BACKGROUND

Microvascular obstruction commonly affects patients with acute ST-segment elevation myocardial infarction and is independently associated with adverse outcomes.

OBJECTIVE

To determine whether or not a strategy involving low-dose intracoronary fibrinolytic therapy infused early after coronary reperfusion will reduce microvascular obstruction.

DESIGN

This was a multicentre, randomised, double-blind, parallel-group, placebo-controlled, dose-ranging trial.

SETTING

The trial took place at 11 hospitals in the UK between 17 March 2016 and 21 December 2017.

PARTICIPANTS

Patients with acute ST-segment elevation myocardial infarction and a symptom onset to reperfusion time of ≤ 6 hours were eligible for randomisation. Radial artery access was a requirement, and further angiographic criteria included a proximal-to-middle coronary artery occlusion or impaired coronary flow in the presence of a definite thrombus in the culprit coronary artery. Exclusion criteria included a functional coronary collateral supply to the infarct-related artery, any contraindication to fibrinolysis and lack of informed consent. Additional exclusion criteria for safety were (1) requirement for immunosuppressive drug therapy for ≤ 3 months and (2) treatment with an antimicrobial agent.

INTERVENTION

A total of 440 participants were randomly assigned 1 : 1 : 1 to treatment with placebo ( = 151), 10 mg of alteplase ( = 144) or 20 mg of alteplase ( = 145) administered by manual infusion directly into the infarct-related coronary artery over 5–10 minutes. The intervention was scheduled to happen after reperfusion and before stent implantation.

OUTCOMES

The primary outcome was the amount of microvascular obstruction (percentage of left ventricular mass) demonstrated by contrast-enhanced cardiac magnetic resonance imaging at 2–7 days after enrolment. The primary analysis was the comparison between the 20 mg of alteplase group and the placebo group; if this comparison was not significant, the comparison of the 10 mg of alteplase group with the placebo group was considered as a secondary analysis.

SAMPLE SIZE

A total of 618 patients (minimum of 558 patients). Recruitment was halted on 21 December 2017 given that conditional power for the primary outcome based on a prespecified analysis of the first 267 randomised participants was < 30% in both treatment groups (futility criterion).

METHODS

The primary outcome was compared between groups using a stratified Wilcoxon rank-sum test (van Elteren test), stratified by the location of the myocardial infarction.

RESULTS

Among the 440 patients (mean age of 60.5 years; 15% women), the primary end point was measured in 396 (90%) patients, 17 (3.9%) withdrew, seven died and all other patients were followed up to 3 months. The amount (mean percentage of left ventricular mass) of microvascular obstruction was 2.3% versus 2.6% versus 3.5% in the placebo, 10 mg of alteplase and 20 mg of alteplase groups, respectively. In the primary analysis, microvascular obstruction did not differ between the 20 mg of alteplase group and the placebo group: 3.5% versus 2.3%, estimated difference 1.16% (95% confidence interval –0.08% to 2.41%;  = 0.32). In the secondary analysis, microvascular obstruction did not differ between the 10 mg of alteplase group and the placebo group: 2.6% versus 2.3%, estimated difference 0.29% (95% confidence interval –0.76% to 1.35%;  = 0.74). By 3 months, major adverse cardiac events (cardiac death, non-fatal myocardial infarction and unplanned hospitalisation for heart failure) had occurred in 15 (10.1%) patients in the placebo group, 18 (12.9%) in the 10 mg of alteplase group and 12 (8.2%) in the 20 mg of alteplase group.

CONCLUSIONS

Adjunctive low-dose intracoronary alteplase given during the primary percutaneous intervention did not reduce microvascular obstruction compared with placebo.

LIMITATIONS

Premature discontinuation of enrolment limited the power of the secondary and safety analyses.

FUTURE WORK

Low-dose intracoronary alteplase or tenecteplase could be compared with placebo at the end of primary percutaneous coronary intervention in patients with an ischaemic time of < 4 hours.

TRIAL REGISTRATION

This trial is registered as ClinicalTrials.gov NCT02257294.

FUNDING

This project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a Medical Research Council (MRC) and National Institute for Health Research (NIHR) partnership. This will be published in full in ; Vol. 7, No. 5. See the NIHR Journals Library website for further project information.