14. Infiltrative and Inflammatory Cardiomyopathies

Infiltrative and inflammatory myocardial disorders produce distinctive mismatches between anatomical wall thickness and surface electrical voltages.

1. Cardiac Amyloidosis: The Voltage-to-Mass Discordance

Pathognomonic Electrocardiographic Hallmark of Cardiac Amyloidosis:

Striking Discordance: Marked concentric left ventricular wall thickening on echocardiography ($>15-18\text{ mm}$) coexists with profoundly low QRS voltage on surface ECG ($<5\text{ mm}$ across all limb leads, or $<10\text{ mm}$ across precordial leads).
Pseudoinfarct Pattern: Pathological Q waves and QS complexes in anterior leads ($V_1 - V_3$) or inferior leads in the absence of obstructive coronary artery disease ($>50\%$ of patients).
Conduction Disease: First-degree AV block, bifascicular block, and high incidence of Atrial Fibrillation with loss of atrial mechanical contraction.

Granulomatous infiltration of the basal interventricular septum and conduction system.
ECG Signatures: Unexplained high-grade or complete AV block in a young/middle-aged adult ($<55$ years), new bundle branch block, or refractory monomorphic ventricular tachycardia.
Diagnosis: $^{18}\text{F-FDG PET-CT}$ showing focal myocardial metabolic uptake and CMR with patchy multifocal LGE.

Technetium-99m Pyrophosphate ($^{99m}\text{Tc-PYP}$) Scintigraphy: Grade 2 or 3 cardiac uptake confirms Transthyretin Cardiac Amyloidosis (ATTR) without endomyocardial biopsy (if serum/urine monoclonal free light chains are negative).
Disease-Modifying Pharmacotherapy:
- Tafamidis ($61\text{ mg}$ daily): TTR tetramer stabilizer that significantly reduces all-cause mortality and cardiovascular hospitalizations in ATTR amyloidosis.
- Immunosuppression: High-dose Corticosteroids + Methotrexate/Infliximab for active inflammatory Cardiac Sarcoidosis.