Normal limits of the electrocardiogram in Chinese subjects

Accurate normal limits of the electrocardiogram (ECG) are the basis on which diagnostic criteria are developed. The ECG, however, is subject to age- and sex-variations and may also be racially determined. Studies into normal ECG limits for the Chinese, comprising one fifth of the world population, are few and have their limitations. We have undertaken to establish normal limits of the ECG from a large sample of healthy Chinese subjects.

Standard simultaneous 12-lead ECGs from 5360 apparently healthy Chinese subjects (3614 men and 1746 women, ages ranging from 18 to 84 years) were collected with a modern digital recorder and processed with a well-validated ECG computer program. The medians, lower limits (2nd percentile) and upper limits (98th percentile) of various ECG measurements were calculated and age and sex differences examined.

Significant age trends were present in, for example, P-wave duration, QTc interval, and frontal QRS axis, with concomitant changes of R amplitudes in the extremity leads. Sex differences existed for heart rate, interval durations, the Sokolow and Cornell indices, and QRS and ST-T amplitudes in different leads. Notably, left-precordial R-wave amplitudes in women increased with age; the Sokolow index showed a clearer age trend for men than for women, the reverse being true for the Cornell index. Some of these findings are at odds with established diagnostic ECG criteria.

Normal ECG limits of Chinese subjects show marked age and sex differences. This merits the definition and use of age- and sex-specific ECG criteria for a Chinese population.