November 4 (HealthDay News) -- The risk of sudden death after a heart attack has improved significantly over the past three decades, but the first 30 days remain a period of great danger, an historical study shows.

The study looked at the experiences of almost 3,000 residents of Olmsted County in Minnesota who had heart attacks between 1979 and 2005.

"There were two main aspects of the study that we did not necessarily anticipate," said Dr. Veronique Roger, a professor of medicine and epidemiology at the Mayo Clinic, and lead author of the report in the Nov. 5 issue of the Journal of the American Medical Association. "One was how much the risk of sudden death after a heart attack has decreased over time. The magnitude of decline was 40 percent over the study period. The second was that if a patient experienced heart failure at any time during the follow-up, the risk of sudden death increased substantially."

In all, 1,160 of those who had heart attacks died, 24 percent of them suffering sudden cardiac death. The incidence of sudden cardiac death was 1.2 percent in the first 30 days. It decreased sharply after that, leveling off at 1.2 percent a year, lower than the rate of sudden death in the general population.

Among heart attack survivors who experienced heart failure, the rate of sudden cardiac death was 2.5 percent in the first 30 days and in each of the following years.

The study "underscores the imperative to work together to provide the best possible care" in the weeks after a heart attack, Roger said. "We need to be particularly alert to monitor patients regularly for any sign of heart failure, to apply additional treatments, therapeutic and management options," she said.

If there are suspicions of heart failure, the progressive loss of the heart's ability to pump blood, an imaging study such as echocardiography should be done to verify the condition, she said. Treatment options include a variety of medications, from beta blockers to cholesterol-lowering statins to aspirin, Roger said. Lifestyle changes such as better diet should also be implemented, she said.

Symptoms of heart failure that require immediate attention include shortness of breath, persistent coughing or wheezing, fatigue, confusion, bloating and swelling.

The study "is not so much a wake-up call as a reminder," said Dr. Howard S. Weintraub, clinical director of the New York University Center for the Prevention of Cardiovascular Disease.

The Mayo Clinic report provides a valuable account of the progress of treating heart attack survivors in one relatively isolated area, Weintraub said. The finding that heart failure increases the risk of sudden death came as no surprise, he said. "The sicker you are after a disastrous event, the more likely it is that another disaster will occur," Weintraub said.

What the study does not provide is identification of specific indicators of the risk of sudden death, he said.

"It's important to know what predisposes one to sudden death," Weintraub said. "We need to be diligent, still."

SOURCES: Veronique Roger, M.D., professor, medicine and epidemiology, Mayo Clinic, Rochester, Minn.; Howard S. Weintraub, M.D., associate professor, medicine, and clinical director, Center for the Prevention of Cardiovascular Disease, New York University; Nov. 5, 2008, Journal of the American Medical Association