Korean Circ J.  2007 Nov;37(11):543-549. 10.4070/kcj.2007.37.11.543.

Characteristics of QT Interval and QT Dispersion in Exercise Electrocardiogram: Healthy Persons versus Stable Angina Patients

• Park JH
• Kim DY
• Kim BS
• Lee HJ
• Kim JH
• Jang HS
• Shin SM
• Kang HJ
• Lee BR
• Jung BC

• KMID: 1909615
• DOI: http://doi.org/10.4070/kcj.2007.37.11.543

Abstract

BACKGROUND AND OBJECTIVES: The QT interval (QTi) and QT dispersion (QTd), which represent the myocardial electrical heterogeneity of repolarization, were studied to recognize the differences between normal controls (n=32) and stable angina patients (n=78).
SUBJECTS AND METHODS
During the treadmill exercise test, standard 12 lead Electrocardiogram (ECG) was obtained at every stage, with the QTi and QTd measured. The corrected QT interval (cQTi) and QT dispersion (cQTd) were calculated using Bazett's formula, with the Delta QT interval (DeltaQTi) measured on leads V5 and aVF.
RESULTS
During exercise, the QTi had a reverse relationship with the heart rate in both groups, but was decreased by a lesser extent in the patient group. The QTd also had a tendency to decrease according to increasing heart rate in both groups and was significantly greater in the patient group. The corrected QTi increased during exercise in both groups, and reached maximum during the pre-peak stage, but was minimized during a 1 minute recovery stage in the patient group. The corrected QTd reached a maximum during the peak exercise stage in both groups, but the values between the two groups were significantly different. Both the QTi and cQTi had tendencies to increase according to the number of vessels with stenosis. The DeltaQTi tended to reflect a regional ischemia in a single vessel disease.
CONCLUSION
The QTi, QTd, cQTi and cQTd were increased in the stable angina patients compared with the normal controls, and augmented during the exercise test.

Keyword

Exercise test

MeSH Terms

Angina, Stable*
Constriction, Pathologic
Electrocardiography*
Exercise Test
Heart Rate
Humans
Ischemia
Population Characteristics

Figure

• 

  Fig. 1 Maximal QT interval (Max QTi) and minimal QT interval (Min QTi) of control and patient groups during exercise test. QT interval (QTi) shortens according to increasing heart rate in both groups. Max QTi of patient group decreases lesser than that of controls, showing significant differences at exercise and recovery stages. Min QTi of patient group falls more rapidly than min QTi of controls, and at peak exercise min QTi's of the two groups show no significant difference (⇧) *Significant difference between two groups. IHD: ischemic heart disease, RRi: RR interval.

• 

  Fig. 2 QT dispersion (QTd) and corrected QT dispersion (cQTd) of the control and patient groups during the exercise test. Comparing the control and patient groups, the QTd and cQTd show significant differences throughout the test. However, there are no significant changes in the QTd values throughout the exercise stages in either group; whereas, the cQTd was significantly increased with exercise in both groups. *Significant difference between two groups. IHD: ischemic heart disease.

Reference

1. Shu J, Zhu T, Yang L, Cui C, Yan GX. ST-segment elevation in the early repolarization syndrome, idiopathic ventricular fibrillation, and the Brugada syndrome: cellular and clinical linkage. J Electrocardiol. 2005. 38:26–32.

2. Zareba W, Moss AJ, le Cessie S. Dispersion of ventricular repolarization and arrhythmic cardiac death in coronary artery disease. Am J Cardiol. 1994. 74:550–553.

3. Day CP, Mc Comb JM, Campbell RW. QT dispersion: an indication of arrhythmia risk in patients with long QT intervals. Br Heart J. 1990. 63:342–344.

4. Kim BS, Kang JH, Lee SW, et al. Effect of coronary angioplasty on QT and JT dispersion. Korean Circ J. 1998. 28:1280–1286.

5. Choi KJ, Lee IS, Lee SG, et al. Change of QT dispersion following PTCA in angina patients. Korean Circ J. 1998. 28:1487–1492.

6. Ahnve S. Correction of QT interval for heart rate: review of different formulas and the use of Bazett's formula in myocardial infarction. Am Heart J. 1985. 109:568–574.

7. Kligfield P, Lax KG, Okin PM. QT interval-heart rate relation during exercise in normal men and women: definition by linear regression analysis. J Am Coll Cardiol. 1996. 28:1547–1555.

8. Elming H, Sonne J, Lublin HK. The importance of the QT interval: a review of the literature. Acta Psychiatr Scand. 2003. 107:96–101.

9. Ahnve S, Vallin H. Influence of heart rate and inhibition of autonomic tone on the QT interval. Circulation. 1982. 65:435–439.

10. Boudoulas H, Ruff PD, Fulkerson PK, Lewis RP, Dervenagas S. Effect of propranolol on post exercise left ventricular ejection time index. Am J Cardiol. 1981. 48:357–360.

11. Boudoulas H, Geleris P, Lewis RP, Leier CV. Effect of increased adrenergic activity on the relationship between electrical and mechanical systole. Circulation. 1981. 64:28–33.

12. Davey P, Bateman J. Heart rate and catecholamine contribution to QT interval shortening on exercise. Clin Cardiol. 1999. 22:513–518.

13. Malik M, Batchvarov VN. Measurement, interpretation and clinical potential of QT dispersion. J Am Coll Cardiol. 2000. 36:1749–1766.

14. Roukema G, Singh JP, Meijs M, Carvalho C, Hart G. Effect of exercise induced ischemia on QT interval dispersion. Am Heart J. 1998. 135:88–92.

15. Lukas A, Antzelevitch C. Differences in the electrophysiological response of canine ventricular epicardium and endocardium to ischemia: role of the transient outward current. Circulation. 1993. 88:2903–2915.

16. Benatar A, Decraene T. Comparison of formulae for heart rate correction of QT interval in exercise ECGs from healthy children. Heart. 2001. 86:199–202.

17. Pak HN, Kim YH, Park SW, et al. Diagnostic value of QT and JT dispersion in exercise ECG. Korean Circ J. 1995. 25:560–567.

18. Dilaveris P, Andrikopuolos G, Metaxas G, et al. Effects of ischemia on QT dispersion during spontaneous anginal episodes. J Electrocardiol. 1999. 32:199–206.

19. Stierle U, Giannitsis E, Sheikhzadeh A, et al. Relation between QT dispersion and the extent of myocardial ischemia in patients with three-vessel coronary artery disease. Am J Cardiol. 1998. 81:564–568.

20. Roukema G, Singh JP, Meijs M, Carvalho C, Hart G. Effect of exercise-induced ischemia on QT interval dispersion. Am Heart J. 1998. 135:88–92.

21. Yunus A, Gillis AM, Traboulsi M, et al. Effect of coronary angioplasty on precordial QT dispersion. Am J Cardiol. 1997. 79:1339–1342.

22. Moreno FL, Vilaneuva T, Karagounis LA, Anderson JL. Reduction in QT interval dispersion by successful thrombolytic therapy in acute myocardial infarction. Circulation. 1994. 90:94–100.

23. Tikiz H, Terzi T, Balbay Y, et al. QT dispersion in single coronary artery disease: is there a relation between QT dispersion and diseased coronary artery or lesion localization? Angiology. 2001. 52:43–51.