Correspondence

QTc dispersion in intracerebral hemorrhage

To the Editor,

I read with interest the article by Huang et al [1] concerning QTc dispersion (QTD) in patients with intrace- rebral hemorrhage (ICH).

QTc dispersion is defined as the difference between the maximum and minimum QT intervals after correcting for heart rate. The association between increased QTD and ventricular dysrhythmias and sudden cardiac death has been extensively evaluated, but the use of this electrocardiographic marker in the setting of ICH is a relatively novel concept. It may be a worthwhile endeavor to further investigate the prognostic significance of an increased QTD in patients with ICH, but there are certain limitations with QTD methodology that warrant mention.

The most significant problem with measurement of QTD is the accurate determination of the end of the T wave especially when these waveforms are flat or biphasic. As would be expected, there can be significant interobserver and intraobserver variability despite the use of image magnification or even computer algorithms [2]. Another issue to consider is the lack of well-defined guidelines regarding which combination of leads to measure, how many leads to include for accuracy, and whether to correct for missing leads [3,4]. In the current investigation by Huang et al [1], the authors note that the QT interval was measured in all 12 leads for the 26 patients included in their retrospective analysis. This is fortuitous but the presence of 12 easily measurable QT intervals is far from universal and electrocardiograms with very different numbers and combi- nations of measurable leads should probably not be compared to one another [5].

There are also a number of other conditions associated with higher interlead dispersion including ischemic heart disease [6], left ventricular hypertrophy [7], hypertension [7], and diabetes mellitus [7]. How these conditions may have affected QTD in the review by Huang et al [1] is unknown, but it is likely that they were present to a variable degree in the study population. Finally, QTD is decreased by certain medications such as Angiotensin converting enzyme inhibitors [8] and calcium channel antagonists [9]. Again, it is unknown whether prior use of such medications may have had an acute effect on QTD in patients with ICH.

It is possible that QTD will be shown to provide definitive prognostic information regarding emergency department patients with acute myocardial ischemia or acute cerebro- vascular events. In order for this to occur, however, there are a number of questions that should be answered–the most important of which is probably the optimal protocol to follow for measuring QTD. Even if standard and accurate means of measurement is agreed upon, it will also be necessary to determine how underlying comorbid disease and medication use change dispersion and whether the prognostic value of QTD is affected by these variables.

References

1. Huang C-H, Chen W-J, Chang W-T, et al. QTc dispersion as a prognostic factor in intracerebral hemorrhage. Am J Emerg Med 2004;22:141 – 4.
2. Glancy JM, Weston PJ, Bhullar HK, et al. Reproducibility and automatic measurement of QT dispersion. Eur Heart J 1996;17:1035 – 9.
3. de Bruyne MC, Hoes AW, Kors JA, et al. QTc dispersion predicts cardiac mortality in the elderly: the Rotterdam study. Circulation 1998; 97:467 – 72.
4. van de Loo A, Arendts W, Hohnloser SH. Variability of QT dispersion measurements in the surface electrocardiogram in patients with acute myocardial infarction and in normal subjects. Am J Cardiol 1994;74: 1113 – 8.
5. Hnatkova K, Malik M, Kautzner J, et al. Adjustment of QT dispersion assessed from 12 lead electrocardiograms for different numbers of analysed electrocardiographic leads: comparison of stability of different methods. Br Heart J 1994;72:390 – 6.
6. Roukema G, Singh JP, Meijs M, et al. Effect of exercise-induced ischemia on QT interval dispersion. Am Heart J 1998;135:88 – 92.
7. Cowan JC, Yusoff K, Moore M, et al. Importance of lead selection in QT interval measurement. Am J Cardiol 1988;61:83 – 7.
8. Gonza’lez-Juanatey JR, Garc’ia-Acun~a JM, Pose A, et al. Reduction of QT and QTc dispersion during Long-term treatment of systemic hypertension with enalapril. Am J Cardiol 1998;81:170 – 4.
9. Karpanou EA, Vyssoulis GP, Psichogios A, et al. Regression of left ventricular hypertrophy results in improvement of QT dispersion in patients with hypertension. Am Heart J 1998;136:765 – 8.

Kirsten Calder, MD

Assistant Professor of clinical emergency Medicine

Keck School of Medicine of the University of Southern California Los Angeles, CA 90033, USA

Medical Director, Main Emergency Admitting

LAC + USC Medical Center Los Angeles, CA 90033, USA

E-mail address: kcalder@usc.edu

0735-6757/$ – see front matter D 2005 doi:10.1016/j.ajem.2004.06.013