Left ventricular volume analysis as a basic tool to describe cardiac function

Abstract

The heart is often regarded as a compression pump. Therefore, determination of pressure and volume is essential for cardiac function analysis. Traditionally, ventricular performance was described in terms of the Starling curve, i.e., output related to input. This view is based on two variables (namely, stroke volume and end-diastolic volume), often studied in the isolated (i.e., denervated) heart, and has dominated the interpretation of cardiac mechanics over the last century. The ratio of the prevailing coordinates within that paradigm is termed ejection fraction (EF), which is the popular metric routinely used in the clinic. Here we present an insightful alternative approach while describing volume regulation by relating end-systolic volume (ESV) to end-diastolic volume. This route obviates the undesired use of metrics derived from differences or ratios, as employed in previous models. We illustrate basic principles concerning ventricular volume regulation by data obtained from intact animal experiments and collected in healthy humans. Special attention is given to sex-specific differences. The method can be applied to the dynamics of a single heart and to an ensemble of individuals. Group analysis allows for stratification regarding sex, age, medication, and additional clinically relevant covariates. A straightforward procedure derives the relationship between EF and ESV and describes myocardial oxygen consumption in terms of ESV. This representation enhances insight and reduces the impact of the metric EF, in favor of the end-systolic elastance concept advanced 4 decades ago.

The Pythagorean theorem reveals the inherent companion of cardiac ejection fraction

“…The working point concept for the volume domain has been explained before [4]. Briefly, the position of point P (Fig.…”

“…Analysis is based on a paradigm coined the volume regulation graph (VRG) which describes the working point concept [3,4]. Quantification of ventricular performance requires a carefully selected indicator which is sound and clinically easy to implement.…”

“…Our starting point is the VRG where each combination of coordinates denoted as {EDV, ESV} refers to the individual working point for the subject studied ( Fig. 1) [1][2][3][4]. Volume data may be indexed (i) for body surface area (BSA), yielding {EDVi, ESVi}.…”

“…The slope of segment c1 (Fig. 1) is the tangent of phi and equals residual fraction (RF) for the working point P2, being defined as {ESVi/EDVi} [1,4]. Remarkably, RF was the original expression in vogue, before the term EF was launched, as reviewed elsewhere [1].…”

“…However, EF cannot be used to interpret the working point unless a second piece of information is explicitly known, e.g. ESV, EDV or stroke volume (SV) [4]. If it is desired to not include any of these traditional variables, then the hypotenuse emerges as an easily recognized EF companion (EFC) candidate.…”