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STROKE AFTER MYOCARDIAL INFARCTION—WHO'S AT RISK?
ANAHEIM, CALIF—Analysis of the National Registry of Myocardial Infarction 3 (NRMI-3), a database that includes more than 500,000 patients and nearly 1,500 non-hemorrhagic stroke events, has yielded new information regarding the risk of non-hemorrhagic stroke after myocardial infarction.
Among the key findings: Women are at greater risk than men for strokes following myocardial infarction; patients with Q-wave or ST-segment elevation infarctions are not at increased risk for stroke; and although the early use of cardiac catheterization increases stroke risk, therapeutic angioplasty reduces the risk of stroke after the coronary event by about half.
The results were presented by lead author Eric A. Shry, MD, of the Cardiology Service at the Brooke Army Medical Center in Fort Sam Houston, Texas, at the American Heart Association’s 2001 Scientific Sessions.
LARGER COHORT, BETTER ESTIMATES
According to Dr. Shry, current estimates suggest that non-hemorrhagic stroke after myocardial infarction occurs in about 1% of patients. That number has been reduced from approximately 5% in the 1970s, after it was shown that anticoagulation with warfarin could prevent these events. The numbers have been further reduced by the advent of thrombolytics and primary angioplasty as reperfusion therapy in patients with myocardial infarction.
However, the events that do occur are often catastrophic, Dr. Shry noted. “The mortality rate is still astronomical, somewhere around 30% to 40%, and the outcomes from these events are very poor, probably because most of these are cardioembolic, large vessel events,” he said.
Although the prevalence and risk factors associated with these events have been previously examined, the number of these events in any given study has been quite small. The largest study to date, the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) trial that randomized more than 40,000 myocardial infarction patients, still had only 250 of these events, meaning that the investigators had only limited opportunity to examine all the potential variables. “As the neurology community well knows, there are dozens of variables that go into it,” Dr. Shry noted.
For the current study, the researchers used data from NRMI-3, a registry containing information on 537,444 myocardial infarction patients from 1,553 participating hospitals. Patients were treated between April 1998 and June 2000. The aim of the study was to define demographic, clinical, and therapeutic predictors of in-hospital non-hemorrhagic stroke associated with myocardial infarction. Of these patients, 6,094 patients (1.1%) had a stroke event.
A large number of exclusions were made to produce the most uniform and complete dataset for this assessment, said Dr. Shry. For example, 230,958 patients were excluded because they had been transferred into or out of one of the NRMI-3 hospitals and therefore had incomplete data on their chart. Some patients had had their stroke prior to arriving at the hospital, and others received a diagnosis of hemorrhagic stroke or stroke of unknown origin.
After exclusions, the study population consisted of 286,158 patients with myocardial infarction, 1,498 (0.5%) of whom had had a non-hemorrhagic stroke documented by computed tomography scanning, making this still “far and away” the largest study of stroke after myocardial infarction, Dr. Shry reported.
WOMEN AT RISK
Univariate and multivariate statistical testing was carried out using more than 60 clinical and historical variables. Multivariate analysis showed a variety of demographic, clinical, and treatment variables that were significantly associated with an increased risk of non-hemorrhagic stroke. Among demographic variables, age, diabetes, hypertension, and previous stroke were significantly associated with increased risk. What had not been previously shown was a significantly increased risk associated with female sex. “Basically, women in every other way do worse after heart attack, and, unfortunately, this is just another way,” said Dr. Shry.
SETTLING A CONTROVERSY
Previous myocardial infarction and congestive heart failure were both associated with a decreased risk. After controlling for other clinical factors, the researchers found that although ST-segment depression on echocardiogram was associated with a significantly increased risk of non-hemorrhagic stroke, ST-segment elevation and Q-wave myocardial infarction were not. “That was a big area of controversy that I think we settled with this paper,” Dr. Shry said. Anterior wall myocardial infarction also did not appear to be connected with increased stroke risk, but atrial fibrillation, hypotension, and congestive heart failure or edema were significantly associated with increased risk.
ANGIOPLASTY SIGNIFICANTLY REDUCES THE RISK
The investigators also examined the effect of various in-hospital therapies on stroke risk. They found that although the use of cardiac catheterization appeared to increase the risk of stroke among these patients, the subsequent use of angioplasty significantly decreased the risk by almost half.
“That has never been described before,” said Dr. Shry, except in a report from the Organization to Assess Strategies for Ischemic Syndromes (OASIS), a registry of non–Q-wave infarctions, which showed a similar trend. The main finding from the OASIS data was that early use of cardiac catheterization after non–Q-wave myocardial infarction increased the risk of stroke. “What we found was that there is a small increased risk in going to the [catheterization] lab, but if you do a procedure that’s therapeutic while you’re there, you significantly reduce that chance.”
Other findings demonstrated a decreased risk of stroke with the use of aspirin and an increased risk of stroke with delayed treatment times following the index myocardial infarction: primary percutaneous transluminal coronary angioplasty at greater than 120 minutes or thrombolytic therapy at more than 30 minutes.
NR
—Susan Jeffrey
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