Left dominant arrhythmogenic cardiomyopathy

Left dominant arrhythmogenic cardiomyopathy is a variant of arrhythmogenic right ventricular cardiomyopathy that predominantly affects the left ventricle of the heart. It may also be known as arrhythmogenic left ventricular cardiomyopathy ⁴.

Clinical presentation

The main clinical diagnostic features include the following ²:

• unexplained arrhythmia originating from the left ventricle
  • ventricular tachycardia with right bundle branch block configuration (sustained or nonsustained, on electrocardiogram, Holter monitoring, or exercise testing)
  • frequent ventricular extrasystoles with right bundle branch block configuration
• lateral or inferolateral T-wave inversions on electrocardiogram (leads V6, V5 ± V4, I, and aVL)

In addition, the diagnosis should be considered in the differential in patients who clinically present with the following ²:

• dilated cardiomyopathy with arrhythmia
• myocarditis

Pathology

The disease is characterized by fibroadipose tissue infiltrating the myocardium.

Location

The entity predominantly affects the posterolateral left ventricular wall and the interventricular septum ¹.

Microscopic appearance

Endomyocardial biopsy of the interventricular septum reveals myocyte loss and fibroadipose replacement ².

Genetics

Many patients have mutations for desmosomal proteins, such as desmoplakin, plakophilin-2, and desmoglein-2 ².

Radiographic features

MRI

The main imaging diagnostic features at cardiac MRI are the following ^2,3:

• left ventricular aneurysms
• mild left ventricular dilation and/or impaired systolic function
• extensive left ventricular late gadolinium enhancement in a subepicardial or midmyocardial distribution

In addition, macroscopic fatty areas may be seen on T1-weighted images without fat saturation or with fat-water separation techniques, but this is not a requirement ⁴. The right ventricular to left ventricular volume ratio is typically <1.

CT

Although not commonly used to establish the diagnosis, CT may show patches of fat attenuation within the left ventricular wall in a subepicardial or midwall distribution ¹.

Differential diagnosis

Considerations for patients with ventricular dysfunction and dilation include the following:

• late stage of classic arrhythmogenic right ventricular cardiomyopathy also involving the left ventricle
  • septal late gadolinium enhancement is uncommon, whereas septal involvement occurs in the majority of patients with left dominant arrhythmogenic cardiomyopathy
  • right ventricular global systolic dysfunction is present and more severe than left ventricular dysfunction, whereas the converse is true in left dominant arrhythmogenic cardiomyopathy ⁵
• biventricular variant of arrhythmogenic right ventricular cardiomyopathy
  • right ventricular to left ventricular volume ratio remains near 1 throughout the disease course ²
• idiopathic dilated cardiomyopathy
  • both may have midmyocardial late gadolinium enhancement, but subepicardial involvement favors arrhythmogenic cardiomyopathy ²
  • arrhythmia occurs in the setting of significant systolic dysfunction in dilated cardiomyopathy, whereas arrhythmia is disproportionate to the morphological or functional abnormalities in arrhythmogenic cardiomyopathy ²
  • an initial clinical presentation of heart failure is much more likely in dilated cardiomyopathy than in arrhythmogenic cardiomyopathy, which primarily presents with arrhythmia

The differential for fatty lesions in the heart is discussed separately.