The site of origin of torsade de pointes

Objective: The electrocardiographic (ECG) characteristics and mode of onset of torsade de pointes (TdP) are well described. Less is known about the site of onset of this arrhythmia. This study was conducted to determine if arrhythmias in the long QT syndrome (LQTS) have a predominant site of origin. Design: A retrospective analysis of all episodes of LQTSrelated arrhythmias recorded in two university hospitals. Patients: Patients with LQTS and no structural heart disease, for whom simultaneous 6-12 leads ECG recording of the onset of TdP was available, were included. Interventions: None. Main outcome measures: The site of origin of TDP was defined according to the morphology of the initiating ventricular complex based on validated criteria. Multiplelead recordings of 1025 LQTS-related arrhythmias, including 151 episodes of TdP and 874 QT-related extrasystoles (impending TdP) were available for 50 patients. Results: The site of origin of TdP was not homogeneously distributed (p<0.001). Instead, the majority of episodes of TdP (56%) and most QT-related extrasystoles (70%) originated from the outflow tract. There was no correlation between site of origin and the aetiology of LQTS or the QT duration. On a given patient, multiple episodes of TdP tended to originate from the same area and the site of origin of QT-related extrasystoles correlated with the site of origin of TdP. Conclusion: The most frequent site of origin of TdP is the outflow tract. Further studies are needed to understand why this relatively small area of the ventricle is a predominant site of origin of diverse ventricular arrhythmias.