What are the uncommon (niche) causes of ventricular tachycardia?

Uncommon Causes of Ventricular Tachycardia

Beyond the typical ischemic and structural heart disease etiologies, niche causes of VT include inherited channelopathies, inflammatory cardiac diseases, endocrine disorders, valvular disease, tachycardia-induced cardiomyopathy, and idiopathic forms occurring in structurally normal hearts.

Inherited Ion Channelopathies

• Long QT syndrome is a critical niche cause, with women having significantly higher risk than men (70% of Long QT Registry subjects are female), and post-pubertal females experiencing predominant cardiac arrests and syncope 1
• Brugada syndrome causes polymorphic VT and sudden death, typically in patients without apparent structural heart disease 2, 3
• Catecholaminergic polymorphic VT (CPVT) presents as bidirectional VT, polymorphic VT, or catecholaminergic ventricular fibrillation, particularly in young patients 2
• These channelopathies do not respond to radiofrequency ablation and require ICD placement in high-risk patients with recurrent syncope or cardiac arrest 2

Inflammatory and Infectious Cardiac Diseases

• Myocarditis and inflammatory cardiomyopathy cause VT in up to 10% of dilated cardiomyopathy cases, with persistent viral infections constituting a major cause of progressive LV dysfunction 4
• Cardiac sarcoidosis is a rare cause (5% of non-ischemic cardiomyopathies referred for VT) with widespread RV scarring and patchier LV involvement in the basal septum and anterior wall, creating multiple re-entrant circuits 4
• Endocarditis with acute aortic regurgitation can result in sustained VT due to acute hemodynamic compromise and requires early surgical intervention 4
• Acute rheumatic fever rarely causes VT, though complete AV block during acute episodes can trigger serious ventricular arrhythmias 4

Endocrine and Metabolic Disorders

• Thyroid disorders: Hypothyroidism causes QT prolongation and VT risk, while thyrotoxicosis rarely causes VT except with electrolyte disturbances 1
• Pheochromocytoma presents with VT due to catecholamine excess and can cause reversible cardiomyopathy 1
• Electrolyte imbalances from primary aldosteronism, Addison disease, or parathyroid disorders cause arrhythmogenesis through QRS and QTc prolongation 1
• Laboratory evaluation including electrolytes, thyroid function, and catecholamine levels is necessary when these conditions are suspected 1

Valvular Heart Disease

• Post-valvular surgery VT occurs in 6% of deaths after valve replacement, with sudden death accounting for 23% of mitral valve replacement deaths and 16% of aortic valve replacement deaths 4
• Bundle branch re-entry VT should be specifically considered following valvular surgery, requiring electrophysiologic study with standby catheter ablation 4
• Valvular heart disease constituted 7% of patients referred for secondary prevention ICD implantation 4

Tachycardia-Induced Cardiomyopathy

• Chronic tachyarrhythmias themselves cause cardiomyopathy through myocardial energy depletion, abnormal calcium handling, and neurohormonal activation 4
• Atrial fibrillation is the most common cause, but any sustained supraventricular or ventricular arrhythmia (including inappropriate sinus tachycardia) can induce cardiomyopathy 4
• Tachycardia may be present for years (mean 8 years) before LV dysfunction develops, but recurrent tachycardia causes rapid decline in LV function within 6 months 4
• Critical pitfall: Sudden death has been described even after rhythm control and near-normalization of ejection fraction, suggesting persistent ultrastructural changes 4

Idiopathic VT in Structurally Normal Hearts

• Right ventricular outflow tract (RVOT) VT is the most common idiopathic form, presenting with left bundle branch block morphology and inferior axis, typically catecholamine-dependent and adenosine-sensitive 2, 3
• Idiopathic left ventricular tachycardia (fascicular VT) originates from the left ventricle, is verapamil-sensitive, and shows right bundle branch block with left axis deviation 2, 4
• Propranolol-sensitive VT may be monomorphic or polymorphic and responds to beta-blockade 2
• These idiopathic forms have excellent prognosis and are often curable with radiofrequency ablation 2, 4

Hypertrophic Cardiomyopathy

• HCM is the most common cause of sudden cardiac death in young people, with 90% of adults demonstrating complex ventricular arrhythmias including nonsustained VT in 20-30% on Holter monitoring 4, 1
• VT in HCM results from electrically unstable myocardial substrate, with risk factors including family history of sudden death, unexplained syncope, and nonsustained VT 4

Familial/Inherited Conditions

• Familial conditions with high risk for life-threatening VT include long QT syndrome and hypertrophic cardiomyopathy, warranting ICD consideration even without prior cardiac arrest 4
• Genetic factors influence susceptibility, with ACE gene deletion polymorphism (DD homozygotes) showing greater tendency to develop cardiomyopathy in the setting of tachycardia 4

Key Diagnostic Approach

• Obtain 12-lead ECG during sinus rhythm to identify QT prolongation, pre-excitation, Brugada pattern, or structural abnormalities 1
• Echocardiography is essential to evaluate for HCM, cardiomyopathy, and valvular disease 1
• Family history of sudden cardiac death or inherited arrhythmia syndromes must be elicited 1
• Consider cardiac MRI for suspected sarcoidosis or myocarditis 4