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 marker of ventri cular repolarization inhomogeneity, may predispose to ventricular arrh ythmias. Data on QT dispersion in patients with congestive heart failu re are scarce. In this study, conventional 12-lead ECGs were recorded in 135 consecutive patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy. Seventy-five patients were exclude d from QT interval assessments due to one or more of the following rea sons: (1) low amplitude of the T wave (n = 3), (2) atrial fibrillation (n = 26) and (3) bundle branch block (n = 46). QT dispersion was calc ulated as (1) QT-range: the difference between the maximum and minimum QT intervals on any of the 12 leads and (2) QT-SD: the standard devia tion of the QT interval in all the 12 leads. RR intervals were measure d in leads II, aVL, V-2 and V-5. QT-SD (20.85 +/- 5.00 ms) was signifi cantly (r = 0.8997, P < 0.001) related To QT-range (65.65 +/- 15.77 ms ), but not to the QT interval. Neither QT-range nor QT-SD was signific antly related to age, left ventricular dimensions, left ventricular en d diastolic pressure, left ventricular ejection fraction or left ventr icular wall thickness. There was no significant difference in QT dispe rsion between survivors and those who died (n = 8) or were transplante d (n = 9) during 34 +/- 23 month follow-up. No significant difference in QT dispersion was observed between patients with and without ventri cular tachycardia (greater than or equal to three consecutive beats) d etected on 24-h Holler ECGs. RR interval variation was significantly l ower in patients who died compared with survivors (standard deviation: 10.37 +/- 3.61 vs 36.02 +/- 35.03 ms, P < 0.001; coefficient of varia nce: 1.87 +/- 0.7% vs 4.50 +/- 4.9%, P = 0.001). This was also true in patients with bundle branch block. These observations suggest that QT dispersion in idiopathic dilated cardiomyopathy is not significantly related to either QT interval or cardiac size and function and does no t predict death. The application of QT dispersion assessment is limite d by the commonly encountered atrial fibrillation and bundle branch bl ock in this patient population. However, reduced RR variation on stand ard 12-lead ECGs has important prognostic implications in these patien ts.