Polymorphic Ventricular Tachycardia (VT)

Introduction

Polymorphic ventricular tachycardia (VT) is a life-threatening arrhythmia characterized by a rapid and irregular heartbeat originating from the ventricles of the heart. It is called "polymorphic" because the QRS complexes on an ECG vary in shape and amplitude. This condition requires urgent medical attention as it may lead to ventricular fibrillation and sudden cardiac arrest.

Causes of Polymorphic VT

The causes of polymorphic VT can be divided into two main categories:

1. Torsades de Pointes (TdP)

• Prolonged QT interval: The most common form of polymorphic VT associated with QT prolongation.
• Electrolyte imbalances: Low potassium (hypokalemia) and low magnesium (hypomagnesemia).
• Medications: Certain antiarrhythmics, antibiotics (e.g., macrolides, fluoroquinolones), and psychotropic drugs can prolong the QT interval.
• Congenital Long QT Syndrome: A genetic condition predisposing individuals to TdP.

2. Polymorphic VT with a Normal QT Interval

• Ischemic heart disease: Acute myocardial infarction or coronary artery disease can induce polymorphic VT.
• Catecholaminergic polymorphic VT (CPVT): A rare genetic disorder triggered by physical activity or emotional stress.
• Structural heart diseases: Cardiomyopathies, myocarditis, or valvular heart disease.

Diagnosis

Electrocardiogram (ECG)

• Torsades de Pointes: QRS complexes appear to twist around the isoelectric line due to prolonged QT interval.
• Polymorphic VT without QT prolongation: Irregular wide-complex tachycardia with varying morphology.

Additional Diagnostic Tests

• Electrolyte levels: To check for hypokalemia and hypomagnesemia.
• Genetic testing: If congenital long QT syndrome or CPVT is suspected.
• Coronary angiography: If ischemic heart disease is suspected.
• Echocardiogram and cardiac MRI: To assess structural abnormalities.

Treatment

Acute Management

• Unstable patients (hypotension, loss of consciousness): Immediate defibrillation.
• Torsades de Pointes: Magnesium sulfate IV, potassium repletion, withdrawal of QT-prolonging medication.
• Ischemic VT: Anti-ischemic therapy (e.g., beta-blockers, revascularization if needed).

Long-Term Management

• Beta-blockers: First-line therapy for CPVT and long QT syndrome.
• Implantable Cardioverter-Defibrillator (ICD): For patients at high risk of sudden cardiac death.
• Lifestyle modifications: Avoid QT-prolonging drugs, correct electrolyte imbalances, and avoid intense physical activity if CPVT is diagnosed.

Conclusion

Polymorphic VT is a serious arrhythmia that requires prompt recognition and management. Early diagnosis, identification of the underlying cause, and appropriate treatment strategies are crucial in preventing life-threatening complications.

Source recommendations

1. American Heart Association Guidelines on Ventricular Arrhythmias

1. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
2. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/tachycardia--fast-heart-rate
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193
4. https://cpr.heart.org/en/resuscitation-science/cpr-and-ecc-guidelines/algorithms
5. https://www.heart.org/en/health-topics/arrhythmia/about-arrhythmia/ventricular-fibrillation

2. European Society of Cardiology Guidelines on Ventricular Arrhythmias

1. https://www.escardio.org/Guidelines/Clinical-Practice-Guidelines/Ventricular-Arrhythmias-and-the-Prevention-of-Sudden-Cardiac-Death
2. https://academic.oup.com/eurheartj/article/43/40/3997/6675633
3. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000549
4. https://pubmed.ncbi.nlm.nih.gov/36017572/
5. https://www.sciencedirect.com/science/article/pii/S2405500X22010945