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SOURCE

Source: Sanoski CA, Bauman JL. The arrhythmias. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146057036. Accessed March 28, 2017.

CONDITION/DISORDER SYNONYM

  • Bradycardias.

DEFINITION

  • Abnormally slow heart rate (<60 beats/min in adults).

ETIOLOGY

  • Sinus bradycardia.

  • Sick sinus syndrome.

  • Atrioventricular (AV) block.

  • Vasovagal syndrome.

PATHOPHYSIOLOGY

  • Usually results from impaired sinoatrial (SA) node function or conduction abnormalities between SA node and atrium, or within AV node or intraventricular conduction pathways.

  • Sinus bradycardia can be due to heart disease, medications, or normal causes (eg, in trained athletes).

  • Sick sinus syndrome caused by malfunction of SA node from organic heart disease or normal aging process.

  • AV block caused by slowed or blocked conduction of electrical impulses in AV conduction system.

  • β-Blockers, digoxin, or nondihydropyridine calcium antagonists may cause AV block, primarily in AV nodal area.

  • Vasovagal syncope thought to be neurally mediated process involving stimulation of cardiac mechanoreceptors (Bezold–Jarisch reflex).

EPIDEMIOLOGY

  • Frequency of sinus bradycardia unknown.

  • Frequency of sick sinus syndrome in patients with heart disease estimated to be 3 in 5000.

RISK FACTORS

  • Advancing age.

  • Hypothyroidism.

  • Drugs (eg, central α2 agonists, cholinesterase inhibitors, calcium channel blockers, digoxin, lithium, β-blockers)

  • Heart disease (eg, myocardial infarction)

  • Electrolyte imbalances.

  • Sleep apnea.

  • Head injury.

  • Hypothermia.

  • Hypoglycemia.

  • Toxin exposure.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

  • Many bradycardias asymptomatic (eg, in trained athletes).

  • Symptoms associated with hypotension (eg, dizziness, syncope, fatigue, confusion).

  • Vasovagal syndrome may cause syncope.

  • If LV dysfunction exists, patients may experience worsening heart failure (HF) symptoms.

  • Signs: Pulse <60 beats/min in adults.

DIAGNOSIS

LABORATORY TESTS

  • Performed if underlying causes suspected (eg, hypothyroidism, electrolyte imbalances).

DIAGNOSTIC PROCEDURES

  • Vagal maneuvers, carotid sinus massage, exercise for AV node bradyarrhythmias.

  • Electrocardiogram (ECG) findings categorize AV block into first-, second-, or third-degree block.

  • Holter monitoring (long-term recording) may be used to document the relationship of bradycardia with symptoms.

  • Electrophysiologic studies may be performed for accurate localization of AV block.

DESIRED OUTCOMES

  • Identify and correct underlying causes.

  • Resolve symptoms.

  • Prevent recurrences.

  • Avoid complications from surgical procedures and medications.

TREATMENT: GENERAL APPROACH

  • Asymptomatic sinus bradyarrhythmias do not usually require intervention.

TREATMENT: NONPHARMACOLOGIC THERAPY

  • Discontinue exacerbating medications, if feasible.

  • Permanent ventricular pacemaker is long-term treatment of choice for most patients with significant symptoms or those that are drug-refractory.

  • Temporary ...

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