NEW HAVEN, Conn. - Patients with ST-segment elevation myocardial infarction (STEMI) treated with angioplasty within 90 minutes of arriving at the hospital stand a much better chance of being discharged alive, no matter how long it's been since their symptoms started.
NEW HAVEN, Conn., June 6 - The faster a patient with an ST-segment elevation myocardial infarction (STEMI) gets into the cath lab, the better his chances for survival, even if he's late getting to the hospital.
Among nearly 30,000 patients with STEMI treated with angioplasty within six hours of presentation, those who didn't get percutaneous coronary intervention until more than 90 minutes after arriving at the hospital had a 42% higher risk of dying in the hospital, reported Robert L. McNamara, M.D., of Yale, and colleagues, in the June 6 issue of Journal of the American College of Cardiology.
Longer door-to-balloon times were associated with higher mortality regardless of the time between the reported onset of symptoms and the patients' time of arrival at the hospital, reported the investigators, writing on behalf of colleagues in the National Registry of Myocardial Infarction.
"The main message that this study re-enforces is not only the concept of 'time is muscle,' but that 'time is life'," said Jeffrey J. Cavendish, M.D., of the Naval Medical Center in San Diego, California, who was not involved with the study.
"There is a belief among some clinicians that patients presenting late will not benefit from faster door-to-balloon time (a 'cow is already out of the barn' philosophy)," said Dr. McNamara.
"We were able to show that door-to-balloon time matters for all patients regardless of time to presentation," he added. "Furthermore, we were able to show that door-to-balloon time mattered for both low- and high-risk patients. In summary, all patients can benefit from shorter door-to-balloon times."
Although it's well documented that rapid fibrinolytic therapy reduces mortality in patients with STEMI, there has been conflicting evidence of the benefits of rapid reperfusion with percutaneous coronary interventions, the authors said.
"Some investigators have found lower mortality for shorter symptom onset-to-reperfusion time for all patients or just certain subgroups such as high-risk patients or those presenting within two hours of symptom onset," they wrote. "Other studies found no lower mortality for shorter symptom onset-to-balloon time but did find lower mortality for shorter door-to-balloon time. Finally, some studies failed to find an association between either symptom onset-to-balloon time or door-to-balloon time and mortality."
Joint American College of Cardiology and American Heart Association guidelines for patients with STEMI call for door-to-balloon times of 90 minutes or less, but only a minority of patients get into the cath lab within that time, perhaps because clinicians aren't convinced that time is of the essence where percutaneous coronary intervention is concerned, the investigators suggested.
To evaluate the relationship between time-to-treatment and mortality, they conducted a cohort study of 29,222 STEMI patients who were treated with percutaneous coronary intervention within six hours of presentation at 395 hospitals participating in the National Registry of Myocardial Infarction -3 and -4 from 1999 to 2002.
The patients included in the cohort had to meet registry criteria for STEMI, which include a diagnosis of acute MI according to ICD-9, and any one of the following: total creatine kinase or creatine kinase-MB that was two or more times the upper limit of the normal range or elevations in alternative cardiac markers; electrocardiographic evidence of acute MI or nuclear medicine testing, echocardiography; or autopsy evidence of acute MI.
The authors used hierarchical models to evaluate the effect of door-to-balloon time on in-hospital mortality. The data were adjusted for patient characteristics in the entire cohort, and for different subgroups of patients based on symptom onset-to-door time, and baseline risk status.
They found that there was a linear increase in in-hospital death rates as the door-to-balloon time dragged on. Patients who had percutaneous coronary intervention started within 90 minutes of arriving had a 3.0% mortality rate, compared with 4.2% of those treated from 91 to 120 minutes after presenting, 5.7% for those treated from 121 to 151 minutes after arriving, and 7.4% for those who didn't get angioplasty until at least 150 minutes had elapsed (P for trend <0.001).
After adjusting for patients characteristics, the investigators found that patients who did not receive angioplasty until 90 minutes or more had elapsed had an odds ratio for mortality of 1.42 (95% confidence interval, 1.24 to 1.62) compared with those who had shorter door-to-balloon times.
Furthermore, in subgroup analyses broken down by time and risk factors, they saw increasing mortality with increasing door-to-balloon time, regardless of symptom onset-to-door time or the presence of high-risk factors.
"From my perspective, the reason that time of onset to hospital presentation is not so important is because many patients may not completely occlude their arteries at the time they first recognize symptoms-and so the actual time of artery occlusion may not be easily predicted from the time it takes them to present to the hospital," said Harlan M. Krumholz, M.D., also from Yale, a co-author.
"Also, some people have waxing and waning symptoms and only present when the symptoms become worse, complicating the determination of the time the heart has been deprived of blood," Dr. Krumholz added.
Dr. Cavendish noted that "emergency medical services and hospitals throughout this country must do better to create a more seamless system to get patients into the catheterization lab in the shortest amount of time. We need a collaborative effort with EMS, emergency departments, nursing, cardiac catheterization lab staff, and cardiologists all working together in order to shorten door to balloon times to less than 90 minutes for all patients 24 hours a day, seven days a week."
Several limitations of the study were noted by the authors: