Ebstein anomaly is characterized by downward displacement of variable severity of the tricuspid valve into the right ventricle. The valve leaflets may be dysplastic, and a variable portion of the proximal part of the right ventricle is in continuity with the right atrium ('atrialized'), because of the abnormally positioned tricuspid valve. The severity of this defect includes a spectrum ranging from severe disturbance in fetal and neonatal life to virtually asymptomatic survival to adult life. Associated extracardiac anomalies in the setting of chromosomal or mendelian disorders occur in about 20% of patients with Ebstein anomaly. Nonsyndromic Ebstein anomaly can occur as a sporadic or a familial defect (summary by Digilio et al., 2011).

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by episodic syncope occurring during exercise or acute emotion. The underlying cause of these episodes is the onset of fast ventricular tachycardia (bidirectional or polymorphic). Spontaneous recovery may occur when these arrhythmias self-terminate. In other instances, ventricular tachycardia may degenerate into ventricular fibrillation and cause sudden death if cardiopulmonary resuscitation is not readily available. The mean onset of symptoms (usually a syncopal episode) is between age seven and 12 years; onset as late as the fourth decade of life has been reported. If untreated, CPVT is highly lethal, as approximately 30% of affected individuals experience at least one cardiac arrest and up to 80% have one or more syncopal spells. Sudden death may be the first manifestation of the disease.

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the SCN5A gene.

Atrial standstill (AS) is a rare condition characterized by the absence of electrical and mechanical activity in the atria. On surface ECG, AS is distinguished by bradycardia, junctional (usually narrow complex) escape rhythm, and absence of the P wave. Nearly 50% of patients with AS experience syncope. AS can be persistent or transient, and diffuse or partial (summary by Fazelifar et al., 2005). For a discussion of genetic heterogeneity of atrial standstill, see ATRST1 (108770).

Atrial standstill (AS) is a rare condition characterized by the absence of electrical and mechanical activity in the atria. On surface ECG, AS is distinguished by bradycardia, junctional (usually narrow complex) escape rhythm, and absence of the P wave. Nearly 50% of patients with AS experience syncope. AS can be persistent or transient, and diffuse or partial (summary by Fazelifar et al., 2005).