How is catheter ablation planned for ventricular tachycardia?

Planning Catheter Ablation for Ventricular Tachycardia

Catheter ablation for ventricular tachycardia requires detailed mapping of the arrhythmia substrate, identification of critical isthmuses within reentry circuits, and selection of appropriate ablation techniques based on the underlying heart disease and VT mechanism. 1

Patient Selection and Pre-Procedure Assessment

• Indications for VT ablation:

  • Incessant VT or electrical storm (urgent indication) 2
  • Recurrent ICD shocks due to sustained VT 2
  • Symptomatic sustained monomorphic VT refractory to medications 2
  • Bundle branch reentrant VT 2
  • VT in patients with ICD receiving multiple shocks not manageable by reprogramming 2

• Pre-procedure evaluation:

  • Cardiac imaging (preferably MRI) to identify structural abnormalities and scar tissue 2
  • 12-lead ECG during VT to determine morphology and likely origin 1
  • Assessment of left ventricular function
  • Electrolyte status optimization
  • Anticoagulation management

Mapping Techniques

The mapping approach depends on the VT mechanism and hemodynamic stability:

1. Activation Mapping (for hemodynamically stable VT):

   • Performed during ongoing VT 2
   • Maps the electrical activation sequence to identify the critical isthmus
   • Requires patient to be in VT during mapping, which may not be tolerated

2. Substrate Mapping (for unstable VT):

   • Performed during sinus rhythm 2
   • Uses 3D electroanatomical mapping to identify abnormal ventricular tissue
   • Identifies low-voltage areas representing scar tissue
   • Locates abnormal electrograms (fractionated, late potentials)

3. Pace Mapping:

   • Compares QRS morphology during pacing with clinical VT
   • Useful for identifying exit sites of VT circuits

4. Non-contact Mapping:

   • Useful for hemodynamically unstable VT 2
   • Creates virtual electrograms without direct contact with the myocardium

Ablation Strategies

The ablation strategy depends on the underlying substrate:

1. Scar-Related VT (post-MI, cardiomyopathy):

   • Point-by-point ablation at the exit site of the reentry circuit 2
   • Linear lesion sets across identified isthmuses 2
   • Scar homogenization (ablation of all abnormal potentials within scar) 2
   • Success rates range from 41-81% acutely, with 46-53% freedom from VT at 6 months 1

2. Idiopathic VT (structurally normal heart):

   • Focal ablation targeting earliest activation site
   • Common locations: right ventricular outflow tract, left ventricular outflow tract 3
   • Higher success rates compared to scar-related VT 3

3. Bundle Branch Reentry VT:

   • Ablation of the right bundle branch
   • High success rates with low recurrence 2

Access Considerations

• Endocardial approach: Standard for most VT ablations
• Epicardial approach: Often required for:
  • DCM or ARVC patients 2
  • Failed endocardial ablation
  • Epicardial substrate suspected based on ECG or imaging
  • Requires pericardial puncture with associated risks 2

Procedural Considerations

• Anesthesia: General anesthesia often preferred for complex procedures
• Hemodynamic support: Consider mechanical support (IABP, ECMO, Impella) for unstable patients
• Anticoagulation: Heparinization for left-sided procedures
• Imaging guidance: Integration of pre-procedural imaging with electroanatomical mapping

Potential Complications

• Damage to coronary vasculature (especially with epicardial approach) 2
• Inadvertent puncture of surrounding organs during epicardial access 2
• Left phrenic nerve palsy 2
• Pericardial tamponade 2
• Vascular access complications
• AV block (particularly with septal VTs)
• Stroke or systemic embolism

Post-Procedure Management

• Continuous cardiac monitoring for 24-48 hours 1
• Maintenance antiarrhythmic therapy for 6-24 hours 1
• Consideration of chronic oral antiarrhythmic therapy 1
• ICD programming review if applicable
• Follow-up imaging to assess for complications

Efficacy Considerations

• Better outcomes in post-MI scar compared to non-ischemic cardiomyopathy 1
• Multiple VTs often present in patients with extensive structural heart disease 2
• Catheter ablation may be palliative rather than curative in complex cases 2
• Consider ICD implantation in eligible patients undergoing ablation 1

Catheter ablation for VT requires specialized expertise and should be performed in centers with experience in complex electrophysiology procedures, as mapping and ablation techniques differ significantly depending on the type of VT and underlying cardiac pathology.