Cardiac arrest happens 535,000 times a year in the U.S. Yet despite the high incidence rate, new research from the University of Michigan shows that very few studies have been conducted to help correct the problem.

Researchers found that over the last 20 years, only 92 gold-standard clinical trials have been conducted on the immediate treatment of cardiac arrest. These randomized clinical trials have involved approximately 64,000 patients. Less than five studies a year have published their results.

"What we found in a nutshell was a striking paucity of randomized clinical trials relative to the burden of cardiac arrest in this country," said Shashank S. Sinha, MD, MSc, a cardiovascular medicine fellow at the University of Michigan Medical School, in a paper published in Circulation: Cardiovascular Quality and Outcomes. "We estimate that only 2.5 such trials have been done for every 10,000 out-of-hospital cardiac arrests, and the number is even lower for in-hospital cardiac arrests."

For some perspective, clinical trials on heart failure, heart attacks and strokes are published 25 to 86 more times than those focused on cardiac arrest.

More than 5,000 published medical journal articles and abstracts were reviewed, but most did not meet the standard needed to draw conclusions about the effectiveness of treatment options.

The pace of trials on cardiac arrest has increased in the last five years, though.

The paper also highlights areas where research on cardiac arrest is most lacking, including protocols for emergency care, post-arrest care and studies of long-term survival and functional outcomes.

Many of the studies reviewed only followed patients through to the return of spontaneous circulation. Others recorded whether patients survived long enough to be discharged from the hospital. Outcomes days, months and years after the cardiac event are largely unstudied.

Patient-centered concerns such as returning to work or quality of life have not been measured.

While new drugs and automated CPR devices used while a cardiac arrest is under way should be studied, there is a need to study post-event care.

The new review did not include studies of public-health interventions such as installation of AEDs. It also excluded studies on infants and children.