That's according to a new study by researchers from the Veterans Affairs Medical Center and Mayo Clinic in Minnesota. The study appears in the Nov. 5 issue of TheJournal of the American Medical Association.
Since 1997, the risk of sudden cardiac death has steeply declined. Even so, it still causes about 325,000 adult deaths each year in the U.S., all linked to complications from heart attacks.
Sudden cardiac death occurs when the heart's electrical system fails. The heart begins beating extremely fast, preventing the ventricles from allowing enough blood to flow throughout the body. Without blood going to the brain and other vital organs, a person quickly loses consciousness and soon dies.
To better understand this problem, as well as the impact of recurrent ischemia (an inadequate flow of blood to a part of the heart) and heart failure on sudden cardiac death, the researchers studied 2,997 residents who survived a heart attack in Olmsted County, Minn., between 1979 and 2005. On average, the patients were 67 years old, and 59% of them were men.
The researchers monitored the patients through their medical records until the time of their death or through the final follow-up in February 2008.
During this time, 1,160 patients died, with 282 of these deaths caused by 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 that seen in the general population. For each following year, however, the rate of sudden cardiac death was lower than expected.
The researchers also found that recurrent ischemia was not associated with sudden cardiac death. However, patients who experienced heart failure during the follow-up period had more than a fourfold risk of experiencing sudden cardiac death than the general population. This translates into an absolute increase in sudden cardiac death risk of 2.5% within 30 days of a heart attack and in each year thereafter.
"The risk of sudden cardiac death is the highest during the first month after myocardial infarction, when it markedly exceeds the rate in the general population," the authors conclude. "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."
In other words, it's important to continue to monitor heart attack patients long after the initial incident because dire complications can still occur long after the initial heart attack episode.
On a positive note, the researchers noted an overall 40% decline in the incidence of sudden cardiac death over the course of the study, parallel with the major changes in treatment of heart attack survivors during this time.