Long QT Syndrome: Risk of Pregnancy
ABSTRACT & COMMENTARY
Synopsis: Data suggest that beta-blocker therapy should be used in patients with a definite diagnosis of the hereditary long QT syndrome. Pregnancy without beta-blocker therapy is safe for asymptomatic first-degree relatives without definite long QTc intervals.
Source: Rashba EJ, et al. Circulation 1998;97:451-456.
The risk of pregnancy in the hereditary long qt syndromes is unknown. Thus, Rashba and associates describe the risk of syncope or cardiac arrest during pregnancy in patients with the hereditary long QT syndrome by identifying patients in the international long QT syndrome registry who had experienced one or more pregnancies. The individuals identified were classified as either probands or first-degree family members. Among the 111 probands, 92 had a personal history of syncope or cardiac arrest, 15 had a long QT and a family history of such events, and four had only an abnormal QT interval. The 311 first-degree family members were subdivided on the basis of a baseline QTc interval as affected (QTc > 0.47 sec), borderline (QTc 0.45-0.47 sec), or unaffected (QTc < 0.45 sec). Cardiac events, syncope, or cardiac arrest were counted during the 40 weeks before the start of each pregnancy, during the pregnancy, and during the 40 weeks postpartum. Many of the pregnancies analyzed occurred before the patients were enrolled in the registry.
The QTc interval was 509 ± 50 msec among the probands and 497 ± 42 msec among the affected first-degree relatives. Syncope accounted for most of the cardiac events during the study. In the proband group, there were two cardiac arrests in the pre-pregnancy interval, two during pregnancy, and seven in the postpartum interval. Among the affected relatives, all three deaths noted were during the postpartum interval. The remainder of the events analyzed consisted of 115 episodes of syncope. There was an excess of cardiac arrest or syncope in the postpartum interval. First events were also more common in the postpartum interval. Therapy with beta blockers was associated with an almost 50-fold reduction in events. Multivariate analysis identified the postpartum interval, a history of syncope or cardiac arrest before the first pregnancy, and the absence of beta-blocker therapy as risk factors for a cardiac arrest. Rashba et al speculate that physiologic changes that occur after delivery to influence hormonal levels or heart rate may be responsible for the increased frequency of events in the postpartum interval.
Rashba et al conclude that their data suggest that beta-blocker therapy should be used in patients with a definite diagnosis of the hereditary long QT syndrome. Pregnancy without beta-blocker therapy is safe for asymptomatic first-degree relatives without definite long QTc intervals.
COMMENT BY JOHN P. DiMARCO, MD, PhD
Patients with the hereditary long QT syndrome often present as adolescents or young adults. Data that could be used to formulate guidelines for counseling female patients regarding the potential risks of pregnancy had not previously been available. Therefore, this analysis from the large database collected by the long QT syndrome registry is valuable, since it allows some quantification of the risks involved.
It is intriguing that there does not seem to be any increased risk during pregnancy, but that the postpartum period is the time of higher risk. The authors' speculation about the role of hormonal changes and increased stress after delivery as contributing factors seems plausible but cannot be proven from this retrospective analysis.
Several limitations to the data are obvious. Many of the pregnancies analyzed occurred before the clinical diagnosis of long QT syndrome was made in the probands. This accounts for the low proportion of patients who were treated during pregnancy and makes conclusions about the efficacy of therapy uncertain. Most of the cardiac events were syncopal episodes for which electrocardiographic documentation was not available. It is not certain that all of these events were episodes of polymorphic ventricular tachycardia, even though many probably were. Finally, the recognition of a number of specific genetic mutations or causes of the long QT syndrome leads one to believe that the different mutations might produce characteristic symptom patterns. Unfortunately, most of the patients in the registry have not yet been genotyped, so we cannot examine this hypothesis from these data.
Despite these limitations, these data should be useful to physicians with female patients with the long QT syndrome. Therapy with beta adrenergic blockers is indicated in symptomatic patients and in first-degree relatives with long QT intervals greater than 0.47 sec. The risk of cardiac events is high enough during pregnancy, especially during the postpartum period, to justify the small risk of exposure to the developing fetus or to the newborn via breast milk.
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