br Detection methods in implantable monitoring

Detection methods in implantable monitoring device State-of-the-art, implantable, dual-chamber cardiac devices provide useful diagnostic information, including the numbers and duration of automatic mode switch (AMS) episodes upon detection of AT/AF. However, to collect accurate diagnostic information, special attention must be paid to the following factors: the device settings; the presence versus absence of ventriculoatrial (VA) conduction, which, when present, often represents repetitive non-reentrant synchrony (RNRVAS) or pacemaker-mediated tachycardia (PMT); the post-ventricular atrial-blanking period (PVAB) and atrial sensitivity; and the sensing of far-field R waves (FFRW) in the atrial channel. Preventing FFRW sensing by the atrial channel is challenging since 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 atrial tachyarrhythmias, they (a) are considered AT/AF episodes by implantable monitoring devices, (b) may be the source of inaccurate diagnostic information and inappropriate AMS from DDD to DDI or VVI mode, and (c) may trigger AT/AF or cause pacemaker syndrome [10–20].
Prevalence of AT/AF in recipients of implantable cardiac devices The reported incidence of symptomatic or asymptomatic AT/AF, detected by AHRE in recipients of implantable monitoring devices, is variable and as high as 51% per year among populations that included patients with or without previously documented AT/AF, and with or without organic alkylation of dna disease [1–6]. One explanation for the variable incidence among studies is the criterion of AT/AF duration, which ranged between ≥30s and ≥1h, depending on the study protocol [1–5]. In the ASSERT trial, AT/AF was arbitrarily defined as lasting for >6min [8,9]. The duration of follow-ups also varied widely between 29 days and 27 months among studies [1–5]. Finally, in most previous studies, the AT/AF was defined on the basis of the numbers of AHRE or of AMS, with or without the application of the atrial overdrive pacing algorithm. Thus, the incidence of AT/AF detected by implantable devices depends on the following factors: (a) the definition of AT/AF, (b) the presence or absence of a history of AT/AF before pacemaker implantation, (c) the cumulative percentage of atrial (Cum% Ap) or ventricular (Cum% Vp) pacing, (d) the ventricular pacing site, (e) the presence or absence of sinus node disease or atrioventricular (AV) block as a pacing indication, and (f) the AHRE settings, which include the atrial sensitivity and detection rate.
Variables influencing the detection of AT/AF by implantable devices
Optimal setting of atrial sensitivity and post ventricular atrial blanking An optimal setting of the atrial sensitivity is crucial to an accurate detection of AT/AF by implantable dual-chamber monitoring devices. The setting of a low atrial sensitivity decreases the likelihood of FFRW oversensing as well as the chances of detecting AT/AF; this is because undersensing of the atrial electrogram during ongoing tachyarrhythmia may lead to the underestimation of the incidence of clinical AT/AF. Conversely, the setting of a high atrial sensitivity increases the chances of detecting AT/AF and the likelihood of FFRW oversensing, which can lead to the overestimation of the incidence of clinical AT/AF. While an optimal setting of atrial sensitivity remains unclear, a<0.5mV setting is generally recommended for recipients of implantable devices who have a history of AF. 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 AT/AF detection, which might decrease the likelihood of detecting AT/AF. Conversely, a short PVAB widens the search window of atrial sensing and of AT/AF detection, thereby decreasing the specificity of AT/AF detection. In clinical practice, a setting of +25ms between the ventricular pacing spike and FFRW sensing is generally recommended for the PVAB [23].