<unk>  <unk>  is a term used to describe a number of different abnormal heart rhythms (arrhythmias) caused by a malfunction of the<unk>  node, the heart's "natural" pacemaker. It encompasses disorders causing reduced automaticity of the sinoatrial node, exit block, and<unk>  arrest. The syndrome primarily affects the elderly, and is associated with paroxysmal atrial fibrillation or flutter in approximately half of the patients and with distal conduction disease in up to one tenth of patients.<unk>  was first described by Dr. Keith and Dr. Flack, in 1907. In 2015, MYH6 gene mutations were first implicated in the pathogenesis of<unk> . In 1972, Dr. Mandel found a new method of assessing<unk>  node function, known as<unk>  node recovery time. There is no classification system for<unk> .<unk>  occurs as an improperly propagated signal from the sinoatrial (SA) node. Age-dependent progressive fibrosis of the<unk>  nodal tissue and Remodeling of a<unk> trial node are the potential mechanisms of this abnormally formed signal propagation. MYH6 gene may also be involved in the pathogenesis of this condition.<unk>  can result in many abnormal heart rhythms (arrhythmias), including<unk>  arrest,<unk>  node exit block,<unk>  bradycardia, and other types of bradycardia (slow heart rate).<unk>  may also be caused by a variety of conditions including but not limited to myocardial infarction, atrial fibrillation, drugs or toxins, infections,medications, electrolyte abnormalities, hypothermia, hypoxemia, hypercarbia, and acidosis.<unk>  must be differentiated from other cause of syncope, lightheadedness, dizziness, and tachycardia-bradycardia syndrome. The incidence of<unk>  increases with increasing age, occurring in 1 of every 600 cardiac patients above the age of 65 years old.<unk>  <unk>  usually occurs in individuals older than 50 years old. There is no difference in incidence of<unk>  between men and women. In addition, the black population was found to have a 41% lower risk of developing<unk>  as compared to the white population. There is insufficient evidence to recommend routine screening for<unk> .<unk>  natural history progress over decades. Patients are usually asymptomatic at first, but then symptoms may present due to the insufficient blood supply.<unk>  pause or severe bradycardia may present with the central nervous system (CNS) under perfusion which manifests with presyncope or syncope. Possible complications of<unk>  include cerebrovascular events, stroke, transient ischemic events, renal, gastrointestinal hypo-perfusion, thromboembolism, Fatigue and exercise intolerance. The syndrome is progressive, which means it usually gets worse over time. Patients with<unk>  <unk>  may present with nonspecific symptoms or be asymptomatic. 50 percent of patients present with syncope or pre-syncope related to the decreased cerebral perfusion secondary to bradyarrhythmias or tachyarrhythmias. Some of the symptoms that may develop among patients include memory loss, dizziness or light-headedness, Palpitations, chest pain or angina, shortness of breath, fatigue, and headache. Patients with<unk>  usually appear normal. Physical examination of patients with<unk>  is usually remarkable for bradycardia, tachycardia, and signs of the organ hypoperfusion. There is no laboratory findings associated with the diagnosis of<unk> . However, electrolyte abnormalities may be one of the causes. Possible metabolic disturbances associated with<unk>  include hyperkalemia, hypokalemia, hypoglycemia, hypocalcemia, and hypoxia.<unk>  is a collection of heart rhythm disorders that include<unk>  bradycardia,<unk>  pauses and<unk>  arrest.<unk>  can evolve towards causing atrial fibrillation, atrial flutter, ectopic atrial tachycardia,<unk>  node reentrant tachycardia, and tachycardia-bradycardia. There are no echocardiography/ultrasound findings associated with<unk> . The management of<unk>  depends on the underlying cause and the presenting symptoms. Asymptomatic patients are usually monitored without therapy. Atropine may be used in the presence of symptoms or hemodynamic compromise. The management of<unk>  depends on the underlying cause and the presenting symptoms. After correcting the reversible causes of<unk> , it can be managed by placing an implantable pacemaker. Indications of the implantable pacemaker include, patients with documented bradycardia and are symptomatic, patients with chronotropic incompetence,<unk>  node dysfunction secondary to medications necessitated by another medical condition, and patients with heart rate < 40 per minute.
Sick sinus syndrome
Siccardi syndrome
Aicardi syndrome
Adams-Stokes syndrome
Acute coronary syndromes
Stress cardiomyopathy
Obesity cardiomyopathy
Avasthey syndrome