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The patient was a 43-year-old male whose chief complaint was syncope. Electrocardiography at the first visit revealed escaped rhythm (38 bpm). After hospitalization he developed reverse common atrial flutter (AFL) and underwent catheter ablation. After termination of atrial flutter by ablation, sinus arrest was noted, allowing a diagnosis of bradycardia-tachycardia syndrome, for which the patient underwent pacemaker implantation. Twenty days after implantation, a marked elevation of atrial threshold was noted, despite absence of a change in lead resistance or position, and atrial capturing was not possible even at the maximum output (8 V/ 1.2 ms). The cause remained unknown and the patient was followed without active intervention. Atrial threshold normalized during the follow-up, but no change was noted in lead resistance or position even at the time of normalization.

The patient was a 43-year-old male whose chief complaint was syncope. Electrocardiography at the first visit revealed escaped rhythm (38 bpm). After hospitalization he developed reverse common atrial flutter (AFL) and underwent catheter ablation. After termination of atrial flutter by ablation, sinus arrest was noted, allowing a diagnosis of bradycardia-tachycardia syndrome, for which the patient underwent pacemaker implantation. Twenty days after implantation, a marked elevation of atrial threshold was noted, despite absence of a change in lead resistance or position, and atrial capturing was not possible even at the maximum output (8 V/ 1.2 ms). The cause remained unknown and the patient was followed without active intervention. Atrial threshold normalized during the follow-up, but no change was noted in lead resistance or position even at the time of normalization. [Copyright &y& Elsevier]

Background: Automatic threshold measurement and output adjustment are used as default settings in modern pacemakers. The purpose of the study was to assess Atrial Capture Management (ACM) of Medtronic pacemakers in pediatric patients. Methods: Forty children were enrolled in two centers. Median age was 9.8 years (range 0.8–17.5 years). Half had undergone surgery for congenital heart defects; 45% of patients had an epicardial atrial lead. The pacing indication was atrioventricular block in 82% of patients and sinus node disease in 18%. Manually determined atrial thresholds and ACM measurements were compared. Results: ACM measurements were within the expected variation in 37/40 (93%) of the patients. In one patient the threshold was 0.625-V lower manually than with ACM. One patient had too high an intrinsic atrial rate for ACM to be able to measure threshold. The mean threshold at 0.4 ms was 0.69 ± 0.32 V manually and 0.68 ± 0.35 V with ACM (two-tailed paired t- test, P = 0.52) in all patients. The mean difference was 0.012 V (95% confidence interval: −0.027, 0.053). The mean endocardial threshold was 0.70 ± 0.36 V manually and 0.69 ± 0.38 V with ACM; epicardial threshold was 0.67 ± 0.27 V manually and 0.68 ± 0.32 V with ACM. The difference between the measurements was 0.012 V for endocardial and 0.014 V for epicardial leads. No atrial arrhythmias due to ACM measurements were observed. Conclusions: ACM measures atrial thresholds reliably in pediatric patients with both endocardial and epicardial leads, allowing its use in both. Constant high intrinsic atrial rate may prevent automatic threshold measurement in young children. (PACE 2010; 33:309–313) [ABSTRACT FROM AUTHOR]

Periodic determination of pacemaker capture threshold is important to ensure appropriate pacemaker function. During dual chamber pacing, it is sometimes difficult to identify evidence of atrial depolarization on surface electrocardiography (ECG), and this can interfere with the ability to ascertain atrial capture. We describe new methods for determining atrial capture threshold using a standard telemetered endocardial atrial electrogram (AEGM). For the first method, the atrial output is decremented until loss of atrial capture is demonstrated by the appearance of native P wave activity on the AEGM, The atrial capture threshold can then he accurately determined as the point at which a stepwise increase in atrial output results in extinction of the native P wave activity. The second method uses the direct visualization of the AEGM recorded between the ring electrode and pacemaker generator during unipolar (lead tip electrode) pacing. This requires the presence of a bipolar lead. Using this method of recording, it is possible to identify a signal after the atrial pacing stimulus artifact during atrial capture, which disappears with loss of capture. This signal is consistent with a paced "evoked atrial potential" and allows verification of atrial capture. After validating the methods in two sets of test patients with clearly identifiable atrial depolarization on surface ECG, one method was successfully applied to a patient in whom atrial depolarization could not he reliably ascertained on surface ECG. These methods promise to he useful in selected patients in whom confirmation of atrial capture would otherwise be difficult. [ABSTRACT FROM AUTHOR]