Cardiac Structures, Valvular Heart Disease, and Cardiomyopathies

Anatomical Foundation of Cardiac Valves

• Atrioventricular (AV) Valves:

  • Mitral Valve: Located between the Left Atrium (LA) and Left Ventricle (LV).
  • Tricuspid Valve: Located between the Right Atrium (RA) and Right Ventricle (RV).

• Semilunar Valves:

  • Aortic Valve: Located between the Left Ventricle (LV) and the Aorta.
  • Pulmonary Valve: Located between the Right Ventricle (RV) and the Pulmonary Artery (PA).

Auscultation and Cardiac Murmurs

• Cardiac Cycle Sound Markers:

  • $S_1$: First heart sound, marking the beginning of ventricular systole.
  • $S_2$: Second heart sound, marking the beginning of ventricular diastole.

• Timing of Cardiac Murmurs:

  • Systolic Murmur: Occurs in the interval between $S_1$ and $S_2$ ($S_1\text{--mRmR--}S_2$).
  • Diastolic Murmur: Occurs in the interval between $S_2$ and $S_1$ ($S_1\text{--}S_2\text{--mRmR--}S_1$).

• Diagnostic Mnemonics for Valvular Murmurs:

  • MTR PASS MVP:
  • Mitral / Tricuspid Regurgitation (physiologic)
  • Aortic Stenosis
  • Systolic murmur
  • Mitral Valve Prolapse
  • MS ARD:
  • Mitral Stenosis
  • Aortic Regurgitation
  • Diastolic murmur

Overview of Valvular Heart Disease

• Etiology:

  • Rheumatic Heart Disease (resulting from rheumatic fever) is the primary cause of most acquired valvular heart lesions.

• Mechanisms of Valve Dysfunction:

  • Regurgitation (Incompetence / Insufficiency): Occurs when the valve leaflets fail to close completely, causing backward leakage of blood into the preceding heart chamber.
  • Stenosis: Occurs when the valve orifice narrows or leaflets fuse, failing to open fully and obstructing forward blood flow.

Mitral Valve Disorders

Mitral Stenosis (MS)

• Etiology and Risk Factors:
  • Valve leaflet fusion.
  • Rheumatic fever (most common underlying cause).
  • Calcium deposits on the valve structure.
  • Atrial myxoma.
  • Intracardiac thrombus formation.
  • Marfan's Syndrome.

• Pathophysiology:

  • Inability of the mitral valve to open normally during diastole.
  • Obstruction of blood flow from the Left Atrium (LA) to the Left Ventricle (LV).
  • Hemodynamic consequences: Increased Left Atrial pressure $\rightarrow$ Increased Left Atrial size (dilation) $\rightarrow$ Increased Pulmonary Artery (PA) pressure (pulmonary hypertension) $\rightarrow$ Increased Right Ventricle (RV) size (hypertrophy and dilation).

• Clinical Assessment and Manifestations:

  • Shortness of Breath (SOB) / Dyspnea.
  • Hemoptysis (blood-tinged sputum).
  • Jugular Venous Distension (JVD).
  • Irregularly irregular pulse secondary to Atrial Fibrillation (AF).
  • Right parasternal pulsations or heave.
  • Auscultation findings: Loud first heart sound ($S_1$), Opening Snap (OS), and Mid-Diastolic Murmur (MDM).
  • Hoarseness of voice (Ortner's syndrome, caused by Left Atrial enlargement compressing the recurrent laryngeal nerve).

Mitral Valve Regurgitation (MR)

• Etiology:

  • Incomplete closure of mitral valve leaflets during ventricular systole.
  • Common causes include Rheumatic Fever, Infective Endocarditis, and Papillary Muscle dysfunction.

• Clinical Assessment and Manifestations:

  • Dyspnea on exertion.
  • Paroxysmal Nocturnal Dyspnea (PND), Orthopnea, and nocturnal dry cough.
  • Hemoptysis.
  • Acute or chronic pulmonary edema (secondary to Left Atrial failure).
  • Right-sided heart failure symptoms.
  • Atrial Fibrillation featuring an irregularly irregular pulse.
  • Systemic embolic phenomena.

Mitral Valve Prolapse (MVP)

• Pathophysiology:
  • Abnormally enlarged or stretchy valve leaflets buckle or prolapse backward into the left atrium during ventricular contraction (systole).
  • Can be asymptomatic or lead to dynamic mitral regurgitation.

Aortic Valve Disorders

Aortic Stenosis (AS)

• Pathophysiology:

  • Narrowing of the aortic valve aperture obstructing blood flow from the Left Ventricle into the Aorta during systole.
  • Leads to compensatory left ventricular hypertrophy, increased myocardial oxygen demand, and decreased systemic perfusion.

• Clinical Manifestations:

  • Angina, Syncope, and Dyspnea on exertion.
  • Systolic ejection murmur.

Aortic Regurgitation (AR)

• Etiology:
  • Rheumatic fever.
  • Infective endocarditis.
  • Aortic dissection.
  • Secondary syphilis.
  • Complication of Transcatheter Aortic Valve Replacement (TAVR).
  • Marfan's Syndrome.

• Eponymous Signs and Presentation:
  • Water-hammer pulse (Corrigan's pulse: rapid, bounding pulse with abrupt collapse).
  • Traube's sign (booming "pistol-shot" sound heard over femoral arteries).
  • Hill's sign (popliteal artery systolic blood pressure exceeding brachial artery pressure by $\ge 30\,\text{mmHg}$).
  • De Musset's sign (rhythmic head bobbing in sync with the heart cycle).
  • Quincke's sign (visible capillary pulsations in the nail beds).
  • Auscultation: Diastolic murmur.

Diagnostic Evaluation for Valvular Heart Disease

• History and Physical Examination.
• Electrocardiogram (EKG / ECG): Evaluates electrical conduction, chamber enlargement, and arrhythmia development.

• Echocardiography:
  • Transthoracic Echocardiogram (TTE).
  • Transesophageal Echocardiogram (TEE).
• Chest X-Ray (CXR): Assesses cardiac silhouette enlargement and pulmonary vascular congestion.
• Cardiac Catheterization: Direct measurement of intracardiac pressures, pressure gradients, and coronary anatomy.

Collaborative Management of Valvular Heart Disease

• Prophylactic Antibiotic Therapy:

  • Indicated for patients with Rheumatic Heart Disease, Valvular Heart Disease, or prior Infective Endocarditis to prevent recurrent endocarditis prior to invasive medical or dental procedures.

• Medical Management:

  • Diuretics to reduce intravascular volume and relieve pulmonary congestion.
  • Pharmacotherapy for rate control and anticoagulation in patients with concomitant Atrial Fibrillation.

• Surgical and Interventional Care:

  • Reconstructive Valve Repair Procedures:
  • Valvuloplasty: Surgical reconstruction and repair of structural valve defects.
  • Annuloplasty: Reconstruction or narrowing of a dilated valve ring using a prosthetic ring and/or purse-string sutures.
  • Commissurotomy: Surgical incision to separate fused valve commissures.
  • Transcatheter Valve Interventions:
  • Transcatheter Mitral Valve Repair (TMVr).
  • Transcatheter Aortic Valve Replacement (TAVR).
  • Valve Replacements:
  • Mechanical Valve Replacement: Highly durable prosthetic valve; requires lifelong systemic anticoagulation therapy.
  • Tissue (Bioprosthetic) Valve Replacement:
    • Allograft: Human cadaver valve.
    • Xenograft: Tissue derived from bovine (cow) or porcine (pig) sources. Does not require lifelong anticoagulation.

Classification and Pathophysiology of Cardiomyopathies

Dilated Cardiomyopathy (DCM)

• Epidemiology and Overview:

  • The most common type of cardiomyopathy, representing $90\%$ of all cardiomyopathy cases.
  • Characterized by gross enlargement of all four cardiac chambers, thinned ventricular walls, and primary systolic dysfunction.

• Pathophysiology:

  • Progressive deterioration of myocardial contractility $\rightarrow$ Decreased Cardiac Output (COP).

• Clinical Assessment:

  • Auscultation: $S_3$ gallop rhythm and regurgitant murmurs.
  • Pulmonary lung rales due to left-sided congestion.
  • Marked cardiomegaly observed on imaging.
  • High risk for intracardiac thrombus formation and Deep Vein Thrombosis (DVT) due to blood stasis.

Takotsubo Cardiomyopathy (Stress-Induced Cardiomyopathy)

• Pathophysiology:
  • Acute, transient ventricular dysfunction triggered by severe physical or emotional stress.
  • The Left Ventricle undergoes apical ballooning during contraction, taking on a characteristic shape resembling a traditional Japanese octopus pot (Tako-Tsubo).

Hypertrophic Cardiomyopathy (HCM)

• Key Characteristics:

  • Asymmetric massive ventricular hypertrophy, disproportionately affecting the interventricular septum.
  • Primary diastolic dysfunction due to an unyielding, thickened myocardium.
  • Associated with significant risk of sudden cardiac death in young athletes.

• Pathophysiology:

  • Septal hypertrophy impairs blood ejection, causing Left Ventricular Outflow Tract (LVOT) obstruction.
  • Diastolic dysfunction reduces ventricular filling $\rightarrow$ Decreased Left Ventricular End-Diastolic Volume (LVEDV).
  • Dynamic obstruction further reduces Cardiac Output under high-contractility or exercise conditions.

• Clinical Assessment:

  • Frequently asymptomatic until sudden cardiac events occur.
  • Syncope (secondary to lethal ventricular arrhythmias or acute LVOT obstruction).
  • Angina (caused by excessive myocardial muscle mass demanding more oxygen than coronaries deliver, coupled with forceful contractions).
  • Dyspnea.
  • Ventricular arrhythmias.
  • Bisferiens pulse (double-peaked pulse).
  • Heaving, forceful Point of Maximal Impulse (PMI).
  • $S_3$ and/or $S_4$ gallop heart sounds.

Restrictive Cardiomyopathy (RCM)

• Key Characteristics:

  • The least common type of cardiomyopathy.
  • Rigid, non-compliant ventricular walls that resist passive stretching during diastole.

• Pathophysiology:

  • Poor ventricular compliance is the primary functional abnormality.
  • Inadequate diastolic filling of ventricular cavities results in reduced stroke volume and congestive heart failure symptoms, while systolic function remains relatively preserved initially.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)

• Key Characteristics:
  • Rare inherited genetic muscle condition passed down through families.
  • Characterized by progressive fibrofatty replacement of the Right Ventricular myocardium.
  • Leads to right ventricular failure, localized aneurysms, and life-threatening ventricular arrhythmias.

Collaborative Management of Cardiomyopathies

• Target Underlying Etiology: Identify and treat specific systemic conditions, metabolic factors, or toxins.

• Pharmacotherapy by Cardiomyopathy Subtype:

  • Dilated Cardiomyopathy (DCM):
  • Diuretics for congestion relief.
  • Digoxin for inotropic support.
  • Nitrates for preload reduction.
  • Angiotensin-Converting Enzyme Inhibitors (ACEI) for afterload reduction and cardiac remodeling inhibition.
  • Anticoagulation therapy to mitigate thromboembolic and DVT risk.
  • Hypertrophic Cardiomyopathy (HCM):
  • Beta-Blockers: Mainstay treatment to prolong diastole, improve ventricular filling, and reduce LVOT obstruction gradient.

• Surgical and Advanced Therapies:

  • Ventriculo-myotomy / Septal Myectomy: Surgical resection of thickened hypertrophic ventricular septal muscle to relieve outflow obstruction in HCM.
  • Heart Transplantation: Definitive surgical therapy for end-stage Dilated Cardiomyopathy (DCM) and Restrictive Cardiomyopathy (RCM).