What the Current Arterial‐Ventricular Coupling Index Fails to Tell Us

Abstract

BACKGROUNDThe arterial‐ventricular (AV) coupling index (k) is often employed to evaluate ventricular performance in relation to arterial properties. The index k is defined as the ratio of end‐systolic (ES) ventricular elastance (Emax) and effective arterial elastance (Ea). Emax describes the nonlinear trajectory of ventricular pressure (P) and volume (V) at end‐systole. Within a sufficiently small range Emax may be approximated by ESP/(ESV − Vo), where Vo is the extrapolated volume axis intercept. Likewise Ea is defined as ESP/SV, where SV is stroke volume. It may be convenient to index (i) volumes for body surface area (BSA). However, in the formula for k, both ESP and BSA cancel out, resulting in a dimensionless index. Unfortunately, the term Vo is neglected in most studies.AIMSThis investigation addresses the question if AV coupling can be described completely by k, or if an additional cofactor (kc) may be necessary, regardless of inclusion of Vo or not.METHODSSince k concerns a ratio, information is lost compared to the constitutive details available, namely SV and (ESV‐Vo). Plotting SV vs (ESV‐Vo) shows k as the tangent, while the missing companion of k (here termed kc) can be identified as the distance from the origin. The Pythagorean theorem states that kc equals the root of the sum of SV and (ESV‐Vo) each squared. We calculated the possible association between k and kc for published data (Asanoi et al., Circ Res 1989;65: 483–493) on 12 healthy individuals and 16 patients with cardiac dysfunction including heart failure. In their study Emax and Vo were obtained via linear regression analysis on more than 5 data points obtained by combined 2D echocardiography and variation of ESP as induced by phenylephrine and sodium nitroprusside i.v., respectively. While omitting Vo (indicated by the prime for k and kc), we also calculated k′ and kc′.RESULTSAlthough there is an association k′ = 0.486 k + 0.4861, R2 = 0.3928 (P<0.001), N=28, the connection strongly diverges for k>1, where a value between 1 and 2 is supposed to correspond with optimal matching. The kc relates to k via kc = −17.22 ln (k) + 71.57, R2 = 0.384, N=28, and likewise kc′ to k′ as kc′ = −31.81 ln (k′) + 77.96, R2 = 0.624, N=28.CONCLUSIONSThe dimensionless metric k is only characterized by SV, ESV and Vo, not by end‐systolic pressure level. The companion kc depends on the same variables, and has the dimension of volume (index). AV‐coupling is more completely characterized by the combination of k and kc. Consideration of the value of k in isolation provides an incomplete description of AV‐coupling characteristics, regardless of the fact whether Vo is included.Support or Funding InformationnoneThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.