Which patients are at risk for polymorphic ventricular tachycardia?

Patients at Risk for Polymorphic Ventricular Tachycardia

Patients at risk for polymorphic ventricular tachycardia include those with inherited cardiac channelopathies (Long QT Syndrome, Brugada Syndrome, Catecholaminergic Polymorphic VT), electrolyte abnormalities, QT-prolonging drug use, and specific structural heart conditions. 1

Primary Inherited Cardiac Channelopathies

Long QT Syndrome (LQTS)

• High-risk LQTS patients:
  • QTc interval >500 ms
  • Genotypes LQT2 and LQT3
  • Females with genotype LQT2
  • Age <40 years
  • Onset of symptoms at <10 years of age
  • History of recurrent syncope 1
• Medication triggers:
  • Use of QT-prolonging medications (antiarrhythmics, some phenothiazines, tricyclic antidepressants, certain oral macrolides) 2
• Metabolic triggers:
  • Hypokalemia
  • Hypomagnesemia 1

Catecholaminergic Polymorphic VT (CPVT)

• Patients with exercise or emotion-induced syncope
• Normal resting ECG but ventricular arrhythmias during:
  • Physical exertion
  • Emotional stress
  • Catecholamine surge 1
• Genetic predisposition (RyR2 mutations) 1

Brugada Syndrome

• Patients with:
  • Spontaneous type 1 Brugada ECG pattern (coved ST elevation in V1-V3)
  • History of cardiac arrest or syncope
  • Family history of sudden cardiac death 1
• Triggers:
  • Fever
  • Vagal stimulation
  • Sodium channel blocker administration 1

Early Repolarization Syndrome

• Patients with early repolarization pattern on ECG who have experienced:
  • Cardiac arrest
  • Sustained ventricular arrhythmias 1

Short QT Syndrome

• Rare condition with QTc interval typically <340 ms
• History of syncope or cardiac arrest 1

Drug-Induced Polymorphic VT

• QT-prolonging medications:

  • Class IA antiarrhythmics (disopyramide, quinidine, procainamide)
  • Class III antiarrhythmics (sotalol, amiodarone)
  • Certain antibiotics (macrolides)
  • Antipsychotics
  • Tricyclic antidepressants 2

• Risk factors for drug-induced Torsades de Pointes:

  • Female gender
  • Excessive QT interval prolongation
  • History of cardiomegaly or heart failure
  • Reduced creatinine clearance
  • Higher medication doses 2

Electrolyte Abnormalities

• Hypokalemia
• Hypomagnesemia
• Hypocalcemia 1, 2

Other Risk Factors

• History of ventricular tachycardia/fibrillation
• Congestive heart failure (7% risk of Torsades de Pointes in patients with sustained VT and heart failure) 2
• Bradycardia (increases risk of Torsades de Pointes) 2
• Recent acute myocardial infarction 2

Clinical Pearls and Pitfalls

• Diagnostic pitfall: Normal QTc doesn't rule out risk - up to 25% of genotype-positive LQTS patients have QTc intervals ≤440 ms 1
• Treatment pitfall: Medications appropriate for one form of polymorphic VT may be contraindicated for another - proper diagnosis is critical 3
• Screening pitfall: In suspected CPVT, exercise testing is essential as resting ECGs appear normal 1
• Management pitfall: Abrupt discontinuation of beta-blockers in patients with channelopathies can precipitate life-threatening arrhythmias 2

For patients with suspected cardiac channelopathies, genetic counseling and mutation-specific genetic testing are recommended for first-degree relatives of affected individuals to identify those at risk 1.