The revised velocity-strain relationship: phase-plane analysis of left ventricular function and dysfunction

Cyclical cardiac mechanical performance has been described by plotting mid-wall left ventricular circumferential velocity or strain rate (V) as a function of instantaneous mid-wall strain (epsilon). This results in individual velocity-strain (V-epsilon) parameters. For any given individual, a standard velocity-strain plot is represented by a sinusoidally varying strain and strain rate. Three standard velocity-strain variables are then defined. The peak velocity, or peak strain rate (VM), the cycle strain at VM (epsilon M), and the system time constant (tau M). The individual velocity-strain parameters are then divided by these standard V-epsilon parameters to result in normalized V-epsilon parameters for both cardiac systole and cardiac diastole. Thirty-six patients were evaluated, consisting of four groups: Normals (N = 15 patients), Compensated Volume Overload (CVO = 6 patients), Decompensated Volume Overload (DVO = 9 patients) and Congestive Cardiomyopathy (CCM = 6 patients). Five individual velocity-strain parameters significantly differentiate the CCM group from the N group. However, they do not differentiate CVO group and DVO group from the N group. Two standard-epsilon parameters and one normalized V-epsilon parameter significantly differentiated the CVO group and the DVO group from the N group. Two standard V-epsilon parameters and one normalized V-epsilon parameter significantly differentiated the CCM group from the N group. It is recommended that future phase-plane analyses of non-linear cardiac phenomena include both standardization and normalization techniques.