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Atrioventricular Dissociation
Atrioventricular (AV) dissociation is defined as a lack of association between the atria and the ventricles or independent function of the atria and ventricles. This simple definition will serve as a reminder that AV dissociation should be considered an umbrella rather than a diagnosis. AV dissociation may occur in the setting of bradycardic rhythms, complete heart block, as well as tachycardic rhythms (ventricular tachycardia, atrial rhythm with associated accelerated junctional rhythm or AV nodal reentrant tachycardia).
Synonyms
- Third-degree AV block
- CHB
- Complete AV block
- AV Dissociation
Epidemiology & Demographics
The prevalence is the sum of the diagnoses that are characterized by AV dissociation.
Physical Findings & Clinical Presentation
Physical examination findings may be normal unless the arrhythmia is causing hemodynamic compromise. If the right atrium contracts against a closed tricuspid valve during ventricular systole, Cannon A waves may be seen in the jugular vein. Patients may present with the following clinical manifestations:
- •Dizziness, palpitations
- •Syncope or presyncope (caused by reduced cardiac output)
- •Fatigue, impaired exercise tolerance
- •Mental status changes
- •Congestive heart failure
- •Angina pectoris
- •Some patients may be asymptomatic
Etiology
- •Slow rate of firing from sinus node
- •Inappropriately fast pacemaker from the ventricle
- •Iatrogenic: Anesthesia, inotrope infusion, ventricular pacing, radiofrequency ablation of slow pathway, digoxin toxicity
- •Sinus node disease, ischemia, hyperkalemia, overactive vagal drive
- •Complete heart block: Progressive fibrosis of the His-Purkinje system, medications, Lyme disease
Differential Diagnosis
- •The differential diagnosis should be targeted toward the diagnoses that include AV dissociation.
- •note: The atrial rate does not need to be faster than the ventricular rate in AV dissociation, as is the case in the definition of complete heart block.
- 1.Isorhythmic AV dissociation: Atrial and ventricular rates are the same but dissociated.
- 2.Interference dissociation: Similar atrial and ventricular rates but conduction occurs sometimes.
Workup
- •Workup such as routine laboratory studies, cardiac biomarkers, and cardiac imaging should be dictated by the clinical circumstances:
- 1.Laboratory studies: Particular attention to electrolyte abnormalities (potassium) and digoxin level
- 2.Lyme antibody titer in the case of complete heart block, particularly in the Northeastern U.S.
Treatment
Acute General Treatment
- •Initial treatment should focus on the hemodynamic stability and symptoms of the patient.
- •Bradycardic rhythms:
- 1.If necessary (i.e., symptoms or hemodynamic compromise), a temporary pacemaker is the most reliable therapy.
- 2.Hold AV-nodal blocking agents.
- 3.Chronotropic medications: Atropine, dopamine, dobutamine, or isoproterenol may be used as second-line agents while preparing for a temporary pacemaker.
- •Tachycardic rhythms (ventricular tachycardia):
- 1.In the setting of hemodynamic compromise, cardioversion is the first-line therapy.
- 2.IV antiarrhythmic drugs: Amiodarone or lidocaine to suppress the arrhythmia.
- 3.Treatment of the underlying cause of ventricular tachycardia: Coronary angiogram if ischemia vs. electrophysiology (EP) study +/− ablation.
Referral
All patients with AV dissociation should be referred to a cardiologist for diagnostic evaluation of the rhythm.
Pearls & Considerations
Comments
- •Recall that AV dissociation is merely an umbrella that includes multiple diagnoses, including both bradycardic and tachycardic arrhythmias.
- •Specific considerations regarding etiology, treatment, and disposition should be directed toward the rhythm that has caused AV dissociation.