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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Sinus rate is less than 60 bpm

  • P waves have normal contour with a constant PR interval

  • PR interval exceeds 120 ms

  • Sinus arrhythmia often coexists

GENERAL CONSIDERATIONS

  • May be a manifestation of sick sinus syndrome

  • High vagal tone (young adults and athletes) or medications (eg, beta blockers) are possible causes

  • Increased intracranial pressure and myxedema are among several other causes

  • Acute myocardial infarction (particularly inferior) is associated with sinus bradycardia

  • Patients with anorexia nervosa may have sinus bradycardia

  • Not uncommon in cardiac transplant recipients

  • During sleep, the heart rate can fall to 35–40 bpm especially in young adults; pauses ≥ 2 seconds are not uncommon

  • Hypothermia, severe hypoxia, coronary angiography, eye surgery, mediastinal tumors, and convalescence from infection are possible causes

  • Obstructive jaundice is a possible cause

  • Eye drops containing beta blockers are an easily overlooked cause

  • Bradycardia after resuscitation from cardiac arrest carries a poor prognosis

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Generally asymptomatic

PHYSICAL EXAM FINDINGS

  • Rarely causes hemodynamic decompensation in acute myocardial infarction

DIFFERENTIAL DIAGNOSIS

  • Ectopic atrial bradycardia

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Depends on clinical situation

  • Thyroid-stimulating hormone

ELECTROCARDIOGRAPHY

  • ECG to document rhythm

  • Rhythm strip to define mechanism

IMAGING STUDIES

  • Usually none required

DIAGNOSTIC PROCEDURES

  • ECG and clinical examination are sufficient for diagnosis

TREATMENT

CARDIOLOGY REFERRAL

  • If part of sick sinus syndrome, referral to an electrophysiologist is required for evaluation of permanent pacemaker

HOSPITALIZATION CRITERIA

  • Does not require hospitalization by itself

  • Hospitalization may be for concomitant illness

MEDICATIONS

  • Usually no specific treatment is needed

  • If patients are symptomatic acutely, atropine may be used to increase the sinus rate

  • Medications such as theophylline and ephedrine may be used cautiously without overshooting to sinus tachycardia

THERAPEUTIC PROCEDURES

  • Patients with recurrent symptoms are treated with a pacemaker

SURGERY

  • None required

MONITORING

  • ECG monitoring if hospitalized

DIET AND ACTIVITY

  • General healthy lifestyle

ONGOING MANAGEMENT

HOSPITAL DISCHARGE CRITERIA

  • Depends on concomitant illness

FOLLOW-UP

  • Usually none required except when symptoms are suggestive of sick sinus syndrome

COMPLICATIONS

  • Syncope secondary to sick sinus syndrome

PROGNOSIS

  • Generally very good

  • A ...

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