Beta blockers appear to be useless when prescribed to heart attack survivors who aren't suffering from heart failure, a new clinical trial indicates.

The study calls into question the routine of prescribing beta blockers to all patients following a heart attack, which has been standard care for decades, researchers said.

About 50% of heart attack survivors don’t have heart failure, which is a decline in the heart’s ability to pump enough blood out to the body, researchers said in background notes.

For those patients, beta blockers make no difference at all in their heart health or risk of death, the results show.

“I think that, following this study, many doctors will not find an indication to routinely treat all their patients with beta blockers following a heart attack,” said lead researcher Dr. Troels Yndigegn, an interventional cardiologist at Lund University in Sweden.

Heart failure is typically assessed in terms of ejection-fraction, or the proportion of blood pushed out of the heart with each heartbeat. An ejection fraction above 40% to 50% is considered normal.

“We believe that the evidence still supports beta blockers for patients with a large myocardial infarction [heart attack] that experience heart failure, but for patients with no signs of heart failure and a normal ejection-fraction, this trial establishes that there’s no indication that routine use of beta blockers is beneficial,” Yndigegn.

Beta blockers are used in heart patients because they inhibit hormones like adrenaline that speed up the heart.

Many doctors prescribe beta blockers after a heart attack based on earlier evidence that they could help prevent a second attack.

However, Yndigegn noted that the clinical trials that led to routine use of beta blockers were conducted before the advent of newer procedures -- balloon angioplasty and stenting --  that are now widely used to reopen blocked arteries.

“At that time, the damage to the heart muscle was greater than we see today,” Yndigegn said. Today's heart attacks tend to be smaller and "do not damage the heart muscle to the same extent," he said.

For this new clinical trial, researchers recruited more than 5,000 patients treated for a heart attack at 45 hospitals in Sweden, Estonia and New Zealand. All the patients had an ejection fraction of 50% or better.

Half were randomly assigned to take beta blockers long-term, and the other half were not.

Over an average 3.5-year follow-up period, there were no significant differences between the two groups when it came to death, another heart attack, heart failure, abnormal heart rhythms, stroke, low blood pressure, chest pain or shortness of breath.

This means that patients with no heart failure don’t need to take beta blockers, which can cause side effects like mood disorders, fatigue and sexual dysfunction, the researchers concluded.

The study was published April 7 in the New England Journal of Medicine, and was also presented simultaneously at the American College of Cardiology’s annual meeting in Atlanta.

“Many patients report side effects or suspected side effects with these medications, so I think this finding will have an impact for thousands of patients,” Yndigegn said in a meeting news release.