History
Symptoms related to atrioventricular (AV) dissociation depend on the patient's underlying heart rate, the presence of structural heart disease and/or comorbidities, and the frequency and persistence of AV dissociation. Patients may present with fatigue, palpitations, or syncope. For example, persistent AV junctional rhythm, after a slow pathway ablation for AV node reentry is often highly symptomatic.
Sometimes, patients may present for a routine evaluation and incidentally have an electrocardiogram demonstrate isorhythmic AV dissociation; this is more commonly noted in a younger patient population and may be due to a high resting vagal tone. An acute clinical acumen is needed to recognize the possibility of AV dissociation being caused by another underlying problem if the clinical context fits.
AV dissociation may be asymptomatic if it is short lived, but if symptoms related to AV dissociation are present, they are related to bradycardia, tachycardia, AV dyssynchrony, and/or loss of atrial "kick" (ie, loss of increased ventricular filling from active atrial contraction) and include the following:
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Exertional dyspnea
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Lightheadedness
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Throbbing sensation in neck
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Palpitations
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Fatigue, malaise
Physical Examination
Evaluation of the patient's vital signs to assess for hemodynamic stability is the first step in the physical examination. It is important to note the heart rate and the blood pressure as significantly high, or low readings may lead to hemodynamic compromise and urgent attention to treatment may be necessary. However, the vital sign findings will not diagnose the cause of the atrioventricular (AV) dissociation.
Careful assessment of the pulse pressure, which can be variable due to the relationship of the atria and ventricles, carotid upstroke, and identifying cannon “A” waves (simultaneous and/or variable contraction of the atrium and ventricle) are useful in trying to identify the etiology of the arrhythmia. There may be variability in the intensity of the first heart sound, paradoxical splitting of the second heart sound, irregularity of the pulse due to ventricular or junctional escape complexes, and beat-to-beat variation in systolic murmur.
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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.
