Cardiomyopathies: Dilated and Hypertrophic

Cardiomyopathies: Dilated vs. Hypertrophic

Introduction to Cardiomyopathies

  • Cardiomyopathies are diseases of the heart muscle. The three main types discussed are:

    • Dilated Cardiomyopathy (DCM)

    • Hypertrophic Cardiomyopathy (HCM)

    • Restrictive Cardiomyopathy (briefly mentioned as infiltration of myocardium by fibrotic substances like carcinoid or amyloidosis)

Dilated Cardiomyopathy (DCM)

  • Most Common Type: DCM is the most frequently encountered cardiomyopathy.

  • Definition and Appearance:

    • Characterized by enlargement of the ventricular chambers with impaired systolic contraction.

    • The left ventricle is dilated with minimal hypertrophy (the walls surrounding the left ventricle, the myocardium, are not thickened).

    • This means the ventricle is enlarged, but the muscle wall itself is not thicker.

    • Often involves all four cardiac chambers, but can sometimes be limited to the left or right side.

  • Key Diagnostic Indicator: Ventricle is dilated with decreased contractile function (contracting less effectively than it should).

  • Chamber Involvement:

    • Most often, both the right and left ventricles are impaired (dilated with decreased contractility).

    • Sometimes dysfunction is limited to the left ventricle (common).

    • Less commonly found only in the right ventricle.

  • Causes:

    • Idiopathic: (Unknown cause), the most common primary cause.

    • Familial/Genetic: A type of genetic predisposition, often seen if other family members have DCM.

    • Infiltrative (Secondary):

      • Viral myocarditis (infection in the myocardium).

      • Connective tissue disease.

    • Toxins:

      • Excessive alcohol consumption.

      • Certain chemotherapy treatments.

    • Metabolic: Conditions affecting metabolism, such as hyperthyroidism.

  • Physiological Consequences:

    • Impaired Myocyte Contractility: The heart muscle (myocardium) cannot contract effectively because the ventricles are dilated.

    • Declined Stroke Volume (SV): The amount of blood pumped out with each beat decreases.

    • Declined Cardiac Output (CO): The total volume of blood pumped by the heart per minute decreases.

  • Mitral and Tricuspid Regurgitation:

    • As cardiomyopathy progresses, ventricles enlarge over time.

    • The mitral and tricuspid valves (leaflets) have a fixed size; they do not stretch or widen with the dilating ventricles.

    • Consequence: Valve leaflets fail to come together and close properly during systole.

    • This leads to valve regurgitation (blood flowing backward).

    • Visual Analogy: If the heart normally opens like ∣∣| |, with dilation, it opens like ∣∣| |, leaving a hole in the middle where blood can flow back.

    • General Rule: 99 out of 1010 times, if something is dilated, some form of regurgitation will occur.

  • Three Consequences of Regurgitation:

    1. Excessive Volume and Pressure in Atria: Blood flows back into the atria, which are already receiving blood from other parts of the body, leading to overload.

    2. Further Decrease in Forward Stroke Volume: Regurgitation of blood back into the left atrium reduces the effective amount of blood pushed forward by the heart.

    3. Further Left Ventricular Dilation: The regurgitated blood returns to the left ventricle during diastole, presenting an even greater volume load, further dilating the ventricle.

  • Pathophysiological Cascade (Domino Effect):

    • Myocyte Injury (DCM) →\rightarrow Decreased Contractility →\rightarrow Reduced Stroke Volume (SV\text{SV})

    • Reduced SV\text{SV} →\rightarrow Decreased Cardiac Output (CO\text{CO}) →\rightarrow Fatigue and Weakness

    • Reduced Contractility / Increased Volume →\rightarrow Left Ventricle Dilation →\rightarrow Mitral Regurgitation

    • Increased Volume →\rightarrow Increased Ventricular Filling Pressure

      • Increased Ventricular Filling Pressure →\rightarrow Pulmonary Congestion →\rightarrow Buildup of blood and fluid in the lungs →\rightarrow Dyspnea (difficulty breathing, improved by sitting up), Orthopnea (difficulty breathing, not improved by sitting up), and Rales (crackling sounds in lungs from fluid).

      • Increased Ventricular Filling Pressure →\rightarrow Systemic Congestion →\rightarrow Blood backs up into body veins →\rightarrow Edema (swelling, usually in legs), Hepatomegaly (enlargement of the liver), and Jugular Venous Distension (JVD) (dilated jugular vein).

  • Key Symptoms/Clinical Findings:

    • Congestive Heart Failure (CHF)

    • Fatigue

    • Lightheadedness

    • Exertional Dyspnea (difficulty breathing during physical activity)

    • Edema (swelling, especially in legs, often a primary trigger for suspicion of heart overload).

      • Diagnosis of Edema: Pitting edema (indentation remains after pressing the skin) indicates fluid buildup, distinguishing it from other causes of swelling (e.g., infection).

  • Diagnostic Studies:

    • Electrocardiogram (EKG): Evaluates for arrhythmias, commonly A fib\text{A fib}, V fib\text{V fib}, and tachycardia.

    • Echocardiogram: Shows dilated chambers, regurgitation in mitral and tricuspid valves, velocities of blood flow, and the extent of ventricular dilation. This is a primary diagnostic tool.

    • Cardiac Catheterization: Performed if cardiomyopathy is advanced, to determine if coexisting coronary artery disease (CAD) contributes to impaired ventricular function.

      • Procedure: A wire is inserted (usually via groin) into the heart. Dye is injected to visualize arteries and identify blockages (embolism, thrombus). This directly relates to understanding coronary artery anatomy and which walls they supply (linking to previous lectures).

  • Treatments:

    • Goals: Relieve symptoms, prevent complications, improve long-term survival.

    • Reversibility: DCM is generally not reversible (dilated ventricles won't shrink back), but it is manageable.

    • Addressing Regurgitation: Valve replacements (e.g., for mitral or tricuspid regurgitation) are options, but the ventricle size itself cannot be changed easily; the goal is to prevent further enlargement.

    • Early Stage Interventions:

      • Frank-Starling Mechanism: Utilizes the heart's intrinsic ability to stretch and contract more forcefully (though it eventually wanes).

      • Hormonal Control: Increase in sympathetic nervous system activity (increases heart rate and contractility).

      • Renin-Angiotensin-Aldosterone System (RAAS) Activation: A hormone system that raises blood pressure and blood volume when needed.

    • Medications: (Work together to manage symptoms and heart function)

      • Diuretics: Help with fluid buildup (edema). Can also help lower blood pressure.

      • ACE Inhibitors: Help with heart contraction and also prevent fluid buildup by lowering blood pressure.

    • Arrhythmia Prevention/Treatment:

      • Maintain electrolyte balance (notably potassium and magnesium), often requiring infusions or supplements.

      • Defibrillator or Pacemaker: May be implanted to shock the heart back into sinus rhythm if A fib\text{A fib} occurs or to regulate heart rhythm.

        • Pacemaker: Tracks heart rhythm and delivers shocks if it goes out of sync. Visually identifiable on scans (tube extending into the heart). Can be a site for plaque buildup.

    • Thrombolytic Agents: Medications to prevent thrombus (blood clot) formation, as dilated hearts can lead to plaque breaking off and forming clots.

    • Worst-Case Scenario: Heart transplant.

      • Considered for severe cases, especially in younger patients (20s-30s) where it may be genetic.

      • Priority for transplant depends on various factors (age, overall health, prognosis).

  • Importance of Patient History and Symptoms: Healthcare providers must listen to patient complaints (orthopnea, exertional dyspnea, edema, lightheadedness) as they are crucial indicators for diagnosing DCM and its associated complications.