Diagnosis
The differential diagnosis for the ventricular tachycardia due to ACM include:

Congenital heart disease
Repaired tetralogy of Fallot
Ebsteins anomaly
Uhls 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
SarcoidosisIn 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 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.
Diagnosis of a pericardial cyst can also be made before birth using ultrasound.The differential diagnosis for a suspected pericardial cyst includes a bronchial cyst, pericardial effusion, teratoma, lymphangioma, pericardial fat, congenital diaphragmatic hernia, neuroenteric cyst, and congenital cyst from the primitive foregut. A pericardial cyst also may look similar on imaging to a pericardial diverticula, which is connected to the pericardium and not fully walled off like a pericardial cyst. Management
Pericardial cysts that are small and cause no symptoms can be followed with repeat imaging through echocardiogram, CT, or MRI to assess for changes. Pericardial cysts that are large or cause symptoms may be candidates for percutaneous aspiration, ethanol sclerosis, or surgery. Percutaneous aspiration removes the fluid from inside the cyst, and ethanol sclerosis uses the injection of ethanol into the cyst after aspiration to decrease the likelihood of cyst recurrence. Percutaneous aspiration with ethanol sclerosis is typically the first treatment for pericardial cyst that requires management. Surgery can remove a pericardial cyst through a thoracotomy, sternotomy, mediastinoscopy, or video-assisted thoracic surgery. The type of surgery is chosen based on the size and location of the pericardial cyst. Prognosis
With most pericardial cysts having no symptoms, the prognosis is very good. The cysts can resolve without intervention. If percutaneous aspiration is performed, the recurrence rate of pericardial cysts is about 30-33%. Although pericardial cysts are benign, the location of cysts can rarely cause life-threatening emergencies by compressing the heart or lungs. Epidemiology
Pericardial cysts have an incidence of 1 in 100,000.