Bradycardia

Bradycardia refers to a heart rate of less than 60 beats/minute. It occurs normally in young adults, trained athletes, and elderly people as well as during sleep. It’s also a normal response to vagal stimulation caused by coughing, vomiting, or straining during defecation. When bradycardia results from these causes, the heart rate rarely drops below 40 beats/minute. However, when it results from pathologic causes (such as cardiovascular disorders), the heart rate may be slower.

By itself, bradycardia is a nonspecific sign. However, together with such symptoms as chest pain, dizziness, syncope, and shortness of breath, it can signal a life-threatening disorder. (See Differential diagnosis: Bradycardia, pages 120 and 121.)

History and physical examination

After detecting bradycardia, check for related signs of life-threatening disorders. (See Managing severe bradycardia.) If bradycardia isn’t accompanied by untoward signs, ask the patient if he or a family member has a history of a slow pulse rate because this may be inherited. Also, find out if he has an underlying metabolic disorder, such as hypothyroidism, which can precipitate bradycardia. Ask which medications he’s taking and if he’s complying with the prescribed schedule and dosage. Monitor vital signs, temperature, pulse rate, respirations, blood pressure, and oxygen saturation.

Medical causes

Cardiac arrhythmias

Depending on the type of arrhythmia and the patient’s tolerance of it, bradycardia may be transient or sustained and benign or life-threatening. Related findings include hypotension, palpitations, dizziness, weakness, syncope, and fatigue.

Cardiomyopathy

Cardiomyopathy is a potentially life-threatening disorder that may cause transient or sustained bradycardia. Other findings include dizziness, syncope, edema, fatigue, jugular vein distention, orthopnea, dyspnea, and peripheral cyanosis.

Cervical spinal injury

Bradycardia may be transient or sustained, depending on the severity of the injury. Its onset coincides with sympathetic denervation. Associated signs and symptoms include hypotension, decreased body temperature, slowed peristalsis, leg paralysis, and partial arm and respiratory muscle paralysis.

Hypothermia

Bradycardia usually appears when the core temperature drops below 89.6° F (32° C). It’s accompanied by shivering, peripheral cyanosis, muscle rigidity, bradypnea, and confusion leading to stupor.

Hypothyroidism

Hypothyroidism causes severe bradycardia in addition to fatigue, constipation, unexplained weight gain, and sensitivity to cold. Related signs include cool, dry, thick skin; sparse, dry hair; facial swelling; periorbital edema; thick, brittle nails; and confusion leading to stupor.

Increased intracranial pressure (ICP)

Bradycardia occurs as a late sign of increased ICP along with rapid respiratory rate, elevated systolic pressure, decreased diastolic pressure, and widened pulse pressure. Associated signs and symptoms include persistent headache, projectile vomiting, decreased level of consciousness (LOC), and fixed, unequal, and possibly dilated pupils.

Myocardial infarction (MI)

Sinus bradycardia is the most common arrhythmia associated with an acute MI. Accompanying signs and symptoms of an MI include an aching, burning, or viselike pressure in the chest that may radiate to the jaw, shoulder, arm, back, or epigastric area; nausea and vomiting; cool, clammy, and pale or cyanotic skin; anxiety; and dyspnea. Blood pressure may be elevated or depressed. Auscultation may reveal abnormal heart sounds.

Other causes

Diagnostic tests

Cardiac catheterization and electrophysiologic studies can induce temporary bradycardia.

Drugs

Beta-adrenergic blockers, some calcium channel blockers, cardiac glycosides, topical miotics (such as pilocarpine), protamine, quinidine and other antiarrhythmics, and sympatholytics may cause transient bradycardia. Failure to take thyroid replacements may cause bradycardia.

Invasive treatments

Suctioning can induce hypoxia and vagal stimulation, causing bradycardia. Cardiac surgery can cause edema or damage to conduction tissues, causing bradycardia.

Special considerations

Continue to monitor vital signs frequently. Be especially alert for changes in cardiac rhythm, respiratory rate, and LOC.

Prepare the patient for laboratory tests, which can include complete blood count; cardiac enzyme, serum electrolyte, blood glucose, blood urea nitrogen, arterial blood gas, and blood drug levels; thyroid function tests; and a 12-lead electrocardiogram. If appropriate, prepare the patient for 24-hour Holter monitoring.

Pediatric pointers

Heart rates are normally higher in children than in adults. Fetal bradycardia—a heart rate of less than 120 beats/minute—may occur during prolonged labor or complications of delivery, such as compression of the umbilical cord, partial abruptio placentae, and placenta previa. Intermittent bradycardia, sometimes accompanied by apnea, commonly occurs in premature infants. Bradycardia rarely occurs in full-term infants or children. However, it can result from congenital heart defects, acute glomerulonephritis, and transient or complete heart block associated with cardiac catheterization or cardiac surgery.

Geriatric pointers

Sinus node dysfunction is the most common bradyarrhythmia in the elderly. Patients with this disorder may cite fatigue, exercise intolerance, dizziness, or syncope as their chief complaint. If the patient is asymptomatic, no intervention is necessary. Symptomatic patients, however, require careful scrutiny of their drug therapy. Beta-adrenergic blockers, verapamil, diazepam, sympatholytics, antihypertensives, and some antiarrhythmics have been implicated; symptoms may clear when these drugs are discontinued. Pacing is usually indicated in patients with symptomatic bradycardia lacking a correctable cause.

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Book Source Details

• Book Title: Professional Guide to Signs & Symptoms (Fifth Edition)
• Author(s): Springhouse
• Year of Publication: 2006
• Copyright Details: Professional Guide to Signs & Symptoms (Fifth Edition), Copyright © 2006 Lippincott Williams & Wilkins.

Other Book Chapters Related to Arrhythmia

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Copyright Details: Professional Guide to Signs & Symptoms (Fifth Edition), Copyright © 2008 Williams & Wilkins.

More About Causes of Arrhythmia

• Back to symptom: Arrhythmia: Introduction (review 234 causes)
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