Cardiopulmonary Exercise Testing to Troubleshoot Rate-Responsive Pacing in an Athlete With Acquired Sinus Node Dysfunction

Background: Athletes with sinus node isolation can become fully dependent on sensor-driven pacing. Default accelerometer settings may underperform during exertion. Case Summary: A 73-year-old former collegiate athlete developed exertional dyspnea after Cox Maze IV procedure; postoperative testing showed sinus node isolation, and he received a dual-chamber pacemaker. A cardiopulmonary exercise test (CPET) revealed a blunted chronotropic response, with his heart rate plateauing at 105 beats/min (device activity setpoint). A repeat CPET with real-time programming (lower activity threshold, higher activities of daily living rate, rate-adaptive atrioventricular delay/limits) restored rate escalation within weeks, with symptom resolution and peak oxygen consumption volume improving from 87% to 102% predicted. Discussion: CPET can both diagnose device-mediated chronotropic limitation and provide a physiologic target for on-table pacemaker programming in highly active patients, where activity sensors often miss intermittent workloads. Take-Home Message: This case underscores the limitations of activity-based sensors in athletes and highlights the utility of CPET in diagnosing and personalizing pacemaker programming to restore functional capacity.