Physiological variation in the termination window of re-entry tachycardia studied by non-invasive programmed stimulation.

In seven patients with re-entry tachycardias and the implanted antitachycardia device Tachylog (Siemens Elema, Sweden) the variation in the termination window related to posture and exertion was investigated. The investigations were performed on an outpatient basis utilizing the interactive pacing mode of the implanted unit. Six patients had supraventricular tachycardia and one patient had exercise-induced ventricular tachycardia. In all patients, double ventricular stimuli were necessary for tachycardia control. In the patients with supraventricular tachycardia, the termination window decreased significantly in the erect position (-46.5%, P less than 0.001) and in two patients it completely disappeared. Two patients could be studied during exercise. In one patient, exertion caused the termination window to shrink to 63% of its duration standing still, whereas in the other patient it widened to twice its value in the erect position. In the patient with ventricular tachycardia, whom we could study erect only, additional exercise caused the termination window to shrink on average 16.5%. These findings demonstrate that the termination window of re-entry tachycardia varies considerably with posture and exercise. This has important implications for the design of antitachycardia algorithms which will be reliably effective during daily life. Repeated non-invasive stimulation studies can be performed as an outpatient procedure allowing investigation of re-entry tachycardia under circumstances mimicking daily life.