Abstract 2558: QT Variability Predicts Mortality in GISSI-HF
Increased temporal variability of repolarization, as reflected by QT interval variability measured over 10 minutes, predicted spontaneous ventricular arrhythmias in ICD patients, but it is unclear how this measure would perform in predicting mortality from 24-hour ambulatory recordings in heart failure patients without ICD. We hypothesized that increased mean QT variability over 24 hours would be associated with increased mortality.
Methods: GISSI-HF prospectively enrolled subjects with heart failure of any cause. 24-hour digital Holter recordings from 372 subjects with chronic heart failure enrolled in GISSI-HF were analyzed using a template-matching, semi-automatic algorithm to measure QT and heart rate time series in sequential 5 minute epochs over 24 hours. The QT variability index (QTVI) was expressed as the log ratio of the normalized QT variance over normalized heart rate variance. Mean QTVI over 24 hours was measured, and survival of those in the top quartile were compared to the lower three quartiles.
Results: 268 subjects had complete, interpretable recordings for all 24 hours; there were 55 deaths (20%), 44 of which were judged to be cardiovascular (16%). There were 213 males and the average age was 64±10 years, NYHA class 2.2±0.5, and ejection fraction 33±8%. Total mortality increased proportionally over the QTVI strata; 30% died in the highest quartile versus 12% in the lowest (18% in the second quartile, and 19% in the next highest; log rank p<0.05). When compared to the bottom three quartiles, mortality was significantly higher in the top quartile (p<0.01). In a multivariate analysis including age, ischemic etiology of heart failure, NYHA class, and left ventricular ejection fraction, top-quartile QTVI was a significant and independent predictor of both total (hazard ratio 2.05, 95% CI 1.17–3.57, p=0.01 ) and cardiovascular mortality (hazard ratio 2.79, 95% CI 1.26 – 6.17, p=0.01).
Conclusions: Increased repolarization lability, as reflected in QT variability over 24 hours, is associated with a significantly increased risk for total and cardiovascular mortality in a heterogeneous population with chronic heart failure.