFR, IMR has superior clinical value for risk stratification and may be considered a reference test for failed myocardial reperfusion.

CLINICAL TRIAL REGISTRATION

URL: https//www.clinicaltrials.gov. Unique identifier: NCT02072850.