Abrupt bradycardia and grouped beating during treadmill testing: A mimic of upper rate behavior

Abstract

p t t Case summary A 67-year-old man with a biventricular implantable cardioverter-defibrillator (Medtronic Concerto C1540WK) presented for exercise treadmill testing. The patient had an ischemic cardiomyopathy and prior anterior infarction with a left ventricular ejection fraction of 25%. One year prior to this presentation, the patient presented with sustained monomorphic ventricular tachycardia and had catheter ablation for ventricular tachycardia, followed by implantation of the current device. An exercise treadmill test (ETT) was performed by using a ramp protocol. During the ETT, at peak exercise, his peak heart rate abruptly dropped and the ETT was stopped (data not shown). The device was again interrogated Programmed settings and measurements are shown in Table 1; the lower rate limit was 60 beats/min. No alerts or episodes were recorded during the ETT. To assess device function, the ETT was repeated with wireless device telemetry engaged. The preexercise 12-lead electrocardiogram and device rhythm strip at rest are shown in Figure 1A, demonstrating baseline atrial-paced and biventricular-paced rhythm. Figure 1B shows electrograms (EGMs) measured on the right ventricular channel of the device and the marker channel during early exercise. During the ETT, the abrupt bradycardia was again observed, this time with a drop from the peak heart rate of 107 to 56 beats/min (Figure 2). Stress testing was quickly terminated,