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]
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Medical Therapy
A patient with inferior wall myocardial infarction and distal high grade complete heart block with a heart rate of more than 60 beats per minute is at immediate danger of asystole and requires an immediate placement of permanent pacemaker compared to a patient with inferior myocardial infarction and complete block at the level of AV node with a heart rate of 35-40 beats per minute.
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. Treatment in emergency situations are atropine and an external pacer.
Acute Pharmacotherapy
Atropine
Atropine can partially or completely restore conduction through the AV node when the cause for complete heart block is acute myocardial infarction (ischemia of the AV node). Atropine, in this setting, reverses the reduced conduction across the AV node (which is due to increased vagal tone). But caution is advised in such cases as the resulting vagolysis leads to unopposed sympathetic activity. This increased sympathetic activity causes ventricular irritability and can progress to fatal ventricular arrhythmias.
Use of atropine in situations where the block is at the level of His bundle can lead to increased atrial rate and a greater degree of heart block with reduced ventricular rate.
Atropine is unsuccessful 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.
Isoproterenol
Isoproterenol may help accelerate a ventricular escape rhythm and restore conduction with distal level of block but the probability for efficacy is low. Active ischemic heart disease is an absolute contraindication for the use of isoproterenol.
DigiFab
DigiFab is an immunoglobulin fragment used in the treatment of digitalis overdose. It has specific high affinity for digoxin and digitoxin molecules and removes them from the tissues. The dose of DigiFab depends on the concentration of digoxin in the body.
- Number of vials of DigiFab = (Digoxin concentration)×(Patient's weight)÷100
Transcutaneous Pacing
Transcutaneous pacing is the treatment of choice in symptomatic patients. Any patient with complete heart block associated with frequent pauses, inadequate ventricular escape rhythm and block below the AV node should be paced temporarily using a transcutaneous pacemaker to attain stability. Disadvantages of using a transcutaneous pacemaker are:
- It is not a reliable method and
- It is extremely uncomfortable for the patient.
If perfect capture is not obtained with a transcutaneous pacer, attempt should be made to pace the patient temporarily using transvenous pacing method. This method is employed in the emergency room for all patients with hemodynamic instability and in whom perfect capture cannot be obtained with a transcutaneous pacer.
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:
- Adenosine
- Atenolol
- Betaxolol
- Bisoprolol
- Brimonidine tartrate and Timolol maleate
- Carteolol
- Diltiazem
- Disopyramide
- Dronedarone
- Flecainide
- Labetalol
- Metoprolol
- Mexiletine
- Nadolol
- Nebivolol
- Penbutolol
- Pindolol
- Procainamide
- Propranolol
- Quinidine gluconate
- Sotalol
- Timolol
- Verapamil
References
- ↑ 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