Makindo Medical Notes

Related Subjects: |Classical Ventricular Tachycardia |Idiopathic Ventricular Tachycardia |Right Ventricular Outflow Tract Tachycardia |Idiopathic Fascicular Left Ventricular Tachycardia |Left Ventricular Outflow Tract Tachycardia |Ventricular Fibrillation |Resuscitation - Adult Tachycardia Algorithm |Resuscitation - Advanced Life Support |Automatic Implantable Cardioverter Defibrillator (AICD)

Idiopathic ventricular tachycardia (IVT) in patients with an anatomically normal heart is a distinct entity whose management and prognosis differ from ventricular tachycardia associated with structural heart disease. Classic VT remains the most common cause of wide complex regular tachycardia—assume classic VT and its associated risks until a cardiologist has proven otherwise.

About

• Tachyarrhythmias originating below the AV node and bundle of His.
• They differ in etiology, prognosis, and treatment compared to classic VT.

Aetiology

• Can be either automatic or reentrant in mechanism.

Idiopathic VT Compared with Classic VT

• Classic VT is typically seen in older patients with ischemic heart disease (IHD) and structurally abnormal hearts.
• Classic VT usually has a QRS duration of 140–200 msec or greater.
• Idiopathic VT, including idiopathic/fascicular VTs, tends to have a QRS duration of 140 msec or less.
• Idiopathic VT may respond to Adenosine or Verapamil, which should not be used in classic VT.
• Idiopathic VTs can be further classified into 3–4 subtypes.

Subtypes

• Right Ventricular Outflow Tract (RVOT) VT: Exhibits an LBBB pattern with an inferior frontal plane axis and is usually responsive to adenosine.
• Fascicular Left Ventricular Tachycardia: A reentrant arrhythmia subdivided into:
  • Posterior Fascicle VT (PFVT): Most common subtype, typically shows RBBB with left axis deviation (LAD) and is sensitive to verapamil.
  • Anterior Fascicle VT (AFVT): Often presents with RBBB and right axis deviation (RAD).
• Left Ventricular Outflow Tract (LVOT) VT: Characterized by a RBBB pattern.
• Bundle Branch Reentrant VT (BBRVT): More commonly associated with structural heart disease and may present with features of both RBBB and LBBB.

Clinical Features

• Typically observed in younger, healthier patients compared with classical VT.
• Severe hemodynamic compromise is unusual.

Investigations

• Blood Tests: Full blood count (FBC), urea & electrolytes (U&E), magnesium (Mg), calcium (Ca), and potassium (K) are all normal.
• ECG: Shows a normal QT interval. The QRS tends to be narrower than in classic VT.
• Echocardiogram: Reveals normal cardiac structure and function.
• Chest X-ray (CXR): Normal findings.

Note: Classical VT is still by far the most common cause of wide complex regular tachycardia, and there is no perfectly reliable way to distinguish classic VT with all its dangers from idiopathic VT or SVT with aberrancy on the surface 12-lead ECG.

Summary

Management

• Initial Stabilization:
  • Follow ABC protocols and assess hemodynamic stability.
  • If the patient is unstable, have a low threshold for electrical cardioversion and seek specialist advice immediately.
• Acute Management:
  • Adenosine: May be used in stable patients if the arrhythmia is catecholamine-sensitive; however, its use is contraindicated in classical VT.
  • IV Verapamil: Administer 10 mg IV over 3–5 minutes in stable patients with proven normal left ventricular function; only use under specialist (senior consultant) guidance.
  • Beta Blockers: Can be used to help suppress the arrhythmia and control heart rate.
• Long-Term Management:
  • Radiofrequency Catheter Ablation: Recommended for patients with recurrent, symptomatic, or drug-refractory IVT, given the high cure rates (approaching 90%).
• Important Note: Treat the arrhythmia as classical VT with all its associated risks until a cardiologist confirms the diagnosis of idiopathic VT.

References

• Idiopathic Ventricular Tachycardias for the EM Physician