The origin of the ectopic beats is usually from one of the three regions of fatty degeneration (the "triangle of dysplasia"): the RV outflow tract, the RV inflow tract, and the RV apex. Signal averaged ECG (SAECG) is used to detect late potentials and epsilon waves in individuals with ACM. Echocardiography
Echocardiography may reveal an enlarged, hypokinetic right ventricle with a paper-thin RV free wall. The dilatation of the RV will cause dilatation of the tricuspid valve annulus, with subsequent tricuspid regurgitation. Paradoxical septal motion may also be present. MRI
Fatty infiltration of the RV free wall can be visible on cardiac MRI. Fat has increased intensity in T1-weighted images. However, it may be difficult to differentiate intramyocardial fat and the epicardial fat that is commonly seen adjacent to the normal heart. Also, the sub-tricuspid region may be difficult to distinguish from the atrioventricular sulcus, which is rich in fat. Cardiac MRI can visualize the extreme thinning and akinesis of the RV free wall. However, the normal RV free wall may be about 3 mm thick, making the test less sensitive. Angiography
Right ventricular angiography is considered the gold standard for the diagnosis of ACM. Findings consistent with ACM are an akinetic or dyskinetic bulging localized to the infundibular, apical, and subtricuspid regions of the RV. The specificity is 90%; however, the test is observer dependent. Biopsy
Transvenous biopsy of the right ventricle can be highly specific for ACM, but it has low sensitivity.
Family screening
All first degree family members of the affected individual should be screened for ACM. This is used to establish the pattern of inheritance. Screening should begin during the teenage years unless otherwise indicated. Screening tests include:

Echocardiogram
EKG
Signal averaged EKG
Holter monitoring
Cardiac MRI
Exercise stress test

Prognosis
There is a long asymptomatic lead-time in individuals with ACM. While this is a genetically transmitted disease, individuals in their teens may not have any characteristics of ACM on screening tests. Many individuals have symptoms associated with ventricular tachycardia, such as palpitations, light-headedness, or syncope. Others may have symptoms and signs related to right ventricular failure, such as lower extremity edema, or liver congestion with elevated hepatic enzymes. ACM is a progressive disease. Over time, the right ventricle becomes more involved, leading to right ventricular failure. The right ventricle will fail before there is left ventricular dysfunction. However, by the time the individual has signs of overt right ventricular failure, there will be histological involvement of the left ventricle. Eventually, the left ventricle will also become involved, leading to bi-ventricular failure. Signs and symptoms of left ventricular failure may become evident, including congestive heart failure, atrial fibrillation, and an increased incidence of thromboembolic events. Epidemiology
The prevalence of ACM is about 1/10,000 in the general population in the United States, although some studies have suggested that it may be as common as 1/1,000. Recently, 1/200 were found to be carriers of mutations that predispose to ACM.