Over the past decade, the door-to-balloon time has been a major focus in both quality assessment and quality improvement for patients undergoing primary PCI for ST-segment elevation myocardial infarction. This study reflects the effect of these efforts, showing significant reductions in door-to-balloon times across the United States between June 2005 and July 2009. Similarly, by 2009, more than 80% of patients undergoing primary PCI for ST-segment elevation myocardial infarction met the goal specified in the ACC–AHA clinical practice guidelines of a door-to-balloon time of 90 minutes or less — a marked improvement in just 4 years. Despite these improvements and despite the fact that mortality among patients with shorter door-to-balloon times was lower than mortality among those with longer times, overall unadjusted and risk-adjusted in-hospital mortality remained virtually unchanged. These results were consistent in multiple high-risk subgroups, including patients older than 75 years of age, those presenting in cardiogenic shock, and those with anterior myocardial infarction. Our findings raise questions about the role of door-to-balloon time as a principal focus for performance measurement and public reporting.

The current emphasis on achieving a door-to-balloon time of 90 minutes or less has been driven, in part, by the concept that a shorter interval between ischemia and reperfusion results in improved myocardial salvage and, thus, presumably better clinical outcomes. This idea, along with observational data associating shorter door-to-balloon times with lower mortality, has spurred the national focus on door-to-balloon time as a quality metric, leading the CMS to begin publicly reporting these data in 2005 and linking them to financial reimbursement. In addition, both the ACC and the AHA launched national campaigns promoting strategies to improve door-to-balloon times through the creation of the D2B Alliance and Mission: Lifeline, respectively.5,6

In fact, however, data regarding the relationship between door-to-balloon time and mortality are inconsistent. Berger et al. observed lower 30-day mortality among patients with a door-to-balloon time of less than 60 minutes and an increase in mortality with increasing door-to-balloon times in data from the Global Use of Strategies to Open Occluded Arteries in Acute Coronary Syndromes (GUSTO-IIb) trial.2 McNamara et al., in a study of data from the National Registry of Myocardial Infarction, reported an odds ratio for increased mortality of 1.42 among patients for whom the door-to-balloon time was longer than 90 minutes, as compared with those for whom the door-to-balloon time was shorter.1 In contrast, Brodie et al. found that improved door-to-balloon times were not associated with a mortality benefit at 1 month or 6 months,15 and an analysis of pooled data from randomized trials, performed by Zijlstra et al., showed a linear association of mortality with longer time to treatment among patients receiving thrombolytic therapy but not among those undergoing primary angioplasty.16

The discordant findings to date may be the result of multiple confounding factors. Animal models have shown a time-dependent “wavefront” of ischemic cell death associated with arterial occlusion, showing that the degree of myocardial salvage is greatly diminished after prolonged periods of ischemia.17,18 Thus, total ischemic time may be a more important clinical variable than door-to-balloon time. Results from some previous studies suggest a correlation between symptom-to-balloon times and mortality; yet these data, too, have been inconsistent.19,20 Furthermore, it has been suggested that the association between door-to-balloon time and mortality may be affected by an “immigration bias” (i.e., bias whereby patients at lower baseline risk either self-select or are selected to be treated differently from patients at greater risk),9 since healthier patients are likely to have shorter door-to-balloon times than are sicker patients with more complex conditions, for whom treatment may be delayed because of the time needed for medical stabilization.20 In addition, institutions with high patient volumes are often better equipped than those with lower volumes to reduce door-to-balloon times along with other improved performance measures.21-23 Thus, improved clinical outcomes may be, in part, a reflection of institutional or operator experience and expertise.

Although multiple studies have evaluated the relationship between door-to-balloon time and clinical end points, data evaluating the effect of a reduction in door-to-balloon time on patient outcomes are more limited. In 2008, Gibson et al., in an analysis of data from the National Registry of Myocardial Infarction, reported a significant reduction in mortality, from 8.6% to 3.1%, associated with a decline in door-to-balloon times from 111 minutes in 1994 to 79 minutes in 2006.24 In 2010, Flynn et al., in a study involving patients included in a quality-improvement database in Michigan, found no change in short-term mortality between 2003 and 2008 despite a decrease in door-to-balloon time from 113 minutes to 76 minutes.9 These data, together with our own, show that remarkable results are achievable through multidisciplinary collaboration aimed at improving an important process of care yet leave open the question of why overall mortality has not declined in the two more recent studies.

Our data suggest that further efforts to reduce door-to-balloon time may not reduce mortality. We therefore conclude that additional factors will probably need to be targeted to accomplish this goal. Door-to-balloon time is one component of total ischemic time; as door-to-balloon time is reduced, it becomes a smaller fraction of total ischemic time, making the time before arrival at a hospital a more important factor. Therefore, efforts with potential to improve outcomes may include increasing patients' awareness of symptoms, reducing the interval from the time of symptom onset to treatment, and shortening the transfer time between medical facilities. In addition, improving both in-hospital care and postdischarge care remain key targets for enhancing long-term outcomes after ST-segment elevation myocardial infarction.

There were some limitations to this study. First, it was an observational study. There were demographic, clinical, and procedural differences among the patients over the course of the study. In addition, it is possible that there were unmeasured changes in the characteristics of the patient population such that an increase in risk during the study period could have prevented a decrease in overall mortality despite improvements in door-to-balloon times. However, the effect of differences in door-to-balloon time cannot be tested in randomized trials; therefore, larger observational studies such as this trial are likely to be the best way to evaluate the effect of current practice. Second, this study may have been underpowered to detect very small differences in mortality. Third, although current door-to-balloon times may have reached the point at which further reductions are unlikely to improve in-hospital mortality, it remains possible that the benefits of shorter door-to-balloon times will be seen in long-term reductions in mortality, improvements in left ventricular function, or reductions in the number of admissions for heart failure. Fourth, the 30-day data should be interpreted cautiously, since the cohort in this linked data set represents only approximately a quarter of the total study population. Finally, this study included patients who were undergoing primary PCI, and therefore the results cannot be generalized to all patients with ST-segment elevation myocardial infarction.

In conclusion, this study shows that between 2005 and 2009, there was a significant decline in national door-to-balloon times along with a steadily increasing percentage of patients meeting the guideline recommendation of a door-to-balloon time of 90 minutes or less for those presenting with an ST-segment elevation myocardial infarction. Despite these improvements, in-hospital and short-term mortality remained virtually unaffected. The lack of significant change in mortality was observed in both the risk-adjusted cohort and high-risk subgroups.