New research shows that increased QT variability is an independent predictor of ventricular tachycardia or ventricular fibrillation in men, while in women QT variability alone does not pose a risk of arrhythmic events.
The new study published in the February edition of the HeartRhythm Journal (Heart Rhythm Society), confirms that gender does in fact play a significant role in predicting the risk of ventricular tachycardia or ventricular fibrillation. The study goes on to reveal that QT variability, when not correlated to heart rate variability, is a uniquely significant predictor of arrhythmic events in women.
The study, led by Dr Mark C P Haigney, Division of Cardiology at Uniformed Services University of the Health Sciences in Maryland, derived a patient population from those enrolled in the MADIT (Multicenter Automatic Defibrillator) II trial. Patients of the MADIT II study underwent 10-minute, resting digitised recordings at study entry and both QT and heart rate were measured for each beat with a semiautomated method. The incidence of ventricular tachycardia or ventricular fibrillation was determined by implantable cardioverter defibrillator interrogation. Utilising data from the MADIT II study, Haigney compared QT variability and heart rate in both men and women to determine if these values influence the occurrence of ventricular tachycardia or fibrillation and whether or not gender impacts the risk.
From the MADIT II patient population of 1,232, there were 805 usable recordings identified – 663 men and 142 women. During a follow-up period averaging 2.6 years, study analysis found increase QT variability or heart rate variance was associated with a significantly higher risk of ventricular tachycardia or fibrillation in men, but not in women. While reduced coherence, QT variability dissociated from heart rate variability, predicted tachycardia or fibrillation in women, reduced coherence was not predictive in men.
“While it is well-established that gender plays a role in the incidence of arrhythmic events, our study attempted to identify the specific predictors of ventricular tachycardia or fibrillation and how they vary in men and women,” stated Haigney. “Our findings confirm that different measures of variability in QT and heart rate determine the level of risk for men and women and we hope that eventually these measures may be used to test exactly who is at risk of ventricular tachycardia or fibrillation.”
The results of this study identify two types of measures of variability that appear to have different prognostic value depending on the gender of the patient – QT variability for men and low coherence in women. Therefore, measuring variance in QT and heart rate may allow for a better prediction of which patients are at risk of ventricular tachycardia or fibrillation and will benefit from implantable cardioverter defibrillator therapy.