Risk of cardiac events in family members of patients with long QT syndrome.

OBJECTIVES: This study sought to identify risk factors for cardiac events (syncope, aborted cardiac arrest or sudden cardiac death) in family members of patients with the long QT syndrome.
BACKGROUND: Patients with the long QT syndrome are known to be at high risk for cardiac events. Whenever the first member of a family is identified as having the long QT syndrome (proband), there is concern regarding the likelihood of cardiac events in other family members.
METHODS: A multivariate logistic regression model was used to evaluate the risk of cardiac events in 637 family members who were first- and second-degree relatives of 151 probands with the long QT syndrome and in a subset of 513 family members who were not receiving beta-adrenergic blocking agents. There were 293 first-degree (46%) and 344 second-degree relatives (54%) (293 men [46%], 344 women [54%]). Fifteen percent of the family members had a corrected QT interval (QTc) > 0.44 s, and relative tachycardia and bradycardia were observed in 12% and 25%, respectively.
RESULTS: The risk of cardiac events occurring before age 40 in family members not taking beta-blockers was influenced by the QTc interval (odds ratio [OR] 1.18/0.01 increase in QTc value; 95% confidence interval [CI] 1.12 to 1.24), relative tachycardia (OR 2.21, 95% CI 0.97 to 5.02) or bradycardia (OR 2.24, 95% CI 1.10 to 4.56) and an interaction term combining gender and closeness of the relationship to the proband (OR for female first-degree relative 3.23 vs. all second-degree relatives, 95% CI 1.67-6.22).
CONCLUSIONS: Female first-degree relatives of patients with the long QT syndrome have a higher risk of cardiac events than male first- or second-degree relatives, independent of recorded electrocardiographic findings. Not only bradycardia, but also tachycardia increases risk of cardiac events in family members of patients with the long QT syndrome.