Abstract 4120: Pause Dependent Torsade de Pointes - Does the Cause of Bradycardia Matter?
Background: Pause dependent torsades de pointes (TdP) is an important complication of heart block. However, reports linking sinus bradycardia to TdP are uncommon. One potential mechanism of TdP is bradycardia induced QT prolongation and early afterdepolarization.
Aim: To compare the differences in the QT intervals in patients with sinus bradycardia and heart block.
Methods: 184 patients with sinus bradycardia or second degree/complete heart block were included in this study. Retrospective analysis of the ECG’s was performed and the QT intervals compared. The following intervals were included in the analysis: computer calculated QT and QTc, QT interval in leads II, V2 and V5 calculated manually and the longest QTc (calculated using the longest QT interval in lead II, V2 or V5 and Bazette’s formula). Also included was presence of premature ventricular complexes and u-waves. Bivariate comparisons between Sinus Bradycardia and Heart Block groups were analyzed using Student t-tests for continuous variables and Chi-Square tests for categorical variables.
Results: Continuous variables are expressed as mean. Categorical variables are expressed as count and percent.
Conclusion: Despite no difference in baseline heart rate, patients with heart block have a significantly longer QT interval. The relative QT prolongation may explain why TdP is noted in heart block and not in sinus bradycardia.