Dilated Cardiomyopathy

A 50-year-old man presents with progressive shortness of breath on exertion, orthopnoea and ankle swelling. He has a history of heavy alcohol use. An echocardiogram reveals dilatation of all four chambers of the heart, with reduced left ventricular ejection fraction.

Pathophysiology

Dilated cardiomyopathy (DCM) is characterized by left ventricular dilatation and a decrease in ejection fraction. The heart muscle becomes weakened and cannot pump blood effectively, leading to systolic dysfunction.  This often progresses to include diastolic dysfunction as well. Although all four chambers of the heart can be affected, the left ventricle is typically more severely affected than the right ventricle.  DCM is characterised by apoptosis and fibrosis of the left ventricular wall, resulting in an enlarged, poorly contractile heart.

Aetiology

DCM is most commonly idiopathic.  However, the most common secondary causes of dilated cardiomyopathy are ischaemia and long-standing hypertension.  Other secondary causes include:

• Alcohol
• Postviral myocarditis
• Postpartum status
• Drugs (doxorubicin, AZT, cocaine)
• Radiation
• Endocrinopathies (thyrotoxicosis, hypothyroidism, acromegaly, pheochromocytoma)
• Infection (coxsackievirus, HIV, Chagas disease, parasites)
• Infiltrative Disease (haemochromatosis, sarcoidosis, amyloidosis)
• Genetic factors
• Nutritional disorders (wet beriberi)

Selenium deficiency is one reversible cause of dilated cardiomyopathy.  30–50% of cases are caused by inherited mutations, mostly autosomal dominant.

Epidemiology & Risk Factors

DCM is the third most common cause of heart failure and the most common reason for cardiac transplant.  It is more common in men than women by a ratio of approximately 3:1.

Clinical Features

The clinical presentation of DCM typically resembles that of heart failure and includes the following:

• Dyspnoea
• Orthopnoea
• Paroxysmal nocturnal dyspnoea
• Angina
• Fatigue
• Ankle swelling

Other possible features include:

• Arrhythmias
• Emboli (including cardioembolic stroke)
• Functional mitral regurgitation

Investigations

• Echocardiogram: This is the primary diagnostic tool for DCM, and it will typically show a reduced left ventricular ejection fraction, thinning of the left ventricular wall, and dilated left ventricle. It can also be used to assess for other abnormalities such as mitral regurgitation, left ventricular thrombus, and myocardial dyssynchrony.
• Electrocardiogram: This can show non-specific T-wave changes and poor R-wave progression.
• Chest X-ray: This may demonstrate cardiomegaly and pulmonary oedema.
• Blood tests: These may include a full blood count, urea and electrolytes, liver function tests, and brain natriuretic peptide.  A low sodium level indicates a poor prognosis.
  • TSH: both hyper- and hypo-thyroidism can cause DCM.
  • Ferritin and Transferrin: for suspected haemochromatosis.
• Cardiac catheterisation with endomyocardial biopsy may be performed if the diagnosis remains uncertain or to evaluate for specific causes such as myocarditis.  
• Cardiac MRI can also be used to assess cardiac structure and function and detect areas of myocardial fibrosis.
• Genetic Testing: May be indicated in cases of familial or idiopathic DCM.

Management

The management of DCM is largely the same as the management of heart failure and should involve a multidisciplinary approach. Referral to a specialist is indicated. 

Lifestyle modifications

• Smoking cessation: Smoking can worsen heart failure symptoms.
• Alcohol restriction: Alcohol can damage the heart muscle and worsen DCM.
• Sodium restriction: Limiting sodium intake can help reduce fluid retention.
• Fluid restriction: In severe cases, limiting fluid intake may be necessary.
• Regular exercise: Moderate exercise can improve heart function but should be undertaken within the limits of the patient's symptoms.

Medical management:

• Angiotensin-converting enzyme inhibitors (ACEIs): ACEIs have been shown to have a mortality benefit when used with β-blockers in NYHA class II–IV heart failure patients.
• β-blockers: Beta-blockers can slow the progression of DCM and improve symptoms.
• Diuretics: For symptomatic relief.
• Aldosterone antagonists: These medications can help improve survival in patients with severe DCM.
• Digoxin: Digoxin can improve heart contractility and reduce symptoms, although its effect on mortality is less clear.
• Anticoagulation: Patients with DCM are at risk of thromboembolism, particularly those with atrial fibrillation. Anticoagulation with warfarin or a DOAC may be recommended.

Device therapy:

• Implantable Cardioverter-Defibrillator: for those with reduced ejection fraction.
• Cardiac Resynchronisation Therapy: for those with reduced ejection fraction, in sinus rhythm and QRS > 150ms.

Surgical management:

• Left Ventricular Assist Device: as a bridge to transplant.
• Heart Transplant: A heart transplant is the definitive treatment for end-stage DCM but is reserved for carefully selected patients.

Complications and Prognosis

DCM can lead to a number of serious complications, including:

• Heart failure: As DCM progresses, the heart's contractile ability deteriorates.
• Arrhythmias: DCM can cause a variety of arrhythmias, including atrial fibrillation, ventricular tachycardia and ventricular fibrillation.
• Thromboembolism: Blood clots can form in the dilated chambers of the heart and can travel to other parts of the body, causing a stroke, pulmonary embolism.
• Sudden cardiac death: DCM can lead to sudden cardiac death, most commonly due to a fatal arrhythmia.

The prognosis for DCM is variable and depends on the underlying cause, the severity of heart dysfunction, and the presence of complications.  Early diagnosis and treatment can improve outcomes and reduce the risk of complications.