Catheter Ablation for Ventricular Tachycardia

Abstract

S ustained ventricular tachycardia (VT) is an important cause of morbidity and sudden death in patients with heart disease. 1 Implantable cardioverter-defibrillators (ICDs) terminate VT episodes, reducing the risk of sudden death.Recurrent VT develops in 40% to 60% of patients who receive an ICD after an episode of spontaneous sustained VT.A first episode of VT occurs in Ϸ20% of patients within 3 to 5 years after ICD implantation for primary prevention of sudden death in high-risk groups.2-4 ICD shocks reduce quality of life and are associated with an increased risk of death.[2][3][4] Antiarrhythmic drug therapy with amiodarone or sotalol reduces VT episodes but with disappointing incidence of side effects and efficacy.2 Catheter ablation is useful for reducing VT episodes and can be life-saving when VT is incessant.1,5,6 Idiopathic VTs occur in patients without structural heart disease and rarely cause sudden death.Electrophysiological study with catheter ablation is often warranted to confirm the diagnosis, to provide further evidence for the absence of ventricular scar or other disease, and often to cure the arrhythmia.Ablation is also an option for symptomatic nonsustained VT and frequent ventricular ectopy in these patients.1 The appearance of the VT on ECG often suggests its likely cause and associated heart disease (Figure 1).Monomorphic VT has the same QRS complex from beat to beat, indicating repetitive ventricular activation from a structural substrate or focus that can be targeted for ablation.Most are due to reentry through regions of ventricular scar.7 Polymorphic VTs have a changing ventricular activation sequence that can be due to functional reentry without a structural target for ablation; myocardial ischemia, acquired long-QT syndrome, and a number of genetic syndromes are causes.Rarely, ablation of the initiating focus is warranted to control frequent episodes.8 Technical Considerations and ComplicationsThe ablation procedure proceeds in steps.After vascular access is obtained, the arrhythmia is induced to confirm the diagnosis and to establish whether abolishing inducible VT is a potential end point for the procedure.Mapping is performed to locate the source, followed by ablation.Testing is then performed to assess the effect of ablation. MappingWhen VT is hemodynamically stable, mapping can be performed during VT.Many patients with heart disease have VTs that are "unmappable" or "unstable" because they require immediate termination because of hemodynamic intolerance, they cannot be reliably induced, or they frequently change from one VT to another.Substrate mapping or multielectrode mapping approaches have been developed to guide ablation of these VTs.Mapping systems that recreate the geometry of the ventricles from point-by-point sampling while providing continuous display of catheter position are in common use.9,10 Electrophysiological data such as the activation time and electrogram amplitude are color-coded for display (Figure 2).Cardiac motion introduces some error.Papillary muscles and other fine anatomic details are not visible.Registration of preacquired computed tomographic or magnetic resonance images on mapping systems shows promise for improving anatomic definition.9,11 Balloon or basket electrode arrays sample from multiple sites simultaneously, potentially allowing activation to be defined from a single beat or brief run of VT.A "noncontact" mapping system mathematically reconstructs potentials from adjacent sites.12,13 Go to Images in Cardiovascular Medicine for related image, "Percutaneous Pericardial Access for Mapping and Ablation of Epicardial Ventricular Tachycardias" by Sosa et al (Circulation.2007;115:e542-e544).