Sinus Bradycardia

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