The Awareness of Incapability for Automatic Mode Switching in a Patient Receiving Pilsicainide after Dual-Chamber Pacemaker Implantation

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Background: Automatic mode switching (AMS) was effective in patients (pt) with paroxysmal atrial fibrillation (Paf) requiring for dual chamber pacer (DDD) but attention must be paid to specific pt receiving anti-arrhythmic therapy for Paf. Case: An 84 y.o. female admitted to the hospital because of palpitation and loss of consciousness. She was diagnosed as having Paf on complete AV block, and was implanted DDD (upper tracking rate, 130 bpm; AMS, on). Pilsicainide (150 mg/day) was initiated for rhythm control. She visited our clinic 7 days after discharge and wide QRS (240 msec) irregular tachycardia with a rate of 130 bpm (460 msec) was documented. Interrogation of the pacer revealed persistent atrial flutter with an average atrial interval of 230 msec. Because post-ventricular atrial refractory period masked the respective atrial potential alternatively, ventricular pacing rate was identical to twice the atrial rate as 460 msec (230×2 msec=130 bpm). Thus clinical tachycardia with the configuration of LBBB was found to be the results of continuous pacing from right ventricle. Serum levels of pilsicainide was elevated (2.95 ng/ml) and drug-induced atrial flutter on negative inotrophic effect was suspected. Discussion and Conclusion: The timing of atrial sensing may be modified when regularized atrial event appeared during anti-arrhythmic therapy for Paf. Incapability of AMS may lead to critical ventricular tachy-arrhythmias.