Benson DW, Wang DW, Dyment M, Knilans TK, Fish FA, Strieper MJ, Rhodes TH,.Diagnosis and treatment of sick sinus syndrome. Over time, the SA node may harden and develop scar-like damage (fibrosis) that prevents it from working properly. In older adults, sick sinus syndrome is often associated with age-related changes in the heart. One of the most common causes of sick sinus syndrome in children is trauma to the SA node, such as damage that occurs during heart surgery. Certain medications, such as drugs given to treat abnormal heart rhythms or high blood pressure, can also disrupt SA node function. These include a variety of heart conditions, other disorders such as muscular dystrophy, abnormal inflammation, or a shortage of oxygen (hypoxia). More commonly, sick sinus syndrome is caused by other factors that alter the structure or function of the SA node. Researchers believe that the MYH6 gene variation changes the structure of myosin, which can affect cardiac muscle contraction and increase the likelihood of developing an abnormal heartbeat. The protein produced from the MYH6 gene forms part of a larger protein called myosin, which generates the mechanical force needed for cardiac muscle to contract. These changes lead to abnormal heartbeats and the other symptoms of sick sinus syndrome.Ī particular variation in another gene, MYH6, appears to increase the risk of developing sick sinus syndrome. Mutations in these genes reduce the flow of ions, which alters the SA node's ability to create and spread electrical signals. The flow of these ions is essential for creating the electrical impulses that start each heartbeat and coordinate contraction of the cardiac muscle. These genes provide instructions for making proteins called ion channels that transport positively charged atoms (ions) into cardiac cells, including cells that make up the SA node.

Mutations in two genes, SCN5A and HCN4, have been found to cause the condition in a small number of families. Genetic changes are an uncommon cause of sick sinus syndrome. In many cases, the cause of the condition is unknown. Sick sinus syndrome can result from genetic or environmental factors. These include a heart rhythm abnormality called atrial fibrillation, heart failure, cardiac arrest, and stroke. The condition increases the risk of several life-threatening problems involving the heart and blood vessels. Sick sinus syndrome occurs most commonly in older adults, although it can be diagnosed in people of any age. However, some people with the condition never experience any related health problems. Once symptoms of sick sinus syndrome appear, they usually worsen with time. During exercise, many affected individuals experience chest pain, difficulty breathing, or excessive tiredness (fatigue). 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.

In some cases, the heartbeat rapidly switches from being too fast to being too slow, a condition known as tachycardia-bradycardia syndrome. Sick sinus syndrome tends to cause the heartbeat to be too slow (bradycardia), although occasionally the heartbeat is too fast (tachycardia).

In others, abnormalities disrupt the electrical impulses and prevent them from reaching the rest of the heart. In some cases, it does not produce the right signals to trigger a regular heartbeat. In people with sick sinus syndrome, the SA node does not function normally. These signals travel from the SA node to the rest of the heart, signaling the heart (cardiac) muscle to contract and pump blood. The SA node generates electrical impulses that start each heartbeat. '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. Sick sinus syndrome (also known as sinus node dysfunction) is a group of related heart conditions that can affect how the heart beats.