P4387Environmental tobacco smoke exposure affects the QT interval during early infancy

Abstract Background The association between long QT interval and sudden infant death syndrome (SIDS) has been clearly established. Environmental tobacco smoke (ETS) exposure is associated with increased risk for SIDS. However, there has been little focus on the relationship between the QT interval and ETS exposure during early infancy. To clarify this, we examined the QT interval with ETS exposure during early infancy. Methods Electrocardiographic study was performed in 624 infants (age: 1–5 months) who have been exposed to tobacco smoking since intrauterine life and 1119 age-matched children without ETS exposure. QT data were extracted from the electrocardiogram monitor built-in echocardiogram. Recordings from lead II on the monitor ECG were used to measure the QT interval. The QT intervals of 5 consecutive beats were measured manually. The QT interval was measured on the first, second, third, fourth, and fifth month. The corrected QT interval (QTc) was calculated by dividing the QT interval by the square root of the RR interval (Bazett's formula). The data of the number of cigarettes per day were collected by a questionnaire. Results In the total study population, the mean QTc showed the highest peak at the second month. The mean QTc at the first and second month (399±21 and 402±18 msec) was significantly longer (p<0.05) than that at the third, fourth, and fifth month (394±19, 393±21, and 392±22 msec) as shown in Figure 1A. The mean QTc in ETS infants at the first, second and third month was significantly greater than that in infants without ETS (404±20 vs. 397±21 msec, 407±19 vs. 399±17 msec and 404±17 vs. 390±18 msec, p<0.01, respectively), but the mean QTc at the fourth and fifth was similar in the 2 groups as shown in Figure 1B. The QTc increased significantly as the category of number of cigarettes per day increased, with a significant prolongation as of the category 6–10 cigarettes per day as shown in Figure 1C. Figure 1 Conclusions The present study indicates that the QT interval during early infancy lengthens by ETS exposure. Further study is needed as to whether QT prolongation associated with ETS exposure is a risk factor for SIDS.