Abstract
Objective: The reproducibility of QT interval measurements is low, even for the mean QT interval based on the standard ECG. In this study we analyzed whether the reproducibility of the mean weighed QT interval was better than the simple mean QT interval. The weighing was based on the amplitude of the T wave or the slope of the steepest tangent on the terminal part of the T wave.
Material and methods: 12‐lead ECGs of 130 postmyocardial infarction patients were obtained. The QT intervals were measured by the tangent‐method on two occasions by the same observer Mismatch QT intervals were defined as QT intervals that were measured at only one occasion. Sixteen ECGs were rejected. The data were split into 34 and 80 ECGs for optimization and validation of the weighing, respectively. The weighed QT dispersion was calculated as the weighed mean of the three longest minus the weighed mean of the three shortest QT intervals.
Results: Weighing with the slope increased the reproducibility by 41% (P = 3 10‐6), but weighing with the amplitude reduced it by 20% (P = 0.02). However, if measurements with errors above 75 ms were rejected, weighing with the slope or the amplitude increased the reproducibility with 26% and 20% (P = 0.02), respectively. Weighing did not change the reproducibility of the weighed QT dispersion.
Conclusion: Weighing with the slope improved the reproducibility of the mean weighed QT interval. However, if measurements with errors above 75 ms were rejected, weighing with the amplitude also increased the reproducibility. Weighing did not change the reproducibility of the weighed QT dispersion. Weighing is particularly efficient at reducing the negative impact of mismatch QT intervals on the reproducibility. A.N.E. 2002;7(1):4–9
Keywords: QT, QT dispersion, reproducibility, T wave morphology
REFERENCES
- 1. Elming H, Holm E, Jun L, et al. The prognostic value of the QT interval and QT interval dispersion in all‐cause and cardiac mortality and morbidity in a population at Danish citizens. Eur Heart J 1998;19:1391–1400. [DOI] [PubMed] [Google Scholar]
- 2. Perkiömäki JS, Koistinen, J , Yli‐Mayry S, et al. Dispersion of QT interval in patients with and without susceptibility to ventricular tachyarrhythmias after previous myocardial infarction. J Am Coll Cardiol 1995;26:174–179. [DOI] [PubMed] [Google Scholar]
- 3. Priori SG, Napolitano C, Diehl L, et al. Dispersion of the QT interval. A marker of therapeutic efficacy in the idiopathic long QT syndrome. Circulation 1994;89: 1681–1689. [DOI] [PubMed] [Google Scholar]
- 4. Schwartz PJ, Moss AJ, Vincent GM, et al. Diagnostic criteria for the long QT syndrome. An update. Circulation 1993;88: 782–784. [DOI] [PubMed] [Google Scholar]
- 5. Swan H, Saarinen K, Kontula K, et al. Evaluation of QT interval duration and dispersion and proposed clinical criteria in diagnosis of long QT syndrome in patients with a genetically uniform type of LQT1. J Am Coll Cardiol 1998;32:486–491. [DOI] [PubMed] [Google Scholar]
- 6. Schwartz PJ, Stramba‐Badiale M, Segantini A, et al. Prolongation of the QT interval and the sudden infant death syndrome. N Engl J Med 1998;338:1709–1714. [DOI] [PubMed] [Google Scholar]
- 7. Pye M, Quinn AC, Cobbe SM. QT interval dispersion: A noninvasive marker of susceptibility to arrhythmia in patients with sustained ventricular arrhythmias Br Heart J 1994;71:511–514. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8. Buja G, Miorelli M, Turrini P, et al. Comparison of QT dispersion in hypertrophic cardiomyopathy between patients with and without ventricular arrhythmias and sudden death. Am J Cardiol 1993;72:973–976. [DOI] [PubMed] [Google Scholar]
- 9. Wei K, Dorian P. Newman D, et al. Association between QT dispersion and autonomic dysfunction in patients with diabetes mellitus. J Am Coll Cardiol 1995;26:859–863. [DOI] [PubMed] [Google Scholar]
- 10. Higham PD, Furniss SS, Campbell RW. QT dispersion and components of the QT interval in ischaemia and infarction. Br Heart J 1995;73:32–36. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11. Ahnve S. QT interval prolongation in acute myocardial infarction. Eur Heart J 1985;6 Suppl D:85–95. [DOI] [PubMed] [Google Scholar]
- 12. de Bruyne MC, Hoes AW, Kors JA, et al. Prolonged QT interval predicts cardiac and all‐cause mortality in the elderly. The Rotterdam Study. Eur Heart J 1999;20: 278–284. [DOI] [PubMed] [Google Scholar]
- 13. Schwartz PJ, Wolf S. QT interval prolongation as predictor of sudden death in patients with myocardial infarction. Circulation 1978;57:1074–1077. [DOI] [PubMed] [Google Scholar]
- 14. Hohnloser SH. Proarrhythmia with class III antiarrhythmic drugs: Types, risks, and management. Am J Cardiol. 1997;80:82G–89G. [DOI] [PubMed] [Google Scholar]
- 15. Kurita T, Ohe T, Shimizu W, et al. Early afterdepolarizationlike activity in patients with class IA induced long QT syndrome and torsades de pointes. PACE 1997;20: 695–705. [DOI] [PubMed] [Google Scholar]
- 16. McKibbin JK, Pocock WA, Barlow JB, et al. Sotalol, hypokalaemia, syncope, and torsade de pointes. Br Heart J 1984;51:157–162. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17. Reilly JG, Ayis SA, Ferrier IN, et al. QTc‐interval abnormalities and psychotropic drug therapy in psychiatric patients Lancet 2000;355: 1048–1052. [DOI] [PubMed] [Google Scholar]
- 18. Moss AJ. Drugs that prolong the QT interval: Regulatory and QT measurement issues from the United States and the European perspectives. Ann Noninvasive Electrocardiol 1999;4:255–256. [Google Scholar]
- 19. Lund K, Lund B, Arildsen H, et al. Spatial properties of QT and the T wave morphology. Ann Noninvasive Electrocardiol 2000;5:214–221. [Google Scholar]
- 20. Lund K, Arildsen H, Perkiömäki JS, et al. Reproducibility of minimum, maximum and median QT intervals in the 12‐lead resting ECG. Ann Noninvasive Electrocardiol 2000;5:354–357. [Google Scholar]
- 21. Lund K, Perkiömäki JS, Brohet C, et al. Improving the reproducibility of QT dispersion measures. Ann Noninvasive Electrocardiol 2001;6:143–152. [DOI] [PMC free article] [PubMed] [Google Scholar]