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==Medical Therapy==
==Medical Therapy==
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<ref>Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society [published correction appears in J Am Coll Cardiol. 2019 Aug 20;74(7):1016-1018]. ''J Am Coll Cardiol''. 2019;74(7):e51‐e156. doi:10.1016/j.jacc.2018.10.044</ref>. A new third degree [[Atrioventricular block|AV block]] is an emergency. Management is slightly different between unstable and stable patients.   
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<ref>Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society [published correction appears in J Am Coll Cardiol. 2019 Aug 20;74(7):1016-1018]. ''J Am Coll Cardiol''. 2019;74(7):e51‐e156. doi:10.1016/j.jacc.2018.10.044</ref>. A new third degree [[Atrioventricular block|AV block]] is an emergency. Management is slightly different between unstable and stable patients.   


===Management of Unstable 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 (Injection)|atropine]] and temporary cardiac pacemaker.
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 (Injection)|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 transplantation|cardiac transplant]] procedure. Treatment with atropine should be followed by [[transcutaneous pacing]] or a chronotropic agent.
*[[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 transplantation|cardiac transplant]] procedure. Treatment with atropine should be followed by [[transcutaneous pacing]] or a chronotropic agent.
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While monitoring patients, management should be as fellows.
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.
* 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 with CABG or PCI had no Difference on Outcomes of Death, non-fatal MI, or CVA for Diabetics with Multi-Vessel Coronary Disease: Results of the CARDia Trial|revascularization]] and do not require a permanent pacemaker.
* 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 with CABG or PCI had no Difference on Outcomes of Death, non-fatal MI, or CVA for Diabetics with Multi-Vessel Coronary Disease: Results of the CARDia Trial|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.
* Many medications that are used to treat cardiovascular conditions such as [[Antihypertensive medication|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.
* 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.
* 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<ref>{{Cite journal|last=Task force members|first=|date=|title=2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA)|url=https://doi.org/10.1093/eurheartj/eht150|journal=Eur Heart J|volume=34|pages=2281-2329|via=}}</ref>. A Dual-chamber pacemaker is preferred to maintain AV synchrony in most patients due to the favorable hemodynamic benefits<ref>Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). ''Eur Heart J''. 2013;34(29):2281‐2329. doi:10.1093/eurheartj/eht150</ref>.  Implantable [[cardioverter-defibrillators]] should be considered in patients with complete AV block and significant left ventricle dysfunction.
Most of the patients of third-degree AV block will require a permanent pacemaker if no reversible cause can be identified<ref>{{Cite journal|last=Task force members|first=|date=|title=2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA)|url=https://doi.org/10.1093/eurheartj/eht150|journal=Eur Heart J|volume=34|pages=2281-2329|via=}}</ref>. A Dual-chamber pacemaker is preferred to maintain AV synchrony in most patients due to the favorable hemodynamic benefits<ref>Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). ''Eur Heart J''. 2013;34(29):2281‐2329. doi:10.1093/eurheartj/eht150</ref>.  Implantable [[cardioverter-defibrillators]] should be considered in patients with complete AV block and significant left ventricle dysfunction.

Revision as of 16:00, 6 June 2020

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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]

Medical Therapy

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[1]. 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.

  • 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[2]. A Dual-chamber pacemaker is preferred to maintain AV synchrony in most patients due to the favorable hemodynamic benefits[3]. Implantable cardioverter-defibrillators should be considered in patients with complete AV block and significant left ventricle dysfunction.

Contraindicated medications

Third degree AV block(except in patients with a functioning artificial pacemaker) is considered an absolute contraindication to the use of the following medications:

References

  1. ↑ Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society [published correction appears in J Am Coll Cardiol. 2019 Aug 20;74(7):1016-1018]. J Am Coll Cardiol. 2019;74(7):e51‐e156. doi:10.1016/j.jacc.2018.10.044
  2. ↑ Task force members. "2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA)". Eur Heart J. 34: 2281–2329.
  3. ↑ Brignole M, Auricchio A, Baron-Esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J. 2013;34(29):2281‐2329. doi:10.1093/eurheartj/eht150

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