Prognosis in myocardial infarction survivors with left ventricular dysfunction is predicted by electrocardiographic RR interval but not QT dispersion

R F Pedretti, O Catalano, L Ballardini, D P de Bono, E Radice, R Tramarin
International Journal of Cardiology 1999, 68 (1): 83-93

OBJECTIVES: The aim of the study was to assess if QT dispersion and RR interval on the standard 12-lead electrocardiogram (ECG) predict cardiac death and late arrhythmic events in postinfarction patients with low left ventricular ejection fraction (LVEF). QT dispersion on a standard electrocardiogram (ECG) is a measure of repolarization inhomogeneity, but its prognostic meaning in myocardial infarction (MI) survivors is unclear, especially in patients with left ventricular dysfunction. RR interval has been shown to predict mortality in post-MI patients, but its prognostic power has not been compared with other noninvasive risk factors.

METHODS: Retrospective cohort study. Ninety patients were identified, from a series of 547 consecutive postinfarction patients admitted to our institution for phase II cardiac rehabilitation, as having a LVEF of <0.40 at two-dimensional echocardiography (mean LVEF 0.35+/-0.04; range 0.20-0.39). QT dispersion and RR interval were analyzed on the admission 12-lead electrocardiogram, 20+/-10 (range 8-45) days after MI, using specially designed software. Additional risk markers were collected from clinical variables, signal-averaged ECG and Holter recording.

RESULTS: During 24+/-18 (range 1-63) months of follow-up, 10 of 90 patients (11%) died, all from cardiac causes, and there were 18 late arrhythmic events, defined as sudden death or the occurrence of a sustained ventricular arrhythmia > or =5 days after the index MI. QT interval and dispersion were not significantly prolonged in patients who died compared to survivors and not significantly different between patients with and without arrhythmic events. Mean RR interval from standard ECG was significantly shorter in patients with both cardiac death (682+/-99 vs. 811+/-134 ms; P=0.004) and arrhythmic events (720+/-100 vs. 818+/-139 ms; P=0.006). A Cox proportional hazards model identified RR interval from standard ECG (P<0.001) and a history of more than one MI (P=0.002) as significant predictors of cardiac death independent of thrombolytic therapy, LVEF, filtered QRS complex duration at signal-averaged ECG, mean RR and its standard deviation at 24-h Holter monitoring.

CONCLUSIONS: Measurement of QT interval and dispersion 3 weeks after MI has no prognostic power in patients with LV dysfunction after a recent MI. RR interval on standard 12-lead ECG is as good a prognostic indicator as other, more expensive, noninvasive markers. These findings may be relevant in this era of limited health care resources.

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