Arrhythmogenic right ventricular cardiomyopathy

ARVC is a disorder of the myocardium of unknown origin. The incidence and prevalence are unknown but ARVC is a well recognised cause of sudden death in adolescents and young people. There is a familial occurrence in about 50% of cases, with autosomal dominant inheritance with variable penetrance and polymorphic phenotypic expression. Several genetic disorders have been identified on chromosomes 14 and 3 and the disease is more frequent in males.

Regarding its physiopathologic mechanism, several hypothesis have been made. It has been considered an increase in apoptosis with fibrofatty replacement of the RV leading to electrical instability and arrhythmias. The disontogenic theory suggests that ARVC is a congenital disease with abnormal development of the right ventricle. A metabolic disorder is considered to affect the RV in the degenerative theory. Lastly, it has been suggested that the replacement by fibrofatty tissue would be the healing process of an episode of myocarditis. Two morphologic variants have been described: the fatty form, confined to the RV and without wall thinning, and the fibrofatty form, with frequent LV involvement, wall thinning and aneurysms (1) .

The clinical manifestations may vary, as there is a wide spectrum of different abnormalities which ranges from an asymptomatic form with ventricular ectopics to heart failure and sudden death in the young. Symptoms are due to arrhythmias originating in the affected myocardium, including ectopic beats, ventricular tachycardia, atrial and ventricular fibrillation. Generally, patients present with palpitations, syncope and sometimes sudden death. It is considered that 20% of sudden death in subjects younger than 35, specially when related to exercise, are due to ARVC. The EKG is abnormal in 90% of cases, showing both repolarization and depolarization alterations in right precordial leads, intraventricular conduction delay, complete or incomplete right bundle branch block, widening of the QRS complex (>110ms) in right precordial leads and epsilon waves just beyond the QRS complex in lead V1 (in 10%).

According to the Task Force Report (2) , the diagnosis is based on the detection of structural, histologic, electrocardiographic, arrhythmic and genetic factors. Several diagnostic criteria have been obtained from clinical characteristics, conventional, signal averaged and 24-hour EKG, exercise tolerance test, imaging techniques including echocardiography, cardiovascular magnetic resonance (CMR) and ultrafast CT, electrophysiologic study, MUGA, cardiac catheterization and endomyocardial biopsy. The fundamental feature is the presence of structural and functional alterations of the right ventricle and the diagnosis is made when the patient presents two major criteria, one major and two minor criteria, or four minor criteria (see table).

The standard of reference for diagnosis of ARVC is the histologic demonstration of transmural fibrofatty replacement of the right ventricular myocardium at autopsy or surgery, with criteria of greater than 3% fat and less than 40% fibrous tissue replacing the myocardial muscle. Endomyocardial biopsy is not sensitive enough, as the specimens are generally obtained from the septum and the pathologic changes of ARVC are segmental and occur mainly in the RV free wall. And also because a variable degree of fatty infiltration of the right ventricle is present in normal hearts of elderly people.

Imaging techniques are of great use in the diagnosis of ARVC. CMR appears to be the optimal technique, as it allows a three-dimensional evaluation of RV anatomy and function (RV free wall, inflow and outflow tracts), with an excellent spatial resolution, accuracy and reproducibility. The typical features of ARVC detected by CMR are:

1) global RV dilatation, including RVOT (severe: major criterion, mild: minor criterion)

2) global RV systolic (major criterion) and diastolic (minor criterion) dysfunction

3) RV wall thinning (major criterion)

4) localised aneuryms of RV and RVOT (major criterion)

5) fatty infiltration, usually visible with high signal intensity on T1-weighted images and recently shown also with helical CT (3)

6) regional wall motion abnormalities of the inferior and anterior RV free wall and of the RV outflow tract (minor criterion).

Also, features of high risk detectable by either echocardiography or CMR, are severe alteration of the right ventricle with decreased ejection fraction and involvement of the left ventricle (4).

Diagnosis of ARVC

The differential diagnosis of ARVC include idiopathic dilated cardiomyopathy and the Uhl anomaly, characterized by a thin right ventricle due to virtually absence of myocardial muscle fibers, with no gender predilection or familial occurrence.

There is no curative treatment, instead, the aim is to detect patients at high risk and prevent complications. The four therapeutic options are pharmacological agents as first choice (ACEI, anticoagulants, diuretics and antiarrhythmic agents as sotalol, verapamil, betablockers, amiodarone, flecainide), catheter ablation if the patient is refractory to drug treatment or the disease is localized, implantable cardioverter defibrillators in refractory patients at risk for sudden death and surgery as the last option, consisting on ventriculotomy and disconnection of the RV free wall or cardiac transplantation if severe terminal heart failure.

ARVC is a progressive disease. Four phases have been described in the disease, silent, appearance of arrhythmias, appearance of structural anomalies, heart failure. It leads to RV failure if sudden death does not occur before. The death rate is approximate 2.5% per year (5) .

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.