Monomorphic Ventricular Tachycardia vs. Polymorphic Ventricular Tachycardia

Attribute	Monomorphic Ventricular Tachycardia	Polymorphic Ventricular Tachycardia
Definition	Regular, wide QRS complex tachycardia originating from a single focus in the ventricles.	Irregular, wide QRS complex tachycardia with a changing morphology caused by multiple ventricular foci.
QRS Complex	Consistently similar QRS morphology.	Varies in shape and amplitude from beat to beat.
Heart Rate	Usually regular and fast, typically between 150-250 beats per minute.	Usually irregular and fast, typically between 150-250 beats per minute.
Causes	Scar tissue from previous heart attack, structural heart disease, electrolyte imbalances, certain medications.	Long QT syndrome, electrolyte imbalances, certain medications, ischemia, genetic disorders.
Risk Factors	Previous heart attack, structural heart disease, older age, male gender.	Family history of sudden cardiac death, long QT syndrome, electrolyte imbalances.
Treatment	Antiarrhythmic medications, catheter ablation, implantable cardioverter-defibrillator (ICD).	Correct underlying cause, antiarrhythmic medications, implantable cardioverter-defibrillator (ICD).

Introduction

Ventricular tachycardia (VT) is a potentially life-threatening arrhythmia characterized by rapid and abnormal heart rhythms originating from the ventricles. It can be classified into two main types: monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT). While both conditions involve abnormal electrical activity in the ventricles, they differ in several key attributes, including their underlying mechanisms, ECG characteristics, clinical presentations, and treatment approaches.

Monomorphic Ventricular Tachycardia

MVT is a regular and sustained ventricular tachycardia with a consistent QRS morphology. It typically arises from a single focus or a reentrant circuit within the ventricles. The most common underlying causes of MVT include coronary artery disease, prior myocardial infarction, cardiomyopathies, and structural heart diseases. The ECG characteristics of MVT show a consistent QRS complex morphology, with a ventricular rate usually between 120 and 200 beats per minute. The QRS complexes are typically wide (>0.12 seconds) and have a uniform appearance throughout the tachycardia episode.

Clinically, patients with MVT may present with symptoms such as palpitations, dizziness, chest discomfort, and syncope. In some cases, MVT can degenerate into ventricular fibrillation, a life-threatening arrhythmia that requires immediate defibrillation. Diagnosis of MVT is confirmed by analyzing the ECG, which shows a regular and wide QRS complex tachycardia with a consistent morphology. Treatment options for MVT include antiarrhythmic medications, catheter ablation, and implantable cardioverter-defibrillator (ICD) placement to prevent sudden cardiac death.

Polymorphic Ventricular Tachycardia

PVT, also known as "torsades de pointes," is a ventricular tachycardia characterized by a constantly changing QRS morphology. It is typically caused by abnormalities in ventricular repolarization, such as prolonged QT intervals, electrolyte imbalances, medications, or inherited channelopathies. Unlike MVT, PVT does not have a consistent QRS morphology and can present with a twisting pattern on the ECG. The ventricular rate in PVT can vary widely, ranging from 150 to 250 beats per minute.

Clinically, PVT can manifest with symptoms similar to MVT, including palpitations, dizziness, and syncope. However, PVT is more prone to degenerate into ventricular fibrillation due to its unstable nature. Diagnosis of PVT is made by analyzing the ECG, which shows a polymorphic QRS complex tachycardia with a constantly changing morphology. Treatment of PVT involves addressing the underlying cause, correcting electrolyte imbalances, discontinuing offending medications, and potentially using antiarrhythmic medications or ICD placement to prevent sudden cardiac death.

Comparison

While both MVT and PVT are forms of ventricular tachycardia, they differ in several important aspects:

Underlying Mechanism

MVT is typically caused by a single focus or a reentrant circuit within the ventricles, often associated with structural heart diseases. In contrast, PVT is primarily related to abnormalities in ventricular repolarization, such as prolonged QT intervals or electrolyte imbalances.

ECG Characteristics

MVT presents with a regular and sustained ventricular tachycardia, characterized by a consistent QRS morphology. The QRS complexes are typically wide and have a uniform appearance throughout the tachycardia episode. On the other hand, PVT shows a constantly changing QRS morphology, often presenting with a twisting pattern on the ECG. The ventricular rate in PVT can vary widely.

Clinical Presentation

Both MVT and PVT can present with similar symptoms, including palpitations, dizziness, chest discomfort, and syncope. However, PVT is more prone to degenerate into ventricular fibrillation due to its unstable nature.

Diagnosis

Diagnosis of MVT is confirmed by analyzing the ECG, which shows a regular and wide QRS complex tachycardia with a consistent morphology. In contrast, the diagnosis of PVT is made by analyzing the ECG, which shows a polymorphic QRS complex tachycardia with a constantly changing morphology.

Treatment

Treatment options for MVT include antiarrhythmic medications, catheter ablation, and ICD placement to prevent sudden cardiac death. On the other hand, the management of PVT involves addressing the underlying cause, correcting electrolyte imbalances, discontinuing offending medications, and potentially using antiarrhythmic medications or ICD placement.

Conclusion

In summary, monomorphic ventricular tachycardia (MVT) and polymorphic ventricular tachycardia (PVT) are two distinct forms of ventricular tachycardia with different underlying mechanisms, ECG characteristics, clinical presentations, and treatment approaches. While MVT is characterized by a regular and sustained ventricular tachycardia with a consistent QRS morphology, PVT presents with a constantly changing QRS morphology and is more prone to degenerate into ventricular fibrillation. Accurate diagnosis and appropriate management of these conditions are crucial to prevent life-threatening complications and improve patient outcomes.