Ventriculo-Arterial Coupling: From Physiological Concept To... : European Journal of Anaesthesiology and Intensive Care
Highlights
- All compartments contribute to overall cardiovascular system homeostasis and performance, although no compartment function can be modified without altering the other.
- Ventriculo-arterial coupling is a physiological concept that describes the interaction of the left ventricle (LV) and the arterial system (principally the aorta).
- ventriculo-arterial coupling = EA/EV
- V0 represents a theoretical left ventricular volume at zero intracavitary pressure. In humans, the normal value of EV is 2.3 ± 1 mmHg ml−1
- we can describe the arterial load by the slope of the relationship between the stroke volume (SV) and end-systolic arterial pressure: the arterial effective elastance (EA). EA does not actually represent the elastance of a specific segment of the arterial tree but a cumulative parameter of the entire arterial system. EA represents arterial function, and it can be assimilated to the net arterial load characterised by the total peripheral resistance, characteristic impedance and systolic and diastolic time intervals
- In humans, the normal value of EA is 2.2 ± 0.8 mmHg ml−1
- In humans, the mean value of EA/EV ratio is 1 ± 0.36
- Cardiovascular performance can not only be evaluated in terms of efficacy (blood pressure and blood flow) but also in terms of efficiency (i.e. energetic cost for the cardiovascular system to provide the same blood pressure and blood flow).
- The PVA is linearly correlated to myocardial oxygen consumption
- Stroke work is the effective left ventricular energy that may be transmitted to the arterial system. Potential energy signifies the dissipated energy during the left ventricular isovolumetric contraction. Left ventricular efficiency is the ratio between stroke work and PVA.
- Left ventricular efficiency is maximised during normal physiological situations with an EA/EV of 0.5
- During stressful haemodynamic situations, stroke work is maximised, reaching a maximum EA/EV ratio of 1
- The energetic balance of the cardiovascular function is optimal when EA/EV is 1, whereas at a ratio of 0.5, maximal cardiac efficiency is observed
- Left ventricular stroke work: Left ventricular energy delivered to the arterial system to maintain pressure
- PVA: stroke work + potential energy, linearly correlated to myocardial O2 consumption
- Left ventricular efficiency = stroke work/PVA
- Dynamic arterial elastance (Eadyn) is the ratio of respiratory variation of pulse pressure to respiratory variation of SV
- Pittarello et al.31 demonstrated that despite a decrease of EA and EV with remifentanil, ventriculo-arterial coupling remains unchanged. A study evaluating the effects of general anaesthesia with propofol/remifentanil infusion and positive pressure ventilation demonstrated a decrease in EV with the induction of anaesthesia and a trend for a decrease in EA; ventriculo-arterial coupling is globally unchanged
- In healthy dogs, an increase in heart rate during exercise is associated with an increase in EV, which can match with EA in maintaining nearly optimal ventriculo-arterial coupling.35 This effect is known as the force–frequency relationship of the ventricle (the Bowditch effect), which is an intrinsic property of cardiac muscle. This effect is altered in heart failure.36 In such situations, ventriculo-arterial coupling is altered at rest, and any increase in heart rate values exacerbates ventriculo-arterial uncoupling because EA is not counterbalanced by an increase in EV
- Acute decompensated heart failure is characterised by a high EA/EV ratio, which is caused by high EA and low EV.50 Because of low EV, patients are highly sensitive to EA, particularly through high heart rate values.51 Tachycardia, in the context of heart failure, is associated with an increase in EA because of a decrease in diastolic time and vascular compliance.
- Cardiogenic shock is the most severe form of circulatory failure. It is associated with a severe decrease in EV and an initial increase and then a decrease in EA
- Preload-dependent patients have a high baseline ventriculo-arterial coupling ratio in relation to high EA. Volume expansion improves ventriculo-arterial coupling by decreasing EA, and in some cases (patients with sepsis), by increasing EV.