Ventricular tachycardia due to arrhythmogenic right ventricular dysplasia
arrhythmogenic right ventricular dysplasia is an inherited disease characterized by the gradual replacement of the cardiac muscle cells by fibro-adipose tissue. Transmission is autosomal dominant with variable penetrance and expression by mutation of the genes encoding for desmosome proteins. Dysplasia predominantly affects men with a male to female ratio of 3:1 and is usually manifested in young subjects, the symptoms appearing most often before the age of 40 years. The replacement of the myocardium with fatty tissue and fibrosis can be widespread and extend to the left ventricle in advanced forms or be more localized at the apex or right ventricular infundibulum. The evolution of the disease varies from one individual to another, with some patients remaining totally asymptomatic or presenting only minor symptoms. Histological abnormalities can contribute to the development of ventricular rhythm disorders that can lead to palpitations, syncope or sudden death due to intense sports activity. This disease is frequently found in high-level athletes having suffered a sudden death and is the second cause (after hypertrophic cardiomyopathy) of sudden death in the young patient. One of the difficulties in the management of these patients is that the first observed clinical manifestation may be the occurrence of sudden death. When the disease evolves, symptoms related to a right and subsequently biventricular heart failure may appear.
Diagnosis is based on the detection of a combination of major as well as minor clinical, ECG or morphological criteria. The aim of the evaluation is to confirm the diagnosis, to assess the risk of sudden death and to specify the extent of the disease.
The surface electrocardiogram plays a central role since some criteria are considered as major others as minor. It can reveal:
- an epsilon wave which corresponds to the presence of a low amplitude electrical potential between the end of the QRS complex and the beginning of the T wave in the right precordial leads (V1-V3); this potential, a marker of delayed activation, is the most specific sign with however a moderate sensitivity, since observed in only 30% of patients; it is a major criterion for the diagnosis of dysplasia;
- a reversal of the T waves in right-sided precordial leads (typically from V1 to V3); the inversion of the T waves in the precordium (sometimes up to V6) reflects the degree of extension of the disease (right ventricle and then left ventricle); this sign is relatively sensitive and observed in a majority of patients with dysplasia but not very specific since frequently observed in patients under 12 years of age and in certain healthy adults;
- the presence of a complete or incomplete right bundle branch block or a parietal block defined by a widening of the QRS in right-sided precordial leads (V1-V3) relative to the left precordial leads (V4-V6) reflecting a localized conduction disorder;
- the presence of isolated ventricular extrasystoles, in couplets/triplets, of nonsustained or sustained ventricular tachycardias with left delay and axis according to its point of origin: vertical if the arrhythmia originates in the infundibulum or the upper aspect of the septum, left if it originates on the diaphragmatic wall of the right ventricle; arrhythmias are frequently triggered by physical exertion; the presence of several morphologies is strongly suggestive of the presence of a heart disease;
In addition to the electrocardiogram, several supplementary exams are performed:
- search for late potentials by a high amplification ECG showing the presence of localized delays in ventricular activation,
- isoproterenol test to investigate the presence of a polymorphism,
- MRI is currently the reference exam with the search of structural and functional abnormalities to confirm the diagnosis and to assess the extension of the disease; search for a dilated right ventricle, fibro-adipose infiltrates, akinetic or dyskinetic areas, ventricular aneurysms, segmental contraction abnormalities, ventricular dysfunction and left ventricular extension.
Therapeutic management varies according to the severity of the disease. Severe cardiac arrhythmias occurring most often upon physical exertion, competitive sports are contraindicated. High dose beta-blockers are the reference medical treatment. Radiofrequency ablation can be proposed essentially in patients with episodes of recurrent ventricular tachycardia resistant to medical treatment. Patients most at risk of sudden death must undergo implantation of a defibrillator. Recognized risk factors are recovered sudden death, syncope, history of familial sudden death or recurring rhythm disorders despite well-monitored medical treatment.