Frequency-based analysis of diastolic function: Detrimental phase-shift of the pressure-flow relation characterizes the 'delayed relaxation' transmitral flow pattern

Cardiologists assess the filling (diastolic) function (DF) of the heart by visually determining whether Doppler echocardiographic transmitral E-waves appear to have "normal", "delayed-relaxation" or "constrictive restrictive" patterns. To achieve a causal method of quantitative DF assessment we present a frequency-based approach. In analogy to impedance of electrical circuits, we characterize DF by analysis of the left ventricular (LV) diastolic pressure (P) to transmitral flow (Q) relation during the Doppler E-wave in the frequency domain in terms of Z(ω)=P(ω)/ Q(ω), characteristic and input impedance. This allows DF to be expressed in terms of a complex reflection coefficient R^* =|R ^*|e^iφ. Twenty subjects bad simultaneous pressure-flow data recorded during catheterization, were dichotomized according to deceleration time (DT) and had E-waves subjected to model-based image processing (MBIP) to determine model parameter c, related to E-wave deceleration. Results show that phase angle φ is linearly related to c; that both φ and c were significantly different (p <0.05) between the short (n=12) and long (n=8) DT group. We conclude that the 'delayed relaxation' pattern is associated with deviation of the phase angle φ from its optimal (π) value that minimizes reflection and maximizes filling, resulting in modification of the optimal pressure -flow relation in early diastole.