Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is the most common type of non-ischemic cardiomyopathy and a common cause of heart failure (HF). The cause may be idiopathic, familial, or secondary to a variety of underlying conditions. The disease is characterized by the enlargement of 1 or both ventricles and reduced systolic function. Patients typically present with symptoms of HF such as shortness of breath, fatigue, weakness, and peripheral edema. Blood tests, ECG, X-rays, echocardiography, and other cardiac studies and procedures are typically done to obtain the diagnosis. Treatment includes medications used to reduce volume overload (e.g., diuretics) and manage HF (e.g., beta-blockers). Devices such as pacemakers and cardioverter-defibrillators may also be needed. In severe cases, a heart transplant is required. Complications include thromboembolic events and sudden cardiac death.

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Overview

Definition

Dilated cardiomyopathy (DCM) is a disease of the cardiac muscle associated with electrical and mechanical dysfunction causing impaired systolic function and featuring the dilatation of 1 or both ventricles.

Epidemiology

  • Most common type of non-ischemic cardiomyopathy
  • Annual incidence: 6 per 100,000
  • 10,000 deaths and 46,000 hospitalizations yearly in the United States
  • Affects men > women
  • Occurs in all ages, most common in those 20–60 years old
  • Most common indication for heart transplant

Etiology

  • Idiopathic in approximately 50% of cases 
  • Familial DCM:
    • Caused by a multitude of gene mutations
    • 20%–35% of cases initially diagnosed as idiopathic are later found to have a familial component after additional family screening.
    • Typical inheritance pattern is autosomal dominant; however, all inheritance patterns have occurred.
  • Ischemic heart disease/coronary artery disease (CAD)
  • Untreated hypertension 
  • Long-standing valvular disease (e.g., mitral or aortic regurgitation)
  • Arrhythmias (particularly those that cause sustained tachycardia, e.g., atrial fibrillation)
  • Infections:
    • Viral infections causing myocarditis (e.g., coxsackievirus, influenza, or HIV)
    • Chagas disease (protozoan infection due to Trypanosoma cruzi)
  • Endocrine disorders (e.g., hyperthyroidism or diabetes)
  • Autoimmune or inflammatory conditions (e.g., lupus or sarcoidosis)
  • Neuromuscular genetic conditions (e.g., Duchenne muscular dystrophy or Friedreich’s ataxia)
  • Deposition diseases (e.g., hemochromatosis or amyloidosis)
  • Medications that cause cardiotoxicity:
    • Chemotherapeutic medications (classically an anthracycline, e.g., doxorubicin, or a monoclonal antibody, e.g., trastuzumab)
    • Antiretrovirals (most classically azidothymidine; also known as AZT)
    • Hydroxychloroquine 
  • Radiation treatment (particularly to the chest)
  • Peripartum cardiomyopathy:
    • Secondary to hemodynamic changes associated with pregnancy
    • Occurs in the last month of pregnancy or the 1st months after giving birth 
  • Toxins:
    • Alcohol abuse
    • Cocaine and other illicit drug use
    • Exposure to heavy metals (e.g., cobalt, arsenic, mercury, or lead)
  • Nutritional deficiencies (e.g., thiamine, selenium, or carnitine)

Pathophysiology

  • Ventricular dilation caused by:
    • Left ventricle (LV) failure
    • Primary injury of heart muscle 
  • Ventricular dilatation leads to:
    • Thinning of heart muscle wall 
    • Weakening and enlargement of heart
    • Systolic failure:
      • Cardiac muscle does not contract efficiently when deformed.
      • Cardiac output decreases.
    • Diastolic failure: valvular insufficiency due to distortion of cardiac architecture 
    • Heart failure (HF)

Clinical Presentation

Symptoms may develop and progress slowly over time, or develop abruptly. Symptoms are similar to those seen with HF.

Symptoms

  • Dyspnea/shortness of breath (especially with exertion)
  • Orthopnea (shortness of breath when lying down)
  • Edema of lower extremities and abdomen
  • Weight gain
  • Dizziness
  • Syncopal episodes
  • Chest pain
  • Palpitations
  • Fatigue 
  • Weakness

Physical exam findings

  • Cardiac:
    • Systolic heart murmur (from mitral or aortic regurgitation)
    • S3 gallop
  • Abdominal: ascites
  • Pulmonary:
    • Rales or crackles over lung fields (secondary to pulmonary edema)
    • Respiratory distress
    • Low oxygen saturation
  • Vascular: jugular venous distention
  • Extremity:
    • Pitting edema in lower extremities
    • Signs of venous stasis with discoloration in lower extremities

Diagnosis

Diagnosis is primarily through history and physical examination, laboratory examination, ECG, and imaging (confirmatory or to exclude other etiologies).

Laboratory studies

  • BNP: marker for heart failure (↑)
  • Troponin: marker for MI (↑)
  • CK-MB: another marker for MI (↑ in 1st 24 hours, then returns to normal by 48–72 hours)
  • ECG: may show sinus tachycardia, left atrial enlargement, ventricular arrhythmias, or atrial fibrillation

Imaging

  • Chest X-ray: may show enlarged heart and effusions (accumulation of fluid)
  • Echocardiography:
    • Assess: 
      • Cardiac size
      • Structure
      • Function
      • Differentiates other forms of cardiomyopathy
    • Shows:
      • Enlarged ventricular diameter (dilation)
      • Normal or decreased wall thickness
      • Decreased inward endocardial systolic motion
      • Reduced left ventricular ejection fraction (LVEF)
    • Evidence of dilation of 1 or both ventricles and reduced systolic dysfunction necessary for diagnosis of dilated cardiomyopathy
  • Cardiac MRI: helps determine extent of myocardial damage and fibrosis
  • Coronary angiography: 
    • Helps rule out CAD
    • May show dilated, hypokinetic LV, normal coronary arteries, and some degree of mitral regurgitation
  • Endomyocardial biopsy with histologic examination: 
    • Done in select cases: 
      • Uncertain cause 
      • New-onset HF with associated hemodynamic compromise, ventricular arrhythmias, Mobitz type II atrioventricular (AV) block, 3rd-degree AV block, or HF refractory to typical treatments
  • Obtain comprehensive family history and genetic testing if familial DCM suspected.

Management

Treatment

  • Medications:
    • Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers: improve systolic function
    • Beta-blockers: increase ejection fraction
    • Diuretics: treat volume overload
    • Vasodilators
  • Oral anticoagulation (vitamin K antagonists, e.g., warfarin) if LVEF < 35%
  • Device therapies (e.g., pacemaker or implanted cardioverter-defibrillator) if:
    • LVEF < 35%
    • Arrhythmias or other conduction disorders
    • LVEF > 35% with family history of sudden cardiac death or gene mutations (e.g., LMNA) associated with a high risk for sudden cardiac death
    • Syndromic diseases (e.g., muscular dystrophy)
  • Heart transplant warranted in severe cases

Complications

  • Arrhythmias
  • Thromboembolic events (e.g., pulmonary embolism or cerebrovascular accident)
  • Sudden cardiac death

Prognosis

Prognosis is generally poor for individuals with this condition. 

Differential Diagnosis

  • Restrictive cardiomyopathy: a condition secondary to scarring and/or infiltration of the heart muscle (amyloidosis most common cause) characterized by a stiffening of the ventricles resulting in diastolic dysfunction and eventual HF. Presentation includes signs and symptoms of HF. Similar studies as DCM are used to help determine the diagnosis. Treatment is also similar, including medications and implantable devices such as pacemakers and cardioverter-defibrillators. A heart transplant may be needed when symptoms become severe and no longer responsive to treatments. Prognosis and survival are worse than with DCM. 
  • Hypertrophic cardiomyopathy (HCM): Gene mutations affect the contractile components of the heart (sarcomeres) resulting in LV asymmetrical wall thickening, diastolic dysfunction, and LV outflow tract obstruction. Patients may be asymptomatic or suffer sudden cardiac death as the 1st sign of disease. Symptomatic individuals have dyspnea on exertion, chest pain, presyncope, or syncope. Diagnosis is made via ECG, echocardiogram, stress test, and cardiac MRI. Treatment involves beta-blockers as 1st-line therapy with additional management depending on the presence of arrhythmias and LV outflow tract obstruction. 
  • Takotsubo cardiomyopathy: a type of non-ischemic cardiomyopathy occurring due to extreme psychological or physical stress; also known as stress-induced cardiomyopathy or “broken heart syndrome.” Takotsubo cardiomyopathy is characterized by transient, regional systolic dysfunction of the LV. Patients present with symptoms of acute coronary syndrome, including chest pressure and shortness of breath, and an ECG may show ST-segment elevation. Coronary angiography can help to differentiate this condition from MI. An echocardiogram can confirm the diagnosis by demonstrating characteristic apical wall motion abnormalities. Treatment includes the removal of inciting stressors and beta-blockers.

References

  1. (2021). Dilated Cardiomyopathy. Medline Plus. Retrieved February 3, 2021, from https://medlineplus.gov/ency/article/000168.htm
  2. Schaufelberger M. (2019). Cardiomyopathy and pregnancy. Heart. 105:1543-1551. Retrieved February 3, 2021, from https://heart.bmj.com/content/105/20/1543.info
  3. Weigner, M. & Morgan, J. P. (2019). Causes of dilated cardiomyopathy. UpToDate. Retrieved February 4, 2021, from https://www.uptodate.com/contents/causes-of-dilated-cardiomyopathy
  4. Cooper, L.T. (2019). Definition and classification of the cardiomyopathies. UpToDate. Retrieved February 4, 2021, from https://www.uptodate.com/contents/definition-and-classification-of-the-cardiomyopathies
  5. Hershberger, R.E. (2020). Familial dilated cardiomyopathy: Prevalence, diagnosis, and treatment. UpToDate. Retrieved February 4, 2021, from https://www.uptodate.com/contents/familial-dilated-cardiomyopathy-prevalence-diagnosis-and-treatment

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