CONGRESS ABSTRACT

Case presentation A 68-year-old-man was admitted to our outpatient clinic for his yearly pacemaker (PM) follow-up visit. A dual-chamber PM had been previously implanted in 2021 to control a complete atrio-ventricular (AV) block. His past medical history was otherwise unremarkable. While checking the device, a spontaneous atrial rhythm triggering a 2:1 ventricular pacing was found (Figure 1A), and the patient reported a history of exertional dyspnea. A 12-lead electrocardiogram (ECG) was recorded (Figure 2A) and, to better evaluate the origin of the atrial rhythm, we temporarily reprogrammed the PM to VVI modality at 30 bpm. A stable atrial tachycardia with a cycle length of 445 ms and a P wave morphology compatible with a sinus/near-sinus origin was registered (Figure 2B). The patient confessed to be strongly emotional during hospital stays, so we waited some time to let him relax, and later registered a normal 1:1 conduction with lower heart rate (Figure 1B), suggesting the diagnosis of sinus tachycardia temporary exceeding the upper tracking rate (UTR). Tools to perform a treadmill or cycle-ergometer exercise test were not readily available at the time. Therefore, to better evaluate the PM behavior during exercise, a 6-minute walking test (6MWT) during ECG telemetry monitoring was performed. As the sinus rate increased, the telemetry initially showed PM Wenckebach behavior and later a 2:1 block was developed with a concomitant halving of the ventricular rate; at that moment, symptoms occurred. This behavior arose when the UTR and the total atrial refractory period (TARP) were exceeded. The device was then reprogrammed with a higher UTR and a shorter post-ventricular atrial refractory period (PVARP). At subsequent follow-up visits the patient reported resolution of exertional symptoms. Discussion In PM-dependent patients, with a dual-chamber PM, atrial rate increases can be tracked in a 1:1 ventricular pacing up to the UTR. The maximum UTR results by a combination of AV delay and PVARP (i.e. TARP). When the atrial rate exceeds UTR and TARP, PM Wenckebach and subsequently 2:1 block occur, together with a sudden reduction in ventricular rate that can cause symptoms such as dyspnea and fatigue. Conclusion A 6MWT may represent a cheap and easily accessible way to study patients’ exercise capacity and to observe rate response of the PM. It may be considered when exertional symptoms are reported by PM-dependent patients in order to optimize PM programming.