Abstract 2830: The Site of Origin of Torsade De Pointes
Introduction: The right ventricular outflow tract (RVOT) is the site of origin of the most common form of idiopathic benign monomorphic ventricular tachycardia (VT). In addition, the RVOT is a predominant site of origin of malignant polymorphic ventricular arrhythmias observed in catecholaminergic polymorphic VT, Brugada syndrome and some cases of idiopathic ventricular fibrillation.
Objective: To determine if arrhythmias in the long QT syndrome (LQTS) have a predominant site of origin and if this region is disease-specific (i.e., differs between congenital and acquired LQTS) or patient-specific (that is, if multiple episodes of TdP in the same patient share the site of origin).
Methods: Patients with LQTS and no structural heart disease, for whom electrocardiographic recording of the onset of torsade de pointes (TdP) is available in simultaneous 6 to 12 leads recording, were studied. The site of origin of QT-related arrhythmias was defined according to the morphology of the ventricular complex initiating the arrhythmia and using established VT-morphology criteria.
Results: Simultaneous multiple-lead recordings of the onset of TdP were available for 31 patients. These included 343 QT-related extrasystoles (impending TdP) and 74 episodes of TdP. The distribution of sites of origin for TdP was as follows:
RVOT (including typical right-sided and probable left-sided outflow tract tachycardia) = 47.3%;
Inferior zone of the left ventricle = 35.1%;
Inferior zone of the right ventricle = 17.6%.
The site of origin of TdP was not disease specific (that is, there was no correlation between site of origin and the etiology of LQTS). On the other hand, the site of origin was patient-specific: Multiple episodes of TdP tended to originate from the same area and the site of origin of QT-related extrasystoles predicted the site of origin of TdP.
Conclusions: The most frequent site of origin of TdP is the outflow tract area. Further studies are needed to understand why this relatively small area of the ventricle is a predominant site of origin of diverse monomorphic and polymorphic arrhythmias. Moreover, when typical RVOT extrasystoles are recorded, careful analysis of the QT interval must be performed before a diagnosis of “idiopathic benign RVOT-extrasystoles” is made.