This research aims to present the ECG references of Northern Thai people, derived from ambulatory patients at Maharaj Nakorn Chiang Mai Hospital, the largest hospital in northern Thailand, and compare the ethnic differences of ECG intervals and axes with Chinese, Nigerian, American, and Thai subjects. However, a study of Thai subjects (South East Asia inhabitants) has never been reported. QTcB interval increased with age only in women and QRS axes shifted to the left with increasing age.Īs mentioned above, several studies have already documented the effect of gender, age, and race on the ECG values in different groups of the population. The PR interval increased with age whereas QRS duration was stable in all age groups. Similar to the Wu report, the range of heart rate was 48–98 bpm and it decreased with increasing age in both men and women. They suggested the new recommended normal range of heart rate was between 48–98 bpm, PR interval was between 113–212 ms, QRS duration was between 69–109 ms, QRS axis was between −40° to 91°, and QTcB was between 361–457 ms. Mason et al 4 also proposed that ECG reference ranges should be modernised in regard to the large influence of age and gender factors. The SL index in men was higher than for women in all age groups and the threshold in men should be renewed to 4.2 mV. The QRS axis shifted to the left with increasing age. The upper limit of QTcB tended to increase with age and it was always above the standard cut point.
QRS duration was quite constant in both genders but the upper limit for women should be lowered to 109 ms. The PR interval gradually increased with age but the upper limit was still under 200 ms in all age groups. The Chinese study showed that the average heart rate in women was higher than in men, but heart rate decreased with increasing age only for women. 2–10 The study of normal limits derived from 5360 Chinese people by Wu et al 2 proposed that the normal range of heart rate should be adjusted from 60–100 bpm to 50–95 bpm for ethnic Chinese. Several studies have reported that race, gender, and age are major factors affecting normal limits of ECG references. However, global diagnostic criteria cannot be applied generically for all patients. Left or right QRS axis deviation (normal value −30° to +90° 1) and high SV1+RV5 amplitude (Sokolow Lyon index (SL index), normal value <3.5 mV 1) help clinicians to detect ventricular hypertrophy. 1 Hypokalaemia results in a prolonged QT which may indicate an increased risk for developing ventricular fibrillation. The normal range of heart rate-corrected QT interval, obtained by using Bazett's formula (QTcB), recommends that QTcB is generally accepted to be ≤440 ms and the upper limit should be set at 450 or 460 ms. 1 QRS duration which is wider than the traditional upper limit of 120 ms is considered to be a bundle branch block. 1 PR interval exceeding 200 ms indicates first degree atrioventricular (AV) block (normal range 120–200 ms). For example, heart rates which are lower than 50 beats/min (bpm) or higher than 100 bpm are classified as bradycardia and tachycardia, respectively (normal range 60–100 bpm). Cardiologists use ranges of ECG numerical values as criteria to classify the different types of arrhythmias. For many decades the ECG has been well established as a useful tool for diagnosing cardiac diseases.
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