A new study confirms that whites are more likely than blacks to survive an “out-of-hospital” cardiac arrest - the sudden loss of heart function caused by a heart attack or a blow to the chest.

The study also suggests that the initial heart rhythm irregularity - and hence the underlying cause of cardiac arrest - accounts for the racial disparities in survival after cardiac arrest.

Dr. Sandro Galea, of the University of Michigan, Ann Arbor, and associates evaluated data on 3,891 out-of-hospital cardiac arrests that occurred in New York City. Among whites, the survival rate for at least 30 days after discharge was 3.4 percent - more than double the 1.3 percent survival rate among blacks.

There were no apparent racial/ethnic differences in how the cardiac arrests were managed. Response times did not differ by much, and such differences were not significantly associated with survival.

Thus, there is little evidence that “differences in the circumstances of out-of-hospital cardiac arrest contributed substantially to racial/ethnic differences in survival,” the investigators note. They also ruled out social and demographic differences as significant contributors.

They did notice, however, that whites were more likely than blacks to initially have an irregular heartbeat known as ventricular fibrillation, which is characterized by the abnormally rapid and feeble beating of the main pumping chambers of the heart.

According to Galea and colleagues, the lower prevalence of ventricular fibrillation as the initial heart rhythm abnormality appears to have been a “strong contributor to the poorer observed survival among black patients.”

They suggest that racial/ethnic differences in ventricular fibrillation may be related to differences in the underlying cause of cardiac arrest, such as physiologic differences, genetic factors, and non-heart-related causes of cardiac arrest.

SOURCE: American Journal of Epidemiology, September 2007.