A 67-year-old woman with a history of breast cancer is admitted to the intensive care unit for severe community-acquired pneumonia and requires ventilator support and norepinephrine intravenous pressure support. During her admission, an ECG is obtained (Figure 1).
Figure 1:
Which of the following best explains this ECG?
Show Answer
The correct answer is: A. Atrioventricular dissociation due to accelerated junctional rhythm.
Figure 2:
The ECG shows sinus rhythm at a rate of 60 bpm with accelerated junction rhythm 75 bpm resulting in atrioventricular (AV) dissociation, as demonstrated by the arrows (Figure 2); despite AV dissociation, there is no heart block as the non-conducted sinus P waves are due to functional refractoriness in the AV node due to the faster junctional rhythm. Another finding to note is that every third or fourth sinus beat (round arrow) resulted with concealed penetration of the AV node which led to "resetting" the junctional rhythm. However, when the sinus P wave (+) occurred long enough after the prior junctional beat it was conducted through the AV node and resulted in right bundle aberrant QRS (long-short sequence). There is no retrograde atrial conduction of junctional rhythm as noted with the uninterrupted sinus P waves timings. There is no indication for pacing in this case as this is normal physiology due to use of beta-adrenergic agonist (norepinephrine).
References
Wang K, Benditt DG. AV dissociation, an inevitable response. Ann Noninvasive Electrocardiol 2011;16:227-31.
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