Abstract
Long considered a disorder of cardiac repolarization mediated by sodium channel mutations, Brugada Syndrome (BS) is now more clearly a disorder primarily of depolarization due to fibrosis on the epicardial aspect of the right ventricular outflow tract (RVOT). Fibrosis in this region leads to abnormal electrograms recorded from epicardial (but not endocardial) mapping, as well as the characteristic right precordial ECG findings of the syndrome and its worst manifestation, ventricular fibrillation. Recent investigations have shown that epicardial mapping and ablation to eliminate abnormal electrograms in the RVOT region can normalize the surface ECG findings and prevent many, if not most, episodes of malignant ventricular arrhythmia. This chapter deals with catheter ablation therapy for inherited arrhythmia syndromes, with BS as an example.
Keywords
Brugada syndrome, catheter ablation, epicardial mapping, inherited arrhythmia syndromes
Key Points
- •
The right ventricular outflow tract (RVOT) epicardium is the culprit arrhythmogenic substrate site of Brugada syndrome (BrS).
- •
Abnormal fractionated electrograms and double potential electrograms are localized only in the anterior aspect of the RVOT epicardium. Epicardial and interstitial fibrosis often coexists with abnormal electrograms.
- •
Radiofrequency ablation by targeting the substrate areas that are defined after ajmaline/procainamide results in normalization of the Brugada electrocardiogram pattern and prevents ventricular tachycardia/ventricular fibrillation (VF) recurrences. It is recommended to use an irrigated-tip catheter with a contact sensor to ablate epicardial arrhythmogenic substrate.
- •
The long-term follow-up (mean of 3 years) after ablation is excellent and without serious complications.
- •
A prospective, multicenter randomized study, Ablation in Brugada Syndrome for the prevention of VF Episodes (BRAVE study) may confirm the hypothesis that catheter ablation alone in a subset of patients with BrS is effective without an implantable cardioverter-defibrillator.
Genetically triggered ventricular tachycardia (VT) and/or ventricular fibrillation (VF) could be categorized into 2 groups: (1) those caused by genetically predisposed electrical alteration properties, primary electrical diseases without cardiac structural abnormalities; and (2) those caused by the presence of arrhythmogenic substrates that are created by genetically induced myopathic changes. The first group is also known as inherited arrhythmia syndromes (IAS), which are primary electrical disease including long QT syndromes (LQT), Brugada syndrome (BrS), early repolarization syndrome (ERS), catecholaminergic polymorphic ventricular tachycardia (CPVT), short QT syndrome, and Andersen syndrome. In the latter category, myopathic changes in the heart lead to VT/VF; this group includes hypertrophic cardiomyopathy, dilated cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy.
IAS is responsible for almost 10% of sudden death in Europe and United States of America. It is the leading cause of sudden death in the young especially in the East and Southeast Asia. Thus it is imperative to obtain better understanding of genetics and electrophysiologic mechanisms, and risk stratification for IAS is needed so that one can find an effective treatment and prophylactic intervention for prevention VT/VF in each of the various IAS subgroups. Among IAS subsets, LQT and BrS are the most common. The purpose of this chapter is to discuss the role of catheter ablation as a treatment modality for IAS. Since at present, data and studies on catheter ablation for LQT, CPVT, ERS, and short QT syndrome is quite scarce and only confined to a few case reports of VF-trigger ablation during electrical storm, the guideline statement from Heart Rhythm Society, Asia-Pacific Heart Rhythm Society, and European Heart Rhythm Association recommends ablation as a viable treatment only on symptomatic BrS patients. Thus I will focus only on the role of catheter ablation for BrS patients in this chapter.
The early attempt at catheter ablation in treating BrS syndrome patients was limited to a few reported cases of patients with electrical storm. The initial approach was designed to target initiating PVCs that trigger VF, which were found to come from the right ventricular outflow tract (RVOT). The ablation was performed on the endocardial site of the RVOT. However, this approach has a significant limitation and has not been widely used largely because patients with BrS rarely had frequent PVCs to be mapped, and therefore it was quite difficult to identify precise targets for ablation and clearly assess the acute outcomes of the ablation. Almost a decade after the initial report of BrS ablation for VF triggers, we reported successful arrhythmogenic substrate ablation on the anterior RVOT epicardium in symptomatic BrS patients. Our findings have subsequently been confirmed by numerous reports from multiple institutions worldwide and indeed proven that substrate ablation is effective as a treatment modality for high risk, symptomatic BrS patients.
Brugada Syndrome Substrate
After its initial description in 1992, the BrS has drawn worldwide attention as an important clinical entity that causes premature death in young adults who are otherwise apparently healthy individuals. This has led to an abundance of research conducted worldwide. However, the pathophysiology of the BrS is not well explained and controversies exist with ongoing heated debate about the underlying pathophysiology of the syndrome–repolarization abnormality versus depolarization abnormality. Fortunately, stemming from the two opposing views is a consensus that right ventricular outflow tract (RVOT) is the most likely substrate site regardless of which mechanisms are responsible.
The observation that placing the electrodes of right precordial leads at the second and third intercostal spaces (ICS)—the location where there are no other cardiac structures except the RVOT—increases the likelihood of producing a BrS electrocardiogram (ECG) pattern compared with just placing the electrodes only on the standard fourth ICS and strongly suggests that the RVOT is a culprit substrate site. This contention is supported by the findings that VF-triggering premature ventricular contractions (PVCs) often emanated from the RVOT in patients with VF storm. Ablations of these triggering PVC from the endocardial site abated VF storms. Similarly, in an animal model, Morita et al. demonstrated that RVOT epicardium was the main substrate site. Perhaps the most compelling findings attesting that RVOT epicardium is the primary substrate sites for BrS came from our study in patients with frequent implantable cardioverter-defibrillator (ICD) discharges.
We found that all our BrS patients who underwent epicardial and endocardial mapping during sinus rhythm had abnormal low voltage, fractionated late potentials clustering in the anterior aspect of the RVOT epicardium as shown in Fig. 36.1 . Ablation at this area normalized the Brugada ECG pattern and prevented recurrent VF episodes. Of interest, the endocardial sites juxtaposed to the corresponding epicardial sites exhibit normal voltage potentials without fractionation ( Fig. 36.2 ). Fig. 36.3 shows epicardial electrograms recorded from various sites of the epicardium in both the left ventricular and right ventricular (RV) epicardium. Note that abnormal fractionated electrograms and double potential electrograms are localized only in the anterior aspect of the RVOT epicardium.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
