Overview of Cardiomyopathies

Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). The list of causes is extensive, ranging from familial disorders to underlying diseases and infections. Patients often present with chest pain, dyspnea, palpitations, and/or syncope. Some patients may be completely asymptomatic, while others may present with sudden cardiac death as the first sign of an underlying condition. Diagnosis is made through the use of ECG and cardiac imaging such as echocardiography and cardiac MRI. Management involves medications typically used to treat heart failure, as well as implantable devices. In severe cases, heart transplantation may be necessary.

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Overview

Definition

Cardiomyopathies are diseases that affect the structure and function of the heart muscle (myocardium) in the absence of secondary causes (e.g., coronary artery disease, hypertension, valvular disease, and congenital heart disease).

Epidemiology

  • Incidence and prevalence difficult to estimate due to inconsistent reporting
  • Second most common cause of sudden death after ischemic heart disease
  • Both sporadic and familial forms exist.
  • No clear gender or racial predominance

Etiology

Causes vary:

  • Infectious diseases
  • Inflammatory/autoimmune conditions
  • Endocrinologic disorders
  • Toxins
  • Medications
  • Nutritional deficiencies
  • Deposition diseases
  • Familial storage diseases
  • Genetic neurologic and neuromuscular disorders
  • Hematologic/oncologic disorders
  • Cardiovascular disorders
  • Endomyocardial diseases
  • Genetic (gene mutations)

Approximately ⅓ of cases have a genetic cause.

Classification

By morphology:

  • Dilated cardiomyopathy (DCM): 
    • Heart appears enlarged.
    • Muscle is thinned.
  • Restrictive cardiomyopathy (RCM): 
    • Heart is normal size (or smaller).
    • Muscle is stiffened.
  • Hypertrophic cardiomyopathy (HCM)
    • Heart is enlarged.
    • Muscle is thickened.
  • Arrhythmogenic right ventricular cardiomyopathy/dysplasia
  • Unclassified cardiomyopathy

By etiology:

  • Primary: arises from an exclusively cardiac issue
    • Genetic
    • Mixed (nongenetic/genetic)
    • Acquired
  • Secondary: caused by or associated with a known underlying systemic condition 
    • Disorders of connective tissue 
    • Muscular dystrophies
    • Autoimmune disease
    • Infections of the heart muscle
    • Infiltrative diseases (hemochromatosis, sarcoidosis, or amyloidosis)
    • Endocrine disorders (thyroid conditions, diabetes)
    • Chronic substance abuse (especially alcohol or cocaine)
    • Pregnancy

Pathophysiology

  • Myocardium: thickest layer of the heart
    • Specialized form of striated muscle
    • Composed of cardiomyocytes connected by intercalated discs
    • Structure, size, and arrangement of muscle fibers and heart chambers optimized for pumping force
  • End effect of cardiomyopathies: structural change in heart muscle
    • May cause hypertrophy or dilation of one or both of the heart ventricles
    • Changes shape and capacity of ventricles
  • Cause systolic or diastolic dysfunction, depending on the disease process
    • Systolic dysfunction is characterized by a decrease in heart muscle contractility.
    • Diastolic dysfunction is characterized by a decrease in left ventricular relaxation and ability to fill with blood and is often associated with increased filling pressures.
  • Net end effect is inability to pump blood efficiently:
    • Heart failure
    • Volume overload

Diagnosis

Diagnostic approach varies based on the type of cardiomyopathy. Physicians must have a high index of suspicion for disorders of the myocardium in patients with heart failure.

  • Echocardiography with Doppler: 
    • Used in evaluation of all cases
    • Assesses cardiac size, anatomy, structure, and function 
  • Cardiac MRI:
    • Advanced imaging technique
    • Allows greater characterization of cardiac structure and function 
    • Used to determine extent of myocardial damage, infiltration, and fibrosis
  • ECG: 
    • Low sensitivity for diagnosis of cardiomyopathies
    • Used to identify abnormal heart rhythms, such as associated arrhythmias or conduction delays

Management

Goals:

  • Optimize cardiac output:
    • Increase contractility.
    • Allow for ventricular filling.
    • Optimize ejection fraction.
  • Treat or slow underlying disease progression.
  • Manage symptoms of heart failure:
    • Volume overload
    • Blood pressure
  • Manage symptoms caused by distortion of heart muscle:
    • Arrhythmias: medication, pacemaker, or internal cardioverter–defibrillator (ICD) 
    • Blood clots: anticoagulants

In cases refractory to treatment, heart transplantation may be indicated.

Complications:

  • Heart failure
  • Arrhythmias
  • Sudden cardiac death

Comparison of the Cardiomyopathies

DilatedRestrictiveHypertrophicArrhythmogenic right ventricular CM
Etiology
  • Idiopathic
  • Genetic
  • Alcohol abuse
  • Postpartum
  • Medication
  • Amyloidosis
  • Sarcoidosis
  • Hemosiderosis
  • Post radiation therapy
  • Postsurgical
  • Diabetes
  • Genetic
  • Chronic hypertension
  • Idiopathic
  • Genetic
Clinical presentation
  • Fatigue
  • Dyspnea
  • Dizziness
  • Exercise intolerance
  • Dyspnea
  • Exercise intolerance
  • Lower-extremity edema
  • Weight gain
  • Cough
  • Fatigue
  • Asymptomatic
  • First symptom may be sudden cardiac death.
  • Syncope
  • Exercise intolerance
  • Palpitations
  • Dyspnea
  • Sudden cardiac death
  • Syncope
  • Palpitations
  • Dyspnea
  • Chest pain
Physical exam findings
  • S3 gallop
  • Systolic regurgitant murmur
  • Jugular venous distention
  • Ascites
  • S3 gallop
  • Systolic heart murmur (from mitral or tricuspid regurgitation)
  • Kussmaul’s sign (jugular distention on inspiration)
  • May be normal.
  • S3 or S4 gallop
  • Split S2
  • Harsh crescendo/decrescendo systolic murmur
  • Pansystolic murmur of mitral regurgitation
  • Systolic thrill at the apex
  • Palpable left ventricular heave
  • Often normal
  • S3 or S4 gallop
  • Wide split S2 sound may be present.
  • Peripheral edema
  • Tachycardia
Ejection fraction↓ or normal↑ or normal
L ventricular diastolic dimensionNormal
Left ventricular wall thicknessNormal or ↑↑↑Normal
Atrial sizeNormal
Diagnosis
  • Echocardiography
  • Cardiac MRI
  • Echocardiography
  • Cardiac MRI
  • ECG
  • Echocardiography
  • Cardiac MRI
  • ECG
  • Echocardiography
  • Cardiac MRI
CM: cardiomyopathy

References

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