Different Forms of Ventricular Tachycardia Involving the Left Anterior Fascicle in Nonischemic Cardiomyopathy: Critical Sites of the Reentrant Circuit in Low-Voltage Areas

Endomyocardial substrate of ventricular arrhythmias in patients with autoimmune rheumatic diseases

INTRODUCTION

Delayed enhancement-magnetic resonance imaging (DE-MRI) has demonstrated that nonischemic cardiomyopathy is mainly characterized by intramural or epicardial fibrosis whereas global endomyocardial fibrosis suggests cardiac involvement in autoimmune rheumatic diseases or amyloidosis. Conduction disorders and sudden cardiac death are important manifestations of autoimmune rheumatic diseases with cardiac involvement but the substrates of ventricular arrhythmias in autoimmune rheumatic diseases have not been fully elucidated.

METHODS AND RESULTS

20 patients with autoimmune rheumatic diseases presenting with ventricular tachycardia (VT) (n = 11) or frequent ventricular extrasystoles (n = 9) underwent DE-MRI and/or endocardial electroanatomical mapping of the left ventricle (LV). Ten patients with autoimmune rheumatic diseases underwent VT ablation. Global endomyocardial fibrosis without myocardial thickening and unrelated to coronary territories was detected by DE-MRI or electroanatomical voltage mapping in 9 of 20 patients with autoimmune rheumatic diseases. In the other patients with autoimmune rheumatic diseases, limited regions of predominantly epicardial (n = 4) and intramyocardial (n = 5) fibrosis or only minimal fibrosis (n = 2) were found using DE-MRI. Endocardial low-amplitude diastolic potentials and pre-systolic Purkinje or fascicular potentials, mostly within fibrotic areas, were identified as the targets of successful VT ablation in 7 of 10 patients with autoimmune rheumatic diseases.

CONCLUSION

Global endomyocardial fibrosis can be a tool to diagnose severe cardiac involvement in autoimmune rheumatic diseases and may serve as the substrate of ventricular arrhythmias in a substantial part of patients.

Recent insights into mechanisms and clinical approaches to electrical storm

Electrical storm, characterized by repetitive ventricular tachycardia/fibrillation (VT/VF) over a short period, is becoming commoner with widespread use of implantable cardioverter-defibrillator (ICD) therapy. Electrical storm, sometimes called "arrhythmic storm" or "VT-storm", is usually a medical emergency requiring hospitalization and expert management, and significantly affects short- and long-term outcomes. This syndrome typically occurs in patients with underlying structural heart disease (ischemic or non-ischemic cardiomyopathy) or inherited channelopathies. Triggers for electrical storm should be sought but are often unidentifiable. Initial management is dictated by the hemodynamic status, while subsequent management typically involves ICD interrogation and reprogramming to reduce recurrent shocks, identification/management of triggers like electrolyte abnormalities, myocardial ischemia, or decompensated heart failure, and antiarrhythmic-drug therapy or catheter ablation. Sympathetic nervous system activation is central to the initiation and maintenance of arrhythmic storm, so autonomic modulation is a cornerstone of management. Sympathetic inhibition can be achieved with medications (particularly beta-adrenoreceptor blockers), deep sedation, or cardiac sympathetic denervation. More definitive management targets the underlying ventricular arrhythmia substrate to terminate and prevent recurrent arrhythmia. Arrhythmia targeting can be achieved with antiarrhythmic medications, catheter ablation or more novel therapies such as stereotactic radiation therapy that targets the arrhythmic substrate. Mechanistic studies point to adrenergic activation and other direct consequences of ICD-shocks in promoting further arrhythmogenesis and hypocontractility. Here, we review the pathophysiologic mechanisms, clinical features, prognosis, and therapeutic options for electrical storm. We also outline a clinical approach to this challenging and complex condition, along with its mechanistic basis.

Diagnosis and Management of Complex Reentrant Arrhythmias Involving the His-Purkinje System

The His-Purkinje system is a network of bundles and fibres comprised of specialised cells that allow for coordinated, synchronous activation of the ventricles. Although the histology and physiology of the His-Purkinje system have been studied for more than a century, its role in ventricular arrhythmias has recently been discovered with the ongoing elucidation of the mechanisms leading to both benign and life-threatening arrhythmias. Studies of Purkinje-cell electrophysiology show multiple mechanisms responsible for ventricular arrhythmias, including enhanced automaticity, triggered activity and reentry. The variation in functional properties of Purkinje cells in different areas of the His-Purkinje system underlie the propensity for reentry within Purkinje fibres in structurally normal and abnormal hearts. Catheter ablation is an effective therapy in nearly all forms of reentrant arrhythmias involving Purkinje tissue. However, identifying those at risk of developing fascicular arrhythmias is not yet possible. Future research is needed to understand the precise molecular and functional changes resulting in these arrhythmias.

Ventricular arrhythmias involving the His-Purkinje system in the structurally abnormal heart

His-Purkinje-related ventricular arrhythmias are a subset of ventricular tachycardias that use the specialized cardiac conduction system. These arrhythmias can occur in various different forms of structural heart disease. Here, we review the basic science discoveries and their analogous clinical observations that implicate the His-Purkinje system as a crucial component of the arrhythmia circuit. While mutations serve the molecular basis for arrhythmias in the heritable cardiomyopathies, transcriptional and posttranslational changes constitute the adverse remodeling leading to arrhythmias in acquired structural heart disease. Additional studies on the electrical properties of the His-Purkinje network and its interactions with the surrounding myocardium will improve the clinical diagnosis and treatment of these arrhythmias.

[Bundle branch reentry VT : Diagnosis, mapping, and ablation]

Macroreentry in the His-Purkinje system can result in sustained ventricular tachycardia (VT) termed bundle branch reentry VT. Bundle branch reentry is usually associated with His-Purkinje disease and depressed left ventricular function. In the case of typical bundle branch reentry, the right bundle is activated in the anterograde direction and ventricular depolarization begins at the distal end of the right bundle on the ventricular septum generating a typical left bundle branch block QRS morphology. However, atypical surface ECGs can also be found in patients with severe left ventricular dysfunction and involvement of the right ventricle complicating the diagnosis of bundle branch reentry VT. It is important to diagnose bundle branch reentry VT because patients with bundle branch reentry VT may suffer from a high rate of serial implantable cardioverter defibrillator (ICD) interventions based on VT recurrences due to immediate reinitiation of the arrhythmia. Ablation of the right bundle branch easily cures bundle branch reentry VT and can prevent frequent ICD interventions. After ablation of bundle branch reentry VT, mortality remains high due to the severe left ventricular dysfunction in many patients, and the patients are candidates for cardiac resynchronization therapy (CRT-D).

Catheter-based intramyocardial delivery (NavX) of adenovirus achieves safe and accurate gene transfer in pigs

BACKGROUND

Hepatocyte growth factor (HGF) is one of the major angiogenic factors being studied for the treatment of ischemic heart diseases. Our previous study demonstrated adenovirus-HGF was effective in myocardial ischemia models. The first clinical safety study showed a positive effect in patients with severe and diffused triple coronary disease.

METHODS

12 Pigs were randomized (1:1) to receive HGF, which was administered as five injections into the infarcted myocardium, or saline (control group). The injections were guided by EnSite NavX left ventricular electroanatomical mapping.

RESULTS

The catheter-based injections caused no pericardial effusion, malignant arrhythmia or death. During mapping and injection, alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, serum creatinine and creatine kinase-MB levels have no significant increase as compared to those before and after the injection in HGF group(P>0.05). HGF group has high HGF expression with Western blot, less myocardial infarct sizes by electroanatomical mapping (HGF group versus after saline group, 5.28 ± 0.55 cm(2) versus 9.06 ± 1.06 cm(2), P<0.01), better cardiac function with Gated-Single Photon Emission Computed Tomography compared with those in saline group. Histological, strongly increased lectin-positive microvessels and microvessel density were found in the myocardial ischemic regions in HGF group.

CONCLUSION

Intramyocardial injection guided by NavX system provides a method of feasible and safe percutaneous gene transfer to myocardial infarct regions.

The risk of delayed atrioventricular and intraventricular conduction block following ablation of bundle branch reentry

BACKGROUND

The aim of the study was to determine the long-term reliability of atrioventricular and intraventricular conduction and the implications for cardiac resynchronization therapy (CRT-D) following catheter ablation of bundle branch reentry tachycardia (BBRT) and interfascicular tachycardia.

METHODS AND RESULTS

Fourteen patients with recurrent monomorphic ventricular tachycardia (VT) (n = 11) and incessant VT (n = 3) underwent catheter ablation of BBRT (n = 7), interfascicular tachycardia (n = 5) or both arrhythmias (n = 2). Successful ablation was achieved in all patients without intraprocedural atrioventricular (AV) block. Within 2 months after ablation, three patients with BBRT and pre-existing prolonged QRS developed a delayed third-degree AV block. During the follow-up of 2 years, two patients with interfascicular tachycardia developed a new left bundle branch block (LBBB) associated with worsening of heart failure. Three patients underwent upgrading of implantable cardioverter defibrillator therapy to CRT-D early after ablation which improved heart failure during the 6 months follow-up. During the long-term follow-up of 39 ± 13 months, VT storm recurred in one patient. Four of the 14 patients died of deterioration of heart failure and one had to undergo heart transplantation.

CONCLUSIONS

Catheter ablation for BBRT in patients with prolonged QRS is associated with a high risk of delayed third-degree AV block. Ablation of interfascicular tachycardia can be associated with delayed LBBB. After ablation of bundle branch reentry, patients with prolonged QRS are candidates for cardiac resynchronization therapy but the mortality remains high.

Monomorphic and polymorphic ventricular tachycardias arising from the His–Purkinje system: what do we know?

Monomorphic and polymorphic Purkinje-related ventricular tachycardias (VTs) may occur in patients with and without underlying structural heart disease. Monomorphic Purkinje-related VTs can be divided into different entities: verapamil-sensitive left fascicular VTs; bundle branch reentry tachycardias (BBRT); interfascicular VTs and focal Purkinje VTs. The most frequent fascicular VT is left posterior fascicular VT, characterized by macro-reentry within the posterior Purkinje network. However, the reentry may also be located in the anterior Purkinje network (left anterior fascicular VT). BBRT is also a macro-reentry-tachycardia, utilizing both the right and the left bundle branch as the antegrade and the retrograde limb and is often associated with pre-existing conduction disturbances in the specific conduction system. Interfascicular VT is rare and characterized by a macro-reentry within the left fascicles. BBRT and interfascicular VT may also occur in the same patient. In contrast to the mentioned macro-reentry mechanisms there are focal Purkinje-related VTs arising from the anterior or posterior Purkinje system. Focal Purkinje triggered premature ventricular contractions originating from the distal Purkinje arborization in patients without a structural heart disease, as well as in patients with known ischemic heart disease or an underlying channelopathy such as Brugada syndrome may induce polymorphic VTs. Catheter ablation is an effective treatment option for both monomorphic as well as polymorphic Purkinje-related VTs, often resulting in noninducibility and freedom from VT recurrence. A systematic analysis of the surface ECG and the intracardiac electrograms is essential for successful ablation of these heterogeneous and potentially curable VTs.