Ferri – Atrioventricular Dissociation

Mar 20, 2020 admin TIM MẠCH 0

Atrioventricular Dissociation

  • Aleem Mughal, M.D.

 Basic Information

Definition

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 (Fig. 1 and Fig. 2) (complete heart block [Fig. 3], as well as tachycardic rhythms [ventricular tachycardia, atrial rhythm with associated accelerated junctional rhythm or AV nodal reentrant tachycardia]).

FIG.1 

An electrocardiogram (ECG) was obtained at the primary care practitioner’s office. Computer interpretation indicated junctional bradycardia at a rate of 42 beats per minute. While the rate was regular, not every QRS complex was preceded by a P wave. There were no acute ST- or T-wave changes consistent with ischemia.
From Singh GD, Wong BG, Southard JA, et al.: Food for thought: atrioventricular dissociation, Am J Med, 126(12):1050–1053, 2013.
FIG.2 

This flow chart demonstrates the relationship between atrioventricular dissociation due to complete heart block vs. atrioventricular dissociation from a ventricular rate that is greater than the atrial rate. AV, atrioventricular; TP, temporary pacemaker; PPM, permanent pacemaker.
From Singh GD, Wong BG, Southard JA, et al.: Food for thought: atrioventricular dissociation, Am J Med 126(12):1050–1053, 2013.
FIG.3 

A, In the initial rhythm strip—also shown in Fig. 1—solid black arrows indicate atrial complexes initiated by the sinus node. Note that for each beat, the sinus impulse is progressively closer to the QRS complex, then becomes obscured within the QRS complex, and finally is seen beginning to emerge on the downstroke of the R wave in the last 3 QRS complexes. The junctional pacemaker, at 42 beats per minute, is slightly faster than the atrial rate of 41 beats per minute. B, Another ECG was performed after the patient was treated for dyspepsia. The rhythm strip shows sinus bradycardia with a rate of 45 beats per minute.
From Singh GD, Wong BG, Southard JA, et al.: Food for thought: atrioventricular dissociation, Am J Med 126(12):1050–1053, 2013.

Synonyms

  1. Third-degree AV block

  2. CHB

  3. Complete AV block

ICD-10CM CODES
I44.2 Atrioventricular block, complete

Epidemiology & Demographics

  1. •

    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:

  1. •

    Dizziness, palpitations

  2. •

    Syncope or presyncope (caused by reduced cardiac output)

  3. •

    Fatigue, impaired exercise tolerance

  4. •

    Mental status changes

  5. •

    Congestive heart failure

  6. •

    Angina pectoris

  7. •

    Some patients may be asymptomatic

Etiology

  1. •

    Slow rate of firing from sinus node

  2. •

    Inappropriately fast pacemaker from the ventricle

  3. •

    Iatrogenic: anesthesia, inotrope infusion, ventricular pacing, radiofrequency ablation of slow pathway, digoxin toxicity

  4. •

    Sinus node disease, ischemia, hyperkalemia, overactive vagal drive

  5. •

    Complete heart block: progressive fibrosis of the His-Purkinje system, medications, Lyme disease

Diagnosis

Differential Diagnosis

  1. •

    The differential diagnosis should be targeted toward the diagnoses that include AV dissociation.

  2. •

    Note: The atrium 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

  1. •

    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 Rx

  1. •

    Initial treatment should focus on the hemodynamic stability and symptoms of the patient.

  2. •

    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.

  3. •

    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

  1. •

    Recall that AV dissociation is merely an umbrella that includes multiple diagnoses, including both bradycardic and tachycardic arrhythmias.

  2. •

    Specific considerations regarding etiology, treatment, and disposition should be directed toward the rhythm that has caused AV dissociation.

 

 

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