Bradycardia arrhythmia may have many causes, both cardiac and non-cardiac. Non-cardiac causes are usually secondary, and can involve recreational drug use or abuse, metabolic or endocrine issues, especially hypothyroidism, an electrolyte imbalance, neurological factors, autonomic reflexes, situational factors, such as prolonged bed rest, and autoimmunity. Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease, or degenerative primary electrical disease. Ultimately, the causes act by three mechanisms: depressed automaticity of the heart, conduction block, or escape pacemakers and rhythms. In general, two types of problems result in bradycardias: disorders of the SA node, and disorders of the AV node. With SA node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the SA node into the surrounding atrial tissue (an "exit block"). Second-degree sinoatrial blocks can be detected only by use of a 12-lead ECG. It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia, but the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker. AV conduction disturbances (AV block; primary AV block, secondary type I AV block, secondary type II AV block, tertiary AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the bundle of His. The clinical relevance pertaining to AV blocks is greater than that of SA blocks. Beta<unk>  medicines also can slow the heart rate and decrease how forcefully the heart contracts. Beta-blockers may slow the heart rate to a dangerous level if prescribed with<unk>  channel<unk> -type medications.Bradycardia is also part of the mammalian diving reflex.
symptom of Calcium channel blocker toxicity
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symptom of Channelopathy
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symptom of Type 1 diabetes