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Synopsis: QT dispersion has no significant prognostic value in patients with advanced heart failure and reduced left ventricular systolic function.
Source: Brendorp B, et al. Circulation. 2001;103: 831-835.
Brendorp and colleagues tested the value of QT dispersion as a potential prognostic marker for arrhythmias and death in patients with advanced heart failure. This study was a predefined substudy in the Danish Investigations of Arrhythmia and Mortality on Dofetilide in Congestive Heart Failure (Diamond-CHF) trial. Diamond-CHF was a study to see if dofetilide would improve mortality in patients with congestive heart failure. Patients were eligible for the trial if they had severe left ventricular dysfunction with New York Heart Association functional class III or IV symptoms within the previous month. Patients were randomized between dofetilide and placebo. Since this was a trial involving dofetilide, an antiarrhythmic drug that prolongs the QT interval, patients with a corrected QT interval greater than 450 m/sec or one greater than 500 m/sec with bundle branch block were excluded from the trial. An analysis of the prognostic value of QT dispersion was a prespecified substudy in Diamond-CHF. QT dispersion could be determined on baseline electrocardiograms from 703 patients. The QT intervals were measured in all 12 leads using a computerized digitizer tablet. The QT dispersion was defined as the maximum minus minimum QT interval in the 12 leads measured. When U waves were present, the end of the QT interval was measured at the nadir between the T and U waves.
There were 285 deaths among the 703 patients in this study (41%). Of these deaths, 219 were classified as cardiac, and of these, 131 were arrhythmic and 81 nonarrhythmic deaths. The upper quartile for QT dispersion was greater than 102 m/sec. There was no difference between the survival curve in total mortality between those patients with QT dispersion greater than 102 m/sec and those with QT dispersion of 100 m/sec or less. Similarly, QT dispersion was not a significant predictor for any of the following end points: cardiac death, arrhythmic cardiac death, or nonarrhythmic cardiac death. The prognostic value of QT dispersion was also tested in various subgroups with stratifications by sex, age, ejection fraction, smoking status, presence of bundle branch block, renal function, New York Heart Association class, diabetes, ischemic heart disease, hypertension, or therapy with beta blockers, digoxin, or dofetilide. In all subgroups, the risk ratio for QT dispersion was found to be near 1.0 with small 95% confidence intervals. The 3 prognostic factors that were associated with increased risk for all-cause mortality, cardiac death, and cardiac arrhythmic death were increasing age, increasing New York Heart Association functional class, and decreasing ejection fraction or wall motion index. Brendorp et al conclude that QT dispersion has no significant prognostic value in patients with advanced heart failure and reduced left ventricular systolic function.
Comment by John P. DiMarco, MD, PhD
In the last several years, several groups have proposed that QT dispersion may be a specific predictor for subsequent cardiac events in patients with various forms of heart disease. The most conclusive data come from patients with acute myocardial infarction and in patients with the congenital long QT syndrome. In patients without these diagnoses, however, the value of QT dispersion has been controversial. This study from the Diamond-CHF trial indicates that measurement of QT dispersion does not have prognostic value in patients with chronic congestive heart failure.
A possible limitation of this report is the fact that patients with obviously abnormal QT intervals or T wave morphologies were excluded from the study. In order to participate in Diamond-CHF, the patient had to be eligible for randomization to dofetilide. Certainly, patients with bizarre QT intervals or T wave morphologies were excluded by Brendorp et al. In these patients, large values for QT dispersion may be important to note. However, such patients are relatively uncommon and this study clearly indicates that the routine measurement of QT dispersion is of little prognostic value in unselected populations with chronic congestive heart failure.
The practical value of QT dispersion measurement remains limited. The QT interval may be difficult to measure reproducibly, and individuals show significant day-to-day and circadian variations. Patients with heart failure and depressed ejection fractions should all be considered to be a significant risk for arrhythmias.