Delay in mechanical reperfusion treatment during ST-segment elevation myocardial infarction (STEMI) may be associated with greater injury to the microcirculation, according to results of the HORIZONS-AMI (Harmonizing Outcomes with Revascularization and Stents in Acute Myocardial Infarction) trial, recently published in JACC: Cardiovascular Interventions.

Previous studies have examined the relationship between ischemia duration and myocardial perfusion, but these studies were conducted prior to modern antiplatelet therapy and routine use of stents.

The HORIZONS-AMI investigators studied the effects of both symptom onset-to-balloon (SBT) and door-to-balloon time (DBT) on myocardial reperfusion during primary percutaneous coronary intervention (PCI) in STEMI. They used 2 well-validated measures of myocardial perfusion and reperfusion success: resolution of ST-segment elevation (STR) and myocardial blush grade (MBG).


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The primary analysis was the relationship between SBT of ≤2 hours, >2 to 4 hours, and > 4 hours and DBT ≤1 hour, >1 to 1.5 hours, >1.5 to 2 hours, and >2 hours with MBG and STR.

SBT was defined as “time from symptom onset until balloon inflation” and DBT was defined as “time from arrival at the hospital (first hospital in transferred patients) until balloon inflation.”

Of the 2056 patients who had complete SBT and DBT data available, 7.9% (162), 47.4% (976), and 44.7% (918) presented within SBT of ≤2, 2 to 4, and >4 hours, respectively. Patients with longer SBT were more likely to have absent microvascular perfusion (MBG 0/1) after primary PCI.  Symptom-to-door time (SBT – DBT) and myocardial perfusion demonstrated a similar relationship. SBT, anterior infarction, reference vessel diameter, lesion minimum lumen diameter, hyperlipidemia, and current smoking were all independent predictors of MBG 0/1, according to multivariable analysis.

In each SBT group, the 3-year unadjusted mortality rates were 2.6% (≤2 hours), 4.4% (2 to 4 hours), and 7.2% (>4 hours). In the DBT groups, the mortality rates were 3.6% (≤1 hour), 4.6% (>1 to 1.5 hours), 6.3% (>1.5 to 2 hours), and 6.6% (>2 hours).

MBG was considered an independent predictor of 3-year mortality in a multivariable model that included MBG 0/1 and STR <30% (odds ratio [OR]: 1.79; 95% confidence interval [CI]: 1.17-2.72; P=.007), but not STR <30% (OR: 1.27; 95% CI: 0.82-1.97; P=.28). Diabetes, peripheral vascular disease, history of smoking, and age were considered other independent risk factors.

“We observed a ‘time-dependent’ relationship between SBT duration and the likelihood of impaired myocardial perfusion following primary PCI,” the researchers wrote. “This relationship appears more robust for the ischemia duration (SBT) than for DBT.”

The researchers suggested further investigation of treatment strategies designed to prevent microvascular injury in STEMI. “This has proven to be an elusive goal to date; moreover, there is a need to reconsider the current focus on DBT as the primary quality metric and examine the utility of broader time metrics such as first medical contact to balloon time and total ischemic time.”

Reference

Prasad A, Gersh BJ, Mehran R, et al. Effect of ischemia duration and door-to-balloon time on myocardial perfusion in ST-segment elevation myocardial infarction: an analysis from HORIZONS-AMI trial. JACC Cardiovasc Interv. 2015;8(15):1966-1974.