Diagnosis of ARVD
Arrhythmogenic right ventricular dysplasia (ARVD) should be suspected in a young or middle aged person who has ventricular arrhythmias with left bundle branch block morphology and who does not have other cardiac disease. Presentation as right ventricular failure is uncommon. A 12-lead electrocardiogram should be carefully examined for
1) T wave inversion beyond lead V1
2) epsilon waves, which are reproducible small deflections seen just beyond the QRS complex in lead V1 or V2.
3) Right ventricular parietal block as evidenced by a QRS duration
in V1 + V2 + V3 that is longer than that in leads V4, V5, V6 by a ratio of 1:2.
The sensitivity to detect these ECG abnormalities is enhanced by careful skin preparation to eliminate artifacts and by recording the electrocardiogram at double speed (50 mm/second) and double the usual amplitude (20 mm/mvolts).
The major differential diagnosis in a patient who has left ventricular arrhythmias of left bundle block morphology with a configuration of inferior QRS axis (negative QRS in lead AVL) is that of right ventricular outflow tract (RVOT) tachycardia. Patients with RVOT tachycardia do not usually have the ECG abnormalities associated with ARVD and the signal-averaged electrocardiogram is generally normal. They may have some dilatation and decrease in contractility limited to the right ventricular outflow tract.
It is important to determine if the patient has ARVD or RVOT tachycardia for two reasons. First, the prognosis of the two conditions is different. RVOT tachycardia has an excellent prognosis and seldom results in arrhythmic death. In contrast, there is a risk of sudden death as great as 1% per year in patients with ARVD who have ventricular arrhythmias. Secondly, ARVD may be hereditary whereas RVOT tachycardia is not. Therefore, when the diagnosis of ARVD is made, it is recommended that first degree relatives (parents, brothers, sisters, and children of the affected person) be evaluated for presence of this condition in order to prevent the unusual occurrence of arrhythmic death in family members.
he signal-averaged electrocardiogram is usually abnormal in ARVD patients who have sustained ventricular tachycardia. An abnormal signal averaged ECG is supportive of the diagnosis of ARVD but a negative test does not exclude this diagnosis.
The right ventricle has an irregular shape and is heavily trabeculated. Its contraction pattern is not concentric and uniform Therefore, slight abnormalities either may be undetected or it may be difficult to be certain that an abnormality in fact, does exist. Right ventricular size, volume, and contractility must be quantitated using standardized views in order to differentiate normal from abnormal right ventricular structure and function. ARVD does not affect the right ventricle uniformly. The right ventricular free wall is involved in particular locations, especially the right ventricular outflow tract, the right ventricular apex, and the posterior subtricuspid area. The septum is usually spared.
Echocardiography when properly performed by focusing attention on right ventricular function and wall motion abnormalities is an excellent way of screening for ARVD. The posterior and inferior wall of the right ventricular inflow tract under the tricuspid valve is the most important region that must be visualized because it is most frequently affected. This may be seen in the parasternal long axis view with the probe angled toward the inferior vena cava or the liver. Another projection to visualize this area as well as the RV apex is the apical RV two-chamber view with the probe angled toward the right ventricle by 20-30 degrees.The angiographic features of arrhythmogenic right ventricular dysplasia (ARVD) include global and/or regional function and morphological abnormalities of the right ventricle including localized akinetic or dyskinetic bulges, outpouchings, dilatation of the infundibulum, trabecular hypertrophy and/or disarray with deep fissures. The study has a standardized echo protocol and the Echo Core Laboratory is under the direction of Dr. Michael Picard, Massachusetts General Hospital.
Once an RV angiogram has been performed with appropriate views and adequate contrast, interpretation of wall motion abnormalities pose a distinct challenge, particularly when minor abnormalities are suspected. At present, angiography appears to be most reliable for the above assessment, although in the future, 3D echocardiography and MRI may be used in place of angiography for the evaluation of structure and function of the right ventricle. The study has a standardized angiogram protocol and the Angiogram Core Laboratory is under the direction of Dr. Thomas Wichter, Muenster, Germany.
When a patient has the overt manifestations of the disease including evident right ventricular abnormalities, the MRI can be confirmatory by its unique ability to identify and characterize fatty tissue infiltration in the right ventricular free wall. However, in patients with ventricular arrhythmias of left bundle branch block morphology who have minimal anatomic abnormalities of the right ventricle, the sensitivity and specificity of the MRI to distinguish normals from ARVD has not been defined. In addition, there may be variable degrees of penetration of epicardial fat into the medial layer of the right ventricle in normal individuals. Also the right ventricular free wall is only 4-5 mm thick and the resolution of the MRI to detect thinning of several millimeters is questionable. Finally, most radiologists have limited experience in the diagnosis of ARVD by MRI. Until these issues are clarified, cardiologists should be cautioned not to solely rely on the MRI to diagnose ARVD. The study has a standardized protocol for MRI evaluation and MRIs are sent to the MRI Core Laboratory under the direction of Dr. David Bluemke, Johns Hopkins Hospital.
It is essential to examine the involvement of the myocardium of the right ventricular free wall with fibrous and /or fatty replacement and validate the clinical diagnosis by pathological examination of right ventricular endomyocardial biopsy samples. The interventricular septum is usually not involved in ARVD. Myocarditis predominantly affecting the right ventricle can mimic the clinical presentation of ARVD. Structural abnormalities of development of the right ventricle may be difficult to differentiate from ARVD with certainty without histopathology. The Pathology Core Laboratory is under the direction of Dr. Gaetano Thiene, Padua, Italy.