Monitor-induced tachycardia in a patient with a rate-responsive pacemaker

A patient with a ventricle-paced, ventricle-sensed and inhibited, respiratory rate-responsive pacemaker presented for orthopaedic surgery. She had been operated upon recently without any adverse effects. In the recovery unit her electrocardiograph showed a paced ventricular tachycardia of about 140 beats x min(-1) without any other adverse sign or symptom. Although this tachycardia initially decreased to 70 beats x min(-1) after about 30 min, it later rose again to 140 beats x min(-1). A pacemaker technician was consulted, who suggested that there may be interference between the bioelectric impedance signals of the patient monitoring system that was being used to measure respiratory rate and the pacemaker's own measurement systems.