Second degree AV block medical therapy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mohammed Salih, M.D. Cafer Zorkun, M.D., Ph.D. [2] Syed Musadiq Ali M.B.B.S.[3]

Overview

Treatment for a Mobitz type I second-degree AV block (Wenckebach) is often not necessary. Occasionally Mobitz type 1 second degree AV blocks may result in bradycardia leading to hypotension and responds well to atropine. If unresponsive to atropine or beta-adrenergic agonists, pacing (transcutaneous or transvenous) should be initiated for stabilization. If the patient is on any beta-blockers, calcium channel blockers or digoxin, the medications should be discontinued. All patients with Mobitz 1 block should be admitted and monitored. Treatment for a Mobitz type II involves initiating pacing as soon as this rhythm is identified. Mobitz type II second-degree AV blocks may imply structural damage to the AV conduction system. This rhythm often deteriorates into a complete heart block. These patients require transvenous pacing until a permanent pacemaker is placed. Unlike Mobitz type I second degree AV block (Wenckebach), Mobitz type II rhythm often do not respond to atropineor beta-adrenergic agonists.

Medical Therapy

Recommendations for acute medical therapy for bradycardia associated atrioventricular block

Medical therapy (Class IIa, Level of Evidence C):

❑ Atropine is reasonable for patients with symptomatic bradycardia associated second-degree or third degree atrioventricular block at the atrioventricular nodal level

Medical therapy (Class IIb, Level of Evidence B):

❑ Beta adrenergic agonist such as isoproterenol, dopamine, dobutamine is recommended for symptomatic bradycardia associated second degree or third degree atrioventricular block with low likehood of ischemia

Medical therapy (Class IIb, Level of Evidence C):

❑ Aminophylline is recommended for symptomatic bradycardia associated second or third degree atrioventricular block in the setting of acute inferior MI

The above table adopted from 2018 AHA/ACC/HRS Guideline

• Atropine is a parasympatholytic drug that increase atrioventricular nodal conduction and automaticity when atrioventricular block is at the atrioventricular nodal level or bradycardia is related to excess vagal tone.
• Dosage is 0.5- to 1.0-mg IV, may be repeated.
• Atropine may enhance atrioventricular conduction in the setting of inferior MI.
• For atrioventricular block at the level of His bundle or His-Purkinje, atropine may worsen atrioventricular conduction or compromise hemodynamic.
• Common adver effects of atropine include dry mouth, blurred vision, anhidrosis, urinary retention, and delirium , increased heart rate in the setting of MI.

• Beta-adrenergic agonists such as isoproterenol, dopamine, dobutamine, and epinephrine may have direct effect to increase atrioventricular nodal and, to a lesser degree, His-Purkinje conduction.
• The efficacy of dopamine was equal to transcutaneous pacing in 1 small randomized trial of patients with unstable bradycardia unresponsive to atropine.

• Common adverse effects of beta-adrenergic agonists may include ventricular arrhythmias , induction of coronary ischemia, particularly in the setting of acute MI.
• Isoproterenol because of the vasodilatory effects may exacerbate hypotension.
• Aminophylline is a nonselective adenosine receptor antagonist and phosphodiesterase inhibitor.
• Safety and efficacy of aminophylline for reversing bradycardia associated atrioventricular block in the setting of excess adnosine production in inferior MI was shown.
• There was no benefit for aminophylline in resuscitation for out-of-hospital brady-asystolic cardiac arrest based on a large randomized trial and a systematic review.

Recommendations for Acute Management of Bradycardia Attributable to Atrioventricular Block

Symptomatic sinus bradycardia or atrioventricular block

❑ Atropine 0.5-1 mg IV (may be repeated every 3-5 min to a maximum dose of 3 mg) ❑ Dopamine 5 to 20 mcg/kg/min IV, starting at 5 mcg/kg/min and increasing by 5 mcg/kg/min every 2 min Dosages of >20 mcg/kg/min may lead to vasoconstriction or arrhythmias ❑ Isoproterenol 20-60 mcg IV bolus followed doses of 10-20 mcg, or infusion of 1-20 mcg/min based on heart rate response Monitoring of ischemic chest pain ❑ Epinephrine 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV titrated to desired effect

Second or third degree atrioventricular block associated acute inferior MI :

❑ Aminophylline 250-mg IV bolus

Calcium channel blocker overdose

❑ 10% calcium chloride 1-2 g IV every 10-20 min or an infusion of 0.2-0.4 mL/kg/h ❑ 10% calcium gluconate 3-6 g IV every 10-20 min or an infusion at 0.6-1.2 mL/kg/h

Betablocker or Calcium channel blocker overdose

❑ Glucagon 3-10 mg IV with infusion of 3-5 mg/h ❑ High dose insulin therapy IV bolus of 1 unit/kg followed by an infusion of 0.5 units/kg/h Checking potassium and glocagon level

Digoxin overdose

❑ Digoxin antibody fragment Every vial for 0.5 mg of digoxin, over 30 min, maybe repeated ❑ Dosage is dependent on the amount ingested or known digoxin concentration

Post heart transplant

❑ Aminophylline 6 mg/kg in 100-200 mL of IV fluid over 20-30 min ❑ Theophylline 300 mg IV, followed by oral dose of 5-10 mg/kg/d Therapeutic serum level 10-20 mcg/mL, posttransplant dosages average 450 mg±100 mg/d

Spinal cord injury

❑ Aminophylline 6 mg/kg in 100-200 mL of IVfluid over 20-30 min ❑ Theophylline Oral dose of 5-10 mg/kg/d titrated to effect Effective serum level 10-20 mcg/mL

The above table adopted from 2018 AHA/ACC/HRS Guideline

Mobitz I

• Patients with type I second degree AV block are usually asymptomatic and do not require treatment..
• Correction of reversible causes of the block such as ischemia, medications, and vagotonic conditions should be addressed.
• Atropine can be used in Type I second degree AV blocks with hypotension and bradycardia.
• Transvenous or transcutaneous Pacing may be needed to stabilize the patient when bradycardia is unresponsive to atropine.

Mobitz II

• Correction of reversible causes of the block such as ischemia, medications, and vagotonic conditions should be considered..
• Patients may need immediate transvenous pacing until a permanent pacemaker is placed.
• Treatment in emergency situations are atropine, adneregic agonist, epinephrine and an external pacer..

References

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