INTRODUCTION

Granulomatous myocarditis comprised of cardiac sarcoidosis and cardiac tuberculosis is an underrecognized entity. Diagnosis of these entities have more often been made on autopsy, highlighting the difficulty in diagnosing these conditions antemortem.^1–5 This review discusses the clinical and electrophysiological characteristics and catheter ablation of ventricular tachycardia (VT) in cardiac sarcoidosis and cardiac tuberculosis, especially pertaining to epicardial ablation.

Corticosteroids and methotrexate⁶ are the mainstay of therapy in sarcoidosis, while antitubercular therapy and corticosteroids are key therapies in tuberculosis. Therapy with disease-specific agents along with antiarrhythmic drugs prevents recurrence of VTs in more than 50% of patients in the active phase of disease.^7–11 Catheter ablation can be considered in drug refractory granulomatous myocarditis, especially if there is no ongoing inflammation. Both the diseases have a tendency for patchy involvement of the heart with granulomas infiltrating the midmyocardium and subepicardial layers of the myocardium.¹² Thus, ventricular tachyarrhythmia can arise from both the endocardial and epicardial regions of the right and left ventricle respectively.

CLINICAL AND ELECTROPHYSIOLOGIC CHARACTERISTICS OF VT IN GRANULOMATOUS MYOCARDITIS

Tachycardia in granulomatous myocarditis may vary from frequent premature ventricular contractions (PVCs), nonsustained VT (NSVT), sustained monomorphic VT (SMMVT), and incessant VT to polymorphic VT (PMVT) and ventricular fibrillation (VF).^{2,7,8,13–19} While most patients present with SMMVT, Panda et al.,²⁰ reported polymorphic VT (PLVT) in patients with cardiac sarcoidosis. The same patient can have VT morphologies differing from the index VT in the subsequent episodes indicating ongoing inflammation in the myocardium in different areas (Figure 35.1).

There are few case reports describing the electrophysiologic characteristics and catheter ablation of VT in cardiac sarcoidosis,^8,18,21–27 and an isolated case report for cardiac tuberculosis.¹⁶ Inflammation and fibrosis both participate in arrhythmogenesis. Thus, both early inflammation and scar phase of the disease could cause VTs in granulomatous myocarditis.^2,10,28–30 Triggered activity and abnormal automaticity is observed both in cardiac sarcoidosis and cardiac tuberculosis, which are attributed to inflammation.

It has been suggested that the mechanism of VT in patients with cardiac sarcoidosis is reentry occurring through surviving myocyte bundles in and around the scar.^14,21 Both these diseases are characterized by myocardial inflammation and interstitial fibrosis, which can lead to conduction slowing and macro-reentrant arrhythmias.^{17,18,21,23,24,31–33} Thus, reentrant substrate is present in both the active and inactive phase. Inducibility of VT with programmed extrastimulation also supports that it is a reentrant VT.^18,34

Inducibility of VT may not be associated with disease activity in cardiac sarcoidosis.^10,25,34,35 The surface ECG morphology of inducible VT varies in granulomatous myocarditis in that they may vary from right bundle branch block and left bundle branch morphology to PLVT and PMVT to VF.^{2,8,10,14–19,21,28} Naruse et al.⁸ demonstrated induction of Purkinje-related VTs, along with scar-related reentry VT, in their cohort of patients with cardiac sarcoidosis. All patients with Purkinje related VT had some form of conduction disease. Noda et al.²³ demonstrated a critical isthmus responsible for VT between two scar-like areas with a figure-eight pattern macroreentrant VT in a patient with cardiac sarcoidosis. Induction of nonclinical VTs in the electrophysiology laboratory is not uncommon. Multiple morphologies of VTs are induced in each patient,2,15,18,21,28,34 which is attributable to diffuse and heterogenous involvement of myocardium (Figure 35.2).

Figure 35.1 12-lead ECG of a case of cardiac sarcoidosis who was initially diagnosed as idiopathic RVOT VT (a index VT) in whom, over next few weeks, at least three different morphologies of clinical VTs were later documented (b–d). Abbreviation: RVOT VT, right ventricular outflow tract tachycardia. Used with permission from the RIM registry for granulomatous myocarditis maintained at the authors’ center with local ethics committee clearance.

Figure 35.2 A case of cardiac sarcoidosis with drug refractory VT. Twelve-lead ECG showing 18 different morphologies of VT induced in the electrophysiology lab, all with different tachycardia cycle lengths. Abbreviation: VT, ventricular tachycardia. Used with permission from the RIM registry for granulomatous myocarditis maintained at the authors’ center with local ethics committee clearance.

Recurrence rates are higher when VTs with multiple morphologies are induced.8 Abnormal signals during EAM in the form of late potentials, fragmented signals in the low-voltage areas (< 1.5V), are seen both at the site of inflammation and fibrosis.^10,21 Epicardial scars overlay and exceed the region of corresponding endocardial scar. Also, the epicardial scar may not correspond to the region of the endocardial scar.¹⁸

AUTHORS’ EXPERIENCE

Of 180 patients who presented with VT due to granulomatous myocarditis between July 2004 and March 2018, 27 underwent catheter ablation. Six patients had confirmed diagnosis of tuberculosis (culture positive). Interestingly, out of 21 patients with cardiac sarcoidosis, 10 (47.6%) required epicardial ablation with or without endocardial ablation. Among 6 patients with tuberculosis, 5 (83.3%) required epicardial ablation with or without endocardial ablation.

EPICARDIAL MAPPING AND ABLATION TECHNIQUE

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