Mode switching during managed ventricular pacing algorithm: what is the mechanism?

diomyopathy had a dual-chamber defibrillator(Virtuoso DR, Medtronic, MN, USA) implantedfor primary prevention. Table I shows the basicpacing programming of the device. At routinefollow-up, an atrial high-rate event was detected.Figure 1 shows the dot plot of the atrial high-rate event with the mode switch from AAI to DDI.Priortothemodeswitch,therecordedatrialeventshave a variable cycle length (CL) ranging betweenapproximately 200 ms and 600 ms. Despite thisvariability, the coincidental ventricular rate was