13. Hypertrophic Cardiomyopathy and Apical Yamaguchi Syndrome
Hypertrophic Cardiomyopathy (HCM) is an autosomal dominant genetic disorder of the cardiac sarcomere characterized by unexplained left ventricular hypertrophy, dynamic outflow tract obstruction, and electrical vulnerability.
Figure 13.1: 12-lead ECG of Hypertrophic Cardiomyopathy displaying high precordial QRS voltage and deep T-wave inversions across anterior and lateral leads. Rendered with solid white background.
1. Classical Asymmetric Septal Hypertrophy (ASH) vs Apical HCM (Yamaguchi Syndrome)
| Diagnostic Parameter | Classic Asymmetric Septal HCM | Apical HCM (Yamaguchi Syndrome) |
|---|---|---|
| Anatomical Site of Hypertrophy | Basal and mid-interventricular septum ($>15\text{ mm}$, or $>13\text{ mm}$ with positive family history). | Confined to the Left Ventricular Apex ($>15\text{ mm}$). |
| Classical 12-Lead ECG Hallmark | "Dagger-Like" Septal Q Waves: Deep, narrow ($<40\text{ ms}$) Q waves in lateral leads (I, aVL, $V_5-V_6$) and inferior leads; tall R waves; strain pattern. | Giant Negative T Waves ($>10\text{ mm} / 1.0\text{ mV}$) across precordial leads ($V_2 - V_6$); massive precordial QRS voltage. |
| Echocardiographic & Angiographic Finding | Systolic Anterior Motion (SAM) of the anterior mitral leaflet; dynamic LVOT gradient $>30-50\text{ mmHg}$. | "Ace-of-Spades" configuration of the LV cavity during end-diastole on left ventriculography and contrast echocardiography. |
| Hemodynamic Complications | Dynamic LVOT obstruction, secondary mitral regurgitation, exertional syncope. | Apical aneurysm formation, apical thrombus, ventricular arrhythmias. |
2. Multimodality Investigations
- Cardiac Magnetic Resonance (CMR): Identifies patchy, mid-myocardial Late Gadolinium Enhancement (LGE) at the RV insertion points; $\text{LGE} > 15\%$ of LV mass indicates elevated sudden death risk.
- Genetic Testing: Comprehensive sarcomeric multigene panel ($MYH7, MYBPC3, TNNT2, TNNI3$).
3. Evidence-Based Management Protocols
- First-Line Medical Therapy: Non-vasodilating Beta-Blockers (Metoprolol succinate, Atenolol) titrated to resting HR $55-60\text{ bpm}$.
- Novel Cardiac Myosin Inhibitors: Mavacamten ($2.5-15\text{ mg}$ daily) directly inhibits excess actin-myosin cross-bridging, reducing LVOT gradients and eliminating SAM.
- Septal Reduction Therapy: Surgical Septal Myectomy (Morrow Procedure) or Alcohol Septal Ablation (ASA) for severe symptoms refractory to medical therapy with resting/provocable gradient $\ge 50\text{ mmHg}$.
- Sudden Cardiac Death Risk & ICD Implantation: Calculated using the HCM Risk-SCD Score (5-year risk $\ge 6\% \implies$ Class IIa recommendation for primary prevention ICD).