On vs Off-hour PPCI in STEMI Patients (On vs Off PPCI)

ST-elevation myocardial infarction (STEMI) remains a leading cause of morbidity and mortality globally, and timely reperfusion with primary percutaneous coronary intervention (PPCI) is the gold-standard treatment1. Current guidelines recommend a door-to-balloon (DTB) time of 90 minutes or less, as the benefits of PPCI increase in direct correlation with the brevity of reperfusion time.

However, there is consistent epidemiological evidence that STEMI patients presenting during off-hours (nights, weekends, and holidays) experience delays in reperfusion and worse in-hospital outcomes compared to those presenting during regular business hours. Two competing hypotheses dominate the literature. The systems hypothesis suggests that delays in care delivery during nights and weekends-including longer catheterization laboratory activation time, reduced availability of experienced operators, and logistical constraints-are the primary drivers of worse outcomes. In support of this, some studies have found that the mortality difference between off-hours and on-hours presentations is attenuated after adjusting for DTB time (Chung et al., 2020), suggesting that system-level process measures may be actionable targets for quality improvement.

Alternatively, the intrinsic severity hypothesis suggests that nocturnal STEMI presentations represent inherently more severe infarcts-characterized by higher thrombus burden, larger myocardial infarction size, and more frequent complications such as cardiogenic shock-independent of how rapidly reperfusion is achieved. Recent studies examining circadian variation in infarct size and myocardial injury biomarkers have found evidence of larger infarcts and worse systolic function in nocturnal-onset STEMI, with long-term mortality implications.

Critically, the vast majority of evidence in this field derives from retrospective registry data, particularly from North American and Western European cohorts. Data from the Middle East and North Africa (MENA) region, where demographic and healthcare system profiles differ substantially from developed nations, are essentially absent from the literature. Furthermore, contemporary data on the prospective relationships between time-of-PPCI, operator experience, procedural quality parameters (such as myocardial blush grade and ST-segment resolution), and outcomes remain limited.

A prospective study with granular intra-procedural data collection offers the opportunity to: (1) quantify the magnitude of the off-hours effect in a Middle Eastern context; (2) decompose the DTB time into its components to identify specific system bottlenecks; (3) assess whether operator seniority and team composition confound or mediate the off-hours effect6; and (4) evaluate whether procedural quality metrics (reperfusion grade, thrombus burden, microvascular perfusion) differ between daytime and nighttime PPCI and contribute to outcome disparities independent of system factors.