Safety and Efficacy of Catheter Ablation of Idiopathic Ventricular Arrhythmias Arising From Cardiac Outflow Tracts

Overview

Ventricular arrhythmias arising from cardiac outflow tract affect quality of life and can cause decrease in left ventricular ejection fraction. Drugs used for treating those arrhytmias may be ineffective or may have side effects. Radiofrequency catheter ablation can be used safely for treatment of outflow tract arrhythmias. There are different sites where those ventricular arrhythmias may originates, each site has different electrocardiographic characteristics, different procedural success rates and challenges in localization and ablation.

The right and left ventricular outflow tracts (RVOT/LVOT) are the most common sites of origin for idiopathic ventricular tachycardia (VT) and premature ventricular contractions (PVCs) in patients without structural heart disease.1 Frequent PVCs was associated with PVC-induced cardiomyopathy, and radiofrequency (RF) catheter ablation of frequent PVCs was associated with improvement of left ventricular ejection fraction (LVEF).2 The most common underlying pathophysiological mechanism was identified to be triggered activity and RF catheter ablation treatment is highly effective with low complication rates.1,3 Drug therapy has limited effectiveness (in case β-blockers and calcium-channel blockers) or drug-related side effects ( in case of flecainide, propafenone and amiodarone).4 RF catheter ablation is recommended in cases of high PVC burden associated with decreased LV ejection fraction (LVEF) or in highly symptomatic patients despite optimal drug therapy.3 Although the RVOT is the most common site (about 70-80% of cases) for idiopathic VAs1,5, only few studies have reported on the prevalence and RF catheter ablation of ventricular arrhythmias (VAs) arising from the pulmonary artery (21-46% among the RVOT VAs)6 and even less prevalence is reported in VAs arising from the pulmonary sinus cusps (11%).7 Compared with VAs originating from the RVOT, ablation of LVOT-VAs is more complex and reported to be 12-45% of all idiopathic VAs.8-11 The success rate of ablation of LVOT-VA sites was previously reported to be lower (55-60%) without using antegrade/transseptal approaches.12,4 Rarely, it requires epicardial ablation via the GCV/AIV or subxiphoid puncture.13,14 There are some cases in which RF catheter ablation cannot successfully be performed from either LVOT or RVOT. In such cases the VAs may originate from the LV-summit which is the most common site of idiopathic epicardial VAs from the LVOT region.13 Although most idiopathic VAs originating from the cardiac OTs are suitable targets for endocardial RF catheter ablation, a small percentage of failures in these patients may be because of an inaccessible site of origin from epicardial or intramural septal locations.15The identification, mapping and RF catheter ablation of these idiopathic VAs may be challenging for the electrophysiologist and need special consideration.16

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