QT dispersion and RR variations on 12-lead ECGs in patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy

Increased QT dispersion, which has been proposed as a markerof ventricular repolarization inhomogeneity, may predisposeto ventricular arrhythmias. Data on QT disper sion in patientswith congestive heart failure are scarce. In this study, conventional12-lead ECGs were recorded in 135 consecutive patients withcongestive heart failure secondary to idiopathic dilated cardiomyopathy.Seventy-five patients were excluded from QT interval assessmentsdue to one or more of the following reasons: (1) low amplitudeof the T wave (n=3), (2) atrial fibrillation (n=26) and (3)bundle branch block (n=46). QT dispersion was calculated as(I) QT-range: the difference between the maximum and minimumQT intervals on any of the 12 leads and (2) QT-SD: the standarddeviation of the QT interval in all the 12 leads. RR intervalswere measured in leads II, aVL, V₂ and V₅ QT-SD (20·85± 5·00 ms) was significantly (r=0·8997,P<0·00l) related to QT-range (6565 ± l5 ms),but not to the QT interval. Neither QT-range nor QT-SD was significantlyrelated to age, left ventricular dimensions, left ventricularend diastolic pressure, left ventricular ejection fraction orleft ventricular wall thickness. There was no significant differencein QT dispersion between survivors and those who died (n=8)or were transplanted (n=9) during 34 ± 23 month follow-up.No significant difference in QT dispersion was observed betweenpatients with and without ventricular tachycardia ( three consecutivebeats) detected on 24-h Holter ECGs. RR interval variation wassignificantly lower in patients who died compared with survivors(standard deviation: 10·37 ± 3·61 vs 36·02± 35·03 ms, P<0·001; coefficient ofvariance: 1·87 ± 0·7 vs 4·50 ±4·9%, P=0 This was also true in patients with bundlebranch block. These observations suggest that QT dispersionin idiopathic dilated cardiomyopathy is not significantly relatedto either QT interval or cardiac size and function and doesnot predict death. The application of QT dispersion assessmentis limited by the commonly encountered atrial fibrillation andbundle branch block in this patient population. However, reducedRR variation on standard 12-lead ECGs has important prognosticimplications in these patients.