Heart attack patients given antiarrhythmic (irregular heartbeat) drugs are more likely to die.

The National Heart, Lung and Blood Institute, in Bethesda, Maryland, combining the results of 128 randomized, controlled trials on 98,000 patients, found that all anti arrhythmic drugs (called class I agents) caused a significant increase in deaths over patients given either nothing or another drug.

The use of arrhythmic drugs stems from the "arrhythmia suppression hypothesis"; since three quarters of all sudden deaths are due to ventricular fibrillation irregular heartbeat the theory is that these deaths can be prevented by suppressing cardiac arrhythmias through drugs.

Quinidine, in particular, showed a doubling of mortality risk (and a trebling in another study cited in the article), but data on moricizine, encainide hydrochloride and flecainide also showed harm.

"Extreme caution should be exercised in prescribing any class I agent," concluded the researchers. "Until clear proof of a reduction in mortality is evident with a specific agent, it may be reasonable to view all class I agents as being potentially harmful."

Beta blockers on the other hand, were shown to reduce the likelihood of dying.