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Mixed results on benefits of antiarrhythmic drugs for out-of-hospital cardiac arrest

Paramedics often give heart rhythm stabilizing drugs to patients who are suffering out-of-hospital cardiac arrest when they fail to regain a stable heart rhythm after electrical shock treatment. In a study presented at the American College of Cardiology’s 65th Annual Scientific Session, these drugs, specifically amiodarone and lidocaine, did not significantly improve such patients’ likelihood of surviving to hospital discharge overall. However, among patients whose cardiac arrest was witnessed by a bystander, those who received either amiodarone or lidocaine during resuscitation had a 5 percent greater chance of survival to hospital discharge compared with those who received a placebo, which was a statistically significant difference. Witnessed cardiac arrests represented more than half of the study’s population.

This trial is the first and largest randomized, double-blind, placebo-controlled study to assess the impact of amiodarone and lidocaine on survival to hospital discharge after out-of-hospital cardiac arrest triggered by two types of dangerous heart rhythms known as ventricular fibrillation and pulseless ventricular tachycardia. More than 80,000 cardiac arrest cases per year are specifically caused by these heart rhythms, and in more than half of these cases, paramedics are unable to restore a stable heart rhythm using defibrillator shocks alone. Amiodarone and lidocaine are thought to work by stabilizing the electrical signaling within the heart.

Among all study participants, patients receiving amiodarone fared slightly better in terms of survival to hospital discharge, the study’s primary endpoint, but did not achieve statistical significance. The finding that both these drugs significantly improved rates of survival to hospital discharge when the cardiac arrest was witnessed by a bystander suggests their benefit may be linked to how quickly such events are recognized and drug treatment is started.

“You can see these results as a cup half empty or a cup half full,” said Peter Kudenchuk, M.D., a cardiac electrophysiologist and professor of medicine at the University of Washington and the study’s lead author. “From a statistical perspective, neither drug significantly improved survival to hospital discharge in the overall group of treated patients. Still, a beneficial clinical effect from these medications is undeniable. Both drugs significantly improved the chances of survival to hospital admission, so they clearly did their job in stabilizing dangerous heart rhythms and getting patients to the hospital alive.”

Surviving cardiac arrest requires cardiopulmonary resuscitation (CPR) and immediate medical attention. Patients whose cardiac arrest is witnessed by a bystander are believed to have a better chance of survival because they are recognized sooner after their collapse and less likely to have already sustained fatal organ damage upon receiving medical attention.