A new study by researchers at the Veterans Affairs Medical Center in Minneapolis and Mayo Clinic in Rochester, Minn., shows that the risk of sudden cardiac death is the highest in the first month after an attack.

The researchers examined the medical records of 2,997 residents who survived a heart attack in Olmsted County, Minn., between 1979 and 2005. The average age of the participants was 67. During follow-up through the end of February 2008, 24 percent of the patients (282 persons) died from sudden cardiac death. The rate of sudden cardiac death for patients who had suffered a heart attack within 30 days was four times higher than researchers expected. After 30 days, the rate of sudden cardiac death was lower than expected.

Sudden deaths declined by more than 40 percent over the past 25 years, the researchers reported. However, the researchers said the cumulative incidence of sudden cardiac death in the first 30 days was four times higher than expected.

"Among 30-day survivors, the risk of sudden cardiac death declines rapidly, but it is markedly increased by the occurrence of heart failure during follow-up," the researchers report in the Journal of the American Medical Association.

These findings "underscore the importance of continued surveillance" of heart attack patients, and "the importance of evidence-based therapy" for these patients, according to the study. It is important to continue to monitor heart attack patients long after the initial heart attack because complications can still occur later.