E-wave deceleration time may not provide an accurate determination of LV chamber stiffness if LV relaxation/viscoelasticity is unknown

Average left ventricular (LV) chamber stiffness (ΔP _avg/ΔV_avg) is an important diastolic function index. An E-wave-based determination of ΔP_avg/ΔV_avg (Little WC, Ohno M, Kitzman DW, Thomas JD, Cheng CP. Circulation 92: 1933-1939, 1995) predicted that deceleration time (DT) determines stiffness as follows: ΔP_avg/ΔV_avg = N(π/DT)² (where N is constant), which implies that if the DTs of two LVs are indistinguishable, their stiffness is indistinguishable as well. We observed that LVs with indistinguishable DTs may have markedly different ΔP_avg/ ΔV_avg values determined by simultaneous echocardiography- catheterization. To elucidate the mechanism by which LVs with indistinguishable DTs manifest distinguishable chamber stiffness, we use a validated, kinematic E-wave model (Kovács SJ, Barzilai B, Perez JE. Am J Physiol Heart Circ Physiol 252: H178-H187, 1987) with stiffness (k) and relaxation/viscoelasticity (c) parameters. Because the predicted linear relation between k and ΔP_avg/ΔV_avg has been validated, we reexpress the DT-stiffness (ΔP_avg/ΔV_avg) relation of Little et al. as follows: DT_k ≈ π/(2 √k). Using the kinematic model, we derive the general DT-chamber stiffness/viscoelasticity relation as follows: DT_k,c = π/(2 √k) + c/(2k) (where c and k are determined directly from the E-wave), which reduces to DT_k when c ≪ k. Validation involved analysis of 400 E-waves by determination of five-beat averaged k and c from 80 subjects undergoing simultaneous echocardiography-catheterization. Clinical E-wave DTs were compared with model-predicted DT_k and DT_k,c. Clinical DT was better predicted by stiffness and relaxation/viscoelasticity (r² = 0.84, DT vs. DT_k,c) jointly rather than by stiffness alone (r² = 0.60, DT vs. DT_k). Thus LVs can have indistinguishable DTs but significantly different ΔP_avg/ΔV_avg if chamber relaxation/viscoelasticity differs. We conclude that DT is a function of both chamber stiffness and chamber relaxation viscoelasticity. Quantitative diastolic function assessment warrants consideration of simultaneous stiffness and relaxation/viscoelastic effects.