Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM), also known as arrhythmogenic right ventricular cardiomyopathy (ARVC) or arrhythmogenic right ventricular dysplasia (ARVD), is an inherited heart disease. It is caused by genetic defects in components of the cardiac muscle known as desmosomes, which link muscle cells together.

These defects lead to structural and functional abnormalities, predominantly affecting the right ventricle but potentially involving both ventricles.

Signs and Symptoms

Individuals with ACM may be asymptomatic despite significant structural heart abnormalities. When symptoms do occur, they often present as abnormal heart rhythms (arrhythmias) such as palpitations or blackouts. Sudden death might be the first indication of ACM without preceding symptoms. Though commonly seen in adolescence and early adulthood, signs of ACM can rarely appear in infants. As the disease progresses, the right ventricle typically weakens first, causing fatigue and ankle swelling. In advanced stages, involvement of both ventricles can lead to shortness of breath, especially when lying flat.

Causes

Genetics

ACM is predominantly inherited in an autosomal dominant manner with variable expression. Only 30-50% of those affected will test positive for known genetic mutations in desmosomal proteins. Mutations in the desmin (DES) gene, linked to desmosomes, have also been implicated. The disease shows a higher penetrance in Italy. Types of ACM are classified based on different gene loci, such as TGFB3, RYR2, and DSP.

Exercise-induced ARVC

Long-term high-endurance exercise can lead to exercise-induced ARVC (EIARVC), potentially due to excessive right ventricular wall stress during intense physical activity. This form of ARVC often develops in the absence of desmosomal abnormalities.

Pathogenesis

The pathogenesis of ACM is not fully understood but involves apoptosis of myocardial cells. The disease may affect both ventricles, starting from the subepicardial region and progressing towards the endocardium. There are two pathological patterns: fatty infiltration and fibro-fatty infiltration. Fatty infiltration involves replacement of myocardium with fatty tissue, while fibro-fatty infiltration includes fibrous tissue replacement, often accompanied by inflammatory infiltrates.

Ventricular Arrhythmias

Ventricular arrhythmias in ACM typically originate from the right ventricle and range from frequent premature ventricular complexes (PVCs) to ventricular tachycardia (VT) and ventricular fibrillation (VF). Arrhythmias are often exercise-related and sensitive to catecholamines.

Diagnosis

Electrocardiogram (EKG)

90% of individuals with ACM exhibit EKG abnormalities, with T wave inversions in leads V1 to V3 being common. The epsilon wave, a terminal notch in the QRS complex, is seen in about 50% of cases.

Echocardiography

Echocardiography can reveal an enlarged, hypokinetic right ventricle with a thin RV free wall and tricuspid regurgitation.

Magnetic Resonance Imaging (MRI)

MRI can identify fatty infiltration and akinesis of the RV free wall, although differentiating between intramyocardial and epicardial fat can be challenging.

Angiography and Biopsy

Right ventricular angiography is the gold standard for ACM diagnosis, showing akinetic or dyskinetic bulging in specific RV regions. Biopsies can be highly specific but have low sensitivity due to the segmental nature of the disease.

Genetic Testing

Genetic testing can confirm ACM diagnosis in about 40-50% of cases by identifying mutations in desmosomal proteins.

Management

Management aims to reduce the risk of sudden cardiac death. High-risk individuals include those with extensive RV disease, left ventricular involvement, or a malignant familial history. Treatment options include pharmacological therapy, catheter ablation, implantable cardioverter-defibrillators (ICDs), and heart transplantation. Pharmacological management involves antiarrhythmic agents like sotalol and anticoagulation for those with decreased RV ejection fraction.

Family Screening

Family screening is essential to identify at-risk individuals. Screening tests include echocardiograms, EKGs, Holter monitoring, cardiac MRI, and exercise stress tests.

Prognosis

ACM is a progressive disease with a long asymptomatic period. Right ventricular failure typically precedes left ventricular dysfunction, eventually leading to bi-ventricular failure, congestive heart failure, and increased thromboembolic events.

Epidemiology

ACM affects about 1/10,000 people in the U.S. but has a higher prevalence in Italy. It accounts for up to 17% of sudden cardiac deaths in young individuals.

Society and Culture

Notable Cases

Notable individuals who died from ACM include Columbus Crew midfielder Kirk Urso, Sevilla FC's Antonio Puerta, and English cricketer James Taylor.

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Self-assessment MCQs (single best answer)

What is the primary cause of arrhythmogenic cardiomyopathy (ACM)?

Which ventricle is predominantly affected in ACM?

What is a common first indication of ACM in asymptomatic individuals?

ACM is predominantly inherited in which manner?

Which gene mutation is NOT typically associated with ACM?

Which diagnostic tool is considered the gold standard for ACM diagnosis?

What is the characteristic EKG finding in ACM?

Which of the following is a common treatment option for high-risk ACM patients?

In the pathogenesis of ACM, what is typically seen in the myocardial cells?

Which country has a higher prevalence of ACM?