What is scar VT (Ventricular Tachycardia)?

Scar-Related Ventricular Tachycardia (VT)

Scar-related ventricular tachycardia is a reentrant arrhythmia that occurs when myocardial scar tissue creates areas of slow conduction, forming complex three-dimensional circuits that facilitate sustained monomorphic VT. 1

Pathophysiology

• Myocardial scarring (most commonly from prior infarction, cardiomyopathy, or cardiac surgery) creates the substrate for VT by forming areas of slow conduction that facilitate reentrant circuits 1, 2
• The reentry circuit typically spans several centimeters and can involve endocardial, midmyocardial, or epicardial tissue in a complex three-dimensional structure 1
• The critical isthmus (area of slow conduction) within the VT reentry circuit is the primary target for ablation therapy 1
• QRS morphology during VT is determined by the exit site where reentry wavefronts propagate from the scar to depolarize the ventricular myocardium 1

Clinical Characteristics

• Presents as sustained monomorphic VT, though multiple VT morphologies may be induced in the same patient 1
• May cause hemodynamic instability, syncope, or electrical storm (recurrent VT/VF with frequent appropriate ICD firing) 1
• Can significantly impair quality of life, especially when associated with ICD shocks 1
• While most commonly associated with left ventricular scars, can exceptionally arise from right ventricular free-wall scars in post-infarction patients 3

Diagnostic Approach

• 12-lead ECG during VT provides valuable information about the exit site of the reentry circuit 1
• Cardiac magnetic resonance imaging (CMR) with delayed enhancement is the preferred non-invasive imaging modality to identify and characterize myocardial scar 1
• Scar size >5% of left ventricular mass is associated with significantly increased risk of arrhythmic events, independent of ejection fraction 1
• Electrophysiological studies with 3D electroanatomical mapping help delineate scar tissue and identify critical isthmuses 1, 4
• Local abnormal ventricular activities (LAVAs) can be found in VT isthmus but also in non-critical areas, with the VT isthmus typically located in areas where LAVAs overlap between different activation wavefronts 4

Management

Acute Management

• Direct current cardioversion is recommended for patients presenting with sustained VT and hemodynamic instability 1
• For stable VT, antiarrhythmic medications may be considered, though electrical cardioversion remains first-line 1

Long-term Management

• Implantable Cardioverter Defibrillator (ICD) effectively terminates VT but does not prevent arrhythmia recurrence 1
• ICD shocks are associated with higher mortality and impaired quality of life 1
• Urgent catheter ablation is recommended in patients with scar-related heart disease presenting with incessant VT or electrical storm 1
• Catheter ablation is recommended in patients with ischemic heart disease and recurrent ICD shocks due to sustained VT 1
• Ablation should be considered after a first episode of sustained VT in patients with ischemic heart disease and an ICD 1

Ablation Techniques

• Techniques include point-by-point ablation at the exit site of the reentry circuit (scar dechanneling), deployment of linear lesion sets, and ablation of local abnormal ventricular activity for scar homogenization 1
• More extensive ablation with more lesions (28 ± 8 vs. 12 ± 8) and creation of linear lesions rather than focal lesions are associated with better success rates and lower recurrence rates 5
• Functional-based substrate mapping may improve specificity in localizing arrhythmogenic regions within the scar 4
• Surgical ablation guided by electrophysiological mapping is recommended in patients with VT refractory to antiarrhythmic drugs after failed catheter ablation 1

Special Considerations

• Epicardial mapping and ablation are more often required in patients with dilated cardiomyopathy 1
• Potential complications of epicardial procedures include damage to coronary vasculature, inadvertent puncture of surrounding organs, left phrenic nerve palsy, or pericardial tamponade 1
• Psychological assessment and treatment of distress are recommended in patients with recurrent ICD shocks 1
• Emerging therapeutics include stereotactic arrhythmia radioablation, gene therapy, artificial intelligence, and precision medicine approaches 2

Prognosis

• Catheter ablation decreases the likelihood of subsequent ICD shocks and prevents recurrent episodes of VT in patients with ischemic heart disease 1
• Beta-blocker therapy combined with amiodarone can reduce the number of ICD shocks, though side effects may limit use 1
• Quality of life issues should be discussed before ICD implantation and during disease progression 1