Right Ventricular Failure Explained: Pressure-Volume Loops, Ees/Ea and Ventriculo-Pulmonary Coupling
- Faraz Afzal
- Apr 25
- 16 min read
About this article series
Why does the right ventricle fail so abruptly – even when it initially seems to cope? Right ventricular failure is best understood through pressure-volume loops, elastance (Ees), afterload (Ea), and ventriculo-pulmonary coupling. These concepts explain how the right ventricle generates pressure, responds to increased pulmonary vascular load, and ultimately fails when the balance between contractility and afterload is lost. In clinical practice, this framework provides a practical way to interpret RV hemodynamics, recognize early decompensation, and guide treatment in conditions such as pulmonary hypertension, acute pulmonary embolism, and cardiogenic shock.
This is Part 3 in a series on right-sided heart failure and the right ventricle (RV). In Part 1, we reviewed clinical signs and diagnostic approaches, while Part 2 focused on the underlying pathophysiology and the progressive downward spiral of RV failure.
In this article, we take the next step by exploring how pressure-volume loops (PV loops), elastance (Ees), afterload (Ea), and ventriculo-pulmonary coupling explain right ventricular function in practice – and why it ultimately fails.
What is a pressure-volume curve – really?
The pressure-volume curve is one of those tools in cardiology that often seems to confuse more than it helps. You find it in textbooks, in lectures, in articles on heart failure – but almost always explained in a way that gives you the axes without giving you the intuition.
Let us start with the basics.
The definition – precise, but understandable
A pressure-volume curve is a graphical representation of a single heartbeat, where pressure (P) is plotted on the y-axis and volume (V) on the x-axis. With each heartbeat, the curve traces a closed loop – hence the term loop.
But what makes pressure-volume curves, or so-called PV loops, genuinely useful is not the graph itself – it is what they allow you to see at the same time: the strength of the pump, the load it faces, the efficiency of energy use, and what actually comes out as stroke volume.
One pressure-volume curve = one heartbeat, displayed as a trace of pressure and volume throughout the entire cardiac cycle. Clinically, this means that every time you look at a hemodynamic measurement – pressure, volume, or cardiac output – you are in reality only looking at a slice of this loop.
The balloon analogy – the one you should keep in mind
When you look at a PV loop, do not think graph. Think movement. Imagine a balloon filled with water:
You slowly fill the balloon with water → volume increases, pressure remains low
You begin to squeeze it → pressure rises, but little water has left yet
You press harder and water exits through the opening → volume falls
You let go → pressure falls back
The pressure-volume curve is simply the imprint this movement leaves behind when pressure is plotted against volume along the way. The curve you see is not abstract – it is a geometric expression of the mechanics of the heartbeat.
Key point: what does the width of the curve mean?
The width of the pressure-volume curve along the x-axis = stroke volume (SV).
The wider the curve, the more blood was pumped out per beat.
A narrower loop = reduced stroke volume.
The area inside the loop = the work performed by the ventricle per beat, also called stroke work.
A narrower curve in a patient means lower cardiac output – and, in the extreme, hypotension and organ failure.
Phase | What happens physiologically | What you see in the loop |
1. Isovolumetric contraction | All valves are closed. Pressure rises without a change in volume. | Vertical line upwards, on the right side of the loop |
2. Ejection | The pulmonary valve opens. Blood is pumped out – volume falls. | The curve moves to the left |
3. Isovolumetric relaxation | All valves are closed again. Pressure falls without a change in volume. | Vertical line downwards, on the left side |
4. Filling, diastole | The tricuspid valve opens. Blood flows in – volume increases. | The curve moves to the right |
Note that the right ventricle (RV) already differs fundamentally from the left ventricle (LV) at this stage: isovolumetric contraction in the RV is very short or almost absent.
Elastance – what is it?
From compliance to elastance – one step at a time
Compliance = how easily something can be stretched or filled.
Thin, soft balloon → high compliance
Thick, stiff balloon → low compliance
Compliance = how much volume increases per rise in pressure:
ΔV / ΔP
Elastance (E) is the mathematical inverse:
E = ΔP / ΔV
Put simply: elastance is a measure of stiffness. High elastance means that a large pressure change is needed for a small change in volume. Low elastance means that a small pressure change produces a large change in volume.
Situation | What it means |
High ventricular elastance | Stiff/active ventricle |
Low ventricular elastance | Relaxed/passive ventricle |
Elastance in systole | Contractile force |
Elastance in diastole | Passive stiffness |
Time-varying elastance – the ventricle
Elastance varies throughout the cardiac cycle
Ees = maximal elastance at end-systole, and lowest at end-diastole
Ees is the best measure of contractility
Ees is load-independent
It is important not to confuse this with arterial elastance (Ea), which we will return to later.
Ees and Ea describe two fundamentally different things.
Ees is a property of the ventricle itself – how much force it can develop. Ea is a property of the system the ventricle pumps against – how much resistance it encounters.
Only when these two are considered together can we understand how the ventricle actually functions in practice.
ESPVR and EDPVR – the two lines that tell you everything
ESPVR – End-Systolic Pressure-Volume Relationship
ESPVR tells us:
“How much pressure the ventricle is able to generate per unit of volume at end-systole.”
Slope = Ees
Steep = strong ventricle
Flat = weakened ventricle
In practice, ESPVR is load-independent – it reflects the intrinsic contractile properties of the myocardium. Ees is therefore a good measure for assessing systolic function in PV-loop analysis.
EDPVR – End-Diastolic Pressure-Volume Relationship
EDPVR is the curve that describes pressure in the ventricle at end-diastole, across different volumes. Unlike the straight ESPVR line, EDPVR is exponentially curved. EDPVR can also vary somewhat throughout the cardiac cycle, but to a much lesser degree than ESPVR.
EDPVR tells us:
“How much pressure builds up during filling.”
In practice, this means that a patient may have severe dysfunction in one part of ventricular function without the other necessarily being equally affected – which helps explain why clinical presentations can vary substantially.
Parameter | Interpretation |
Steep ESPVR | Good contractility |
Flat ESPVR | Reduced contractility |
Steep EDPVR | Stiff ventricle |
Flat EDPVR | Good compliance |
One important point is often misunderstood: ESPVR and EDPVR describe two fundamentally different properties of the ventricle. ESPVR is about systolic function: force and contractility. EDPVR is about diastolic function: stiffness and relaxation.
They may be affected independently of each other – and in patients with RV failure, both often change, but at different stages of the disease course.
Ea – arterial elastance and what afterload really is
Afterload is a term used everywhere in cardiology, but it is rarely explained precisely enough to become intuitive. Let us do it properly.
The everyday analogy
Imagine that you are trying to inject water through a hose or pipe:
Through a wide, open pipe → little resistance → the water flows easily
Through a narrow, stiff pipe → high resistance → you need to use a lot of force
Through a pipe blocked with cork → enormous resistance → almost impossible
Ea, or arterial elastance, is measured as pressure per unit volume of blood ejected.
High Ea = it is difficult to pump blood out.
What determines Ea?
Pulmonary vascular load determines right ventricular afterload (Ea) and consists of two physiologically distinct components:
1. The resistive component (PVR)Pulmonary vascular resistance reflects the steady, non-pulsatile load and is primarily determined by vascular tone, vessel diameter, and structural remodeling.
2. The pulsatile component (compliance and impedance)This reflects how the pulmonary circulation accommodates stroke volume and is determined by pulmonary vascular compliance, vascular stiffness, pulse-wave reflections, and importantly, elevated left-sided filling pressures (increased left atrial pressure or PCWP).
Clinical takeaway
Conditions such as hypoxic vasoconstriction, pulmonary embolism, and vascular remodeling primarily increase PVR → ↑ resistive afterload
Conditions such as elevated left-sided filling pressures, interstitial edema, and vascular stiffening primarily reduce compliance → ↑ pulsatile afterload
Both mechanisms increase Ea, but through different physiological pathways. The net effect is the same: a higher load on the right ventricle and a shift in the Ees/Ea ratio toward ventriculo-pulmonary uncoupling.
Hypoxia as a driver of Ea, or afterload
One of the most important – and most underestimated – drivers of increased afterload in the right ventricle is hypoxia. It deserves attention. In the systemic circulation, hypoxia causes vasodilation. In the lungs, the opposite happens: alveolar hypoxia triggers constriction of the pulmonary arteries, increasing pulmonary vascular resistance (PVR).
With local hypoxia, for example pneumonia or atelectasis, this is appropriate because blood is redirected toward better ventilated areas. But with global hypoxia – as in severe lung disease, hypoventilation, or high altitude – the response becomes diffuse.
The result is increased pulmonary artery pressure and a significant increase in afterload (Ea) for the right ventricle. In practice, this means that hypoxia does not only cause poor oxygenation – it also increases the hemodynamic load on the right ventricle.
Ea in the pressure-volume curve
Line from the end-systolic point to EDV
Steeper line = higher afterload
Result: higher pressure, lower stroke volume
In the pressure-volume curve, afterload (Ea) can be understood as a straight line from end-diastolic volume (EDV) on the x-axis to the end-systolic point. The slope of this line reflects how much resistance the ventricle encounters during ejection.
When Ea increases, the line becomes steeper, and the end-systolic point shifts upward and to the right: the ventricle must generate higher pressure, but at the same time empties less effectively, so residual volume increases. In practice, this means that the ventricle not only faces more resistance – it must also use more energy per beat to maintain the same output.
The result is a narrower PV loop with reduced stroke volume.
Ventriculo-pulmonary coupling – the heart’s balance
We now have all the components in place. The PV loop as a map of a single heartbeat. ESPVR and Ees as measures of contractile strength. EDPVR as a measure of diastolic stiffness. Ea as a measure of afterload. Now we can put it all together into the most important concept in RV physiology:
Ventriculo-pulmonary coupling = the relationship between the ventricle’s contractile capacity (Ees) and the load it faces from the pulmonary vascular system (Ea).
Coupling = Ees / Ea.
In practice, this ratio determines whether the patient maintains circulation – or develops circulatory collapse.
Value | Interpretation |
1.5–2.0 | Normal |
<1.0 | Uncoupling |
<0.5 | Critical failure |
The weightlifting analogy – the one that makes it intuitive
Think of ventriculo-pulmonary coupling as a weightlifting exercise, for example a bench press:
Ees = your maximal lifting capacity, or strength
Ea = the weight on the bar
Coupling = the relationship between strength and weight
When you lift a weight that is well within your capacity, the movement is controlled, efficient, and demanding in a sustainable way. Good coupling.
When the weight approaches your maximum, you start to shake. You use more energy per kilo lifted. Efficiency falls. Beginning uncoupling.
When the weight exceeds your capacity, the bar stops. No output. Energy is wasted in isometric contraction. Complete uncoupling.
The important point is not simply how strong the ventricle is, or how large the load is – but the relationship between the two. Clinically, this becomes the question: is the problem that the ventricle is too weak, that the load is too high – or both?
In clinical practice, we see this as patients who initially compensate well, but then rapidly decompensate once the load passes a critical threshold.
In the heart, exactly the same mechanics are taking place – except that pressure and volume are the “weights,” and ATP consumption by the myocytes is the “energy cost.”
What happens geometrically in the pressure-volume curve during uncoupling?
When Ea increases relative to Ees, something characteristic happens in the PV loop. This is the same loop we described earlier – but now you can see how its shape actually changes when the physiology breaks down.
The curve shifts upward – higher pressure is generated
The curve narrows – stroke volume falls
End-systolic volume increases – the ventricle does not empty completely, and the end-systolic point shifts to the right
The area inside the loop, stroke work, changes inefficiently: a higher curve with less width
In other words, a “tall and narrow” loop is the visual sign of afterload mismatch and beginning uncoupling. This is what we see clinically in pulmonary hypertension and acute RV overload – and it predicts hemodynamic collapse. Even a normally functioning ventricle will fail if the load increases enough.
This is often the point where the patient moves from being hemodynamically stable to deteriorating rapidly.
RV vs LV – two fundamentally different pumps
Physiologically, the right and left ventricles are two different pumps, optimized for two radically different tasks.
The fundamental asymmetry: the LV is a pressure pump – the RV is a volume pump.
Property | Left ventricle (LV) | Right ventricle (RV) |
Normal systolic pressure | Approx. 120 mmHg | <30 mmHg |
Normal diastolic pressure | Approx. 5–12 mmHg | 0–5 mmHg |
Wall thickness | Approx. 6–10 mm | Approx. 3–5 mm |
Wall topology | Circular/ellipsoid, thick wall | Crescent-shaped, concave |
Contraction pattern | Concentric, with both radial and longitudinal shortening | Dominated by longitudinal shortening and septal motion |
Ees, normal | Method-dependent, typically higher than RV | Method-dependent, typically lower than LV |
Ea, normal | Method-dependent, often around 1 mmHg/mL as a rough order of magnitude | Method-dependent, lower than LV |
Tolerance for acute pressure | High | Low |
Tolerance for acute volume | Moderate | Relatively better |
The shape of the pressure-volume curve – the subtle but decisive difference
If you look at a pressure-volume curve for the LV and the RV, they are not the same. The LV curve is almost rectangular – with sharp corners and a clear isovolumetric phase. The RV loop is more rounded at the edges.
The reason is physiologically meaningful: the RV operates in a low-pressure system, the pulmonary circulation. The pressure required to open the pulmonary valve is 10–15 mmHg, compared with 70–80 mmHg for the aortic valve. This means that the RV does not need a long isovolumetric contraction phase – the valve opens quickly, and ejection begins early in systole. The geometric consequence is the somewhat rounder shape of the RV pressure-volume curve.
Practical consequence of the RV shape
The RV physiologically operates in a low-pressure system
An acute increase in pulmonary pressure, for example pulmonary embolism, rapidly changes the PV loop
The RV dilates acutely
Energy efficiency and ventriculo-pulmonary coupling
Stroke work (SW) corresponds to the area inside the pressure-volume curve.
Mechanical efficiency (η) can be described as the relationship between work and oxygen consumption:
η = SW / MVO₂
Increased pressure or volume load, Figure 4 panel B and especially panel C, changes the loop by making it taller and/or wider, but at the same time increases wall stress and therefore myocardial oxygen consumption (MVO₂) disproportionately. The result is reduced mechanical efficiency.
Optimal coupling, Ees/Ea ≈ 1.5–2.0, coincides with maximal energy efficiency, whereas both volume overload, panel B, and pressure overload, panel C, shift the system toward lower efficiency. This is particularly critical for the right ventricle, where increased afterload both increases oxygen demand and can reduce coronary perfusion, thereby reinforcing a vicious circle of energy failure and contractile failure.
What happens to the pressure-volume curve in RV failure?
Figure 1, see attached figure, shows three patterns of RV dysfunction in PV loops – each with its distinct shape and distinct pathophysiological pattern. Let us go through them systematically.
Scenario A: Reduced contractility
This is the classic picture in primary myocardial failure – cardiomyopathy, ischemia, myocarditis.
The ESPVR line is flat, low Ees → reduced intrinsic contractility
The loop is small and narrow → low stroke volume
The generated pressure is low → the ventricle cannot build sufficient pressure
EDV is not markedly increased initially
Clinically: this is pump failure – the ventricle is weak. Ea is not necessarily elevated. The problem is primarily reduced Ees.
Analogy: you have lost muscle mass. The weight on the bar is the same, but you are weaker. The coupling ratio falls because Ees falls.
Scenario B: Volume-overloaded RV
Typical in tricuspid regurgitation, ASD, or significant pulmonary shunts.
The loop shifts to the right – EDV is markedly increased
ESPVR is relatively preserved initially – contractility is not primarily reduced
The RV dilates to maintain stroke volume, through the Frank-Starling mechanism
Stroke volume may be maintained, but at the cost of dilation
This compensation has a cost. When the ventricle dilates, wall stress increases, according to Laplace, and so does oxygen consumption. Stroke volume may be maintained for a period – but at an increasingly high energetic cost. Over time, this becomes a form of “energetic penalty,” where the ventricle uses more energy without a corresponding gain in output.
This hits the right ventricle particularly hard. Unlike the left ventricle, which can hypertrophy and adapt to increased load over time, the right ventricle has limited ability to develop pressure and compensate for increased wall stress. The result is that what starts as an effective compensation relatively quickly becomes a mechanism that drives further failure.
Scenario C: Pressure-overloaded RV
This is the classic picture in pulmonary hypertension, pulmonary embolism, and advanced left-sided failure with secondary pulmonary hypertension.
Ea is markedly increased → higher afterload
The loop is tall, high pressure generated, and narrow, low stroke volume – the classic “tall-narrow” morphology
Ees initially tries to increase, through adaptive hyperadrenergic activation and hypertrophy. This is an attempt to maintain coupling – but capacity is limited
Over time: Ees falls under persistent pressure load
The Ees/Ea ratio falls → uncoupling
The critical point is when the load exceeds what the ventricle can compensate for – then uncoupling becomes a fact, and the system begins to collapse.
Clinically, this is what we see in acute pulmonary embolism or severe pulmonary hypertension, where an apparently stable patient can collapse within a short period of time.
Step | Mechanism | Pressure-volume curve – change |
1 | ↑ Ea, for example pulmonary hypertension → initial adaptive increase in contractility, ESPVR/Ees | Steeper Ea line; slight upward displacement of the end-systolic point |
2 | RV dilates to maintain stroke volume, Frank-Starling | Rightward shift of the loop, ↑ EDV; initially wider loop |
3 | ↑ Radius → ↑ wall stress → ↑ MVO₂ | Increased pressure, higher curve; inefficient energy use |
4 | Subendocardial ischemia → ↓ contractility → ↓ Ees | ESPVR flattens; end-systolic point shifts downward and to the right |
5 | ↓ Ees/Ea → uncoupling → reduced stroke volume | The curve becomes narrower, ↓ SV, with a clear rightward shift |
6 | Secondary LV dysfunction, septal deviation and pericardial constraint | Reduced LV filling → indirectly reduced systemic output |
7 | ↓ Cardiac output → cardiogenic shock | Collapsed curve: low pressure and low stroke volume |
This sequence can, in practice, unfold over hours in acute loading conditions, or over months in chronic disease.
Pericardium and interdependence
RV failure also affects the left side through ventricular interdependence, as discussed in Part 2. Because both ventricles share the same tight house – the pericardium – acute enlargement of the RV will physically compress the LV. The septum is pushed toward the left, the D-sign on echocardiography, which prevents the LV from filling properly. The result is that even if the problem began in the lungs or the RV, the patient often dies from low cardiac output from the left side. This is also why aggressive fluid administration can worsen the situation in RV failure.
Therefore, treatment of RV failure is often as much about protecting the left ventricle as it is about supporting the right.
From physiology to the clinic
Understanding PV loops and coupling is not merely academic – it has direct implications for how we treat RV failure. The framework helps us identify what we are treating, Ea, Ees, or both, and therefore what we should do.
All treatment of RV failure can, in practice, be understood as an attempt to influence either Ea, Ees, or preload. The choice of treatment therefore depends on which part of the system is primarily disturbed.
Table: therapeutic axes in right ventricular failure
Therapeutic target | Physiological effect, PV loop | Clinical examples |
Reduce Ea, afterload | Lower pulmonary resistance → wider curve and increased stroke volume | PDE5 inhibitors, endothelin receptor antagonists, prostanoids, O₂ |
Increase Ees, contractility | Steeper ESPVR → improved ventriculo-pulmonary coupling, ↑ Ees/Ea | Dobutamine, levosimendan, milrinone, norepinephrine, with caution |
Optimize preload | Moves EDV toward the optimal point on the EDPVR → maximal stroke volume without overdistension | Cautious fluid administration or diuresis based on clinical assessment |
Invasive hemodynamic monitoring – reading the system
In critically ill patients with RV failure, direct hemodynamic monitoring can provide near-PV-loop information:
PA catheter, Swan-Ganz: provides RAP, PAP, PCWP, and CO – the basis for calculating Ea
TAPSE/PASP ratio, echocardiography: non-invasive surrogate measure of coupling
RV FAC, fractional area change: estimate of RV function
Strain analysis, RV GLS: longitudinal contractility as a surrogate for Ees
The combination of PAP estimates and contractility estimates gives the clinician an intuitive assessment of coupling status – even without a pressure-volume curve. The goal is to understand how these measures together describe the balance between load and capacity. An isolated value rarely gives the answer – it is the pattern that matters.
Summary
We have now gone through all the conceptual building blocks. Let us tie them together into one coherent whole.
The complete explanatory model for RV physiology
PV loop = the graphical imprint of one heartbeat – pressure and volume throughout the cycle
Ees, the ESPVR slope, describes how forcefully the ventricle contracts
Ea = arterial elastance = afterload – “the weight that must be lifted”
Ees/Ea = the coupling ratio – describes how well the ventricle is matched to the load it faces
The normal RV operates in a low-pressure system – low Ea, relatively low Ees, good coupling
The RV is not built for pressure – it is built for volume. A sudden rise in Ea is its Achilles heel
Uncoupling occurs when the load exceeds the ventricle’s capacity, and stroke volume begins to fall
The pericardium and ventricular interdependence amplify collapse through LV compression
The RV fails when it is forced from being an efficient volume pump into becoming an inefficient high-pressure pump – where increased resistance (Ea), increased wall tension (Laplace), and mechanical limitation (the pericardium) together drive the Ees/Ea ratio downward toward uncoupling and circulatory collapse.
In practice, all RV failure can be understood as a mismatch between capacity (Ees) and load (Ea). When clinically assessing a patient with right-sided failure, this is essentially the balance you are evaluating – without drawing the pressure-volume curve, but with the same principles in mind. It is about recognizing when the balance is beginning to break down – and intervening before the system collapses.
Frequently Asked Questions
What is right ventricular failure?
Right ventricular failure occurs when the right ventricle can no longer generate sufficient pressure or stroke volume to move blood effectively through the pulmonary circulation. It is most commonly driven by increased afterload, reduced contractility, volume overload, or impaired ventriculo-pulmonary coupling.
How do pressure-volume loops explain right ventricular failure?
Pressure-volume loops illustrate how pressure and volume change throughout a single heartbeat. In right ventricular failure, the loop typically becomes narrower, reflecting reduced stroke volume. In pressure overload states, the loop often becomes tall and narrow, indicating increased afterload and reduced efficiency.
What is Ees in right ventricular physiology?
Ees, or end-systolic elastance, reflects the contractile strength of the right ventricle. It is represented by the slope of the end-systolic pressure-volume relationship. A higher Ees indicates stronger contractility, while a lower Ees suggests systolic dysfunction.
What is Ea and how does it relate to RV afterload?
Ea, or arterial elastance, represents the effective afterload the right ventricle must overcome. It reflects pulmonary vascular resistance, compliance, impedance, and filling pressures. An increase in Ea means the ventricle must generate more pressure to eject blood.
What does the Ees/Ea ratio mean?
The Ees/Ea ratio represents ventriculo-pulmonary coupling, meaning how well the ventricle’s contractile capacity matches the load it faces. A normal ratio indicates efficient coupling, while a low ratio reflects uncoupling, reduced stroke volume, and increased risk of circulatory failure.
Why does hypoxia worsen right ventricular failure?
Hypoxia worsens right ventricular failure because it causes pulmonary vasoconstriction, increasing pulmonary vascular resistance and afterload. As a result, hypoxia is not only a gas exchange problem, but also a key driver of hemodynamic deterioration.
How is ventriculo-pulmonary coupling assessed clinically?
Ventriculo-pulmonary coupling can be assessed invasively using right heart catheterization combined with imaging, or non-invasively through surrogate measures such as the TAPSE/PASP ratio. These methods provide insight into the relationship between contractility and afterload.