What is SCAR (Scar-related Ventricular Tachycardia) VT?

Scar-Related Ventricular Tachycardia (SCAR VT)

Scar-related ventricular tachycardia is a life-threatening arrhythmia that occurs when electrical circuits form within myocardial scar tissue, creating reentry pathways that sustain abnormal ventricular rhythms, and requires aggressive management with catheter ablation as the preferred treatment for recurrent episodes.

Definition and Pathophysiology

Scar-related ventricular tachycardia (VT) is a specific type of ventricular arrhythmia that originates from areas of myocardial scarring. This condition is characterized by:

• Mechanism: Reentrant circuit within or around scar tissue
• Substrate: Myocardial scar from previous infarction, cardiomyopathy, or other structural heart disease
• Electrophysiology: Slow conduction through channels within the scar creates critical isthmuses that support reentry
• Morphology: Typically monomorphic VT with consistent QRS appearance during episodes

The reentry circuit may span several centimeters and can involve endocardial, mid-myocardial, or epicardial layers in a complex three-dimensional structure 1.

Clinical Presentation

Patients with scar-related VT may present with a spectrum of symptoms:

• Asymptomatic: Detected incidentally on monitoring (35% of cases)
• Mild symptoms: Palpitations (57%), mild lightheadedness (35%)
• Moderate symptoms: Dyspnea (25%), chest pain (27%)
• Severe symptoms: Near-syncope (15%), syncope (15%)
• Life-threatening: Sudden cardiac death, electrical storm

The severity of symptoms correlates with VT rate and underlying heart disease severity 2. Importantly, the absence of severe symptoms does not rule out VT, as approximately 50% of patients may have mild or no cerebral symptoms 2.

Diagnosis

Diagnosis of scar-related VT involves:

1. 12-lead ECG: During tachycardia to document VT morphology

   • Typically shows monomorphic VT
   • QRS morphology determined by exit site of reentry circuit
   • Can aid in mapping and ablation procedures

2. Cardiac imaging:

   • Cardiac MRI: Gold standard for identifying scar tissue
   • Echocardiography: Assesses structural abnormalities and LV function

3. Electrophysiologic study:

   • Confirms diagnosis
   • Maps reentry circuits
   • Guides ablation strategy

Management

Acute Management

For acute termination of scar-related VT:

1. Electrical cardioversion/defibrillation: First-line therapy for hemodynamically unstable VT 1

2. Antiarrhythmic medications:

   • Amiodarone: 150 mg IV over 10 minutes, followed by infusion of 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours 3
   • Lidocaine: May be considered for recurrent sustained VT not responding to beta-blockers or amiodarone 1
   • Beta-blockers: Should be administered during hospital stay and continued thereafter 1

Definitive Management

Catheter ablation is recommended as the definitive treatment for patients with scar-related VT who have recurrent episodes despite optimal medical therapy 1, 3. Specific indications include:

1. Urgent catheter ablation is recommended for:

   • Incessant VT or electrical storm
   • Recurrent ICD shocks due to sustained VT 1, 3

2. Catheter ablation should be considered after a first episode of sustained VT in patients with ischemic heart disease and an ICD 1

3. Ablation techniques:

   • Activation mapping: During ongoing VT
   • Substrate ablation: In sinus rhythm using 3D electroanatomical mapping
   • Ablation strategies: Point-by-point ablation at exit sites, linear lesions across isthmuses, or scar homogenization 1, 3
   • Epicardial approach: Often required in non-ischemic cardiomyopathy 1

4. ICD implantation: Recommended for prevention of sudden cardiac death in patients with documented sustained VT who are receiving optimal medical therapy 1

Medical Therapy

Long-term medical therapy includes:

• Beta-blockers: First-line therapy, should be continued after hospital discharge 1
• Amiodarone: Effective for prevention of recurrent VT but has significant long-term side effects 3
• Sotalol: Alternative for patients who cannot tolerate amiodarone 1

Outcomes and Prognosis

• Acute success rates of catheter ablation range from 41% to 81% 3
• Freedom from VT at 6 months ranges from 46% to 53% 3
• Better outcomes in post-MI scar compared to non-ischemic cardiomyopathy 3
• Recurrence risk: Higher in patients who were on amiodarone before ablation and then discontinued the medication (44% vs 22%) 4

Special Considerations

1. Electrical storm: Defined as ≥3 episodes of sustained VT within 24 hours, requires urgent intervention

   • Consider LV assist device or extracorporeal life support in hemodynamically unstable patients 1

2. Multiple VT morphologies: Common in patients with extensive scarring

   • May require more extensive ablation strategies

3. Failed endocardial ablation: Consider epicardial approach, especially in non-ischemic cardiomyopathy 1, 3

4. Potential complications of catheter ablation:

   • Damage to coronary vasculature
   • Inadvertent puncture of surrounding organs
   • Left phrenic nerve palsy
   • Pericardial tamponade 1

Conclusion

Scar-related VT represents a significant management challenge requiring a systematic approach. Early recognition and appropriate referral for catheter ablation are critical for reducing mortality and improving quality of life in affected patients.