case_images: PMC7252805_01
case_images: A: Recordings from the first postoperative day following OHT performed six years prior. Donor atrial rate was 97 bpm. Recipient atrial rate was 55 bpm (marked by  ) and was dissociated from the donor atrial (marked by  ) and ventricular rates. B: Presenting ECG. Complete heart block with junctional rate of 71 bpm and dissociated P-waves at a rate of 100 bpm. ST elevations are present in V3 to V6.
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case_images: On review of prior electrocardiograms (ECGs) recorded immediately postoperatively following OHT (Figure 1A), he showed unexpected evidence of dissociated P-waves representing dual atrial depolarizations despite a history of receiving OHT with the bicaval technique. Only one sinus node should be present, but the possibility of dual atrial tissues existing similar to in the case of the historical biatrial technique (donor and recipient) had to be entertained. The presenting ECG with AV dissociation (Figure 1B) could represent accelerated junctional rhythm in the setting of (1) sinus arrest of recipient atria and complete AV block of intact donor atrial P-waves or (2) sinus arrest of donor atria with accelerated junctional rhythm and surgically isolated recipient P-waves.
case_images: A: Pacemaker setting is AAI 70 bpm until the last three beats, at which point it transitions to AAI 90 bpm. Telemetry ECG lead V1 shows dissociated P-waves (marked by  ) at a rate of 100 bpm to 110 bpm with an accelerated junctional rhythm of 73 bpm. Atrial electrograms, with the lowest sensitivity threshold, intermittently undersensed low-amplitude atrial signals with long AV intervals of 816 ms to 824 ms and, most notably, without evidence of sensing the dissociated surface P-waves. The last two beats of intracardiac tracing show that the small atrial signal is absent with atrial pacing and the acceleration of ventricular activity to 90 bpm with an AV delay of 200 ms, further supporting the idea that the small atrial signals represent donor atrium with isorhythmic dissociation from the underlying junctional rhythm. Alternatively, the low-amplitude atrial signals can represent far-field ventricular signals that are not present at the end of the strip due to amplitude autogain from the device programmer in the setting of consistent atrial pacing. B: Telemetry lead V1 shows P-waves ( ) at a rate of 100 bpm to 110 bpm with continued dissociation from atrial pacing at 90 bpm with 1:1 acceleration of the ventricle and an AV time of approximately 200 ms. The location of the atrial lead is therefore in the donor atrium and demonstrates intact antegrade AV conduction from this pacing site.
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case_images: AV conduction time of 200 ms, confirming that the donor atrium had normal AV conduction (Figures 2A and 2B). As the P-waves continued to be dissociated despite atrial capture and ventricular acceleration, it was concluded that the dissociated P waves represented the electrically isolated recipient atrial activity. A chest X-ray demonstrated the standard atrial lead position (Figure 3).
case_images: Portable chest X-ray demonstrates standard positions of the atrial lead and single-coil ventricular lead in the right ventricle.
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case_images: PMC7252805_01_icrm-10-3472-g003.jpg
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case_images: AV conduction time of 200 ms, confirming that the donor atrium had normal AV conduction (Figures 2A and 2B). As the P-waves continued to be dissociated despite atrial capture and ventricular acceleration, it was concluded that the dissociated P waves represented the electrically isolated recipient atrial activity. A chest X-ray demonstrated the standard atrial lead position (Figure 3).