Abstract Body (Do not enter title and authors here): Background: The worldwide first genetically modified porcine-to-human cardiac xenotransplantation was successfully performed in January 2022 at the University of Maryland with the recipient surviving 60 days.

Aim: Assess the ECG parameters and cardiac rhythm during the death of the worldwide first porcine-to-human xenotransplant.

Methods: Continuous 6-lead ECG telemetry was used to analyze ECG parameters and cardiac rhythm during the final 9 minutes after withdrawal of life support.

Results: At the time of withdrawal (W), the patient was in sinus rhythm (70bpm, PR interval 280ms, right bundle branch block (RBBB) with QRS 140ms, QT 400ms; Figure). PR prolongation up to 360ms with loss of P wave was noted at W+2:55min. Irregular junctional rhythm with blocked PACs and bradycardia (23 bpm) occurred around W+3:25min. At that time, widening of RBBB to 160ms with non-specific repolarization abnormalities and QT prolongation were observed. At W+4:30min, increasing pauses of up to 8.5s with mild QRS axis shift occurred. At W+6min, asystole (up to 20s) with rare PVCs from the left anterolateral LV base were seen. Final rhythm at W+6min consisted of ventricular escape beats from the infero-basal LV before electrical activity ceased at W+6:45min. No other atrial or ventricular arrhythmias were noted.

Conclusion: The porcine-to-human cardiac xenotransplant showed a terminal rhythm of bradycardia, sinus arrest, and junctional and ventricular escape beats. This is consistent with ischemia-related failure of impulse generation, slowing intra-atrial/AV-conduction delay, and failure of impulse propagation. Notably, no tachyarrhythmias were seen despite ectopic atrial and ventricular beats with prolongation of depolarization and repolarization. This is similar to traditional terminal rhythms observed in humans and does not suggest unexpected arrhythmic proclivities between pig myocardium and the human environment (“pig heart in human body”).