Chest

Chest

Volume 80, Issue 5, November 1981, Pages 613-617
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Clinical Investigations
Linear Relationship Between Electrical Systole, Mechanical Systole, and Heart Rate

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The relationship between the duration of electrical systole (QT) and heart rate (HR) and the relationship between the QT interval and total electromechanical systol (QS2) were studied in the resting state in 200 patients (100 males and 100 females) without evidence of cardiovascular disease. A linear relationship was found between the QT and HR in males and females (males, QT = 521 msec – 2.0 HR, r = .91; females, QT = 511 msec – 1.8 HR, r = .90). In 20 male and 20 female subjects, the relationship between QT and QS2 was studied. The QT was slightly shorter but paralleled the QS2 (males QT = 529 msec – 2.1 HR, QS2 = 541 msec – 2.2 HR; females QT = 511 msec – 1.9 HR, QS2 = 540 msec – 2.0 HR). Thus, over the physiologic range of resting HR, a linear relationship exists between QT and HR. The QT interval is slightly shorter but parallels the QS2 in patients without heart disease. These linear relationships permit a direct comparison of the duration of electrical and mechanical systole.

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MATERIALS AND METHODS

Two hundred hospitalized patients undergoing minimally stressful diagnostic tests were studied. One hundred were males (mean age 40 ± 13, 1SD, range 19 to 77) and one hundred were females (mean age 39.5 ± 15, range 18 to 79). None of the patients had evidence of cardiovascular disease by history, physical examination, chest x-ray film, ECG. Patients with obvious physical or emotional stress were excluded. None of the patients received any pharmacologic agents during the study period.

The QT

RESULTS

Figure 1, Figure 2 show the relationship between QT interval and HR in males and in females. A regression model with sex included reveals that sex is an important variable in this relationship. The individual regression lines for males and females showed that the slope was the same but the intercepts were different (P < 0.05).

Figure 3, Figure 4 show the relationship between QS2 interval and HR according to the equations of Weissler et al,8 and the relationships between QT interval and HR

DISCUSSION

The results of this study show that over the resting range of HR in patients with no evidence of heart disease, a linear relationship exists between the QT interval and HR. In addition, the data indicate that the QT interval is slightly shorter but parallels the QS2. The fact that changes in both mechanical systole and electrical systole with the HR were parallel is of interest but not explained by our data. This is currently under investigation in our laboratory.10

In the range of HR from 40 to

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Copyright © 1981 The American College of Chest Physicians. Published by Elsevier Inc. All rights reserved.