Background Pregnancy is one of the biggest concerns for women with long QT syndrome (LQTS).

Objectives This study investigated pregnancy-related arrhythmic risk and the efficacy and safety of β-blocker therapy for lethal ventricular arrhythmias in pregnant women with LQTS (LQT-P) and their babies.

Methods 136 pregnancies in 76 LQT-P (29±5 years old; 22 LQT1, 36 LQT2, one LQT3, and 17 genotype-unknown) were enrolled. We retrospectively analysed their clinical and electrophysiological characteristics and pregnancy outcomes in the presence (BB group: n=42) or absence of β-blocker therapy (non-BB group: n=94).

Results All of the BB group had been diagnosed with LQTS with previous events, whereas 65% of the non-BB group had not been diagnosed at pregnancy. Pregnancy increased heart rate in the non-BB group; however, no significant difference was observed in QT and T_peak–T_end intervals between the two groups. In the BB group, only two events occurred at postpartum, whereas 12 events occurred in the non-BB group during pregnancy (n=6) or postpartum period (n=6). The frequency of spontaneous abortion did not differ between the two groups. Fetal growth rate and proportion of infants with congenital malformation were similar between the two groups, but premature delivery and low birthweight infants were more common in those taking BB (OR 4.79, 95% CI 1.51 to 15.21 and OR 3.25, 95% CI 1.17 to 9.09, respectively).

Conclusions Early diagnosis and β-blocker therapy for high-risk patients with LQTS are important for prevention of cardiac events during pregnancy and the postpartum period, and β-blocker therapy may be tolerated for babies in LQT-P cases.