Third 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: Cafer Zorkun, M.D., Ph.D. [2] Raviteja Guddeti, M.B.B.S. [3] Soroush Seifirad, M.D.[4] Qasim Khurshid, M.B.B.S. [5]

Overview

The management of third-degree heart block varies widely from observation to the placement of a pacemaker. The new onset of third-degree heart block is a medical emergency.

Medical Therapy

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

Class IIa

"1 Digoxin Fab antibody fragment is recommended in patients presented with digoxin toxicity resulting in symptomatic bradycardia or hemodynamic compromised. (Level of Evidence C)"

Class III

"1 Dialysis is not benefit in patients presented with bradycardia associated digoxin toxicity (Level of Evidence C)"

Recommendations for Acute Management of Reversible Causes of Bradycardia Attributable to Atrioventricular Block

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

❑ In patients with transient or reversible causes of atrioventricular block including Lyme carditis or drug toxicity, medical therapy and transient pace maker insertion is recommended before making decision for implantation of PPM

PPM implantation ( Class IIa, Level of Evidence B) :

❑ In patients with symptomatic second-degree or third-degree atrioventricular block who are on chronic stable doses of medically necessary antiarrhythmic or beta-blocker therapy, PPM is recommended without further evaluation about drug washout or reversibility ❑ In patients with second-degree or third-degree atrioventricular block associated with cardiac sarcoidosis, PPM with defibrillation is recommended if life expectancy > 1 year, without further evaluation about reversibility

PPM implantation : (Class IIb, Level of Evidence C)

❑ In patients with symptomatic second-degree or third-degree atrioventricular block associated with thyroid function abnormalities but without clinical myxedema, PPM is recommended without further evaluation about reversibility

Abbreviations: PPM: Permanent pacemaker;

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

Notes

• In the presence of new atrioventricular block, evaluation about reversible causes is recommended.
• Complete heart block due to lyme carditis or digoxin toxicity are reversible with medical therapy.
• Commonly, atrioventricular block due to overdose of antiarrhythmic drugs, calcium channel blocker or betablocker are reversible.

• Atrioventricular bliock in the setting of the therapeutic dose of calcium channel blocker or betablocker was irreversible and insertion of permanent pacemaker was needed in some cases.

The management of third-degree AV block depends on the severity of signs, symptoms, and the underlying cause. In symptomatic patients and with hemodynamic distress, pharmacological therapy should be initiated immediately to increase heart rate and cardiac output. Most of the patients who do not respond to pharmacologic therapy require a temporary pacemaker. After stabilizing the patients, assessment and treatment of potentially reversible causes should be done. Some patients without reversible cause or unidentified etiology require a permanent pacemaker. A new third degree AV block is an emergency. Management is slightly different between unstable and stable patients.

Management of Unstable Patients

The most critical factor in determining the management of third-degree AV block patients is hemodynamic stability. Patients of third-degree AV block with hemodynamic instability should be urgently treated with atropine and temporary cardiac pacemaker.

• Atropine should be given urgently with an initial dose of 0.5 mg IV and can be repeated every three to five minutes with a total dose of 3 mg. Atropine is most effective if the AV block is due to abnormal conduction through the AV node. Atropine is not useful in wide complex bradyarrhythmias (block below the AV node). It is also not helpful in a denervated heart, like in patients who have undergone a cardiac transplant procedure. Treatment with atropine should be followed by transcutaneous pacing or a chronotropic agent.
• Hemodynamically unstable patients should be immediately provided with a temporary cardiac pacemaker. Transcutaneous pacing can be initiated more rapidly as compared to a transvenous pacemaker, which requires more expertise. However, a transvenous pacemaker is more durable and comfortable for the patient. Transcutaneous pacing should be used temporarily until temporary transvenous pacing can be provided.
• In patients presenting with hypotension and third-degree AV block, dopamine should be given as IV infusion, starting at a dose of 3mcg/kg/min and can be titrated up to 20 mcg/kg/min for stabilization of blood pressure and heart rate.
• In patients presenting with heart failure symptoms and left ventricular dysfunction associated with third-degree AV block,  dobutamine is given via IV infusion, with a starting dose of 5 mcg/kg/minute and can be titrated up to 40 mcg/kg/minute if required.

After stabilizing the hemodynamically unstable patients, the approach to further management is the same as for initially stable patients.

Management of Stable Patients

Hemodynamically stable patients of third-degree heart block do not require urgent treatment with atropine and pacemaker. However, many ventricular escape rhythms have the potential to become unstable, so patients should be monitored on the telemetry floor or ICU.

While monitoring patients, management should be as fellows.

• Reversible causes of third-degree heart block should be evaluated before implantation of the permanent pacemaker. Such causes include myocardial ischemia, hyperkalemia, increased vagal tone, and medications that depress the conduction through the AV node.

• Patients of third-degree AV block due to acute myocardial infarction can be managed with revascularization and temporary cardiac pacing. Most of the patients improve after revascularization and do not require a permanent pacemaker.

• Many medications that are used to treat cardiovascular conditions such as antihypertensive, antianginal, and antiarrhythmic drugs cause AV block that resolves after the removal of the offending agents. These medications can induce or aggravate a third-degree heart block. The most common drugs include beta-blockers, calcium channel blockers, antiarrhythmics, and digoxin. Patients of third-degree heart block caused by drug toxicities should be managed in the same fashion(e.g., atropine and pacemaker) as caused by other etiologies. But these patients should also get treatment for respective drug toxicity. Most of the time, a permanent pacemaker is not required in these patients.

• Patients with third-degree (complete) AV block because of hyperkalemia should receive therapy to reduce serum potassium levels. If third-degree AV block subsequently resolves, a permanent pacemaker is not usually needed.
• Third-degree (complete) AV block caused by Lyme carditis typically improves to lesser degrees of AV block within one week of treatment with antibiotics, and more minor conduction disturbances usually resolve within six weeks. These patients may initially require temporary cardiac pacing, but permanent cardiac pacing should be reserved for patients with a persistent third degree (complete) AV block following an adequate course of therapy for Lyme disease.

Most of the patients of third-degree AV block will require a permanent pacemaker if no reversible cause can be identified. A Dual-chamber pacemaker is preferred to maintain AV synchrony in most patients due to the favorable hemodynamic benefits. Implantable cardioverter-defibrillators should be considered in patients with complete AV block and significant left ventricle dysfunction.