Mitral regurgitation (MR) is one of those Step-friendly lesions that shows up everywhere: murmurs, heart failure physiology, atrial remodeling, and classic associations like MVP, ischemic papillary muscle dysfunction, and endocarditis. If you can explain why the murmur changes with handgrip and how MR dilates the left atrium (LA) and left ventricle (LV), you’re basically holding the answer key for a ton of cardio questions.
Quick definition (what MR is)
Mitral regurgitation = systolic backflow of blood from LV → LA due to incomplete mitral valve closure.
It causes volume overload of both the LA (during systole) and the LV (during diastole, when the regurgitated volume returns to the LV plus normal pulmonary venous return).
Pathophysiology (the “why it matters”)
Hemodynamics: chronic vs acute MR
MR behaves very differently depending on whether the LA/LV have had time to adapt.
Chronic MR
Over time:
- LA dilates to accommodate regurgitant volume → higher risk of atrial fibrillation
- LV dilates (eccentric hypertrophy) because preload increases (more blood returns each diastole)
- Forward stroke volume may initially be maintained by increased preload, but decompensation eventually leads to HFrEF
Key consequences:
- Increased LV end-diastolic volume (preload)
- Decreased effective forward cardiac output (some SV goes backward)
- Pulmonary congestion can develop when LA compensation fails
Acute MR (high-yield emergencies)
Examples: papillary muscle rupture after MI, infective endocarditis, chordae tendineae rupture.
The LA is not dilated yet, so it can’t buffer the sudden volume:
- Rapid rise in LA pressure → flash pulmonary edema
- Often hypotension (drop in forward output)
- Murmur may be short/soft despite severe disease (pressure equalizes fast)
Etiologies (know the Step associations)
Common causes (organized by what “breaks”)
Leaflet abnormality
- Mitral valve prolapse (MVP) (myxomatous degeneration)
- Rheumatic heart disease (classically MS, but can cause MR too)
Chordae tendineae abnormality
- Rupture (MVP complications, trauma, endocarditis)
Papillary muscle dysfunction/rupture
- Ischemia after MI (especially inferior MI affecting posteromedial papillary muscle)
- Rupture = acute MR emergency
Annular dilation / functional MR
- Dilated cardiomyopathy
- Longstanding HF with LV remodeling
Infective endocarditis
- Leaflet perforation or destruction → MR
Clinical presentation (how patients actually show up)
Symptoms
- Often asymptomatic early (especially chronic MR)
- Dyspnea on exertion, orthopnea, PND (pulmonary congestion)
- Fatigue (low forward output later)
- Palpitations (AF from LA dilation)
Physical exam
Murmur characteristics (very testable)
- Holosystolic (pansystolic) blowing murmur
- Best heard at the apex
- Radiates to the axilla
- Often with S3 (increased LV volume / rapid filling)
Maneuvers (Step 1 classic)
| Maneuver | SVR/Preload effect | MR murmur |
|---|---|---|
| Handgrip | ↑ SVR | Increases (more regurgitant flow back into LA) |
| Squatting | ↑ SVR and ↑ venous return | Increases (usually) |
| Valsalva (strain) / standing | ↓ preload | Decreases |
| Inspiration | ↑ right-sided murmurs | MR usually not increased (left-sided) |
High-yield concept: MR is a left-sided regurgitant murmur → gets louder when afterload increases (handgrip).
Complications to remember
- Atrial fibrillation (LA dilation)
- Pulmonary hypertension → can progress to right-sided failure
- Left-sided heart failure
- Infective endocarditis risk (esp. MVP with regurgitation)
Diagnosis (what to order and what you’ll see)
First-line test
Transthoracic echocardiography (TTE)
Confirms:
- Regurgitant jet (color Doppler)
- Severity (vena contracta, regurgitant volume/fraction)
- LV size and systolic function (LVEF)
- LA size
- Mitral apparatus anatomy (leaflets, chordae, papillary muscles)
ECG findings (not diagnostic, but common)
- Atrial fibrillation
- LA enlargement signs (e.g., broad P waves) in chronic disease
Chest X-ray
- LA enlargement (straightening of left heart border, double density)
- Pulmonary congestion/edema if decompensated
Hemodynamic tracings (if they ask)
On pulmonary capillary wedge pressure (PCWP) tracing:
- Large v waves due to increased LA filling during systole (blood regurgitating into LA)
Treatment (Step 2 flavor: stabilize first, then definitive)
Treatment depends on severity, symptoms, and LV function.
Acute severe MR (emergency)
Goals: reduce regurgitation and treat pulmonary edema/shock.
- Afterload reduction (e.g., IV vasodilators like nitroprusside if BP allows)
- Diuretics for pulmonary edema
- Inotropes if cardiogenic shock (case-dependent)
- Urgent surgical repair/replacement often required (e.g., papillary muscle rupture)
Chronic MR
Medical management (symptom control / bridge)
- Diuretics for congestion
- Manage HTN (reduces afterload)
- Rate/rhythm control and anticoagulation as indicated for AF
- Guideline-directed HF therapy if HFrEF develops
Definitive management
- Mitral valve repair preferred over replacement when feasible (better preservation of LV function)
- Consider intervention for:
- Symptomatic severe MR
- Asymptomatic severe MR with LV dysfunction or dilation (they love thresholds—know the concept: intervene before irreversible LV dysfunction)
High-yield differentiations (don’t mix these up)
MR vs MVP vs VSD vs TR
| Lesion | Murmur | Best heard | Radiation | Increases with handgrip? |
|---|---|---|---|---|
| MR | Holosystolic, blowing | Apex | Axilla | Yes |
| MVP | Mid-systolic click + late systolic murmur | Apex | — | Murmur/click shift with preload changes |
| VSD | Holosystolic, harsh | LLSB | Often none | Yes |
| TR | Holosystolic | LLSB | To right sternal border | Yes, plus increases with inspiration |
MVP preload trick (Step 1 classic):
- ↓ preload (standing/Valsalva) → click occurs earlier, murmur longer
- ↑ preload (squatting) → click occurs later, murmur shorter
Acute vs chronic MR clues
- Acute MR: sudden pulmonary edema, hypotension, may have soft murmur
- Chronic MR: displaced apical impulse (LV dilation), LA enlargement, AF, louder classic holosystolic murmur
First Aid cross-references (where this lives in FA)
In First Aid for the USMLE Step 1 (Cardiovascular section), MR is typically covered under:
- Valvular heart disease murmurs (holosystolic murmurs and maneuver effects)
- Mitral valve prolapse (myxomatous degeneration, click + murmur timing with maneuvers)
- Papillary muscle rupture after MI (mechanical complications)
- Infective endocarditis (valvular destruction → regurgitation)
Use FA’s murmur tables with maneuvers and pair them with:
- Handgrip → louder MR/AR/VSD
- Inspiration → louder right-sided murmurs
USMLE-style “if you see this, think MR”
- Holosystolic murmur at apex radiating to axilla → MR
- Inferior MI + acute pulmonary edema + new systolic murmur → papillary muscle rupture → acute MR
- LA dilation + AF + S3 in a chronic setting → chronic MR with volume overload
- Large v waves on wedge pressure → MR
- Endocarditis (fever + new murmur) → consider new/worsening regurgitation
Mini self-check (rapid recall)
- MR is systolic regurgitation LV → LA → LA + LV volume overload
- Murmur: holosystolic blowing, apex → axilla, louder with handgrip
- Chronic MR → LA dilation → AF, LV eccentric hypertrophy, S3
- Acute MR (papillary muscle rupture) → flash pulmonary edema, may be soft murmur, needs urgent management
- Best test to confirm: echocardiography