Abstract

Key Points

Abbreviations and Acronyms

AF

atrial fibrillation

AV

atrioventricular

CPVT

catecholaminergic polymorphic ventricular tachycardia

EP

electrophysiology

ICD

implantable cardioverter-defibrillator

VF

ventricular fibrillation

Introduction

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a heritable arrhythmia disorder most commonly caused by pathogenic variants in the cardiac ryanodine receptor RYR2.^1–9 Abnormal diastolic calcium release, in response to adrenergic stimulation, results in life-threatening ventricular arrhythmias.^10,11 Although ventricular arrhythmias in CPVT have been well characterized, less is known about whether atrial arrhythmias result in rapid conduction to the ventricles triggering the ventricular arrhythmias or whether arrhythmias within the atria and ventricles occur independently. This article presents the first known report of atrioventricular (AV) node ablation as a management strategy in a patient with suspected atrial-driven ventricular arrhythmias in CPVT. The presented evidence suggests that AV nodal ablation is not an optimal treatment modality for this patient population and indicates that atrial and ventricular arrhythmias in CPVT can occur as independent arrhythmias; hence, elimination of AV nodal conduction may not prevent ventricular tachycardia or fibrillation.

Case Report

Management

The patient underwent placement of a single-chamber implantable cardioverter-defibrillator (ICD) at an adult center. Multiple antiarrhythmic medications were attempted, including sotalol (58 mg/m²/d), amiodarone (4 mg/kg/d), and metoprolol XL (0.5 mg/kg/d); however, her atrial arrhythmias persisted. She therefore underwent an electrophysiology (EP) study by experienced adult electrophysiologists at the age of 13 years. During this study, AF could not be induced. No abnormalities were identified during mapping or with atrial voltages. Given her clinical atrial arrhythmia, although AF could not be induced, a standard pulmonary vein isolation was performed using radiofrequency ablation. Two months later, she was diagnosed with atrial flutter and underwent a repeat EP study at the same center. During this EP study, atrial flutter could not be induced, and a prophylactic cavotricuspid isthmus block was performed. She had persistent ICD discharges for both atrial arrhythmias and VF. She was then trialed on single-agent, high-dose atenolol (3.7 mg/kg/d), followed by single-agent mexiletine (8.3 mg/kg/d), and then a trial of combination nadolol (2 mg/kg/d) and verapamil sustained release (3.3 mg/kg/d). Because the VF was thought to be caused by rapid AV nodal conduction of AF, she underwent an AV nodal ablation at the age of 14 years. The nadolol and verapamil were discontinued after AV nodal ablation. Despite complete AV block and pacemaker dependence (Fig. 1), she continued to have both atrial and ventricular arrhythmias, including isolated atrial arrhythmias in the absence of ventricular tachycardia or VF (Fig. 2) and simultaneous atrial and ventricular tachycardias (Fig. 2 and 3). For this patient, ICD discharges indicated that defibrillation failed to terminate atrial or ventricular arrhythmias (Fig. 4). An important feature of CPVT is the lack of response of some arrhythmias to defibrillation^3,4; for this reason, device revision would not be recommended. Therefore, combination high-dose nadolol (4.4 mg/kg/d), verapamil sustained release (3.3 mg/kg/d), and flecainide (65 mg/m²/d) were initiated. Because of recurrent atrial and ventricular arrhythmias and persistent ICD discharges, at age 15 years, she underwent bilateral sympathetic denervation.

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Discussion

Catecholaminergic polymorphic ventricular tachycardia is one of the most malignant heritable arrhythmia syndromes.^1–9 In this case, the diagnosis may have initially been missed because her primary arrhythmia was supraventricular tachyarrhythmias rather than ventricular tachycardia. This case report offers several important learning points. Importantly, this report highlights that atrial arrhythmias can be the predominant and presenting rhythm in CPVT and should be considered in this diagnosis, particularly when seen in combination with ventricular arrhythmias. Atrial arrhythmias in CPVT have been observed even in the initial description of CPVT but have been less well characterized than ventricular arrhythmias in this disease.^2–4,6–9 It is important to consider CPVT as a diagnosis even when the presenting rhythm is an atrial tachyarrhythmia.

Second, because rapid conduction of atrial arrhythmias can cause ventricular tachyarrhythmias, AV nodal ablation as a treatment strategy has been raised for CPVT. In patients with CPVT, even among those with ICDs, it can be difficult to determine whether atrial arrhythmias are conducting rapidly to the ventricle and resulting in ventricular arrhythmias or whether the atrial and ventricular arrhythmias are occurring independently. This report demonstrates that atrial and ventricular arrhythmias can be independent and simultaneous events and, importantly, that AV nodal ablation may not be an effective treatment modality for prevention of ventricular arrhythmias in the CPVT patient population. The effectiveness of AV nodal ablation for CPVT has not been established, and this case suggests that AV nodal ablation should not be a treatment strategy in this patient population. These data may be helpful in directing future management and treatment for this disease. Last, this case report highlights how patient care can be improved when adult and pediatric centers work together to make a diagnosis, particular in genetically driven syndromes among young patients. Catecholaminergic polymorphic ventricular tachycardia is a rare but lethal disease, and these learning points will be helpful to all clinicians caring for these patients.