You’re going to see pressure–volume (PV) loops in a lot of disguises on Step 1 and Step 2: murmurs, shock, inotropes, valves, afterload/preload changes, and “what happens to stroke volume?” questions. The trick isn’t memorizing one loop—it’s learning how to interrogate every answer choice using the same few rules.
Tag: Cardiovascular > Cardiac Physiology
The Clinical Vignette (Q-bank style)
A 68-year-old man with long-standing hypertension presents with acute crushing chest pain and diaphoresis. ECG shows ST-segment elevations in the anterior leads. He becomes hypotensive. A bedside echocardiogram shows new left ventricular systolic dysfunction.
Which of the following changes is most likely present on the patient’s left ventricular pressure–volume loop?
A. Increased end-systolic volume and decreased ejection fraction
B. Decreased end-systolic volume due to increased contractility
C. Increased end-diastolic volume due to decreased afterload
D. Increased stroke volume due to increased preload
E. Increased left ventricular end-diastolic pressure due to improved lusitropy
Correct Answer: A. Increased end-systolic volume and decreased ejection fraction
Acute MI → decreased contractility (negative inotropy).
On the PV loop, decreased contractility:
- Decreases slope of ESPVR (end-systolic pressure–volume relationship; the “contractility line”)
- Causes the ventricle to generate less pressure at any given volume
- Leads to less ejection → higher end-systolic volume (ESV)
- Therefore stroke volume decreases and ejection fraction decreases
High-yield definitions
- Stroke volume (SV):
- Ejection fraction (EF):
So if contractility drops, ESV rises, SV falls, and EF falls—exactly answer A.
PV Loop Basics You Must Be Able to “Read” Quickly
The 4 phases (counterclockwise)
- Ventricular filling (mitral valve open): volume increases at low pressure
- Isovolumetric contraction (both valves closed): pressure increases at constant volume
- Ejection (aortic valve open): volume decreases while pressure first rises then falls
- Isovolumetric relaxation (both valves closed): pressure drops at constant volume
Anchors that show up in answer choices
- EDV (rightmost point): end of filling (preload proxy)
- ESV (leftmost point): what’s left after ejection (strongly affected by afterload & contractility)
- ESPVR slope: contractility
- Loop width: stroke volume
- Area inside loop: stroke work
Why Each Distractor Is Wrong (and what it’s testing)
B. Decreased end-systolic volume due to increased contractility
This describes increased contractility, the opposite of an acute anterior MI.
If contractility increases:
- ESPVR slope increases (steeper line)
- ESV decreases (more complete emptying)
- SV and EF increase
Classic causes: dobutamine, digoxin, exercise, sympathetic stimulation.
Exam tip: If they mention MI with cardiogenic shock, think down-and-right shift of the end-systolic point (higher ESV, lower systolic pressure).
C. Increased end-diastolic volume due to decreased afterload
This is internally inconsistent physiology and a common trap.
- Decreased afterload (e.g., vasodilators) usually allows more ejection, so ESV decreases, SV increases.
- It does not directly cause EDV to increase. EDV is more about preload (venous return) and filling time/compliance.
What can happen indirectly: if SV rises, the next beat’s EDV might change depending on venous return and reflexes—but PV loop questions nearly always treat EDV as preload-driven.
Key association:
- ↓ afterload → leftward shift of end-systolic point (↓ ESV) and wider loop (↑ SV)
D. Increased stroke volume due to increased preload
Increasing preload can increase stroke volume (Frank–Starling), but it doesn’t match this patient.
In acute systolic failure, the ventricle is weak:
- For a given preload increase, the SV rise is blunted
- And in cardiogenic shock, you’re not “helpfully” increasing preload; you’re failing to eject.
Also, PV-loop-wise, increased preload primarily:
- Increases EDV (rightward shift of the loop’s right border)
- Often increases SV (wider loop), unless contractility is impaired enough that ESV rises disproportionately.
How to think on test day:
If the stem screams “pump failure,” the primary PV change is ↓ contractility → ↑ ESV, ↓ SV, not “preload went up and fixed it.”
E. Increased LV end-diastolic pressure due to improved lusitropy
This is a double wrong turn.
- Improved lusitropy means better relaxation (diastolic function improves).
- Better relaxation/compliance tends to lower LVEDP for a given volume (or allow more filling with less pressure).
In MI (especially ischemia), you can actually get worse lusitropy:
- Impaired relaxation → higher LVEDP and pulmonary congestion
- But that would be due to worsened, not improved, lusitropy.
High-yield link:
- Diastolic dysfunction (↓ compliance) shifts the EDPVR up/left → higher diastolic pressures at smaller volumes.
The “PV Loop Rulebook” (What each intervention does)
| Change | EDV | ESV | SV (width) | ESPVR slope | Classic examples |
|---|---|---|---|---|---|
| ↑ Preload | ↑ | ~ | ↑ | no change | fluids, venoconstriction |
| ↓ Preload | ↓ | ~ | ↓ | no change | hemorrhage, nitrates |
| ↑ Afterload | ~ | ↑ | ↓ | no change | HTN, aortic stenosis, phenylephrine |
| ↓ Afterload | ~ | ↓ | ↑ | no change | ACE inhibitors, hydralazine |
| ↑ Contractility | ~ | ↓ | ↑ | ↑ | dobutamine, exercise |
| ↓ Contractility | ~ | ↑ | ↓ | ↓ | MI, HFrEF, beta-blockers (acute) |
~ means “no primary change” in the simplified PV-loop model.
Rapid-Fire Classic Patterns (USMLE favorites)
1) Aortic stenosis (AS): “Afterload problem”
- ↑ afterload → ↑ ESV, ↓ SV
- Often ↑ LV systolic pressure markedly
- Murmur: systolic crescendo–decrescendo radiating to carotids
2) Mitral regurgitation (MR): “No true isovolumetric phases”
- Regurg begins when pressure rises → blood can move into LA
- Isovolumetric contraction and relaxation are blunted/absent
- Often ↑ EDV (volume overload), ↓ effective forward SV
3) Aortic regurgitation (AR): “Big EDV, wide pulse pressure”
- ↑ EDV (volume returns during diastole)
- No true isovolumetric relaxation (leak during diastole)
- Bounding pulses, wide pulse pressure
4) HFrEF (systolic failure): “Contractility line down”
- ↓ contractility → ↑ ESV, ↓ SV, often ↑ EDV over time (compensation)
Step-Style Takeaways (What to say out loud to yourself)
- Contractility changes tilt ESPVR. MI → less tilt → ESV up.
- Afterload changes move the end-systolic point. Afterload up → ESV up.
- Preload changes move the right border. Preload up → EDV up.
- If an answer claims improved relaxation raises LVEDP, it’s backwards.
Mini Self-Check (10 seconds)
In acute anterior MI:
- Contractility: down
- ESPVR slope: down
- ESV: up
- SV and EF: down
If an answer choice says those words in that order, it’s almost certainly correct.