OBSERVATIONS ON THE CHANGE OF VENTRICULAR SYSTOLE (QT INTERVAL) DURING EXERCISE 1

Abstract

In a previous communication (1) we have briefly described the electrocardiographic changes of the QT interval during exercise in normal subjects. On the average the corrected QT interval or K was 7% greater than that observed during rest, and with the onset of recovery it diminished by 9%o within the first two minutes and gradually returned to the original value at rest. There was no significant alteration of QRS complex, ST segment or T wave associated with the change of QT interval. The significance of QT interval in various conditions has been recently studied. In normal persons it varies with age, sex and heart rate (2, 3). Shortening of QT interval occurs in conditions where the blood calcium is high (i.e., hyperpara-thyroidism [4, 5]) and after digitalis administration (6, 7). It is prolonged in many conditions including dilatation and hypertrophy of the heart (8), cardiac failure (9), myocardial ischemia and infarction (2, 3), various types of myocarditis (no-tably rheumatic [2, 10] and diphtheritic [2]), disturbance of electrolytes (hypopotassemia [11], and hypocalcemia [ 12, 13]), and quinidine poisoning (13). The effect of exercise on the electrocardiogram in the diagnosis of coronary insufficiency by the application of Master's two-step test has been extensively studied and is well known (14-17). The essential abnormal changes include an ST depression of more than 0.5 mm. and a reversal of T waves. But no emphasis was made on the change of QT interval. Hartwell and his associates (18) have likewise studied the effect of exercise on normal human electrocardiograms. The tracings were taken before, during, and after exercise with the 'Aided by grants from the Hochstetter and Lovejoy Funds. 2 Bertha Hochstetter Buswell Research Fellow in Medicine. subject sitting on the orthopedic exerciser. They observed that the T wave was usually lowered during exercise and returned to its former height after exercise. Meier (19) during World War II examined the electrocardiographic changes before and after exercise in 45 subjects wearing gas masks. No significant changes were observed which could be ascribed either to accumulation of CO2 or to relative anoxemia. Auricular premature beats were observed in some normal subjects after severe exercise of short duration and not under conditions of moderate exercise for a longer time. In both reports the authors, too, did not mention any change of QT interval. In reviewing the literature from 1920 to 1948 only a few scattered reports on the electrocardio-graphic change of QT interval in relation to exercise were found. In 1920 Bazett (20) studied the QT changes after exercise in three subjects. Although he claimed that the QT interval was prolonged after exercise, it is interesting to note that in all the three subjects there was a shortening of corrected QT interval in the first one or two minutes after exercise in comparison with the late recovery. In 1929 White and Mudd (5) observed the changes of QT interval in 10 normal subjects before and after exercise (running up and down four flights of stairs). Measurements were made in all of them after the first run, in three after the second run, and in one after the third run. The results obtained by them (observed QT interval being converted into corrected QT interval, or K, by using Bazett's formula) and those by Bazett are tabulated in Table I for comparison. Savilahti (21) has studied the change of QT interval before and after moderate exercise of 10 minutes' duration in 60 normal subjects under 45 years of age, and in 50 persons over 45 years of age. He found that among the young persons the 279