What is the cardiac murmur grading system and how are the grades I through VI defined?

Cardiac Murmur Grading System

The Standard Grading Scale

Cardiac murmurs are graded on a 1-through-6 intensity scale for systolic murmurs, with each grade representing progressively louder sounds that help distinguish innocent from pathological murmurs. 1

The Six Grades Defined

• Grade 1/6: Very faint murmur, barely audible even with optimal listening conditions 2

• Grade 2/6: Soft murmur but readily heard with the stethoscope on the chest 2

• Grade 3/6: Moderately loud murmur without a palpable thrill; this grade represents a critical threshold where echocardiography becomes necessary as the murmur is more likely to represent organic heart disease 1, 2

• Grade 4/6: Loud murmur with an associated palpable thrill (vibration felt on the chest wall) 2

• Grade 5/6: Very loud murmur that can be heard with the stethoscope barely touching the chest, with palpable thrill 2

• Grade 6/6: Extremely loud murmur that can be heard with the stethoscope held just off the chest wall, with palpable thrill 2

Alternative Grading for Diastolic Murmurs

• Diastolic murmurs are typically graded on a simpler 4-point scale (Grade 1 being very faint, Grade 4 being very loud), though this distinction is less clinically relevant since all diastolic murmurs, regardless of grade, virtually always represent pathological conditions and require immediate echocardiographic evaluation 2, 3

Clinical Significance by Grade

Low-Grade Murmurs (1-2/6)

• Grade 1-2 systolic murmurs in asymptomatic adults with normal S2 splitting, no other abnormal cardiac findings, and normal ECG/chest X-ray are typically innocent and require no further workup 2

• However, even soft grade 1-2 murmurs require echocardiography when accompanied by symptoms (syncope, angina, heart failure, thromboembolism), signs of endocarditis, or abnormal physical findings 2

High-Grade Murmurs (≥3/6)

• Any midsystolic murmur of grade 3 or greater intensity mandates echocardiographic evaluation, as these are more likely to represent organic valvular disease rather than innocent flow murmurs 1, 2

• Historical data from Freeman and Levine's landmark 1933 study demonstrated that all patients with grade 3 or 4 murmurs had either organic heart disease or anemia, establishing this threshold as clinically significant 4

Critical Timing and Type Considerations

Murmurs Requiring Evaluation Regardless of Grade

• All holosystolic (pansystolic) murmurs require echocardiography regardless of intensity, as they indicate flow between chambers with widely different pressures throughout systole (e.g., mitral regurgitation, ventricular septal defect) 2, 3

• All late systolic murmurs at the apex or left sternal border require echocardiography regardless of grade 2

• All diastolic murmurs require immediate cardiac evaluation regardless of intensity—this is a non-negotiable rule 1, 2, 3

• All continuous murmurs require evaluation except for the clearly innocent venous hums and mammary souffles 1

Complete Assessment Beyond Intensity

The grading system is only one component of murmur assessment. Complete characterization requires documenting: 1

• Timing: Systolic (holosystolic, midsystolic, early, late), diastolic (early, mid, presystolic), or continuous 1

• Configuration: Crescendo, decrescendo, crescendo-decrescendo (diamond-shaped), or plateau 1

• Location: Primary auscultation site (apex, left lower sternal border, right upper sternal border, etc.) 2

• Radiation: To carotids, axilla, back, or other distant sites 2

• Pitch: High, medium, or low frequency 2

• Response to dynamic maneuvers: Changes with respiration, Valsalva, standing, squatting, handgrip exercise 1

Common Pitfalls to Avoid

• Never dismiss a diastolic murmur based on low grade—even a grade 1 diastolic murmur represents pathology and requires echocardiography 2, 3

• Do not assume grade 1-2 systolic murmurs are innocent in elderly patients with hypertension, as these may represent sclerotic aortic valve leaflets or flow into noncompliant vessels 2

• Avoid overlooking holosystolic or late systolic murmurs even when soft, as these indicate regurgitant lesions requiring evaluation 3

• Remember that symptoms override murmur characteristics—any murmur accompanied by syncope, angina, heart failure, or thromboembolism requires echocardiography regardless of grade 2, 3

• Be aware that echocardiography may detect trivial physiological regurgitation in normal patients who have no audible murmur at all, so correlation with clinical findings is essential 2