bradycardia
BRADYCARDIA

Bradycardia is having a heart rate of <60 beats/minute that may not affect the hemodynamic status of some patients.
A heart rate that is inadequate for the patient's current condition and may not be able to support life is a clinically significant bradycardia.

Bradycardia can be caused by problems in the sinoatrial node, problems in the conduction pathways of the heart, metabolic problems or heart attack/disease that caused damage to the heart.

The different types of bradycardia are sinus bradycardia, sick sinus syndrome, tachycardia-bradycardia syndrome, hypersensitive carotid sinus syndrome, sinus pause/arrest, sinoatrial node exit block and atrioventricular block.

Principles of Therapy

  • Management of sinus bradycardia is not necessary unless with inadequate cardiac output and/or with life-threatening arrhythmia
  • Observation and monitoring is recommended for hemodynamically stable patients
  • Second-line therapy and transcutaneous pacing may be considered only when a patient with acute symptomatic bradycardia is unresponsive to Atropine

Pharmacotherapy

1st-Line Agent

Atropine

  • Used for symptomatic sinus bradycardia, hypersensitive carotid sinus syndrome, and atrioventricular (AV) blocks
  • Reverses cholinergic-mediated decrease in heart rate by exerting its parasympathomimetic effect on the myocardium
  • Improves signs and symptoms and cardiac rate
  • Use cautiously in patients with acute myocardial infarction or acute coronary ischemia
  • May not be effective in patients who have undergone cardiac transplantation
  • Temporizing measure for pending transcutaneous pacing
  • Prepare for transcutaneous pacing if symptomatic bradycardia does not improve after Atropine administration

2nd-Line Agents

  • Consider in patients with unsatisfactory response to Atropine and as temporizing measure while awaiting pacemaker insertion

Epinephrine

  • Epinephrine infusion may be used in patients with symptomatic bradycardia, especially associated with hypotension, in whom Atropine may be inappropriate or after Atropine and transcutaneous pacing fails
  • Strong alpha- and beta-adrenergic agonist

Dopamine

  • May be used in patients with symptomatic bradycardia, especially associated with hypotension, in whom Atropine may be inappropriate or after Atropine fails
  • Dopamine infusion may be given in addition to Epinephrine or may be administered alone
  • Has both alpha- and beta-adrenergic agonist actions

Glucagon

  • Consider if the potential cause for bradycardia is overdose of a beta-blocker or Calcium channel antagonist
  • Vasoactive peptide that counteracts the effects of beta blockers by activating hepatic adenyl cyclase which promotes glycogenesis

Isoproterenol (Isoprenaline)

  • May be considered for transient heart block but should be used with utmost caution
    • Not to be used in patients with acute MI
  • Increases heart rate or atrioventricular-nodal conduction in patients with acute symptomatic bradyarrhythmia
  • Nonselective beta agonist with chronotropic and inotropic effects

Other Agents:

  • Aminophylline, Theophylline, Glycopyrrolate, Terbutaline

Device-Based Therapies

  • Indication is determined by severity of bradycardia
  • Recommended for patients with symptomatic sinus bradycardia, atrioventricular (AV) block, hypersensitive carotid sinus syndrome
  • May be considered for patients at risk of asystole, hemodynamically unstable, and those unresponsive to Atropine
    • Also in patients ≥40 years old with recurrent unpredictable reflex syncope and/or documented symptomatic pauses due to sinus arrest or atrioventricular (AV) block, patients with history of syncope with asymptomatic pauses of >6 seconds secondary to sinus arrest, sinoatrial (SA) block, or atrioventricular (AV) block

Temporary Pacing

  • Emergency intervention used during the interval prior to permanent pacemaker implantation or resolution of bradycardia

Transcutaneous Pacing

  • Non-invasive intervention applicable for symptomatic bradycardias
  • Recommended for patients who fail to respond to Atropine therapy or if hemodynamically unstable especially those with high-degree atrioventricular (AV) blocks
  • Hemodynamic stability and electrocardiogram (ECG) results should be monitored during pacing

Transvenous Pacing

  • Invasive intervention involving the insertion of a temporary pacemaker wire to acquire venous access into the thoracic region
    • Most common insertion sites are the internal jugular vein and subclavian vein
  • Performed if Atropine therapy and transcutaneous pacing fails
  • Should only be used in patients with high degree atrioventricular (AV) block without escape rhythm, and life-threatening bradyarrhythmias
  • Should be used for a minimum period necessary as back-up pacing or to provide hemodynamic support to prevent asystole in order to avoid complications

Permanent Pacemaker Implantation

  • Prevents recurrence of syncope, improves symptoms, and increases survival rates
  • Indications include:
    • Symptomatic sinus bradycardia
    • Symptomatic patients with atrioventricular (AV) block
      • Patients with intermittent or paroxysmal intrinsic 2nd- to 3rd-degree atrioventricular (AV) block
      • Patients with type I 2nd-degree atrioventricular (AV) block should be symptomatic if being considered
      • Patient with type II 2nd-degree  atrioventricular (AV) block with wide QRS interval should be considered regardless if symptomatic or not
    • Symptomatic sinus node dysfunction with heart rate <40 beats per minute
    • Patients with sinus node dysfunction without symptoms but with heart rate of <40 beats per minute
    • Patients with unexplained syncope with abnormal findings in electrophysiological studies (EPS)
    • Patients with recurrent syncope accompanied by ventricular asystole of >3 seconds due to spontaneously occurring carotid sinus stimulation and pressure
  • Also recommended for acute myocardial infarction (MI) patients with atrioventricular (AV) block, congenital atrioventricular (AV) block, and atrioventricular (AV) block associated with enhanced vagal tone
  • May be considered in patients with neuromuscular diseases ie myotonic muscular dystrophy, Erb dystrophy, peroneal muscular atrophy with bifascicular block or any fascicular block, regardless if with symptoms or not
  • Should be excluded if bradycardia is due to reversible causes, asymptomatic 1st-degree atrioventricular block, asymptomatic 2nd-degree Mobitz I with supra-Hisian conduction block, or atrioventricular (AV) block expected to resolve

Modes of Pacing:

  • Single chamber pacemaker is considered for patients needing a single-lead atrial sensing ventricular pacemaker
  • Dual chamber pacing is beneficial for patients with history of stroke, embolism, atrial fibrillation, reduced exercise capacity, pacemaker syndrome compared to single chamber pacing but with more complications recorded
  • Dual chamber pacemaker is preferred for patients with sinus node disease, acquired atrioventricular (AV) block when rate response is desired
    • Reduces risk of atrial fibrillation, stroke, pacemaker syndrome and improves overall quality of life
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