A new algorithm to calculate the rheobase, the chronaxie and the charge at the electrode-myocardial interface

A new algorithm is presented to calculate the Theobase (R:min.stimulation independent of duration) and chronaxie (CH:min.stimulation at twice the rheobase). The curve is described as I=B/t+R where I is the threshold current, B is the charge at the electrode-myocardial interface. By substituting z=1/t the curve becomes a straight line I=B.z+R intersecting the I axis (z=0) at R and the z axis at -1/CH. The slope B is the constant charge in the electrode-myocardial interface, the slope C is the total charge at stimulation threshold. During pacemaker implant stimulation threshold is measured at five points (0.1, 0.2, 0.5, 1.0, 2.0 ms). To validate the method two points (0.5 and 1.0 ms) were selected, the straight line calculated and the remaining three threshold points were read on the line and compared to the measured values. 500 groups of threshold data were analyzed. The standard error for the three calculated points (0.1, 0.2, 2.0 ms) were: 18, 15 and 16%, respectively, and the average normalized values of 1.09, 1.06, 1.06 were small as the compounded errors of three measurements were included