Patent ID: 7657305

Claim:
An implantable medical device comprising: at least a sensing stage connected or being connectable to an electrode for picking up electric potentials from inside a heart, the time course of said electric potentials representing a heart signal, said heart signal being sampled in constant sampling intervals and a control unit that is connected to said sensing stage and that is adapted to process a sequence of data points that each represent a magnitude A of a time-varying signal at equidistant points of time t, said processing of the sequence of data points includes: determining end points of data segments by a) determination of a first difference quotient D 1 =(A n −A n-1 )/(t n −t n-1 ) with respect to an actual data point A n at t n and an immediately preceding, second last data point A n-1 at t n-1 , b) determination of a second difference quotient D 2 (A n −A e )/(t n −t e ) or D 2 =(A n-1 −A e )/(t n-1 −t e ) with respect to an actual data point A n at t n or a second last data point A n-1 and t n-1 , respectively, and a last end point A e at t e , said last end point A e being a previously determined end point or a first data point of said sequence of data points, wherein t e represents the point of time belonging to said end point A e , c) selecting the second last data point A n-1 as a new end point, if the magnitude of the difference between the two difference quotients D D =D 1 −D 2 exceeds a predetermined first threshold value T, D D >T, and determining a data segment length L=t n −t e between the point of time t n of an actual data point A n and the point of time t e of a last end point A e , and selecting A n-1 as a new end point, if said data segment length L exceeds a predetermined maximum length L max , and storing said selected end points in association with a segment length between each stored endpoint and an immediately preceding end point as a compressed data representation of said time varying signal.