Restrictive Cardiomyopathy

Restrictive cardiomyopathy (RCM) is a fairly uncommon condition characterized by progressive stiffening of the cardiac muscle, which causes impaired relaxation and refilling of the heart during diastole, resulting in diastolic dysfunction and eventual heart failure. It most often occurs secondary to scarring, damage, and/or infiltration of the heart muscle, with amyloidosis being the most common cause. Infrequently, it may be idiopathic or inherited. Signs and symptoms include shortness of breath, low exercise tolerance, fatigue, and peripheral edema. Diagnosis is made through clinical suspicion and confirmed through ECG, X-ray, echocardiography, and cardiac MRI. Treatment includes medications for heart failure, implantable devices such as pacemakers and cardioverter–defibrillators, and heart transplantation in refractory cases.

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Overview

Definition

Restrictive cardiomyopathy (RCM) is a disease of the heart muscle characterized by decreased compliance of the ventricles, nondilated heart muscle, and diastolic dysfunction (impaired filling of the ventricles).

Epidemiology

  • Rarest cardiomyopathy
  • 5% of all cases
  • Incidence and prevalence are etiology-dependent:
    • Amyloidosis
      • Most common RCM in the United States
      • Men = women
      • Common in elderly
    • Sarcoidosis
      • Women > men
      • Highest incidence in Japan
      • Highest prevalence among Black women
    • Hemochromatosis
      • 1 in 200
      • Men = women
    • Loeffler endocarditis
      • Increased incidence and frequent cause of death in the tropics of Africa, Asia, and South and Central America
      • Secondary to high incidence of endomyocardial fibrosis in those areas

Etiology

  • Idiopathic
  • Familial:
    • Various known gene mutations
    • Typically associated with amyloidosis or considered part of familial hypertrophic cardiomyopathy
  • Underlying disease or condition causing scarring or damage to the heart muscle:
    • Amyloidosis (most common cause)
    • Sarcoidosis
    • Hemochromatosis
    • Endomyocardial fibrosis
    • Loeffler endocarditis (eosinophillic endocarditis)
    • Postradiation fibrosis
    • Scleroderma
    • Tumors

Pathophysiology

  • Cardiac muscle becomes increasingly stiff owing to:
    • Infiltration with abnormal cell/substances
    • Excessive deposition of metabolic by-products
    • Direct fibrosing injury
  • Reduced compliance and impaired ability to expand → impaired relaxation of the heart (diastole) 
  • Heart muscle cannot fill properly during diastole → increased filling pressures and diastolic dysfunction → atria become dilated/enlarged secondary to the increased pressures → pulmonary and systemic congestion 
  • With increases in heart rate, heart is unable to adequately ↑ cardiac output
  • Systolic function is usually normal.
  • No ventricular dilation or thickening

Clinical Presentation

Presentation is similar to that seen with right heart failure.

Symptoms

  • Dyspnea (shortness of breath), especially with exertion
  • Orthopnea (shortness of breath when lying down, as while sleeping)
  • Intolerance to exercise
  • Swelling in lower extremities and possibly abdomen
  • Weight gain
  • Dizziness
  • Syncopal episodes
  • Chest pain
  • Palpitations
  • Cough
  • Fatigue 
  • Weakness

Physical exam

  • Cardiac:
    • S3 gallop
    • Systolic heart murmur (from mitral or tricuspid regurgitation)
    • Point of maximal impulse typically normal
    • Jugular venous distention, particularly Kussmaul’s sign (jugular distention on inspiration), may be present.
  • Pulmonary: rales or crackles over lung fields (secondary to pulmonary edema)
  • Abdominal: hepatomegaly
  • Pitting edema in lower extremities
Jugular venous distension HF

Jugular venous distension:
Elevated filling level of jugular vein can be a nonspecific finding in heart failure.

Image by Lecturio.

Diagnosis

History and physical exam

  • Signs and symptoms suggestive of heart failure:
    • Ascites
    • Dependent edema
    • Decreased exercise tolerance
  • Signs of causative pathologies:
    • Hemochromatosis: bronze skin
    • Amyloidosis: carpal tunnel syndrome
    • Sarcoidosis: respiratory symptoms

Laboratory studies

  • ↑ BNP:
    • BNP is a marker of heart failure.
    • Renal failure can also increase BNP, making it less diagnostic in those cases.
  • Measure BUN and creatinine to monitor renal function/perfusion.
  • To investigate underlying cause, perform additional tests such as serum and urine protein tests (amyloidosis).

Electrocardiography

  • Typically abnormal but nonspecific 
  • May include ST changes, conduction delays, and other arrhythmias
  • Low voltage may be noted in amyloidosis.
ECG showing restrictive cardiomyopathy

Patient with cardiac amyloidosis:
Right and left ventricular tracing with concordant change in pressures during expiration and inspiration confirming the diagnosis of restrictive cardiomyopathy

Image: “Cardiac amyloidosis” by Division of Cardiology, University of South Alabama, Mobile, Alabama, USA. License: CC BY 2.5

Chest radiography

  • May show normal or enlarged heart with biatrial dilatation and pleural effusions
  • Presence of pericardial calcification leads to suspicion for constrictive pericarditis as an alternative diagnosis

Echocardiography

  • Assess cardiac:
    • Size
    • Structure
    • Function 
    • Differentiate from other causes.
  • Findings:
    • Biatrial enlargement 
    • Abnormal diastolic function with a restrictive filling pattern
    • Relatively preserved ventricular size, wall thickness, and left ventricular systolic function
  • Ventricles may have abnormal appearance in setting of infiltrative processes or storage deposition diseases.

Cardiac magnetic resonance imaging with gadolinium enhancement

Cardiac MRI with gadolinium enhancement can identify and determine extent of:

  • Myocardial damage
  • Fibrosis
  • Scarring
  • Necrosis
  • Infiltrative processes

Other considerations and tests

  • Endomyocardial biopsy may be done to confirm diagnosis in cases in which prior workup has been inconclusive.
  • Further evaluation is required to determine underlying cause.
  • If no secondary/underlying cause is identified, further evaluation of family history for possible familial hypertrophic cardiomyopathy is recommended.
  • Idiopathic RCM is a diagnosis of exclusion.

Management

Treatment

Treatment is aimed at managing heart failure and underlying secondary causes.

Goals of treatment:

  • ↓ Pulmonary and systemic venous congestion
  • ↓ Venous pressure
  • HR control to ↑ filling time (with caution to avoid bradycardia)
  • Maintain atrial contractions.
  • Manage/correct conduction disturbances.
  • Manage/avoid anemia, electrolyte imbalances, nutrient deficiencies, and calcium overload.

Medication:

  • Loop diuretics (i.e., furosemide (Lasix)) to ↓ edema/fluid overload
  • Calcium channel blockers (i.e., verapamil) to control HR and ↑ filling time
  • Beta-blockers may control HR, ↑ filling time, and ↑ ventricular relaxation.
  • ACE inhibitors or angiotensin II receptor blockers (ARBs) are helpful in select cases.
  • Oral anticoagulation, such as with warfarin, is necessary if atrial fibrillation is present.

Surgical intervention:

  • Devices (pacemaker or implanted cardioverter–defibrillator) in significant arrhythmias or conduction disorders
  • Cardiac transplantation in patients with severe heart failure refractory  to treatment

Complications

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

Prognosis

  • Poor with ↓ survival rates
  • Those with restrictive cardiomyopathy due to radiation/chemotherapy or amyloidosis have worse prognosis.
  • Male sex, age > 70 years, and more advanced diastolic dysfunction are also associated with poor prognosis.

Differential Diagnosis

  • Constrictive pericarditis: a disorder in which the pericardial sac becomes thickened and fibrotic, impairing the heart’s ability to function properly: Signs and symptoms are similar to those of RCM. Anything that can cause acute pericarditis (inflammation of pericardial sac) can cause constrictive pericarditis as well. It may be differentiated from RCM by the presence of a pericardial knock noted on exam, calcifications in the pericardium seen on a chest radiograph, and differentiating findings on cardiac MRI. Treatment involves removing the pericardium.  
  • Dilated cardiomyopathy (DCM): most common type of nonischemic cardiomyopathy: Etiology may be idiopathic, familial, or secondary to a variety of underlying conditions. Dilated cardiomyopathy is characterized by enlargement of one or both ventricles and reduced systolic function. Patients typically present with signs and symptoms of heart failure. Similar studies as those performed for RCM help to obtain the diagnosis. Treatment is also similar to that for RCM, including medications and devices. Dilated cardiomyopathy is the most common reason for cardiac transplantation. 
  • Hypertrophic cardiomyopathy (HCM): the most common inherited cardiomyopathy: Gene mutations affect contractile components of the heart called sarcomeres. The inheritance pattern is autosomal dominant; however, de novo mutations also occur. HCM is characterized by left ventricular asymmetrical wall thickening, diastolic dysfunction, and left ventricular outflow tract obstruction. Patients may be asymptomatic or suffer sudden cardiac death as the first sign of disease. Symptomatic individuals have dyspnea on exertion, chest pain, presyncope, or syncope. Diagnosis is made via ECG, echocardiography, stress testing, and cardiac MRI. Treatment for symptomatic individuals involves beta-blockers as first-line therapy with additional management depending on the presence of arrhythmia and left ventricular outflow tract obstruction.

References

  1. Dilated cardiomyopathy. (2021). Medline Plus. Retrieved February 5, 2021, from https://medlineplus.gov/ency/article/000168.htm
  2. Angelini A, Calzolari V, Thiene G, et al. (1997). Morphologic spectrum of primary restrictive cardiomyopathy. Am J Cardiol 80(8):1046–50. https://pubmed.ncbi.nlm.nih.gov/9352976/ 
  3. Fitzpatrick AP, Shapiro LM, Rickards AF, Poole-Wilson PA. (1990). Familial restrictive cardiomyopathy with atrioventricular block and skeletal myopathy. Br Heart J 63(2):114–8. https://pubmed.ncbi.nlm.nih.gov/2317404/ 
  4. Kushwaha SS, Fallon JT, Fuster V. (1997). Restrictive cardiomyopathy. N Engl J Med. https://pubmed.ncbi.nlm.nih.gov/8995091/ 
  5. Benotti JR, Grossman W, Cohn PF. (1980). Clinical profile of restrictive cardiomyopathy. Circulation. https://pubmed.ncbi.nlm.nih.gov/6445242/
  6. Ammash NM, Seward JB, Bailey KR, Edwards WD, Tajik AJ. (2000). Clinical profile and outcome of idiopathic restrictive cardiomyopathy. Circulation. https://pubmed.ncbi.nlm.nih.gov/10831523/

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