How are heart murmurs classified and what are their causes?

Heart Murmur Classification and Causes

Heart murmurs are classified based on their timing in the cardiac cycle, configuration, location, radiation, pitch, intensity (grades 1-6), and duration, with diastolic and continuous murmurs almost always representing pathological conditions requiring further evaluation. 1

Primary Classification of Murmurs

Timing in the Cardiac Cycle

1. Systolic Murmurs

   • Holosystolic (Pansystolic): Occur from S1 to S2 with plateau configuration

     • Causes: Mitral regurgitation, tricuspid regurgitation, ventricular septal defect 1, 2
     • Mechanism: Flow between chambers with widely different pressures throughout systole

   • Midsystolic (Ejection): Start after S1, peak in mid-systole, end before S2

     • Causes: Aortic/pulmonic stenosis, increased flow states (pregnancy, anemia, thyrotoxicosis), innocent murmurs 1
     • Configuration: Typically crescendo-decrescendo (diamond-shaped)

   • Early Systolic: Begin with S1 and end in mid-systole

     • Causes: Tricuspid regurgitation without pulmonary hypertension, acute mitral regurgitation 1

   • Late Systolic: Start after mid-systole and end at or before S2

     • Causes: Mitral valve prolapse, papillary muscle dysfunction 1

2. Diastolic Murmurs (always pathological)

   • Early Diastolic: Begin with or shortly after S2

     • Causes: Aortic regurgitation, pulmonic regurgitation 1

   • Mid-Diastolic to Late Diastolic: Occur during mid to late diastole

     • Causes: Mitral stenosis, tricuspid stenosis 1

3. Continuous Murmurs: Span both systole and diastole

   • Pathological causes: Patent ductus arteriosus, arteriovenous fistula
   • Innocent causes: Venous hums, mammary souffles 1

Intensity Grading (1-6)

• Grade 1: Very faint, heard only in optimal conditions
• Grade 2: Quiet but clearly audible
• Grade 3: Moderately loud, no thrill
• Grade 4: Loud with a palpable thrill
• Grade 5: Very loud, thrill easily palpable, audible with stethoscope partially off chest
• Grade 6: Extremely loud, audible with stethoscope off the chest 3

Configuration Patterns

• Crescendo: Increasing intensity
• Decrescendo: Decreasing intensity
• Crescendo-decrescendo (diamond-shaped): Typical of ejection murmurs
• Plateau: Constant intensity throughout (typical of holosystolic murmurs) 1

Diagnostic Approach to Murmurs

Dynamic Maneuvers to Aid Diagnosis

Maneuver	Effect on Murmurs
Respiration	Right-sided murmurs increase with inspiration; left-sided murmurs louder during expiration
Valsalva	Most murmurs decrease; exceptions: HCM (louder), MVP (longer/louder)
Exercise	Murmurs of stenotic valves, MR, VSD, and AR increase with handgrip
Standing	Most murmurs diminish; MVP murmurs become louder [1]

Pathological vs. Innocent Murmurs

Features suggesting pathological murmurs:

• Holosystolic or diastolic timing
• Grade 3 or higher intensity
• Harsh quality
• Abnormal S2
• Maximum intensity at upper left sternal border
• Systolic click
• Increased intensity when standing 2, 4

Features of innocent murmurs:

• Grade 1-2/6 intensity
• Mid-systolic timing
• Soft, musical quality
• Normal S2
• Position-dependent
• No radiation
• No associated symptoms 5

Common Causes by Murmur Type

1. Mitral Regurgitation (Holosystolic)

   • Location: Apex
   • Radiation: To axilla
   • Response: Increases with handgrip, decreases/unchanged with inspiration 2

2. Tricuspid Regurgitation (Holosystolic)

   • Location: Lower left sternal border
   • Response: Increases with inspiration (Carvallo's sign) 2

3. Ventricular Septal Defect (Holosystolic)

   • Location: Left sternal border
   • Radiation: Across precordium
   • Response: No significant change with respiration 2

4. Aortic Stenosis (Midsystolic)

   • Location: Right upper sternal border
   • Radiation: To carotids
   • Associated findings: Slow-rising carotid pulse (parvus et tardus) 1

5. Mitral Valve Prolapse (Late Systolic)

   • Location: Apex
   • Associated findings: Mid-systolic click
   • Response: Murmur lengthens with standing 1

Clinical Approach

When evaluating a heart murmur, follow this approach:

1. Determine timing (systolic, diastolic, continuous)
2. Assess configuration and intensity
3. Note location, radiation, and pitch
4. Perform dynamic maneuvers to aid diagnosis
5. Look for associated cardiac and non-cardiac findings

Diastolic and continuous murmurs almost always warrant echocardiographic evaluation, as do holosystolic murmurs and any murmur of grade 3 or higher intensity. 1, 5