Q-Bank Breakdown: Wiggers diagram — Why Every Answer Choice Matters

A Wiggers diagram question is one of those “either you see it instantly or you drown in arrows” moments. The trick isn’t memorizing a picture—it’s knowing how to anchor each labeled point to a valve event, a pressure relationship, and a heart sound. Let’s walk through a classic q‑bank vignette the same way you should on test day: identify the correct choice fast, then eliminate every distractor by stating what would have to be true physiologically.

Tag: Cardiovascular > Cardiac Physiology

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The Clinical Vignette (Q‑Bank Style)

A 67-year-old man with long-standing hypertension presents with exertional dyspnea. On exam, an S4 is heard at the apex. ECG shows left ventricular hypertrophy. The question provides a Wiggers diagram and labels a point X occurring just after the QRS complex, during which:

• LV pressure is rising steeply
• LV volume is unchanged
• Left atrial pressure shows a small upward deflection

Which of the following best describes the event occurring at point X?

Answer choices: A. Aortic valve opens
B. Mitral valve closes
C. Mitral valve opens
D. Aortic valve closes
E. Rapid ventricular filling occurs

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Step 1: Locate Point X on the Wiggers Diagram

Clues:

• Just after QRS → ventricular depolarization → start of systole
• LV pressure rising, LV volume unchanged → isovolumetric contraction
• LA pressure small upward deflection → c wave (bulging of closed mitral valve into LA)

That combination is basically a fingerprint.

✅ Correct answer: B. Mitral valve closes

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Why B Is Correct: Mitral Valve Closure = Start of Isovolumetric Contraction

What must be true when the mitral valve closes?

Mitral valve closes when LV pressure exceeds LA pressure.

At that moment:

• Both valves are closed (mitral closed, aortic still closed)
• LV contracts against a fixed volume → isovolumetric contraction
• S1 occurs (closure of AV valves: mitral + tricuspid)

High-yield associations

• S1: AV valve closure → onset of systole
• c wave: AV valve bulges into atrium during isovolumetric contraction
• S4 in the vignette: stiff LV (e.g., LVH) → atrial kick into noncompliant ventricle (late diastole), not directly “at X,” but it’s a clue you’re in classic pressure/volume territory

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The Wiggers Diagram Anchors You Need (Memorize These, Not the Whole Picture)

Valve events and phases (most tested)

Pressure relationships that determine valves

• Mitral closes when $P_{LV} > P_{LA}$
• Aortic opens when $P_{LV} > P_{Ao}$
• Aortic closes when $P_{Ao} > P_{LV}$
• Mitral opens when $P_{LA} > P_{LV}$

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Systematically Destroy the Distractors (Why Every Answer Choice Matters)

A. Aortic valve opens ❌

Why it’s tempting: It’s early systole, pressure is rising.

Why it’s wrong: Aortic valve opening marks the end of isovolumetric contraction and the start of ejection.

To open the aortic valve, you need:

• $P_{LV} > P_{Ao}$

What would you see then?

• LV volume would start decreasing (blood leaving the ventricle)
• Aortic pressure would begin to rise with ejection

But the stem says LV volume is unchanged → not ejection yet.

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C. Mitral valve opens ❌

Why it’s tempting: Students associate atrial pressure waves with “something happening at the mitral valve.”

Why it’s wrong: Mitral valve opening happens in early diastole, after the LV has relaxed enough that:

• $P_{LA} > P_{LV}$

What would you see then?

• LV pressure is low and falling/flat, not steeply rising
• LV volume would increase (ventricular filling)

Point X is right after QRS with rising LV pressure → wrong timing.

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D. Aortic valve closes ❌

Why it’s tempting: Valve closure questions often get tied to labeled notches/waves.

Why it’s wrong: Aortic valve closure happens at the end of systole when:

• $P_{Ao} > P_{LV}$

Classic correlates:

• S2
• Dicrotic notch in aortic pressure tracing
• Start of isovolumetric relaxation (volume constant, pressure falling)

But point X is just after QRS, which is the beginning of systole—not the end.

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E. Rapid ventricular filling occurs ❌

Why it’s tempting: People remember “filling = volume change” but forget which side of the cycle they’re on.

Why it’s wrong: Rapid ventricular filling occurs in early diastole:

• Mitral valve is open
• LV volume increases rapidly
• Can generate S3 (especially in volume overload states or dilated ventricles)

The stem says LV volume unchanged and LV pressure rising → opposite of filling.

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Quick “One-Liners” for Waves, Sounds, and Timing (USMLE Gold)

Atrial pressure waves

• a wave: atrial contraction (late diastole; can be absent in afib)
• c wave: bulging of closed AV valve during isovolumetric contraction (early systole)
• v wave: venous filling of atrium against closed AV valve (late systole)

Heart sounds

• S1: AV valve closure (start systole)
• S2: semilunar valve closure (end systole)
• S3: rapid ventricular filling (early diastole)
  • Can be normal in children/pregnancy; pathologic in volume overload (e.g., HFrEF)
• S4: atrial kick into stiff ventricle (late diastole)
  • Associated with LVH, diastolic dysfunction; absent in afib

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How to Answer Any Wiggers Diagram Question in 10 Seconds

1. Find the QRS → systole begins right after it.
2. Ask: Is LV volume changing?
   • No change → isovolumetric phase (contraction or relaxation)
   • Decreasing → ejection
   • Increasing → filling
3. Use pressure inequalities:
   • Rising LV pressure with constant volume = mitral just closed
   • Falling LV pressure with constant volume = aortic just closed
4. Tie to sounds:
   • Start systole = S1
   • End systole = S2

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Takeaway

Point X is mitral valve closure, because it’s early systole (right after QRS) with rising LV pressure and no change in LV volume—the definition of isovolumetric contraction. Every distractor fails because it requires either a different pressure relationship (valve event) or a different volume pattern (filling/ejection).