Medication Summary
The goals of pharmacotherapy are to reduce morbidity and to prevent complications.
Anticholinergic agents
Class Summary
Competitive inhibitor at autonomic, postganglionic, and cholinergic receptors.
Atropine IV/IM
Atropine is a competitive inhibitor at autonomic, postganglionic, and cholinergic receptors. It may be administered in patients in whom a very slow sinus node activation is seen with a junctional escape rhythm.
Inotropic Agents
Class Summary
Inotropic agents are used to increase the force of cardiac contractions. Intravenous positive inotropic agents should only be used in inpatient settings—and then only in patients who manifest signs and symptoms of low cardiac output syndrome (volume overload with evidence of organ hypoperfusion).
Dopamine (Intropin)
Dopamine is an inotrope and may increase renal blood flow, cardiac output, and heart rate. At a low dose (2-10 mcg/kg/min) it has primarily beta1 properties and increases the heart rate, but at doses above 10 mcg/kg/min, it has inotropic properties.
This agent may be used when severe sinus bradycardia leads to a junctional escape rhythm causing AV dissociation and thereby help restore 1:1 AV conduction by increasing the sinus rate. Dopamine should be used with caution, as it may cause an increased risk for the development of junctional or ventricular tachycardia in certain situations.
Adrenergic agonist agents
Class Summary
Stimulate myocardial performance and improve coronary artery blood flow.
Isoproterenol (Isuprel, Isopro)
Isoproterenol is a beta1/beta2 agonist; it may increase the sinus node rate in cases of severe bradycardia to treat AV dissociation caused by the initiation of a subsidiary pacemaker in the AV junction. The sinus node rate increases and would prevent the junctional pacemaker from initiating. However, similar to dopamine, isoproterenol must be used with caution, as junctional or ventricular tachycardia may occur.
Antidotes
Class Summary
Used to treat digitalis intoxication.
Digoxin immune Fab (Digibind)
Digoxin immune Fab is an immunoglobulin fragment with a specific and high affinity for both digoxin and digitoxin molecules. Removes digoxin or digitoxin molecules from tissue binding sites.
Each vial of Digibind contains 40 mg of purified digoxin-specific antibody fragments that bind approximately 0.6 mg of digoxin or digitoxin. The dose of antibody depends on the total body load (TBL) of digoxin; estimates of TBL can be calculated in three ways: (1) estimating the quantity of digoxin ingested in the acute ingestion and assume 80% bioavailability (mg ingested × 0.8 = TBL); (2) obtaining a serum digoxin concentration and, using a pharmacokinetics formula, incorporate the volume of distribution (Vd) of digoxin and the patient's body weight in kg (TBL = digoxin serum level [ng/mL] × 6 L/kg × body weight in kg); and (3) using an empiric dose based on average requirements for an acute or chronic overdose in an adult or child.
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Atrioventricular Dissociation. Significant slowing of the sinus node allows for a subsidiary pacemaker (atrioventricular [AV] junction) to activate, causing AV dissociation.
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Atrioventricular Dissociation. This rhythm strip reveals interference atrioventricular dissociation, as there is a P wave conducting to the ventricle in the third and seventh beats, whereas the P wave fails to conduct to the ventricle in the other beats.
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Atrioventricular Dissociation. Isorhythmic AV dissociation. There is AV dissociation with independent atrial and ventricular conduction at similar rates.
