ArticlesRelation between door-to-balloon times and mortality after primary percutaneous coronary intervention over time: a retrospective study
Introduction
Door-to-balloon (D2B) time predicts survival in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (pPCI).1, 2, 3 This relation has been thought to be causal, supported by studies in animals4 and observational evidence5, 6 indicating that shorter times to reperfusion are linked to decreased myocardial damage and mortality. As a result, clinical guidelines and national quality initiatives in the past decade have focused on shortening D2B times, including the large D2B Alliance sponsored by the American College of Cardiology (ACC) and the Mission:Lifeline Program led by the American Heart Association (AHA).7, 8, 9 Yet some studies10, 11, 12 have reported that contemporary decreases in annual D2B times have not been associated with temporal improvements in mortality in the population of patients undergoing pPCI. These unexpected results have raised uncertainty about the value of existing quality initiatives and questions about the true relation between D2B time and mortality.13
Results from these studies warrant further assessment. The findings have been interpreted, in some quarters, to suggest that a decrease in D2B times do not result in improved outcomes for individual patients.14, 15 However, for such an assertion to be true the relation between mortality and patient-specific D2B times (ie, the D2B time that an individual patient experiences) needs to be disentangled from secular trends in the overall size, profile, and outcomes of the pPCI population that was simultaneously occurring. The expanded use of the procedure in later years through developing STEMI systems of care could have led to a group of patients with an overall increased risk of survival undergoing the procedure (ie, survivor-cohort effect), which might not be fully captured by traditional variables obtained in clinical registries. Although this possibility could mask the effects of shorter D2B times on outcomes at the population level, it would not obviate a clinically meaningful relation between D2B times and mortality for an individual patient.
Accordingly, the goal of this study was to unravel the relation between patient-specific D2B time and mortality from secular trends in outcomes for the pPCI population. Our hypothesis was that the changing population of patients undergoing pPCI contributed to secular trends toward an increasing mortality risk, despite consistently lower mortality in individual patients with shorter D2B times. With support from the National Cardiovascular Data Registry (NCDR) CathPCI Registry, we included a cohort of patients identical to that of a previous study,12 but extended this previous work by examining both in-hospital and 6-month mortality outcomes, incorporating more recent data than that used before, and using multilevel models as a principal part of our methods. Multilevel models are invaluable in this setting as they allow for the individual-level relation of D2B times to be examined in the context of broader changes at the population level, and to study both these associations separately.16, 17 By providing access to the same data sources, this study also represents an open science approach by the NCDR programme by allowing other investigators to build on important issues raised by a previous publication using the same data source.18
Section snippets
Data sources and study sample
We obtained data sources from the NCDR CathPCI Registry, co-sponsored by the American College of Cardiology (ACC) and the Society for Cardiovascular Angiography and Interventions (SCAI). The NCDR CathPCI Registry is the largest national registry of patients undergoing PCI in the USA, with a rapid doubling in participation from about 600 hospitals in 2005 to over 1400 hospitals by 2011.19 Although large, participation of hospitals in the NCDR CathPCI Registry is done voluntarily and, therefore,
Study sample
For this study, we identified 512 321 catheterisation laboratory visits associated with STEMI between Jan 1, 2005, and Dec 31, 2011. We excluded patients not undergoing pPCI (n=52 372), transfer patients for pPCI (n=129 579), patients with D2B times less than 15 min or more than 3 h (n=45 391), and patients at hospitals that did not consistently report data in each year across the study period (n=134 863).
150 116 pPCI procedures were done in 146 940 patients at 423 hospitals during Jan 1, 2005,
Discussion
Previous studies linked a decrease in patient-specific D2B times with a decrease in mortality after pPCI at the individual level. However, recent decreases in annual D2B times at the population-level have not been associated with decreases in mortality as predicted (panel). The purpose of this study was to offer additional insights on this seemingly paradoxical finding and its implications for STEMI care. Through multilevel models, which simultaneously estimated both the individual and
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