Bradycardia

Differential Overview

Sinus Bradycardia

❑ Hypothyroidism

❑ Hypervagotonia

❑ Hypersensitive carotid sinus

❑ Hypothermia

❑ Acute increased intracranial pressure

Complete Heart Block

❑ Inferior myocardial infarction

❑ Drugs

❑ Sick sinus syndrome

❑ Viral myocarditis

❑ Lyme disease

❑ Sarcoidosis

❑ Acute rheumatic fever

Diagnostic Approach

The mean normal heart rate is 70 beats/minute, with 2 standard deviations below being 46 in men and 51 in women. Sinus bradycardia may occur in the absence of heart disease in young adults, well-conditioned athletes, and during sleep. Symptoms of bradycardia include paroxysmal dizziness, fatigue, presyncopal lightheadedness, and syncope. Sinus bradycardia is manifest as a regular slow rhythm. Complete heart block is usually accompanied by a very slow, usually irregular escape rhythm, and a symptomatic reduction in cardiac output producing lightheadedness and shortness of breath.

Relative bradycardia—that is, failure to respond to fever with tachycardia—suggests typhoid fever, mycoplasma pneumonia, factitious fever, or concomitant beta blockers.

Clinical Findings

Hypothyroidism  Cardinal findings include weight gain, dry skin, coarse hair, hoarseness, delayed relaxation phase of the ankle jerks, and thyroid enlargement.

Hypervagotonia  Most often observed in aerobically trained athletes, it can also be observed in patients with vasovagal syncope, if examined while experiencing symptoms. Precipitating manuvers include carotid sinus pressure, vomiting or coughing, valsalva while straining at stool, sudden facial immersion in cold water and prolonged standing via the Bezold-Jarisch reflex.

Hypersensitive carotid sinus  Carotid massage produces a prolonged pause (>5 seconds), correlated with symptoms.

Hypothermia  Bradycardia occurs with environmental cold exposure, especially in near drowning, due to the diving reflex. Hypothermia can be underestimated unless the core temperature is measured with a special hypothermia thermometer.

Acute increased intracranial pressure  Bradycardia due to the Cushing reflex occurs in patients with intracerebral hemorrhage, malignant hypertension, or brain edema.

Inferior myocardial infarction  A patient with protracted substernal chest pressure complains of nausea and diaphoresis. The right coronary artery supplies the SA node in the majority of patients.

Drugs  Digoxin, beta blockers, calcium channel blockers, amiodarone, lithium, and cimetidine are the usual causal agents. A junctional rhythm at a rate of 60 appears in digoxin toxicity.

Sick sinus syndrome  Sinus node dysfunction may be first manifest as failure to cardioaccelerate with fever or exercise, or with excessive bradycardia when given a beta blocker or calcium channel blocker. Symptoms of dizziness, confusion, fatigue, syncope, and congestive heart failure occur in association with bradycardia and long pauses.

Viral myocarditis  Although it begins with fever, tachycardia, congestive heart failure, and vague chest pains, development of heart block is marked by bradyarrhythmia.

Lyme disease  Other manifestations of Lyme disease, such as erythema marginatum and arthritis, precede it.

Sarcoidosis  Bradycardia may occur in the setting of a granulomatous cardiomyopathy. Adenopathy is a clue.

Acute rheumatic fever  A recent sore throat, fever, polyarthritis, and erythema marginatum are key clues.

Book Source Details

• Book Title: Field Guide to Bedside Diagnosis
• Author(s): David S. Smith
• Year of Publication: 2007
• Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.

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Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2008 Williams & Wilkins.

More About Causes of Heart rhythm symptoms

• Back to symptom: Heart rhythm symptoms: Introduction (review 1482 causes)
• Next Book Extract About Heart rhythm symptoms: Arterial Pulse Variants (Field Guide to Bedside Diagnosis)
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More About This Book: Title: Field Guide to Bedside Diagnosis Authors: David S. Smith Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-78178-165-5

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