a. Ventriculo-arterial coupling (VAC) is
calculated as a ratio of the arterial elastance (Ea, afterload) to LV end systolic elastance (Ees, contractility). A
normal ratio (Ea/ Ees) ranges from 0.5 to 1, representing optimal cardiac VAC
efficiency ratio.
a. Arterial Elastance (Ea): = 
(Where ESP is End systolic pressure, stroke
volume SV (single beat method by Chen, et al)
SV=
= 3.14x 12 x
10 = 31.4 ml
Ea= 0.9x 90/ 31.4= 81/31.4=
2.6mmHg/ ml
Ea is elevated here.
Ventricular end systolic elastance (Ees)
|
End(est) is
the estimated normalized ventricular elastance at the onset of ejection (1)
|
Manual
calculation of Ees is prone for error and unnecessary.
|
|
|
Clinicians
should use validated digital tools like the i Elastance App. This application
was developed by Pietro Bertini to assist clinicians (Bertini P, et al 2016,
i Elastance, research gate).
Calculated
Ees is 0.71mmHg/ ml
Ees
is markedly reduced here.
|
|
Ea/ Ees ratio=
2.6/.71=3.6
|
So, there is
severe uncoupling
|
b. Yes, this statement is correct. In cardiogenic shock, there is typically high afterload
relative to poor contractility. Also, most commonly due to LV dysfunction, eg: post-MI,
primary problem is decrease in contractility.
The failing myocardium can not generate adequate force which leads to
decrease in stroke volume and cardiac output. As a result of compensatory
mechanism, the body tries to maintain perfusion via sympathetic activation
along with vasoconstriction. This causes increased systemic vascular resistance
and afterload. So, yes, afterload is
disproportionately high compared to contractility.
c. No, this statement is not correct. In cardiogenic shock
the Ea/Ees ratio is high, not low. Ea reflects afterload and Ees reflects
contractility. In cardiogenic shock, there is decrease in contractility, so Ees
will be reduced. This decrease in contractility causes compensatory increase in
vasoconstriction. So the ratio of Ea/ Ees will be high. Low Ea / Ees is seen in
vasodilatory state like septic shock (early stage).
d. Yes,
inotropes help to improve coupling. In cardiogenic shock, contractility
reduces, and afterload is high. Ea/ Ees ratio increases and there is
uncoupling. Inotropes increase contractility (Ees). This reduces Ea/Ees ratio
toward normal. So best initial strategy is to start inotropes (e.g. d obutamine)
to increase Ees and restore the coupling.
References:
1. Holm H, Magnusson M, Jujic A, et al. How to
calculate ventricular-arterial coupling? Eur J Heart Fail 2022;24:600-2.