Arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC), also referred to as arrhythmogenic right ventricular dysplasia (ARVD) or simply arrhythmogenic cardiomyopathy, is classified as a type of cardiomyopathy. It is seen particularly in young males and is one of the more common causes of sudden death in these patients. 

Epidemiology

The estimated population prevalence is thought to range around 1 in 1000-5000 ⁸. It typically presents in young individuals. There is a recognised male predilection, with a male-to-female ratio of 2.7:1. Several reports suggest that there is a familial occurrence of ARVC of about 30-50%, with mainly autosomal dominant inheritance, various penetrance, and polymorphic phenotypic expression.

Clinical presentation

ARVC is characterised clinically by ventricular arrhythmias with left bundle branch block (LBBB) that may lead to cardiac arrest. As such, it may present as a sudden onset collapse or syncopal episode and should be a consideration in a young fit individual with such a presentation. 

Associations

• as the name implies this is associated with fatal arrhythmias and sudden cardiac death
• other nonfatal arrhythmias include
  • left bundle branch block: LBBB
  • ventricular tachycardia

Diagnosis is based on the presence of structural, histologic, electrocardiographic, arrhythmic, and genetic factors ⁴. This involves a combination of characteristic abnormalities in family history, electrocardiography, cardiac imaging as well as endomyocardial biopsy. 

Diagnostic criteria have also been developed, of which patients must have either two major criteria, one major and two minor criteria, or four minor criteria. See diagnostic criteria for arrhythmogenic right ventricular cardiomyopathy ². 

Pathology

Two morphologic variants of ARVC have been reported: fatty and fibrofatty.

The fatty form is characterized by almost complete replacement of the myocardium without thinning of the ventricular wall, and it occurs exclusively in the right ventricle.

The fibro-fatty variant is associated with significant thinning of the right ventricular wall, and the left ventricular myocardial wall may also be involved ^1-2.

Both idiopathic and familial aetiologies have been proposed (see epidemiology above) ².  

As the name implies, it classically involves the right ventricle although, on autopsy studies, a sizeable number of cases also show a degree of left ventricular involvement.

Radiographic features

Plain radiograph

Chest radiographic findings are non-specific and can often be normal. May show evidence of right ventricular dilatation (best seen on a lateral view).

Echocardiography

Echocardiography has inconsistent sensitivity and specificity for the diagnosis of ARVC, and is not considered a primary modality in the final diagnosis ¹².

The major echocardiographic criteria consistent with ARVC are:

• regional right ventricular dyskinesia or aneurysm (required)
• right ventricular outflow tract diameter (measured in the parasternal long axis) of 36 mm or larger
• a fractional area change of 33% or less

The minor criteria are:

• regional right ventricular akinesia or dyskinesia (required)
• right ventricular outflow tract diameter (measured in the parasternal long axis) between 29 and 35 mm
• a fractional area change between 34-39%

The aforementioned wall motion abnormalities are required. Disproportionate enlargement of the basal right ventricle, severe functional TR may occur in the presence of RV dilatation and dysfunction while, visualization of an intensely echogenic moderator band are supportive features in the presence of major or minor criteria ¹³.

MRI

Most sensitive imaging modality for diagnosis although image interpretation can still be difficult due to a degree of RV wall focal fatty infiltration (high signal on T1) in normal individuals ³. ARVC classically demonstrates fibro-fatty deposition in the right ventricular free wall, although this is not currently considered a part of the major or minor diagnostic criteriacriterion ⁹. ARVC also classically shows morphological features of right ventricular dilation and the ventricular wall may be thinned as a result. The left ventricle is usually spared (except in a very small proportion of cases ⁶). SSFP sequences may provide additional information on functional wall impairment. 

Other associated features include:

• right ventricular aneurysm formation
• diffuse right ventricular wall thinning resulting in severe global dilatation
• segmental hypokinesia

CT

May show right ventricular dilation and fatty low attenuation to the right ventricular wall.

Cardiac MRI

Cardiac MRI is the most sensitive diagnostic imaging modality.

Major cardiac MRI diagnostic criteria are:

• Regional RV akinesia or dyskinesia or dyssynchronous RV contraction and 1 of the following:
  • Ratio of RV end-diastolic volume to BSA 110 mL/m² (male) or 100 mL/m² (female)
  • RV ejection fraction 40%

Minor cardiac MRI diagnostic criteria are:

• Regional RV akinesia or dyskinesia or dyssynchronous RV contraction and 1 of the following:
  • Ratio of RV end-diastolic volume to BSA 100 to 110 mL/m2 (male) or 90 to 100 mL/m2 (female)
  • RV ejection fraction >40% to 45%

MRI may show fatty infiltration in the right ventricle (and occasionally in the left ventricle), ⁸. MRI may but this can also detect right ventricular dilatationbe seen in normal myocardium³ and aneurysm formation as well as wall-motion abnormalities including right ventricular dyskinesia, ais no longer part of the diagnostic criteria.⁹ A corrugated pattern to the right ventricular wall may be seen, known as the “accordion sign.”

Focal left ventricular dyskinesia may be present with fatty infiltration within the left ventricle. MRI is also helpful in evaluation of myocardial fibrosis and scarring.

Treatment and prognosis

ARVC is a progressive disease and will probably lead to right ventricular failure in the long term unless sudden cardiac death occurs beforehand.

The four therapeutic options in patients with ARVC include antiarrhythmic agents, catheter ablation, implantable cardioverter defibrillators, and surgery.

Differential diagnosis

Imaging differential considerations include:

• large right ventricular infarction
• idiopathic dilated cardiomyopathy
• Uhl anomaly
  • paper-thin right ventricle due to almost complete absence of myocardial muscle fibers
  • no gender predilection or familial occurrence