EVOKED RESPONSE DETECTOR FOR A HEART STIMULATOR

摘要

An evoked response detector for a heart stimulator determines evoked response in the presence of polarization. To determine the magnitude of the polarization for different stimulation amplitudes, the electrode signals picked up by the lead after the delivery of one high and one low amplitude stimulation pulse are measured. The low amplitude stimulation pulse has amplitude equal to known stimulation threshold plus a predetermined voltage step. Calculating means determine the difference between the electrode signals picked up and forms the quotient between said difference and the difference between the high and low stimulation pulses amplitudes. Analysing means determine the evoked response signal by subtracting from electrode signals subsequently picked up, polarisation signals of a magnitude equal to the actual stimulation pulse amplitudes, multiplied with said quotient. Alternatively, the generator delivers a stimulation pulse of a high amplitude and then stimulation pulses of amplitudes successively lowered by a predetermined voltage step to a low stimulation amplitude equal to the known stimulation threshold plus one of said voltage steps. Calculating means determine and store the magnitude of the polarisation per voltage step, Polstep. Analyzing means determine evoked response signals by subtracting from electrode signals subsequently picked up a polarisation signal of a magnitude equal to the quotient between the actual stimulation amplitude and said voltage step and multiplied by the stored Polstep.