U01.07.016 Heart murmurs

Heart murmurs are classified based on their timing in the cardiac cycle: systolic, diastolic, and continuous. Below is a structured breakdown of the most commonly tested murmurs on the USMLE Step 1, including key auscultation findings and associated conditions.

Classification of Heart Murmurs

Type	Murmur	Key Features	Common Causes
Systolic	Aortic Stenosis	Crescendo-decrescendo systolic ejection murmur; radiates to carotids	Age-related calcification, Bicuspid aortic valve
	Mitral/Tricuspid Regurgitation	Holosystolic, high-pitched “blowing” murmur	Ischemic heart disease, MVP, LV or RV dilation
	Mitral Valve Prolapse	Late systolic crescendo murmur with midsystolic click	Myxomatous degeneration, Marfan, Ehlers-Danlos
	Ventricular Septal Defect	Holosystolic, harsh-sounding murmur	Congenital defect, large VSD has softer murmur
Diastolic	Aortic Regurgitation	Early diastolic decrescendo murmur; wide pulse pressure	Bicuspid valve, Endocarditis, Aortic root dilation
	Mitral Stenosis	Delayed diastolic murmur following opening snap	Rheumatic fever
Continuous	Patent Ductus Arteriosus	Machine-like murmur, loudest at S2	Congenital rubella, Prematurity

Systolic Murmurs

Aortic Stenosis

Murmur: Crescendo-decrescendo systolic ejection murmur, soft S2, possible ejection click
Auscultation: Loudest at the heart base, radiates to the carotids
Pathophysiology: Left ventricle (LV) pressure > aortic pressure during systole
Associated Signs:
- Pulsus parvus et tardus: Weak pulses with delayed peak
- SAD Symptoms: Syncope, Angina, Dyspnea on exertion
Causes:
- Age-related calcification (> 60 years)
- Early-onset calcification in bicuspid aortic valve

Mitral/Tricuspid Regurgitation

Murmur: Holosystolic, high-pitched “blowing” murmur
Auscultation:
- Mitral Regurgitation (MR): Loudest at apex, radiates to axilla
- Tricuspid Regurgitation (TR): Loudest at tricuspid area
Causes:
- MR: Ischemic heart disease (post-MI), MVP, LV dilation
- TR: Right ventricular (RV) dilation
- Rheumatic fever and infective endocarditis can cause both MR and TR

Mitral Valve Prolapse (MVP)

Murmur: Late systolic crescendo murmur with midsystolic click (MC)
Auscultation: Best heard at apex, loudest before S2
Pathophysiology: Sudden tensing of chordae tendineae as mitral leaflets prolapse
Causes:
- Myxomatous degeneration (primary or secondary to connective tissue diseases like Marfan or Ehlers-Danlos syndrome)
- Rheumatic fever, chordae rupture
Complications: May predispose to infective endocarditis

Ventricular Septal Defect (VSD)

Murmur: Holosystolic, harsh-sounding murmur
Auscultation: Loudest at tricuspid area
Pathophysiology:
- Small VSD: Louder murmur
- Large VSD: Softer murmur due to reduced turbulence

Diastolic Murmurs

Aortic Regurgitation (AR)

Murmur: High-pitched “blowing” early diastolic decrescendo murmur
Auscultation:
- Best heard at base (aortic root dilation)
- Left sternal border (valvular disease)
Associated Signs:
- Wide pulse pressure
- Hyperdynamic pulse and head bobbing (if chronic and severe)
Causes (Mnemonic: BEAR)
- Bicuspid aortic valve
- Endocarditis
- Aortic root dilation
- Rheumatic fever
Complication: Progresses to left heart failure

Mitral Stenosis (MS)

Murmur: Delayed rumbling mid-to-late diastolic murmur
Auscultation: Follows opening snap (OS) due to abrupt leaflet halt
Pathophysiology:
- Interval between S2 and OS inversely correlates with severity
- Left atrial (LA) pressure > Left ventricular (LV) pressure during diastole
Causes:
- Late sequela of rheumatic fever
- Complications:
  - Pulmonary congestion/hypertension
  - Left atrial dilation → Atrial fibrillation, Ortner syndrome (hoarseness due to LA enlargement compressing the recurrent laryngeal nerve)

Continuous Murmurs

Patent Ductus Arteriosus (PDA)

Murmur: Continuous machine-like murmur, loudest at S2
Auscultation: Best heard at left infraclavicular area
Causes:
- Congenital rubella
- Prematurity
Mnemonic: “PDAs (Public Displays of Affection) are continuously annoying“

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