3.3 Dilated, Hypertrophic, and Restrictive Cardiomyopathies

3.3 Dilated, Hypertrophic, and Restrictive Cardiomyopathies

Cardiomyopathies comprise a heterogeneous group of myocardial diseases associated with mechanical and/or electrical dysfunction. They are categorized based on structural and functional characteristics into three major morphological types—Dilated, Hypertrophic, and Restrictive—alongside specific stress-induced syndromes such as Takotsubo Cardiomyopathy. Mastery of these disorders is essential for the advanced cardiac nurse managing complex heart failure, hemodynamic collapse, and sudden cardiac death prevention.

Dilated Cardiomyopathy (DCM)

Dilated Cardiomyopathy is characterized by left ventricular (or biventricular) dilation and severe systolic dysfunction (LVEF < 40%) in the absence of abnormal loading conditions (like severe hypertension or valvular stenosis) or ischemic artery disease adequate to cause the global impairment.

Etiologies

1. Genetic / Familial: Account for 30%–50% of non-ischemic DCM cases, most commonly autosomal dominant mutations in the TTN gene (encoding the giant sarcomeric protein titin).
2. Toxic: Chronic alcohol abuse (alcoholic cardiomyopathy), cocaine, amphetamines, and chemotherapeutic agents (anthracyclines like doxorubicin, monoclonal antibodies like trastuzumab).
3. Infectious / Inflammatory: Post-viral myocarditis (Coxsackie B, Parvovirus B19, Human Herpesvirus 6, SARS-CoV-2, Chagas disease).
4. Peripartum Cardiomyopathy (PPCM): Development of HF in the last month of pregnancy or within 5 months post-delivery, driven by anti-angiogenic prolactin cleavage fragments.

Pathophysiology & Clinical Presentation

Impaired cardiomyocyte contractility causes an increase in end-systolic volume. Over time, progressive eccentric hypertrophy leads to chamber dilation, apical thinning, and secondary functional mitral regurgitation due to annular dilation. Patients present with classic HFrEF symptoms: progressive exertional dyspnea, orthopnea, fatigue, elevated JVP, and S3 gallop.

Diagnostic Findings & Nursing Priorities

• Echocardiography: Demonstrates diffuse LV hypokinesis, enlarged LV end-diastolic diameter (> 58 mm), and reduced LVEF.
• ECG: Poor R-wave progression across precordial leads, left bundle branch block (LBBB), and ventricular ectopy.
• Complications & Management:
  • Mural Thrombus: Stasis of blood in dilated, poorly contracting chambers predisposes to apical thrombus formation. Systemic anticoagulation is indicated if thrombus is visualized or if concurrent atrial fibrillation occurs.
  • Arrhythmia Prevention: Primary prevention Implantable Cardioverter-Defibrillator (ICD) placement is indicated for patients with LVEF ≤ 35% despite ≥3 months of optimal GDMT.
  • Cardiac Resynchronization Therapy (CRT-D): Indicated for patients in sinus rhythm with LVEF ≤ 35%, LBBB morphology, and QRS duration ≥ 150 ms to correct electromechanical dyssynchrony.

Hypertrophic Cardiomyopathy (HCM / HOCM)

Hypertrophic Cardiomyopathy is a genetic cardiac disease defined by unexplained left ventricular hypertrophy (wall thickness ≥ 15 mm) occurring in the absence of hypertensive or valvular heart disease. It is the leading cause of sudden cardiac death in young competitive athletes.

Pathophysiology & Dynamic LVOT Obstruction

Approximately two-thirds of HCM patients exhibit dynamic Left Ventricular Outflow Tract (LVOT) obstruction at rest or with provocation (Hypertrophic Obstructive Cardiomyopathy - HOCM).

1. Asymmetric Septal Hypertrophy (ASH): Hypertrophy disproportionately affects the anterior interventricular septum relative to the posterior LV wall (septal-to-posterior wall ratio > 1.3:1).
2. Systolic Anterior Motion (SAM): Rapid systolic ejection through the narrowed LVOT creates a suction drag (Venturi effect), pulling the anterior leaflet of the mitral valve forward into contact with the hypertrophied septum. This results in dynamic LVOT obstruction and coexisting posteriorly directed mitral regurgitation.

Physical Examination & Bedside Maneuvers

On auscultation, HOCM presents with a harsh crescendo-decrescendo systolic murmur at the left sternal border that does not radiate to the carotids (distinguishing it from aortic stenosis). Because LVOT obstruction is dynamic and dependent on LV cavity size, bedside maneuvers alter murmur intensity predictably:

Exam Warning: Giving a patient with HOCM sublingual nitroglycerin or aggressive IV loop diuretics can induce catastrophic LVOT occlusion, sudden collapse, and cardiac arrest!

Diagnostic ECG Findings

• Marked Left Ventricular Hypertrophy (Sokolow-Lyon criteria: S in V1 + R in V5/V6 > 35 mm).
• Deep, narrow, dagger-like Q waves in lateral leads (I, aVL, V5, V6) representing early septal depolarization through hypertrophied tissue.

Pharmacological & Interventional Management

1. First-Line Pharmacotherapy: Non-vasodilating Beta-Blockers (metoprolol, atenolol, propranolol) titrated to a resting heart rate of 55–60 bpm. Beta-blockers prolong diastole (increasing LV filling/volume) and decrease contractility, relieving obstruction. Non-dihydropyridine Calcium Channel Blockers (Verapamil) are second-line.
2. Mavacamten (Camzyos): First-in-class selective cardiac myosin inhibitor. It targets the underlying pathophysiology by reducing functional myosin-actin cross-bridge formation, decreasing hypercontractility, and resolving LVOT gradients. Requires strict FDA REMS program monitoring of LVEF via baseline and serial echocardiograms (hold if LVEF < 50%).
3. Invasive Septal Reduction Therapy (SRT): Indicated for severe refractory symptoms with resting/provoked gradient ≥ 50 mmHg:
   • Surgical Septal Myectomy (Morrow Procedure): Gold standard resection of hypertrophied septal tissue.
   • Alcohol Septal Ablation (ASA): Injection of 1–2 mL of 98% dehydrated ethanol into the first major septal perforator artery via cardiac catheterization to induce a localized controlled septal infarction. High risk of complete heart block requiring permanent pacemaker.

Sudden Cardiac Death (SCD) Risk Stratification

Major risk factors warranting primary prevention ICD placement include:

• History of unexplained sudden syncope.
• Massive LV wall thickness ≥ 30 mm.
• Family history of premature SCD in a first-degree relative.
• Non-sustained ventricular tachycardia (NSVT) on ambulatory Holter monitoring.
• LV apical aneurysm.

Restrictive Cardiomyopathy (RCM)

Restrictive Cardiomyopathy is the least common primary cardiomyopathy, characterized by rigid, non-compliant ventricular walls that severely impede diastolic filling while maintaining near-normal systolic function and ventricular dimensions (in early stages).

Etiologies & Classification

• Infiltrative Diseases:
  • Cardiac Amyloidosis: Extracellular deposition of misfolded protein fibrils. Divided into AL Amyloidosis (immunoglobulin light chain, plasma cell dyscrasia) and ATTR Amyloidosis (Transthyretin type—wild-type/senile or hereditary mutations). Diagnosed via Pyrophosphate (PYP) bone scintigraphy or endomyocardial biopsy.
  • Sarcoidosis: Non-caseating granulomatous infiltration of the myocardium; frequently presents with high-grade AV block, ventricular tachycardia, and heart failure.
• Storage Diseases: Hemochromatosis (iron overload), Fabry disease, glycogen storage disorders.
• Non-Infiltrative / Fibrotic: Endomyocardial fibrosis, radiation-induced cardiomyopathy, scleroderma.

Diagnostic Hallmarks & Clinical Presentation

1. Echocardiography: Rigid ventricles with normal or small cavity sizes, concentric wall thickening, severe biatrial enlargement ("small ventricles with huge atria"), and prominent restrictive diastolic filling pattern (E/A ratio > 2.0, shortened deceleration time).
2. ECG Hallmark: Low-voltage QRS complexes across precordial and limb leads despite marked ventricular wall thickening on echocardiogram. This discordance between low ECG voltage and thick echo walls is pathognomonic for Cardiac Amyloidosis.
3. Physical Exam: Manifestations of predominant right-sided systemic congestion: severe peripheral edema, massive ascites, hepatomegaly, elevated JVP with prominent x and y descents, and Kussmaul's sign (paradoxical rise in JVP during inspiration).

Therapeutic Management

• Disease-Specific Therapy: Tafamidis (Vyndaqel) binds transthyretin to prevent tetramer dissociation in ATTR Amyloidosis. Systemic corticosteroids/immunosuppressants for Sarcoidosis. Phlebotomy/iron chelation for Hemochromatosis.
• Symptomatic Care: Careful diuresis to manage volume overload. Warning: Patients depend on elevated filling pressures to maintain stroke volume; excessive diuresis causes profound hypotension.

Takotsubo Cardiomyopathy (Stress-Induced / Broken Heart Syndrome)

Takotsubo Cardiomyopathy is a transient clinical syndrome characterized by acute regional left ventricular systolic dysfunction extending beyond a single epicardial vascular territory, triggered by severe emotional or physical stress.

[Severe Emotional/Physical Stressor] 
              ↓
[Massive Endogenous Catecholamine Surge (Epinephrine/Norepinephrine)] 
              ↓
[Microvascular Spasm + Direct Cardiomyocyte Toxicity / Beta-2 Receptor Switch] 
              ↓
[Apical & Mid-Ventricular Akinesis + Basal Hyperkinesis ("Japanese Octopus Trap")]

Clinical Presentation & Diagnostic Criteria (Mayo Clinic Criteria)

1. Presentation: Mimics acute STEMI—substernal chest pain, dyspnea, ischemic ECG changes (ST elevations in V2–V5, followed by deep T-wave inversions and QT prolongation), and mild troponin elevation disproportionate to the extensive wall motion abnormality.
2. Coronary Angiography: Crucial rule-out test demonstrating absence of obstructive coronary artery disease or acute plaque rupture.
3. Left Ventriculography: Classic appearance of apical ballooning (akinesis/dyskinesis of the apical and mid-ventricular segments with hyperkinesis of the basal walls).

Clinical Trajectory & Management

• Prognosis: Excellent; complete resolution of LV systolic function typically occurs within 1 to 4 weeks.
• Pharmacotherapy: Supportive care using ACE inhibitors/ARBs and beta-blockers until LVEF recovers completely. Exogenous sympathomimetics and inotropes (e.g., epinephrine) should be strictly avoided as they exacerbate catecholamine toxicity.
• Complications: Acute heart failure/cardiogenic shock, dynamic LVOT obstruction (due to basal hyperkinesis), apical thrombus, and LV free wall rupture. In cardiogenic shock without LVOT obstruction, temporary mechanical circulatory support (IABP or Impella) is preferred over catecholamine inotropes.