ARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.\n\nArrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.

Progressive familial heart block type I (PFHBI, PFHB1) is an autosomal dominant cardiac bundle branch disorder that may progress to complete heart block (Brink and Torrington, 1977; van der Merwe et al., 1986; van der Merwe et al., 1988). It is defined on electrocardiogram by evidence of bundle branch disease, i.e., right bundle branch block, left anterior or posterior hemiblock, or complete heart block, with broad QRS complexes. Progression has been shown from a normal electrocardiogram to right bundle branch block and from the latter to complete heart block. These electrocardiographic features differentiate PFHB type I from progressive familial heart block type II (PFHBII, PFHB2; 140400), in which the onset of complete heart block is associated with narrow complexes. Electrocardiographically the changes represent, respectively, bundle branch disease (PFHB1) and atrioventricular nodal disease with an atrioventricular block and an idionodal escape rhythm (PFHB2). PFHBI is manifested symptomatically when complete heart block supervenes, either with dyspnea, syncopal episodes, or sudden death. Treatment, which is best managed by regular electrocardiographic follow-up, is by the timely implantation of a pacemaker (Brink et al., 1995). Genetic Heterogeneity of Progressive Familial Heart Block Type I Progressive familial heart block type IB (PFHB1B; 604559) is caused by mutation in the TRPM4 gene (606936) on chromosome 19q13.32.

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome.

Atrial fibrillation (AF) is the most common sustained cardiac rhythm disturbance, affecting more than 2 million Americans, with an overall prevalence of 0.89%. The prevalence increases rapidly with age, to 2.3% between the ages of 40 and 60 years, and to 5.9% over the age of 65. The most dreaded complication is thromboembolic stroke (Brugada et al., 1997). For a discussion of genetic heterogeneity of atrial fibrillation, see 608583.

An extremely rare genetic congenital heart disease characterized by the presence of atrial septal defect, mostly of the ostium secundum type, associated with conduction anomalies like atrioventricular block, atrial fibrillation or right bundle branch block.

Atrial fibrillation is the most common sustained cardiac rhythm disturbance, affecting more than 2 million Americans, with an overall prevalence of 0.89%. The prevalence increases rapidly with age, to 2.3% between the ages of 40 and 60 years, and to 5.9% over the age of 65. The most dreaded complication is thromboembolic stroke (Brugada et al., 1997). For a discussion of genetic heterogeneity of familial atrial fibrillation, see ATFB1 (608583).