What is the Difference Between Polymorphic and Monomorphic Ventricular Tachycardia

The key difference between polymorphic and monomorphic ventricular tachycardia is that polymorphic ventricular tachycardia is a type of abnormally fast heart rate with a continuously varying QRS complex morphology in a surface electrocardiogram, while monomorphic ventricular tachycardia is a type of abnormally fast heart rate with uniform QRS complexes within each lead in a surface electrocardiogram.

Ventricular tachycardia (VT) refers to a heart rate greater than 100 beats per minute, which usually begins in the ventricles. It can be classified into various ways based on duration, morphology, and hemodynamic effect. For example, there are two types of VT based on duration as sustained and non-sustained. Sustained VT lasts longer than 30 seconds, while non-sustained VT lasts less than 30 seconds.  Moreover, based on morphology, ventricular tachycardia can be classified as polymorphic ventricular tachycardia and monomorphic ventricular tachycardia.

CONTENTS

1. Overview and Key Difference
2. What is Polymorphic Ventricular Tachycardia
3. What is Monomorphic Ventricular Tachycardia
4. Similarities – Polymorphic and Monomorphic Ventricular Tachycardia
5. Polymorphic vs Monomorphic Ventricular Tachycardia in Tabular Form
6. Summary – Polymorphic vs Monomorphic Ventricular Tachycardia

What is Polymorphic Ventricular Tachycardia?

Polymorphic ventricular tachycardia (PVT) is a type of abnormally fast heart with a continuously varying QRS complex morphology in an electrocardiogram. Therefore, QRS complexes vary in amplitude, axis, and duration in PVT. When ventricular tachycardia originates in different places around the ventricle, it is termed polymorphic ventricular tachycardia. Torsade de Pointes is a very popular example of a life-threatening polymorphic ventricular tachycardia. It is also known as ventricular tachycardia (tachyarrhythmia), with a rapidly changing rate and rhythm of a heart. The rate can change between 150 to 250 beats per minute in polymorphic ventricular tachycardia. This type of tachycardia may spontaneously revert to normal or progress into ventricular fibrillation.

Ventricular fibrillation is a more severe type of ventricular tachycardia. In this case, there is a rapid and sporadic beat. This results in immediate hemodynamic collapse. Therefore, death is likely within minutes of ventricular fibrillation unless advanced cardiac life support measures are given immediately. Polymorphic ventricular tachycardia is likely the most common form of ventricular tachycardia in the critical care setting. The presence of polymorphic ventricular tachycardia can be due to a serious heart disease condition like myocardial ischemia, cardiomyopathies or a genetic arrhythmia syndrome. Furthermore, polymorphic ventricular tachycardia is best treated with intravenous magnesium, removing offending drugs or correcting potassium and calcium imbalances.

What is Monomorphic Ventricular Tachycardia?

Monomorphic ventricular tachycardia (MVT) is a type of abnormally fast heart rate which records identical QRS complexes in an electrocardiogram. Therefore, the QRS complexes are uniform in MVT. When ventricular tachycardia repeatedly originates in the same place of the ventricle, it is classified as monomorphic ventricular tachycardia. MVT is a simple, rapid heart rate with an ectopic beat originating in the ventricle. Patients with underlying structural heart disease most commonly show monomorphic ventricular tachycardia. There is typically a zone of slow conduction that is due to scarring or fibrillar disarray in this ventricular tachycardia.

Causes of monomorphic ventricular tachycardia include prior infarction, any primary cardiomyopathy, surgical scar, hypertrophy, and muscle degeneration. Moreover, an unstable patient with monomorphic ventricular tachycardia should be immediately treated with synchronized direct current cardioversion. In addition, antiarrhythmic drugs such as amiodarone, beta-blockers, propranolol, sedation, and catheter ablation are also used as a treatment for monomorphic ventricular tachycardia

Similarities Between Polymorphic and Monomorphic Ventricular Tachycardia

• Polymorphic and monomorphic ventricular tachycardia are two types of ventricular tachycardia based on morphology.
• Both conditions begin in the ventricles.
• These conditions show abnormal fast heart rate.
• They can be due to a disease in the heart.
• They are treatable with antiarrhythmic drugs.

Difference Between Polymorphic and Monomorphic Ventricular Tachycardia

Polymorphic ventricular tachycardia is a type of abnormally fast heart rate where there are varying QRS complexes in electrocardiograms, while monomorphic ventricular tachycardia is a type of abnormally fast heart rate where there are uniform QRS complexes within each lead in electrocardiograms. So, this is the key difference between polymorphic and monomorphic ventricular tachycardia. Furthermore, ventricular tachycardia originates in different places around the ventricle in PVT, while ventricular tachycardia repeatedly originates in the same place of the ventricle in MVT.

The below infographic tabulates the differences between polymorphic and monomorphic tachycardia in tabular form for side by side comparison.

Summary – Polymorphic vs Monomorphic Ventricular Tachycardia

Ventricular tachycardia refers to a heart rate greater than 100 beats per minute which usually begin in the ventricles. Based on morphology, ventricular tachycardia can be classified as polymorphic ventricular tachycardia and monomorphic ventricular tachycardia. In polymorphic ventricular tachycardia, QRS complexes show a varying morphology in an ECG.  In monomorphic ventricular tachycardia, QRS complexes are identical in an ECG. Moreover, ventricular tachycardia originates in different places around the ventricle in PVT, while ventricular tachycardia originates at the same place of the ventricle in MVT. Thus, this summarizes the difference between polymorphic and monomorphic ventricular tachycardia.

Reference:

1. “Polymorphic Ventricular Tachycardia.” An Overview | ScienceDirect Topics.
2. “Monomorphic Ventricular Tachycardia.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Torsades de Pointes TdP” By Jer5150 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “RVOT Tachycardia” – The original uploader was Ksheka at English Wikipedia. – Transferred from en.wikipedia to Commons. (CC BY-SA 3.0) via Commons Wikimedia