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    • br AF suppression algorithm and prevention mechanism The atr

    2019-06-10


    AF suppression algorithm and prevention mechanism The atrial overdrive pacing algorithm is the most commonly used algorithm for AF prevention. Other pacing strategies have also been developed, including atrial pacing in response to atrial premature beats (post-PAC response), pacing in response to exercise (post-exercise rate control), and post-mode-switch pacing (Fig. 2) [34]. The suppression of potential AF triggers mechanisms, including long pauses after premature beats and atrial refractory hygromycin b dispersion, through the elimination of pauses consequent to bradycardia or the reduction of premature beats is considered the mechanism responsible for overdrive pacing-mediated AF prevention. Atrial pacing has also been suggested to prevent AF by improving the synchronization of atrial depolarization. Therefore, alternative-site pacing such as Bachmann׳s bundle pacing, atrial septum pacing, and multisite pacing have been used to prevent AF in several pacing trials [16,35–39]. Several of these studies have demonstrated the efficacy of alternative site pacing versus conventional right atrial appendage pacing for reducing the incidence of AF; however, other studies have not demonstrated similar efficacies. Therefore, alternative-site pacing currently remains controversial in clinical settings.
    Clinical trials of AF suppression algorithms Many randomized clinical trials of AF suppression algorithms were conducted during the previous decade. Most of these trials demonstrated the efficacy of atrial pacing for AF prevention; however, several studies yielded contrasting results. As a result, a consensus has not been reached regarding the utility of these algorithms. The study conditions, including the study populations, patients׳ ages, concomitant medications, pacing strategies, and study endpoints, varied among the trials. In addition, the study groups were fairly small. In 2005, Knight et al. summarized data obtained from the clinical trials of various AF prevention algorithms and published the findings as an American Heart Association science advisory [40]. Furthermore, Mizutani summarized the various pacing techniques used for AF prevention, including the pacing modes and pacing site or sites [41]. Therefore, we decided to review the clinical trials that were published in 2006 and thereafter. These trials are summarized in Table 1. The study patients ranged in age from 50 to 73 years. A majority of the trials compared atrial pacing in the AF suppression algorithm ON condition vs. the OFF condition. Shuchert et al. [13] used 4 different atrial pacing algorithms for AF prevention: pace conditioning (continuous dynamic overdrive pacing) and 3 triggered pacing algorithms (PAC suppression, post-PAC response, and post-exercise response). The patients were randomly selected to undergo triggered atrial overdrive pacing alone (3 pacing functions; “triggered group”) or a combination of continuous and triggered atrial overdrive pacing (4 pacing functions; “combined group”). Several patients in the combined group could not tolerate the high-rate pacing and were consequently excluded from the evaluation. The percentage of patients undergoing atrial pacing in the combined group was 97%, and the AF burden in Stop codons group was 2.1%. The percentage of atrial pacing in the triggered group was significantly lower at 85%; however, the AF burden was also significantly lower at 0.1%, thus demonstrating the pacing algorithm to be effective for AF prevention. In contrast, Camm et al. [10] had previously used the same device (Selection 9000, Vitatron, Maastricht, Netherlands) and had been unable to confirm the effectiveness of preventative atrial pacing in a very similar population. The discrepant results between these 2 trials highlight the difficulty in establishing convincing evidence for the efficacy of preventative atrial pacing. Most trials have selected 90 beats per minute (bpm) as the upper limit for continuous overdrive pacing because pacing above 90bpm cannot be tolerated for a long period. Only 1 relatively early study, conducted by Pürefellner et al. [9], used a relatively high pacing rate of 90bpm or 120bpm for 10min of post-mode-switch overdrive pacing (PMOP), and the percentage of atrial pacing in that study was high in comparison to that of other trials. Given the results of that trial, the authors recommended programming the device at a PMOP rate of 90bpm and concluded that PMOP could effectively prevent the early occurrence of AF and that the pacing rate was well tolerated. In contrast, Sulke et al. used atrial pacing at an upper limit of 80bpm and did not observe that atrial pacing could effectively reduce the AF burden. The results of these studies suggest that the atrial pacing rate for AF prevention should be sufficiently high to inhibit the AF triggers.