Isovolumic pressure-to-early rapid filling decay rate relation: Model-based derivation and validation via simultaneous catheterization echocardiography

Transmitral Doppler echocardiography is the preferred method of noninvasive diastolic function assessment. Correlations between catheterization-based measures of isovolumic relaxation (IVR) and transmitral, early rapid filling (Doppler E-wave)-derived parameters have been observed, but no model-based, causal explanation has been offered. IVR has also been characterized in terms of its duration as IVR time (IVRT) and by τ, the time-constant of IVR, by approximating the terminal left ventricular IVR pressure contour as P(t) = P∞ + P_oe^-t/τ, where P(t) is the continuity of pressure, P∞ and P_o are constants, t is time, and τ is the time constant of IVR. To characterize the relation between IVR and early rapid filling more fully, simultaneous (micromanometric) left ventricular pressure and transmitral Doppler E-wave data from 25 subjects undergoing elective cardiac catheterization and having normal physiology were analyzed. The time constant τ was determined from the dP/dt vs. P (phase) plane and, simultaneous Doppler E-waves provided global indexes of chamber viscosity/relaxation (c), chamber stiffness (k), and load (x_o). We hypothesize that temporal continuity of pressure decay at mitral valve opening and physiological constraints permit the algebraic derivation of linear relations relating 1/τ to both peak atrioventricular pressure gradient (kx_o) and E-wave-derived viscosity/relaxation (c) but does not support a similar, causal (linear) relation between deceleration time and τ or IVRT. Both predicted linear relations were observed: kx_o to 1/τ (r = 0.71) and viscosity/relaxation to 1/τ (r = 0.71). Similarly, as anticipated, only a weak linear correlation between deceleration time and IVRT or τ was observed (r = 0.41). The observed in vivo relationship provides insight into the isovolumic mechanism of relaxation and the changing-volume mechanism of early rapid filling via a link of the respective relaxation properties.