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
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 with 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.
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