In patients with an acute myocardial infarction (severe obstruction of the coronary arteries), beta blockers have been shown to improve survival, reduce the risk of another myocardial infarction, reduce life-threatening arrhythmias and prevent enlargement of the heart.
“This was the first large, double-blind, randomized, placebo-controlled trial to assess whether giving intravenous beta blockers before these patients undergo coronary angiography would further improve their outcomes. Unfortunately, we showed that it did not,” said Vincent Roolvink, principal investigator and cardiologist of the Isala Heart Center Zwolle.
The Early-BAMI trial is funded by the Dutch Heart Foundation and by Medtronic, Inc. The study is published in the Journal of the American College of Cardiology. Cardiologist Vincent Roolvink presented the study as late breaking trial during the ACC congress. The ACC congress brings together cardiologists and cardiovascular specialists from around the world to share the newest discoveries in treatment and prevention.
In the EARLY-BAMI trial, which was conducted by the Isala Heart Center together with PCI centers and ambulance services in The Netherlands and Spain, 683 patients with acute myocardial infarction symptoms of less than 12 hours’ duration were randomly assigned to receive the beta blocker metoprolol or a placebo before undergoing coronary angiography. The primary endpoint was the severity of the heart attack as measured by magnetic resonance imaging (MRI) at 30 days. Secondary endpoints were levels of cardiac enzymes and number of occurrences of ventricular arrhythmia. Safety endpoints were symptoms of an abnormally slow heart rate, symptoms of abnormally low blood pressure, and cardiogenic shock (sudden inability of the heart to pump enough blood to meet the body’s needs).
At 30 days of follow-up, average heart attack severity measured by MRI (the primary endpoint) was 15.3 percent of left ventricular volume on average in the beta blockers group, compared with 14.9 percent in the placebo group, a difference that was not statistically significant, said Roolvink. Nor were there significant differences between the two groups on blood flow from the left ventricle or levels of cardiac enzymes (secondary endpoints). Ventricular arrhythmias occurred in 3.6 percent of patients who received beta blockers and in 6.9 percent of those who received a placebo, a difference that met the threshold for statistical significance but did not result in a clinically significant difference, Roolvink said. Sixteen patients in the beta blockers group experienced symptoms of an abnormally slow heart rate, symptoms of abnormally low blood pressure, or cardiogenic shock, compared with 21 patients in the placebo group, a different that again was not statistically significant.
Results from two previous trials had suggested that giving intravenous beta blockers to acute myocardial infarction patients before they underwent coronary angiography could reduce heart attack severity or improve blood flow from the left ventricle (the heart’s main pumping chamber), but these trials had shortcomings, said Roolvink. One had a small enrollment and the other, while larger, was not blinded or placebo-controlled and enrolled only patients whose myocardial infarctions involved the front wall of the left ventricle.
A limitation of the study is that overall heart attack severity among enrolled patients was lower than expected, which could explain why beta blocker treatment appeared to offer no benefit, Roolvink said. Also, although MRI analyses for the primary endpoint were blinded for both heart rate and study medication, it was not possible to blind physicians and nurses to patients’ heart rate and blood pressure.
Going forward, researchers say additional large randomized trials are needed to clarify whether intravenous beta blocker treatment before coronary angiography offers any benefit for patients with an acute myocardial infarction.
You can view the presentation at the ACC conference.