Low-Dose Alteplase During Primary Percutaneous Coronary Intervention According to Ischemic Time

BACKGROUND

Microvascular obstruction affects one-half of patients with ST-segment elevation myocardial infarction and confers an adverse prognosis.

OBJECTIVES

This study aimed to determine whether the efficacy and safety of a therapeutic strategy involving low-dose intracoronary alteplase infused early after coronary reperfusion associates with ischemic time.

METHODS

This study was conducted in a prospective, multicenter, parallel group, 1:1:1 randomized, dose-ranging trial in patients undergoing primary percutaneous coronary intervention. Ischemic time, defined as the time from symptom onset to coronary reperfusion, was a pre-specified subgroup of interest. Between March 17, 2016, and December 21, 2017, 440 patients, presenting with ST-segment elevation myocardial infarction within 6 h of symptom onset (<2 h, n = 107; ≥2 h but <4 h, n = 235; ≥4 h to 6 h, n = 98), were enrolled at 11 U.K. hospitals. Participants were randomly assigned to treatment with placebo (n = 151), alteplase 10 mg (n = 144), or alteplase 20 mg (n = 145). The primary outcome was the amount of microvascular obstruction (MVO) (percentage of left ventricular mass) quantified by cardiac magnetic resonance imaging at 2 to 7 days (available for 396 of 440).

RESULTS

Overall, there was no association between alteplase dose and the extent of MVO (p for trend = 0.128). However, in patients with an ischemic time ≥4 to 6 h, alteplase increased the mean extent of MVO compared with placebo: 1.14% (placebo) versus 3.11% (10 mg) versus 5.20% (20 mg); p = 0.009 for the trend. The interaction between ischemic time and alteplase dose was statistically significant (p = 0.018).

CONCLUSION

In patients presenting with ST-segment elevation myocardial infarction and an ischemic time ≥4 to 6 h, adjunctive treatment with low-dose intracoronary alteplase during primary percutaneous coronary intervention was associated with increased MVO. Intracoronary alteplase may be harmful for this subgroup. (A Trial of Low-Dose Adjunctive Alteplase During Primary PCI [T-TIME]; NCT02257294).

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)

New perspectives on the role of cardiac magnetic resonance imaging to evaluate myocardial salvage and myocardial hemorrhage after acute reperfused ST-elevation myocardial infarction

Cardiac magnetic resonance (CMR) imaging enables the assessment of left ventricular function and pathology. In addition to established contrast-enhanced methods for the assessment of infarct size and microvascular obstruction, other infarct pathologies, such as myocardial edema and myocardial hemorrhage, can be identified using innovative CMR techniques. The initial extent of myocardial edema revealed by T2-weighted CMR has to be stable for edema to be taken as a retrospective marker of the area-at-risk, which is used to calculate myocardial salvage. The timing of edema assessment is important and should be focused within 2 - 7 days post-reperfusion. Some recent investigations have called into question the diagnostic validity of edema imaging after acute STEMI. Considering the results of these studies, as well as results from our own laboratory, we conclude that the time-course of edema post-STEMI is unimodal, not bimodal. Myocardial hemorrhage is the final consequence of severe vascular injury and a progressive and prognostically important complication early post-MI. Myocardial hemorrhage is a therapeutic target to limit reperfusion injury and infarct size post-STEMI.

Temporal Evolution of Myocardial Hemorrhage and Edema in Patients After Acute ST-Segment Elevation Myocardial Infarction: Pathophysiological Insights and Clinical Implications

Background

The time course and relationships of myocardial hemorrhage and edema in patients after acute ST‐segment elevation myocardial infarction (STEMI) are uncertain.

Methods and Results

Patients with ST‐segment elevation myocardial infarction treated by primary percutaneous coronary intervention underwent cardiac magnetic resonance imaging on 4 occasions: at 4 to 12 hours, 3 days, 10 days, and 7 months after reperfusion. Myocardial edema (native T2) and hemorrhage (T2*) were measured in regions of interest in remote and injured myocardium. Myocardial hemorrhage was taken to represent a hypointense infarct core with a T2* value <20 ms. Thirty patients with ST‐segment elevation myocardial infarction (mean age 54 years; 25 [83%] male) gave informed consent. Myocardial hemorrhage occurred in 7 (23%), 13 (43%), 11 (33%), and 4 (13%) patients at 4 to 12 hours, 3 days, 10 days, and 7 months, respectively, consistent with a unimodal pattern. The corresponding median amounts of myocardial hemorrhage (percentage of left ventricular mass) during the first 10 days after myocardial infarction were 2.7% (interquartile range [IQR] 0.0–5.6%), 7.0% (IQR 4.9–7.5%), and 4.1% (IQR 2.6–5.5%; P<0.001). Similar unimodal temporal patterns were observed for myocardial edema (percentage of left ventricular mass) in all patients (P=0.001) and for infarct zone edema (T2, in ms: 62.1 [SD 2.9], 64.4 [SD 4.9], 65.9 [SD 5.3]; P<0.001) in patients without myocardial hemorrhage. Alternatively, in patients with myocardial hemorrhage, infarct zone edema was reduced at day 3 (T2, in ms: 51.8 [SD 4.6]; P<0.001), depicting a bimodal pattern. Left ventricular end‐diastolic volume increased from baseline to 7 months in patients with myocardial hemorrhage (P=0.001) but not in patients without hemorrhage (P=0.377).

Conclusions

The temporal evolutions of myocardial hemorrhage and edema are unimodal, whereas infarct zone edema (T2 value) has a bimodal pattern. Myocardial hemorrhage is prognostically important and represents a target for therapeutic interventions that are designed to preserve vascular integrity following coronary reperfusion.

Clinical Trial Registration

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

T2 mapping at 7T MRI can quantitatively assess intramyocardial hemorrhage in rats with acute reperfused myocardial infarction in vivo

PURPOSE

To investigate T2 mapping at 7T magnetic resonance imaging (MRI) for the detection and quantification of reperfused intramyocardial hemorrhage (IMH) in a rat model.

MATERIALS AND METHODS

Myocardial infarction (MI) was induced in 25 female rats. Rats were scanned at a 7T MRI 48 hours after reperfusion, using T2 mapping and late gadolinium enhancement imaging. Gross sections of the left ventricular myocardium and corresponding hematoxylin and eosin staining were assessed for IMH. T2 mapping images were matched with the gross sections. The IMH volume, expressed as a percentage of the left ventricular myocardial volume, of each heart determined by T2 mapping was compared with that calculated by pathological gross examination.

RESULTS

Six rats died. In all, 97 gross sections of the left ventricular myocardium from the 19 rats were matched with T2 mapping images. IMH occurred pathologically in 68 gross sections, which was detected as hypointense cores by T2 mapping in 63 images (93% sensitivity). Three T2 mapping images with hypointense cores showed no hemorrhage on pathological sections (90% specificity). The positive and negative predictive values of hemorrhage on T2 mapping were 95% and 84%, respectively. In terms of the IMH volume, there was no significant difference between T2 mapping and pathological gross measurements (4.8 ± 2.4% vs. 5.3 ± 3.2%; P = 0.11).

CONCLUSION

T2 mapping at 7T MRI can reliably detect and quantify IMH in rats in vivo. This may be useful as a noninvasive quantitative approach to investigating the mechanisms and evolution of MI and reperfusion injury. J. Magn. Reson. Imaging 2016;44:194-203.

CMR of microvascular obstruction and hemorrhage in myocardial infarction

Microvascular obstruction (MO) or no-reflow phenomenon is an established complication of coronary reperfusion therapy for acute myocardial infarction. It is increasingly recognized as a poor prognostic indicator and marker of subsequent adverse LV remodeling. Although MO can be assessed using various imaging modalities including electrocardiography, myocardial contrast echocardiography, nuclear scintigraphy, and coronary angiography, evaluation by cardiovascular magnetic resonance (CMR) is particularly useful in enhancing its detection, diagnosis, and quantification, as well as following its subsequent effects on infarct evolution and healing. MO assessment has become a routine component of the CMR evaluation of acute myocardial infarction and will increasingly play a role in clinical trials of adjunctive reperfusion agents and strategies. This review will summarize the pathophysiology of MO, current CMR approaches to diagnosis, clinical implications, and future directions needed for improving our understanding of this common clinical problem.