• Odie Halberg posted an update 5 days, 5 hours ago

    The presence of AHRE, however, may not invariably indicate the presence of ATA. We have recently reported AHRE that reflected episodes of atrial fibrillation (AF) as well as device-mediated arrhythmic events, such as repetitive non-reentrant ventriculo-atrial synchrony (RNRVAS), buy D-Luciferin mediated tachycardia (PMT), and far-field R wave (FFRW) oversensing, particularly in the presence of long atrioventricular (AV) intervals in the DDD mode, or when rate-responsive pacing or an AOP algorithm was used in recipients of a dual-chamber pacemaker or an implantable cardioverter defibrillator [3]. RNRVAS or PMT require ventriculo-atrial (VA) conduction to develop.Atrial setting in dual-chamber devicesAn optimal setting of atrial sensitivity is key for the accurate detection of ATA by implantable dual-chamber pacing devices. To optimize AF detection and lower the risk of atrial undersensing by dual-chamber implanted devices, a setting of a <0.5mV atrial sensitivity is usually recommended. The setting of a low atrial sensitivity lowers the risk of FFRW oversensing as well as lowering the chances of detecting ATA, due to undersensing the atrial electrogram during ongoing tachyarrhythmia. In this case, the incidence of ATA may be underestimated. Conversely, a setting of high atrial sensitivity increases the chances of detecting ATA and increases the likelihood of FFRW oversensing, in which case the incidence of clinical ATA may be overestimated. Although the optimal atrial sensitivity remains to be defined, a <0.5mV setting is generally recommended for recipients of implantable devices who have a history of AF. However, high atrial sensitivity settings might cause atrial oversensing. Table 1 shows the pitfalls for diagnosing AF. In the presence of atrial undersensing (when the atrial sensitivity is low), the incidence of true AF cannot be detected accurately. Atrial oversensing may result in (1) double counts of the P wave, which includes RNRVAS and FFRW oversensing, or (2) sensing of myopotentials, lead noise, or electromagnetic interference. Atrial undersensing and oversensing may both interfere with the diagnosis of true AF.Device-detected non-atrial fibrillationState-of-the-art, implantable, dual-chamber cardiac devices provide useful diagnostic information, including the number and duration of automatic mode switch (AMS) episodes upon detecting ATA. However, to collect accurate diagnostic information, special attention must be paid to the device settings, to the presence versus absence of VA conduction, which when present, often represents RNRVAS or PMT, to the post-ventricular atrial blanking period (PVAB) and atrial sensitivity, and to the sensing of FFRW in the atrial channel. Preventing FFRW sensing by the atrial channel is challenging as it is inversely correlated with the duration of the PVAB and with the atrial sensitivity. Furthermore, the presence of VA conduction may cause RNRVAS or PMT. Although FFRW sensing, RNRVAS, and PMT are not ATA, they (a) are counted as ATA episodes by implantable monitoring devices, (b) might be the source of inaccurate diagnostic information and inappropriate AMS from DDD to DDI or VVI mode, and (c) may trigger ATA or cause pacemaker syndrome [4–14]. The clinical shortcomings associated with atrial oversensing are shown in Fig. 1.Increasing the duration of PVAB might be an effective means of preventing FFRW oversensing in the atrial channel. However, this narrows the search window of atrial sensing, and shortens the window of ATA detection, which might decrease the likelihood of detecting ATA. Conversely, a short PVAB widens the search window of atrial sensing and of ATA detection, a setting that might decrease the specificity of ATA detection. In clinical practice, therefore, a +25ms PVAB setting between the ventricular pacing spike and FFRW sensing is generally recommended [15].Endless loop tachycardia, which might present as PMT or RNRVAS, both mediated by VA conduction, is a well known, understood, and relatively common complication associated with implantable dual-chamber cardiac devices. While PMT is the most commonly observed pacemaker-induced tachyarrhythmia, RNRVAS, also known as AV desynchronization arrhythmia or VA synchrony non-reentrant arrhythmia, may cause symptoms indistinguishable from those caused by PMT [16–18].

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