Shorter Door-to-Balloon Times — No Change in Mortality
Abstract & Commentary
By Andrew J. Boyle, MBBS, PhD
Assistant Professor of Medicine, Interventional Cardiology, University of California, San Francisco
Dr. Boyle reports no financial relationships relevant to this field of study.
Source: Menees DS, et al. Door-to-balloon time and mortality among patients undergoing primary PCI. N Engl J Med 2013;369:901-909.
Primary percutaneous coronary intervention (PCI) is the preferred strategy for treating ST-segment elevation myocardial infarction (STEMI). The goal is reperfusion of the infarct-related artery as quickly was possible, and the national benchmark is to achieve this within 90 minutes of the patient’s arrival at the hospital (i.e., door-to-balloon time [D2B] < 90 mins). Considerable attention has been placed on the publicly reported metric of a hospital’s D2B time. It has been assumed that achieving shorter D2B times will reduce mortality associated with STEMI. Menees and colleagues took advantage of the American College of Cardiology’s National Cardiovascular Data Registry (NCDR) CathPCI Registry to examine recent temporal trends in D2B times and the corresponding in-hospital mortality rates. They analyzed 96,738 admissions for patients undergoing primary PCI for STEMI from July 2005 through June 2009 at 515 hospitals throughout the country participating in the CathPCI Registry. The primary outcome of the study, in-hospital mortality, is recorded for all patents in the CathPCI Registry. They excluded patients who were transferred from another facility to receive primary PCI and patients whose D2B time was > 3 hours. In a subgroup analysis using a linked Medicare dataset, they also assessed 30-day mortality.
The mean age of the study population was 60.8 years, 28.0% were female, 61.0% had hypertension, 59.2% had dyslipidemia, 43.3% were current smokers, and 18.8% had diabetes. The prevalence of diabetes, hypertension, and dyslipidemia increased in each year of the study. The proportion of patients with a prior MI and previous PCI increased slightly each year. The mean ejection fraction was 46.8% and was unchanged from year to year. Patients presenting with cardiogenic shock accounted for 9.9% of all patients and it remained constant throughout the study.
Median D2B times declined from 83 minutes in 2005-2006 to 67 minutes in 2008-2009 (P < 0.001). The proportion of patients whose D2B was < 90 minutes increased from 59.7% in 2005-2006 to 83.1% in 2008-2009 (P < 0.001). However, despite improvements in D2B times, there was no change in unadjusted in-hospital mortality (4.8% in 2005-2006 and 4.7% in 2008-2009, P = 0.43) or in risk-adjusted in-hospital mortality (5.0% in 2005-2006 and 4.7% in 2008-2009, P = 0.34), nor was a difference observed in 30-day mortality (P = 0.64). They repeated the analyses in three high-risk subgroups: patients > 75 years of age, anterior MI, and cardiogenic shock. In all subgroups, D2B decreased over the study interval but in-hospital mortality did not change. The authors conclude that although national D2B times have improved significantly for patients undergoing primary PCI for STEMI, in-hospital mortality has remained virtually unchanged.
This is a very interesting study that makes us question the validity of using D2B times as a quality metric. There is an entrenched knowledge that reperfusion of the occluded infarct-related artery is beneficial, and that sooner is better than later. However, one is left to ponder just how much must we shorten the duration of ischemia to realize the maximal benefit of reperfusion? Have we already made all the gains that are possible? Is shaving off a few extra minutes of in-hospital time to reperfusion going to further improve outcomes? As the in-hospital ischemic time (i.e., D2B time) becomes shorter, it makes up less of the total ischemic time (i.e., symptom onset to balloon time). Therefore, incremental gains in D2B time are subject to the law of diminishing returns. Perhaps our focus should now shift to reducing total ischemic time, not just D2B time.
This study is strengthened by its rigorous statistical design and the large number of patients included in the analyses. There are several limitations in the data that should be acknowledged when interpreting its significance. First, this is a retrospective, observational study. There is always the potential for unmeasured confounders in observational datasets. Second, public reporting of D2B times and outcomes became more widespread during the study period. Public reporting has been shown to lead to risk-averse behavior, and it is possible that some of the sicker patients, whose outcomes are worse but who gain more benefit from primary PCI, were never offered PCI for their STEMI. Third, over the time period of the study, the patients became higher risk with more having prior MI and diabetes. Although the authors adjusted for risk with known parameters, risk adjustment is an inexact science and the cohorts may not have been directly comparable. Fourth, we are not told of the long-term effects on left ventricular function, subsequent heart failure, quality of life, or readmission rates. Mortality is not the only important endpoint. If shorter D2B time results in less heart failure or better quality of life, then the considerable resources devoted to shortening D2B time may be justified. Further long-term studies are needed.
Should we change practice based on this study? No, I think patients with STEMI should still undergo primary PCI in the most rapid time feasible. However, this study gives us pause to consider whether resources that are aimed at further reducing D2B could be better spent reducing total ischemic time.