What is Paroxysmal Monomorphic Ventricular Tachycardia (PMVT)?

Paroxysmal Monomorphic Ventricular Tachycardia (PMVT)

Paroxysmal Monomorphic Ventricular Tachycardia (PMVT) is a cardiac arrhythmia characterized by three or more consecutive ventricular complexes occurring at a rate greater than 100 beats per minute with a single stable QRS morphology, which starts and terminates abruptly. 1

Definition and Characteristics

• PMVT is classified as a ventricular tachycardia (VT) with a single QRS morphology (monomorphic) that starts and stops suddenly (paroxysmal) 1
• VT is defined as a cardiac arrhythmia of three or more consecutive complexes emanating from the ventricles at a rate greater than 100 bpm (cycle length less than 600 ms) 1
• PMVT can be further categorized as nonsustained (lasting less than 30 seconds and terminating spontaneously) or sustained (lasting more than 30 seconds or requiring termination due to hemodynamic compromise) 1

Clinical Presentation

• Patients may be hemodynamically stable or unstable depending on the duration, rate, and underlying cardiac function 1
• Symptoms range from asymptomatic to severe and may include:
  • Palpitations (described as pounding or racing heartbeats) 1, 2
  • Dizziness or lightheadedness (presyncope) 1
  • Syncope (sudden loss of consciousness) 1
  • Chest discomfort or dyspnea 2
• PMVT differs from polymorphic VT, which has a changing or multiform QRS morphology 1

Mechanisms

• The most common mechanism for monomorphic VT is re-entry, where electrical impulses circulate around a fixed obstacle in a defined circuit 1
• Other mechanisms include:
  • Abnormal automaticity (enhanced pacemaker activity in cardiac cells) 1, 2
  • Triggered activity (disturbances in repolarization causing afterdepolarizations) 1, 2
• In outflow tract VT (a common form of monomorphic VT), the mechanism is often related to triggered activity arising from delayed afterdepolarizations dependent on intracellular calcium overload 1

Diagnostic Evaluation

• 12-lead ECG during tachycardia is essential for diagnosis 1
• ECG characteristics include:
  • Regular rhythm at >100 bpm
  • Wide QRS complexes (>120 ms)
  • Consistent QRS morphology throughout the episode
  • Absence of associated P waves or AV dissociation 1
• Electrophysiological testing may be reasonable for diagnostic evaluation in patients with structurally normal hearts with suspected VT 1

Management

• Treatment depends on hemodynamic stability:

  • For hemodynamically unstable PMVT: immediate direct current cardioversion is recommended 1, 3
  • For hemodynamically stable PMVT: medical management may be attempted, though direct current cardioversion remains most efficacious 3

• Medical management options include:

  • Procainamide (Class IIa recommendation): 10 mg/kg IV at 50-100 mg/min over 10-20 minutes with monitoring 1, 3
  • Amiodarone (Class IIb recommendation): for patients with heart failure or suspected ischemia 1
  • Sotalol (Class IIb recommendation): may be considered for patients with hemodynamically stable sustained monomorphic VT 1

• Long-term management:

  • Catheter ablation is useful in patients with symptomatic, drug-refractory VT or in those who do not desire long-term drug therapy 1
  • ICD implantation can be effective for termination of sustained VT in patients with normal or near-normal ventricular function who are receiving optimal medical therapy 1

Prognosis

• Prognosis varies based on:
  • Presence of structural heart disease
  • Left ventricular function
  • Underlying etiology 1
• PMVT in structurally normal hearts generally has a better prognosis than in those with structural heart disease 1, 3

Important Distinctions

• PMVT must be distinguished from polymorphic VT (which has changing QRS morphology) and torsades de pointes (polymorphic VT associated with long QT interval) 1, 4
• Unlike supraventricular tachycardias, PMVT originates from the ventricles rather than atrial tissue or AV node 1
• The presence of irregular cannon A waves and/or irregular variation in S1 intensity during a regular tachycardia strongly suggests ventricular origin 1

Clinical Pearls and Pitfalls

• Not all wide-complex tachycardias are ventricular in origin; supraventricular tachycardias with aberrant conduction can mimic VT 1
• The presence of AV dissociation strongly supports the diagnosis of VT 1
• PMVT with hemodynamic stability should not be mistaken for a benign condition, especially in patients with structural heart disease 1
• Outflow tract VT (commonly from right ventricular outflow tract) is the most common form of VT in apparently healthy people and generally has a good prognosis 1