Door-to-Balloon Time in STEMI
Abstract & Commentary
By Michael H. Crawford, MD, Professor of Medicine, and Chief of Clinical Cardiology, at the University of California, San Francisco. Dr. Crawford is on the speaker's bureau for Pfizer.
Source: McNamara R, et al. Effect of Door-to-Balloon Time on Mortality in Patients with ST-Segment Elevation Myocardial Infarction. J Am Coll Cardiol. 2006;47:2180-2186.
Although time to reperfusion is correlated with mortality in ST elevation myocardial infarction (STEMI) treated with fibrinolytics, its importance in patients treated with percutaneous coronary interventions (PCI) is less clear. Thus, McNamara and colleagues examined the National Registry of Myocardial Infarction (NRMI) database to explore this issue. From this database of 830,473 acute MI admissions, 29,222 STEMI patients treated by PCI within 6 hours of presentation to 1 of 395 hospitals capable of performing acute PCI were studied. The outcome of interest was in-hospital mortality, and the primary independent variable was door-to-balloon time. Time from symptom onset to hospital arrival (onset-to-door time) and comorbidities that increased risk were also examined.
Results: In-hospital mortality increased significantly with longer door-to-balloon times (< 90 minutes 3%, 120-150 minutes almost 6%). Onset-to-door time was not related to hospital mortality. The relationship of door-to-balloon time to hospital mortality was not affected by clinical characteristics that predict higher risk. McNamara et al concluded that the time from hospital arrival to balloon inflation for acute STEMI patients treated by primary PCI is associated with hospital mortality regardless of symptom onset-to-hospital arrival time and other clinical risk factors for mortality. Efforts to shorten this time could potentially benefit all STEMI patients.
This is a large observational study that supports the importance of door-to-balloon time in the treatment of STEMI. Symptom onset-to-door time was not related to mortality, which is somewhat surprising since symptom onset to injection of thrombolytics time has been shown to relate to mortality. The reason for this apparent discrepancy between the 2 types of treatment is not elucidated in this study, but there are some possible explanations. Symptom onset is an imprecise point, so if the patient is unsure of when symptoms started, many would give them the benefit of the doubt and assume it was less than 6 hours. Therefore, they would more likely get PCI, and symptom onset-to-door time would be noncontributory to their outcome. Also, two-thirds of the patients in this study presented within 2 hours of symptom onset, so there may have been less mortality in this timeframe. In addition, some patients died before reaching the hospital, eliminating these higher-risk patients from the pool and making symptom onset-to-door time more benign. Of interest, is that the majority of patients in NRMI had door-to-balloon times of > 90 minutes. This may have improved the spread of times and made it easier to show a relationship to mortality. Finally, door-to-balloon time may be a marker for better hospital care in general. Whatever the reason, it allows us to focus on a more reliable measure that can be shortened by improved systems.
The ACC/AHA Guidelines recommends a door-to-balloon time of 90 minutes or less, but most available data suggests that it is generally above that in most institutions. The JCAHO and the University Hospitals Consortium averages are just above 120 minutes, and have been there for the last 2 years. Thus, many hospitals have set an internal quality improvement goal of < 120 minutes. According to the data in this paper, that would correspond to an in-hospital mortality of 4%, whereas < 90 minutes would equate to a 3% mortality. What is necessary to decrease the door-to-balloon time average by 30 minutes to gain 1% in mortality is often not easy. We accomplished it in our hospital with great effort, and have found that it requires constant attention to keep it below 90 minutes.
This study excluded transfer patients since it is very difficult to keep their first hospital door to second hospital balloon time at a reasonable time span unless you have a very coordinated system. Also, most of the study patients were men (71%) and white (86%), so the results may not apply to other populations. Many patients had high-risk features such as hypotension in 10%, tachycardia in 12%, diabetes in 19%, and heart failure in 11%. Those with high-risk features had a higher mortality rate, but the relation to door-to-balloon time persisted. Finally, there was no risk sub-group in which door-to-balloon time < 90 minutes did not reduce mortality relative to longer times.