What are the causes of Ventricular Tachycardia (VT) storm?

Causes of Ventricular Tachycardia Storm

Ventricular tachycardia (VT) storm is primarily caused by acute myocardial ischemia, electrolyte abnormalities, decompensated heart failure, and drug toxicity, with immediate correction of these underlying triggers being essential for successful management.

Definition

VT storm is defined as three or more distinct episodes of sustained ventricular tachycardia, ventricular fibrillation, or appropriate implantable cardioverter-defibrillator (ICD) shocks occurring within a 24-hour period 1, 2.

Primary Causes

Cardiac Causes

• Acute myocardial ischemia/infarction: The most common trigger for VT storm 3, 4
• Decompensated heart failure: Progressive ventricular dysfunction can precipitate VT storm 3
• Structural heart disease:
  • Prior myocardial infarction with scar tissue
  • Dilated cardiomyopathy
  • Hypertrophic cardiomyopathy
  • Arrhythmogenic right ventricular cardiomyopathy 4

Electrolyte and Metabolic Disturbances

• Electrolyte abnormalities:
  • Hypokalemia
  • Hypomagnesemia
  • Hypocalcemia 4, 5
• Acid-base disturbances: Acidosis can trigger or exacerbate VT storm 5

Medication-Related Causes

• Proarrhythmic effects of antiarrhythmic drugs: Particularly Class I and III agents 4
• QT-prolonging medications: Can precipitate torsades de pointes 4
• Drug toxicity: Particularly digitalis toxicity (can cause bidirectional VT) 4

Endocrine Disorders

• Thyroid disorders: Both hyperthyroidism and hypothyroidism can trigger arrhythmias 4
• Pheochromocytoma: Catecholamine excess can precipitate VT 4
• Acromegaly: Associated with increased risk of ventricular arrhythmias 4

Other Causes

• Sympathetic nervous system activation: Central to initiation and maintenance of VT storm 2
• Bradycardia-induced polymorphic VT: Particularly in patients with long QT syndrome 3
• Systemic inflammatory response syndrome: Can trigger VT in patients with underlying heart disease 3
• Coronavirus disease (COVID-19): Associated with increased risk of VT/VF storm through multiple mechanisms including myocarditis, systemic inflammation, and hypoxia 6
• Genetic channelopathies:
  • Long QT syndrome
  • Brugada syndrome
  • Short QT syndrome 4

Morphological Classification

VT storm can present as:

1. Monomorphic VT: Single QRS morphology, often related to structural heart disease and scar-related reentry 7
2. Polymorphic VT: Changing QRS morphology, which can be further classified as:
   • Torsades de pointes (associated with long QT)
   • Ischemia-related polymorphic VT (usually with short QT)
   • Polymorphic VT of unknown cause 4

Clinical Implications

Understanding the cause of VT storm is critical for effective management. The ACC/AHA/ESC guidelines emphasize that:

• Patients with sustained monomorphic VT in the presence of antiarrhythmic drugs or electrolyte abnormalities should be evaluated thoroughly, as these factors should not be assumed to be the sole cause of VT 4
• Patients who experience polymorphic VT associated with QT prolongation due to medications should avoid all agents that prolong QT interval 4
• Myocardial revascularization alone is typically insufficient therapy except in patients with VF associated with acute ischemia who have normal ventricular function and no history of MI 4

Important Considerations

• VT storm carries a poor prognosis with significantly increased mortality 2
• Patients with reduced left ventricular ejection fraction are at higher risk for VT storm 3
• The presence of multiple comorbidities increases the risk and complexity of management 6
• Early recognition and aggressive management of underlying causes are essential for improving outcomes 5

Understanding these causes allows for targeted therapy and prevention strategies to reduce the significant morbidity and mortality associated with VT storm.