The differential diagnosis for the ventricular tachycardia due to ACM include: * Congenital heart disease * Repaired tetralogy of Fallot * Ebstein's anomaly * Uhl's anomaly * Atrial septal defect * Partial anomalous venous return * Acquired heart disease * Tricuspid valve disease * Pulmonary hypertension * Right ventricular infarction * Bundle-branch re-entrant tachycardia * Miscellaneous * Pre-excited AV re-entry tachycardia * Idiopathic RVOT tachycardia * Sarcoidosis In order to make the diagnosis of ACM, a number of clinical tests are employed, including the electrocardiogram (EKG), echocardiography, right ventricular angiography, cardiac MRI, and genetic testing. Electrocardiogram 90% of individuals with ARVD have some EKG abnormality. The most common EKG abnormality seen in ACM is T wave inversion in leads V1 to V3. However, this is a non-specific finding, and may be considered a normal variant in right bundle branch block (RBBB), women, and children under 12 years old. RBBB itself is seen frequently in individuals with ACM. This may be due to delayed activation of the right ventricle, rather than any intrinsic abnormality in the right bundle branch. The epsilon wave (marked by red triangle), seen in ARVD. The epsilon wave is found in about 50% of those with ACM. This is described as a terminal notch in the QRS complex. It is due to slowed intraventricular conduction. The epsilon wave may be seen on a surface EKG; however, it is more commonly seen on signal averaged EKGs. Ventricular ectopy seen on a surface EKG in the setting of ACM is typically of left bundle branch block (LBBB) morphology, with a QRS axis of −90 to +110 degrees. 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 MRI in a patient affected by ARVC/D (long axis view of the right ventricle): note the transmural diffuse bright signal in the RV free wall on spin echo T1 (a) due to massive myocardial atrophy with fatty replacement (b). In vitro MRI and corresponding cross section of the heart in ARVD show RV dilatation with anterior and posterior aneurysms (17-year-old asymptomatic male athlete who died suddenly during a soccer game). 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. False positives include other conditions with fatty infiltration of the ventricle, such as long-term excessive alcohol use and Duchenne or Becker muscular dystrophy. False negatives are common, however, because the disease progresses typically from the epicardium to the endocardium (with the biopsy sample coming from the endocardium), and the segmental nature of the disease. Also, due to the paper-thin right ventricular free wall that is common in this disease process, most biopsy samples are taken from the ventricular septum, which is commonly not involved in the disease process. A biopsy sample that is consistent with ACM would have > 3% fat, >40% fibrous tissue, and 1 – V3 * Localized prolongation (>110 ms) of QRS in V1 – V3 * Inverted T waves in V1 -V3 in an individual over 12 years old, in the absence of a right bundle branch block (RBBB) * Ventricular tachycardia with a left bundle branch block (LBBB) morphology, with superior axis * Family history * Familial disease confirmed either clinically or on autopsy or surgery Minor criteria * Right ventricular dysfunction * Mild global RV dilatation and/or reduced ejection fraction with normal LV. * Mild segmental dilatation of the RV * Regional RV hypokinesis * Tissue characterization * Electrocardiographical abnormalities * Late potentials on signal averaged EKG. * Ventricular tachycardia with a left bundle branch block (LBBB) morphology, with inferior or unknown axis * Frequent PVCs (> 500 PVCs / 24 hours)
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