Bradycardia
| Bradycardia | |
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| ICD-10 | R00.1 |
| ICD-9 | 427.81, 659.7, 785.9, 779.81 |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: M.Umer Tariq [2]
Overview
Bradycardia, as applied to adult medicine, is defined as a resting heart rate of under 60 beats per minute, although slower sinus rates are often very well tolerated. Asymptomatic resting bradycardias, particularly in trained athletes and young individuals are not pathological and doesn't not require treatment. Pathologic bradycardias are caused by disorders of impulse generation (impaired automaticity at SA node), impulse conduction (heart block) or escape pacemakers and rhythms. Bradycardia can be underlain by several causes, which are best divided into cardiac and non-cardiac causes. Non-cardiac causes are usually secondary, and can involve recreational drug use, endocrine disorders (hypothyroid); electrolyte imbalance (hyperkalemia); autonomic reflexes; situational factors (prolonged bed rest); infections lyme disease, medications, and autoimmunity disorders. Cardiac causes include acute or chronic ischemic heart disease, vascular heart disease, valvular heart disease, or degenerative primary electrical disease (fibrosis and calcification of the sinus node and conduction system). Evaluation of bradycardia includes assessment of heart rhythm, symptoms, medications, and associated medical conditions (reversible and irreversible). Diagnosis is usually made with the help of a 24-hour ambulatory electrocardiogram (ECG) or telemetry. Symptomatic bradycardias are treated by removal of the underlying causes, medications (atropine) or insertion of a temporary or permanent pacemaker. The term relative bradycardia is used to explain a heart rate that, while not technically below 60 beats per minute, is considered too slow for the individual's current medical condition.
Causes
It is difficult and sometimes impossible to assign a mechanism to any particular bradycardia. However, the underlying mechanism is not clinically relevant to treatment, which is the same in both cases of sick sinus syndrome: a permanent pacemaker. Bradycardia is more common in older patients. There are generally two types of problems that result in bradycardias:
- Disorders of the sinus node -
- Impaired automaticity - Sinus node dysfunction/sick sinus syndrome)
- Exit block - Impaired conduction of the impulse from the sinus node into the surrounding atrial tissue
- Disorders of the atrioventricular node (AV node)
- Atrioventricular conduction disturbances (1o AV block, 2o type I AV block, 2o type II AV block, 3o AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the bundle of HIS.
Complete Differential Diagnosis of the Causes of Bradycardia
(By organ system)
Diagnosis
Symptoms
- Presyncope
- Syncope
- Fatigue
- Angina
- Symptoms of congestive heart failure
Treatment
Urgent Treatment
- Check drug list and remove drugs predisposing to bradycardia like beta blockers, calcium channel blocker, anti-arrhythmic drug.
- Drug treatment for bradycardia is typically not indicated for patients who are asymptomatic.
- In symptomatic patients, underlying electrolyte or acid-base disorders or hypoxia should be corrected first.
- IV atropine may provide temporary improvement in symptomatic patients, although its use should be balanced by an appreciation of the increase in myocardial oxygen demand this agent causes. Atropine 0.5-1 mg IV or ET q3-5min up to 3 mg total (0.04 mg/kg)
Indications For a Temporary Pacemaker
Advanced heart block such as complete heart block is an indication for a temporary pacemaker insertion.
Chronic Management
There are two main reasons for treating any cardiac arrhythmias. With bradycardia, the first is to address the associated symptoms, such as fatigue, limitations on how much an individual can physically exert, fainting (syncope), dizziness or lightheadedness, or other vague and non-specific symptoms. The other reason to treat bradycardia is if the person's ultimate outcome (prognosis) will be changed or impacted by the bradycardia. Treatment in this vein depends on whether any symptoms are present, and what the underlying cause is. Primary or idiopathic bradycardia is treated symptomatically if it is significant, and the underlying cause is treated if the bradycardia is secondary.
See also
References
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