Bradycardia

Bradycardia
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 is defined as a resting heart rate of under 60 beats per minute.

Pathophysiology

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).

Natural History, Complications, Prognosis

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.

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.

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 (1^o AV block, 2^o type I AV block, 2^o type II AV block, 3^o AV block) may result from impaired conduction in the AV node, or anywhere below it, such as in the bundle of HIS.

Causes of Bradycardia By Organ System

Cardiovascular	Atrioventricular Block, Cardiac arrhythmia, Cardiac Dysrhythmias, Cardiomegaly, Right Bundle Branch Block, Second Degree AV Block, ST Elevation Myocardial Infarction Complications, Sinoatrial Block, Pulseless ventricular tachycardia, Sick sinus syndrome,
Chemical / poisoning	No underlying causes
Dermatologic	No underlying causes
Drug Side Effect	Aceclidine, Acepromazine, Acetylcholinesterase inhibitor, Adenosine, Amiodarone, Amodiaquine, Atenolol, Barbiturates, Beta-blockers, Bupivacaine, Calcium channel blocker, Clomipramine, Detomidine, Digitalis, Diltiazem, Diphenhydramine, Donepezil, Doxepin, Glyceryl trinitrate , Hydrocodone, Ibuprofen, Isosorbide dinitrate, Ivabradine, Levobetaxolol, Levobupivacaine, Lidocaine, Lithium, Medetomidine, Mefloquine, Mepivacaine, Methacholine, Methoxamine, Methyldopa, Morphine, Moxonidine, Nadolol, Nalbuphine, Nalmefene, Opioid, Oxymorphone, Phenobarbital, Phenylephrine, Phenytoin, Pilocarpine, Propafenone, Propranolol, Quinidine, Reserpine, Ropivacaine, Sulpiride, Suxamethonium chloride, Tacrine, Timolol, Trazodone, Uncaria tomentosa, Xylazine,
Ear Nose Throat	No underlying causes
Endocrine	Hypothyroidism,
Environmental	Grayanotoxin, Hellebore, Hypothermia,
Gastroenterologic	No underlying causes
Genetic	Congenital Long QT Syndrome, Catecholaminergic polymorphic ventricular tachycardia, Emery-Dreifuss muscular dystrophy,
Hematologic	No underlying causes
Iatrogenic	Enema, Gastric lavage, PCI Complications: Radiocontrast toxicity, Rapid sequence induction,
Infectious Disease	Chagas' disease, Hantavirus pulmonary syndrome, Legionella pneumonia and Mycoplasma pneumonia, Tularaemia, Colorado tick fever, Brucellosis, Trypanosoma cruzi, Typhoid fever,
Musculoskeletal / Ortho	Holt-Oram syndrome, Vertebral subluxation,
Neurologic	Vasovagal syncope, Vagal episode, Neurogenic shock, Subarachanoid hemorrhage, Raised Intracranial pressure, Autonomic neuropathy, Cerebral hemorrhage, Cerebral venous sinus thrombosis, Cushing triad, Cushing reaction, Cushing reflex, Neurocardiogenic Syncope,
Nutritional / Metabolic	Hypercalcemia, Hyperkalemia, Hypokalemia, Anorexia Nervosa,
Obstetric/Gynecologic	Fetal distress, Neonatal lupus erythematosus, Vasa previa,
Oncologic	No underlying causes
Opthalmologic	Oculocardiac reflex,
Overdose / Toxicity	Gamma-Hydroxybutyric acid, Hydroxyethyl starch Speedball (drug), Theobromine poisoning,
Psychiatric	Anorexia Nervosa,
Pulmonary	Apnea of prematurity,
Renal / Electrolyte	No underlying causes
Rheum / Immune / Allergy	No underlying causes
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Miscellaneous	Drowning, Mammalian diving reflex,

Causes in Alphabetical Order

• Anorexia Nervosa
• Brucellosis
• Catecholaminergic polymorphic ventricular tachycardia
• Cerebral hemorrhage
• Cerebral venous sinus thrombosis
• Cushing reflex
• Gamma-Hydroxybutyric acid
• Gastric lavage
• Hantavirus pulmonary syndrome
• Hellebore
• Mepivacaine
• Mycoplasma pneumonia
• Opioid
• Oxymorphone
• Phenobarbital
• Phenytoin
• Rapid sequence induction
• Trazodone
• Typhoid fever
• Vagal episode
• Vasa previa
• Vertebral subluxation
• Aceclidine
• Acepromazine
• Acetylcholinesterase inhibitor
• Adenosine
• Amiodarone
• Amodiaquine
• Anorexia Nervosa
• Apnea of prematurity
• Atenolol
• Atrioventricular Block
• Autonomic neuropathy
• Barbiturates
• Beta-blockers
• Bupivacaine
• Calcium channel blocker
• Cardiac arrhythmia
• Cardiac Dysrhythmias
• Cardiomegaly
• Chagas' disease
• Clomipramine
• Colorado tick fever
• Congenital Long QT Syndrome
• Cushing reaction
• Cushing triad
• Detomidine
• Digitalis
• Diltiazem
• Diphenhydramine
• Donepezil
• Doxepin
• Drowning
• Emery-Dreifuss muscular dystrophy
• Enema
• Fetal distress
• Glyceryl trinitrate
• Grayanotoxin
• Holt-Oram syndrome
• Hydrocodone
• Hydroxyethyl starch Speedball (drug)
• Hypercalcemia
• Hyperkalemia
• Hypokalemia
• Hypothermia
• Hypothyroidism
• Ibuprofen
• Isosorbide dinitrate
• Ivabradine
• Legionella pneumonia
• Levobetaxolol
• Levobupivacaine
• Lidocaine
• Lithium
• Mammalian diving reflex
• Medetomidine
• Mefloquine
• Methacholine
• Methyldopa
• Morphine
• Moxonidine
• Nadolol
• Nalbuphine
• Nalmefene
• Neonatal lupus erythematosus
• Neurocardiogenic Syncope
• Neurogenic shock
• Oculocardiac reflex
• Phenylephrine
• Pilocarpine
• Propafenone
• Propranolol
• Pulseless ventricular tachycardia
• Quinidine
• Radiocontrast toxicity
• Raised Intracranial pressure
• Reserpine
• Right Bundle Branch Block
• Ropivacaine
• Second Degree AV Block
• Sick sinus syndrome
• Sinoatrial Block
• ST Elevation Myocardial Infarction Complications
• Subarachanoid hemorrhage
• Sulpiride
• Suxamethonium chloride
• Tacrine
• Theobromine poisoning
• Timolol
• Trypanosoma cruzi
• Tularaemia
• Uncaria tomentosa
• Vasovagal syncope
• Xylazine

Epidemiology and Demographics

Bradycardia is more common in older patients.

Diagnosis

Evaluation of bradycardia includes assessment of the heart rhythm, symptoms, medications, and associated medical conditions (reversible and irreversible). 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.

Symptoms

• Presyncope
• Syncope
• Fatigue
• Angina
• Symptoms of congestive heart failure

Resting EKG

The heart rate is < 60 beats per minute.

• 

24 Hour Ambulatory Electrocardiogram Monitoring

The diagnosis is usually made with the help of a 24-hour ambulatory electrocardiogram (ECG) or telemetry.

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 brandycardia:

1. 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.
2. 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

• AV Block

References

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