Researchers have discovered that a specific heart rhythm abnormality—idiopathic QT interval prolongation—increased the risk of sudden cardiac death five-fold among patients with coronary artery disease, aaccording to a study published online this week in Circulation.
“More than 80 percent of all cases of sudden cardiac death occur in people who have significant coronary artery disease, but we currently do not have a medical test that consistently identifies patients at risk," said the ongoing study's first author, Sumeet S. Chugh, MD, director of clinical electrophysiology and associate director of the Cedars-Sinai Heart Institute in Los Angeles.
The research was conducted with colleagues in the emergency medicine and pathology departments at Oregon Health and Science University in Portland, Ore., as part of the ongoing Oregon Sudden Unexpected Death study.
Out of 373 cases, 309 participants met criteria for analysis as controls. The researchers said that the mean QT interval was significantly longer in cases than in controls (450 vs. 433 ms).
In a multivariate model, Chugh and colleagues said that gender, diabetes mellitus and QT interval-prolonging drugs were significant determinants of QT interval prolongation in controls. In a logistic regression model predicting sudden cardiac death, diabetes mellitus and use of QT interval-prolonging drugs were predictors of sudden cardiac death among subjects with normal or borderline QT interval. However, abnormally prolonged QT interval in the absence of diabetes and QT-prolonging medications was the strongest predictor of sudden cardiac death.
"Abnormal QT prolongation has significant potential for evaluating risk and developing prevention strategies, but there are many factors—some known and some not known—that contribute to QT prolongation. Diabetes and the use of certain medications were significant predictors of QT interval prolongation and sudden cardiac death risk in our study. However, the most interesting and somewhat unexpected finding was that abnormally prolonged QT interval of unknown etiology—independent of diabetes, medications and other factors—was an even more powerful predictor of sudden cardiac death, with a five-fold increase in odds," Chugh said.
The researchers noted that several gene variations have been linked to prolonged QT intervals, and the discovery of new genetic associations are likely to improve risk-assessment and intervention strategies.
“The continued identification of gene variants that determine QT interval duration has become an important scientific priority in the field,” Chugh said.