Sick sinus syndrome (also known as sinus node dysfunction) is a group of related heart conditions that can affect how the heart beats. "Sick sinus" refers to the sino-atrial (SA) node, which is an area of specialized cells in the heart that functions as a natural pacemaker. The SA node generates electrical impulses that start each heartbeat. These signals travel from the SA node to the rest of the heart, signaling the heart (cardiac) muscle to contract and pump blood. In people with sick sinus syndrome, the SA node does not function normally. In some cases, it does not produce the right signals to trigger a regular heartbeat. In others, abnormalities disrupt the electrical impulses and prevent them from reaching the rest of the heart.\n\nSick sinus syndrome occurs most commonly in older adults, although it can be diagnosed in people of any age. The condition increases the risk of several life-threatening problems involving the heart and blood vessels. These include a heart rhythm abnormality called atrial fibrillation, heart failure, cardiac arrest, and stroke.\n\nSick sinus syndrome tends to cause the heartbeat to be too slow (bradycardia), although occasionally the heartbeat is too fast (tachycardia). In some cases, the heartbeat rapidly switches from being too fast to being too slow, a condition known as tachycardia-bradycardia syndrome. Symptoms related to abnormal heartbeats can include dizziness, light-headedness, fainting (syncope), a sensation of fluttering or pounding in the chest (palpitations), and confusion or memory problems. During exercise, many affected individuals experience chest pain, difficulty breathing, or excessive tiredness (fatigue). Once symptoms of sick sinus syndrome appear, they usually worsen with time. However, some people with the condition never experience any related health problems.

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Jervell and Lange-Nielsen syndrome (JLNS) is characterized by congenital profound bilateral sensorineural hearing loss and long QTc, usually >500 msec. Prolongation of the QTc interval is associated with tachyarrhythmias, including ventricular tachycardia, episodes of torsade de pointes ventricular tachycardia, and ventricular fibrillation, which may culminate in syncope or sudden death. Iron-deficient anemia and elevated levels of gastrin are also frequent features of JLNS. The classic presentation of JLNS is a deaf child who experiences syncopal episodes during periods of stress, exercise, or fright. Fifty percent of individuals with JLNS had cardiac events before age three years. More than half of untreated children with JLNS die before age 15 years.

Congenital long QT syndrome (LQTS) is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Ogden syndrome (OGDNS) is an X-linked neurodevelopmental disorder characterized by postnatal growth failure, severely delayed psychomotor development, variable dysmorphic features, and hypotonia. Many patients also have cardiac malformations or arrhythmias (summary by Popp et al., 2015).

Jervell and Lange-Nielsen syndrome (JLNS) is characterized by congenital profound bilateral sensorineural hearing loss and long QTc, usually >500 msec. Prolongation of the QTc interval is associated with tachyarrhythmias, including ventricular tachycardia, episodes of torsade de pointes ventricular tachycardia, and ventricular fibrillation, which may culminate in syncope or sudden death. Iron-deficient anemia and elevated levels of gastrin are also frequent features of JLNS. The classic presentation of JLNS is a deaf child who experiences syncopal episodes during periods of stress, exercise, or fright. Fifty percent of individuals with JLNS had cardiac events before age three years. More than half of untreated children with JLNS die before age 15 years.

An autosomal dominant condition caused by mutation(s) in the KCNQ1 gene, encoding potassium voltage-gated channel subfamily KQT member 1. It is characterized by a prolonged QT interval that may result in torsade de pointes, ventricular fibrillation and/or sudden cardiac death.

Ventricular arrhythmias due to cardiac ryanodine receptor calcium release deficiency syndrome (VACRDS) is characterized by syncope, cardiac arrest, and/or sudden unexpected death. Polymorphic ventricular tachycardia and ventricular fibrillation have been documented in these patients. Symptoms generally occur with physical activity or emotional stress, but unlike typical catecholaminergic ventricular tachycardia (CPVT), arrhythmias are not reproducible on exercise stress testing or adrenaline challenge (Sun et al., 2021). Mutation in the RYR2 gene also causes catecholaminergic polymorphic ventricular tachycardia-1 (CPVT1; 604772).

TANGO2 deficiency is characterized by developmental delay, intellectual disability, gait incoordination, speech difficulties, seizures, and hypothyroidism. Most individuals have TANGO2 spells, non-life-threatening paroxysmal worsening of baseline symptoms, including sudden onset of hypotonia, ataxia with loss of balance, head and body tilt, increased dysarthria, drooling, lethargy, and disorientation. In addition, life-threatening acute metabolic crises can occur, including rhabdomyolysis with elevated creatine phosphokinase and liver transaminases, hypoglycemia, prolonged QTc on EKG, ventricular arrhythmias, and/or cardiomyopathy.