Abstract Body (Do not enter title and authors here): Background: R-on-T phenomenon occurs when an electrical stimulus is delivered at a critical point during ventricular repolarization. This can initiate ventricular arrhythmias like polymorphic ventricular tachycardia (PMVT). We describe a case of ventricular pacemaker spikes delivered on the T wave causing PMVT.

Case: A 53-year-old female with CAD s/p stent, postpartum cardiomyopathy s/p Bi-V CRT-D (Boston Scientific G124), and paroxysmal atrial fibrillation presented for elective endoscopy and colonoscopy to evaluate her dysphagia and abdominal pain. Her CRT-D was reprogrammed from DDD pacing with lower rate limit (LRL) 50 bpm to an asynchronous Bi-V DOO mode at 50 bpm (‘electrocautery mode’) for the procedure (tachy therapy disabled). Her LV-RV offset was 40 msec. Prior to receiving sedation or medications, she was found unresponsive. Telemetry showed Spike-on-T phenomenon which initiated PMVT. She was externally defibrillated with 200J and received magnesium and an IV amiodarone bolus. She returned to sinus rhythm, but one minute later had another Spike-on-T event initiating PMVT. She was successfully defibrillated with 360J. Post-shock EKG showed an asynchronous Bi-V paced rhythm at 50 bpm.

Decision Making: The patient was admitted to the CCU for post-resuscitation care. Her electrolytes and cardiac enzymes were unremarkable. Her CRT-D was reprogrammed to DDD 80-140 bpm. Transthoracic echocardiogram showed normal biventricular systolic function. Cardiac catheterization did not show obstructive CAD. After reprogramming of her device, she had no further events. After initial treatment with IV amiodarone load, she was discharged home on oral magnesium gluconate.

Discussion: The only intervention prior to her procedure was device reprogramming (DDD 50 bpm to DOO 50 bpm). Telemetry showed pacer spikes initiating PMVT. Given the LV-RV offset of 40 msec, she would have received these two tightly coupled pacemaker spikes in an asynchronous mode, in this unfortunate instance during her T wave. While her bowel preparation may have led to electrolytes abnormalities, post-resuscitation electrolytes were normal. Fortunately, she received prompt therapy and was reprogrammed with increased LRL.

Conclusion: We described a case of Spike-on-T PMVT prior to colonoscopy without obvious provocation other than asynchronous pacemaker spikes. Reprogramming devices in DOO mode with increased LRL may prevent PVCs and asynchronous pacemaker spikes from triggering PMVT.