INAPPROPRIATE RATE RESPONSE IN A VVI-R PACEMAKER

The search for a pacemaker that accurately and easily mimics normal ph ysiology is a continuing effort. Present pacing developments include A V synchrony and rate adaptiveness. The usefulness and clinical value o f some of the new pacing systems remain unclear. Although the hemodyna mic advantages of rate responsive pacing over classical ventricular pa cing are well established (Kristensson et al., 1985), an ideal sensor for physiological demands has not been established. We report a case o f apparently unequivocal increase in heart rate during upper limb move ments in a patient with a VVI-R pacemaker using minute ventilation as a sensor. Inappropriate heart rate acceleration may result from change s in transthoracic impedance due to upper limb exercise and it does no t necessarily represent sensor malfunction. Although this complication is well-known in VVI-R pacemakers using respiratory rate or minute ve ntilation as sensor (Santomauro et al., 1992), one must remain aware o f this sensor-related problem. In this particular patient the problem could be solved by implanting the pacemaker can more medially.