What is the role of cardiac mapping in the diagnosis and treatment of ventricular tachycardia (VT)?

Cardiac Mapping for Ventricular Tachycardia

Cardiac mapping is essential for diagnosis and treatment of ventricular tachycardia (VT), providing precise localization of arrhythmia circuits to guide catheter ablation, which significantly reduces mortality and improves quality of life in patients with recurrent VT.

Types of Cardiac Mapping Techniques

Activation Mapping

• Performed during ongoing VT to identify the earliest site of activation and critical isthmus within the reentry circuit 1
• Gold standard for defining protected isthmus and components of VT circuit when the arrhythmia is hemodynamically tolerated 2
• Limited by non-inducibility or poor hemodynamic tolerance of clinical VT in approximately 25% of patients 2

Substrate Mapping

• Performed during sinus rhythm without requiring VT induction 1
• Uses three-dimensional electroanatomic mapping to localize abnormal ventricular tissue 1
• Allows for catheter ablation in patients with hemodynamically unstable VT 1
• Techniques include point-by-point ablation at exit sites, linear lesion deployment, or local abnormal ventricular activity ablation for scar homogenization 1

Pace Mapping

• Mimics VT by pacing at potential sites of origin 2
• Particularly useful for idiopathic VT without structural heart disease 2
• Complete 12/12 lead ECG match is important for accurate localization 2

Entrainment Mapping

• Defines protected isthmus and components of reentry circuit 2
• Successful ablation achieved in 60-90% of patients with reentrant VT 2
• Requires hemodynamically tolerated VT 2

Advanced Mapping Technologies

• Three-dimensional electroanatomic mapping systems aid in localization of abnormal tissue 1
• Non-contact mapping systems can be utilized for hemodynamically unstable VT 1, 3
• Magnetic resonance imaging can help plan and guide ablation procedures 1

Role of Cardiac Mapping in Different VT Types

Outflow Tract VT

• Precise localization should be guided by activation mapping and/or pacemapping during electrophysiological study 1
• Mapping should begin in the RVOT (including pulmonary artery sinus), followed by great cardiac veins, aortic cusps, and endocardial LVOT 1
• When ablation at a site with early ventricular activation doesn't eliminate the arrhythmia, epicardial mapping may be considered 1

Scar-Related VT

• Catheter ablation has evolved into an important treatment option for patients with scar-related heart disease presenting with VT 1
• Urgent catheter ablation is recommended in patients with scar-related heart disease presenting with incessant VT or electrical storm (Class I, Level B) 1
• Catheter ablation is recommended in patients with ischemic heart disease and recurrent ICD shocks due to sustained VT (Class I, Level B) 1
• Catheter ablation should be considered after a first episode of sustained VT in patients with ischemic heart disease and an ICD (Class IIa, Level B) 1

Idiopathic VT

• Catheter ablation by experienced operators is recommended as first-line treatment in symptomatic patients with idiopathic left VTs (Class I, Level B) 1
• For papillary muscle tachycardia, catheter ablation under echo guidance by experienced operators should be considered after failure of medical therapy 1

Mapping Approaches Based on Cardiac Anatomy

Endocardial vs. Epicardial Mapping

• Epicardial mapping and ablation are more often required in patients with dilated cardiomyopathy or ARVC undergoing VT ablation 1
• Combined epicardial and endocardial mapping strategy helps delineate the myocardial substrate for recurrent VT in both ischemic and nonischemic cardiomyopathy 4
• Patients with ischemic cardiomyopathy tend to have larger endocardial than epicardial scars 4

Outflow Tract Mapping

• RVOT-VT/PVC catheter ablation success rates exceed 95% in patients without structural heart disease when performed by experienced operators 1
• LVOT-VT/PVC ablation requires careful mapping of the LVOT, aortic cusps, pulmonary artery, and epicardium due to anatomical complexity 1
• Aortic cusp VT accounts for 20% of idiopathic outflow tract VTs, with most originating from the left coronary cusp 1

Clinical Outcomes and Recommendations

• Catheter ablation for VT decreases the likelihood of subsequent ICD shocks and prevents recurrent episodes of VT 1
• Catheter ablation of RVOT VT/PVC is recommended in symptomatic patients and/or in patients with failure of anti-arrhythmic drug therapy or LV function decline due to RVOT-PVC burden (Class I, Level B) 1
• Treatment with sodium channel blockers (class IC agents) is recommended in LVOT/aortic cusp/epicardial VT/PVC symptomatic patients (Class I, Level C) 1
• During follow-up of combined epicardial and endocardial mapping approach, 75% of patients remain arrhythmia-free at 12 months 4

Potential Complications and Limitations

• Complications of epicardial puncture and ablation include damage to coronary vasculature, inadvertent puncture of surrounding organs, left phrenic nerve palsy, or pericardial tamponade 1
• LVOT ablation complications include myocardial rupture, tamponade, stroke, valvular damage, and coronary artery damage 1
• Approximately 10-20% of VTs cannot be ablated successfully with current techniques, especially in patients with structural heart disease 2
• Low-voltage areas in nonischemic cardiomyopathy are not always predictive of scarred myocardium, complicating mapping approaches 4