Objective:
Environmental tobacco smoke (ETS) exposure is associated with an increased risk for sudden infant death syndrome (SIDS). The association between a long QT interval and SIDS has been clearly established. However, there has been little focus on the relationship between the QT interval and ETS exposure during early infancy. To examine the effect of ETS exposure on the QT interval during early infancy.

Mathods:
An electrocardiographic study was performed in 624 infants who had been exposed to tobacco smoking since intrauterine life and 1119 age-matched children without ETS exposure. QT data were extracted from an echocardiogram in which an electrocardiogram monitor was incorporated (SSD-ProSound-6500, Hitachi-Aloka, Tokyo, Japan). The corrected QT interval (QTc) using Bazett’s formula was measured in the first, second, third, fourth, and fifth months. Data of the number of cigarettes were collected by a questionnaire.

Results:
The mean QTc at the first and second months was significantly longer than that at the third, fourth, and fifth months (all p<0.05). The mean QTc at the first, second, and third months was significantly greater in ETS infants than in infants without ETS (404±20 vs. 397±21 ms, 407±19 vs. 399±17 ms, and 404±17 vs. 390±18 ms, respectively, all p<0.01). However, the mean QTc at the fourth and fifth months was similar in the two groups. The QTc increased significantly with the number of cigarettes (r = 0.17, p<0.01).

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 for SIDS.