15. Arrhythmogenic Cardiomyopathies (ARVC and Non-Desmosomal Variants)
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is an inherited desmosomal disease characterized by progressive fibrofatty replacement of the right ventricular myocardium, electrical instability, and sudden cardiac death in young adults and athletes.
1. Diagnostic Electrocardiographic Hallmarks
| Electrocardiographic Feature | Diagnostic Criterion (2010 International Task Force Criteria) | Electrophysiological Mechanism |
|---|---|---|
| Epsilon Wave | Major Criterion: Low-amplitude distinct notch / deflection at the terminal end of the QRS complex before the ST segment in leads $V_1, V_2$, or $V_3$. | Localized, delayed intraventricular conduction through fibrofatty islands in the RV outflow tract / free wall. |
| Precordial T-Wave Inversions | Major Criterion: T-wave inversion in right precordial leads ($V_1, V_2, V_3$) in individuals $>14$ years of age in the absence of complete RBBB. | Transmural repolarization delay in the anterior and apical RV myocardium. |
| Terminal Activation Delay (TAD) | Minor Criterion: Duration from the nadir of the S wave to the end of all depolarization deflections $\ge 55\text{ ms}$ in $V_1 - V_3$. | Slowed terminal RV free wall depolarization. |
| Ventricular Arrhythmias | Major Criterion: Sustained or non-sustained VT with LBBB morphology and Superior Axis (originating from the RV inferior wall). | Reentry around fibrofatty myocardial scars in the "Triangle of Dysplasia". |
2. Multimodality Diagnostic Investigations
- Cardiac Magnetic Resonance (CMR): Major criterion: Regional RV akinesia, dyskinesia, or aneurysm PLUS RV end-diastolic volume index $\ge 110\text{ mL/m}^2$ (males) or $\ge 100\text{ mL/m}^2$ (females) or RV ejection fraction $\le 40\%$.
- Signal-Averaged ECG (SAECG): Late potentials present in $\ge 2$ of 3 parameters (filtered QRS duration $\ge 114\text{ ms}$, duration of terminal QRS $<40\ \mu\text{V} \ge 38\text{ ms}$, root mean square voltage of terminal $40\text{ ms} \le 20\ \mu\text{V}$).
- Genetic Sequencing: Identifies pathogenic desmosomal mutations ($PKP2, DSP, DSG2, DSC2, JUP$).
3. Evidence-Based Clinical Management Protocols
- Strict Exercise Restriction: Competitive sports and high-intensity endurance training accelerate desmosomal detachment, disease progression, and lethal arrhythmias $\to$ Class I Recommendation for Discontinuation.
- Implantable Cardioverter-Defibrillator (ICD): Class I indication for secondary prevention in cardiac arrest survivors or sustained VT; indicated in primary prevention based on the ARVC Risk Calculator (5-year risk $>10-15\%$).
- Substrate-Based Catheter Ablation: Epicardial-endocardial combined RF ablation targeting fragmented, low-voltage late potentials across the RV free wall.