Mélèze Hocini

Chapter 112 – Catheter Ablation of Atrial Fibrillation: Triggers and Substrate

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in humans, occurring in 2% of the unselected adult population, increasing with each decade of life to a prevalence of 5.9% in the population older than 65 years. It results in an increased mortality rate and significant morbidity rate related to thromboembolic stroke, loss of atrial systole, and tachycardia-mediated atrial and ventricular cardiomyopathy. 1 Management strategies have been two tiered, either using palliative measures of rate control coupled with anticoagulation or the restoration and maintenance of sinus rhythm. Emerging evidence suggests that the pharmacologic maintenance of sinus rhythm has limited efficacy and value, at least in older patients and in those with persistent AF or structural heart disease. 2 3 4 Consequently, there is heightened interest in the nonpharmacologic, catheter-based approaches to maintain sinus rhythm that may prevent the significant adverse consequences associated with this arrhythmia. This chapter focuses on the current mapping techniques and the advantages and limitations of catheter ablation techniques targeting the triggers and substrate of AF.

Early Repolarization Syndrome: Epidemiology, Genetics, and Risk Stratification

Early repolarization (ER) involving the inferolateral leads, previously considered a benign electrocardiographic (ECG) phenomenon, has recently been associated with sudden cardiac death. Although the mechanisms underlying early repolarization are unknown, ER is the latest of the primary electrical cardiac disease discovered to have significantly high prevalence in SCD cases and contribute to increased risk of death from cardioarrhythmic cause. Population-based studies have demonstrated an association between early repolarization and sudden death, primarily when the ECG demonstrates ≥0.2 mV of ST elevation. Risk stratification, especially for asymptomatic patient, remains challenging. However, clinical features as personal history of syncope, familial history of sudden cardiac death and characteristics of the J-wave (>0.2 mV, wide distribution, horizontal/descending ST segment) should be considered at higher risk.

Catheter Ablation of Ventricular Tachycardia and Fibrillation

As in atrial fibrillation (AF), while both triggers and substrate may theoretically be the target of catheter ablation strategies, the presently published literature on catheter ablation of ventricular fibrillation (VF), including isolated case reports, has focused on targeting triggers.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11The large mass of ventricular myocardium, the importance of maintaining normal mechanical ventricular function, and the risk of creating other forms of malignant arrhythmias mean that ablation strategies aimed at substrate modification are not suitable using the currently available technology. However, previous work in AF has shown that both triggers and substrate may share a close structural relationship. The pulmonary veins play an important role in the initiation and maintenance of AF,12 and recent studies have shed light on their role in the maintenance of AF in some patients. Similarly, several experimental studies demonstrated that Purkinje fibers act as initiators and perpetuators of VF.13,14 Hence, by ablating an area in which the triggering ectopics are found to originate, an additional effect might be substrate modification if the area is implicated in the maintenance of VF.