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Sick sinus syndrome 2, autosomal dominant(SSS2)

MedGen UID:
320273
Concept ID:
C1834144
Disease or Syndrome
Synonyms: ATRIAL FIBRILLATION WITH BRADYARRHYTHMIA; SICK SINUS SYNDROME 2; SICK SINUS SYNDROME 2 WITH OR WITHOUT CARDIAC NONCOMPACTION AND/OR ASCENDING AORTA DILATION; SINUS BRADYCARDIA SYNDROME, FAMILIAL, AUTOSOMAL DOMINANT; SINUS NODE DISEASE, FAMILIAL, AUTOSOMAL DOMINANT; SSS2
 
Gene (location): HCN4 (15q24.1)
 
Monarch Initiative: MONDO:0008102
OMIM®: 163800

Definition

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.

Sick 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.

Sick 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. [from MedlinePlus Genetics]

Clinical features

From HPO
Sudden cardiac death
MedGen UID:
38841
Concept ID:
C0085298
Pathologic Function
The heart suddenly and unexpectedly stops beating resulting in death within a short time period (generally within 1 h of symptom onset).
Aortic regurgitation
MedGen UID:
8153
Concept ID:
C0003504
Disease or Syndrome
An insufficiency of the aortic valve, leading to regurgitation (backward flow) of blood from the aorta into the left ventricle.
Atrial fibrillation
MedGen UID:
445
Concept ID:
C0004238
Finding
An atrial arrhythmia characterized by disorganized atrial activity without discrete P waves on the surface EKG, but instead by an undulating baseline or more sharply circumscribed atrial deflections of varying amplitude an frequency ranging from 350 to 600 per minute.
Cardiac arrest
MedGen UID:
5456
Concept ID:
C0018790
Finding
An abrupt loss of heart function.
Mitral valve prolapse
MedGen UID:
7671
Concept ID:
C0026267
Disease or Syndrome
One or both of the leaflets (cusps) of the mitral valve bulges back into the left atrium upon contraction of the left ventricle.
Sick sinus syndrome
MedGen UID:
20749
Concept ID:
C0037052
Disease or Syndrome
An abnormality involving the generation of the action potential by the sinus node and is characterized by an atrial rate inappropriate for physiological requirements. Manifestations include severe sinus bradycardia, sinus pauses or arrest, sinus node exit block, chronic atrial tachyarrhythmias, alternating periods of atrial bradyarrhythmias and tachyarrhythmias, and inappropriate responses of heart rate during exercise or stress.
Syncope
MedGen UID:
21443
Concept ID:
C0039070
Sign or Symptom
Syncope is a syndrome in which loss of consciousness is of relatively sudden onset, temporary (usually less than 1 to 2 minutes), self-terminating, and of usually rapid recovery. Syncope leads to a generalized weakness of muscles with loss of postural tone, inability to stand upright, and loss of consciousness. Once the patient is in a horizontal position, blood flow to the brain is no longer hindered by gravitation and consciousness is regained. Unconsciousness usually lasts for seconds to minutes. Headache and drowsiness (which usually follow seizures) do not follow a syncopal attack. Syncope results from a sudden impairment of brain metabolism usually due to a reduction in cerebral blood flow.
Torsade de pointes
MedGen UID:
21214
Concept ID:
C0040479
Disease or Syndrome
A type of ventricular tachycardia characterized by polymorphioc QRS complexes that change in amplitue and cycle length, and thus have the appearance of oscillating around the baseline in the EKG.
Ventricular fibrillation
MedGen UID:
21844
Concept ID:
C0042510
Disease or Syndrome
Uncontrolled contractions of muscles fibers in the left ventricle not producing contraction of the left ventricle. Ventricular fibrillation usually begins with a ventricular premature contraction and a short run of rapid ventricular tachycardia degenerating into uncoordinating ventricular fibrillations.
Sinus bradycardia
MedGen UID:
39316
Concept ID:
C0085610
Pathologic Function
Bradycardia related to a mean resting sinus rate of less than 50 beats per minute.
Left ventricular hypertrophy
MedGen UID:
57442
Concept ID:
C0149721
Disease or Syndrome
Enlargement or increased size of the heart left ventricle.
Paroxysmal atrial fibrillation
MedGen UID:
115990
Concept ID:
C0235480
Disease or Syndrome
Episodes of atrial fibrillation that typically last for several hours up to one day and terminate spontaneously.
Prolonged QTc interval
MedGen UID:
294666
Concept ID:
C1560305
Pathologic Function
A longer than normal interval (corrected for heart rate) between the Q and T waves in the heart's cycle. Prolonged QTc can cause premature action potentials during late phase depolarizations thereby leading to ventricular arrhythmias and ventricular fibrillations.
Left ventricular noncompaction
MedGen UID:
450531
Concept ID:
C1960469
Disease or Syndrome
Left ventricular noncompaction is a heart (cardiac) muscle disorder that occurs when the lower left chamber of the heart (left ventricle), which helps the heart pump blood, does not develop correctly. Instead of the muscle being smooth and firm, the cardiac muscle in the left ventricle is thick and appears spongy. The abnormal cardiac muscle is weak and has an impaired ability to pump blood because it either cannot completely contract or it cannot completely relax. For the heart to pump blood normally, cardiac muscle must contract and relax fully.\n\nSome individuals with left ventricular noncompaction experience no symptoms at all; others have heart problems that can include sudden cardiac death. Additional signs and symptoms include abnormal blood clots, irregular heart rhythm (arrhythmia), a sensation of fluttering or pounding in the chest (palpitations), extreme fatigue during exercise (exercise intolerance), shortness of breath (dyspnea), fainting (syncope), swelling of the legs (lymphedema), and trouble laying down flat. Some affected individuals have features of other heart defects. Left ventricular noncompaction can be diagnosed at any age, from birth to late adulthood. Approximately two-thirds of individuals with left ventricular noncompaction develop heart failure.

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