INOTROPIC STATE INDEX. ISI = (d Z/dt)max x TFC. The dimension is on1/sec/sec. ISI represents a normalized image of maximum acceleration of aortic blood flow, described in cardiology literature as a parameter affected only by inotropes. ISI is an end-result of the left ventricular impulse, produced at the instant of aortic valve opening by a quadratic rate and magnitude of isovolumic pressure rise.