Systolic Murmur
A murmur occurring after S1 ("lub") is a systolic murmur, which occurs during ventricular contraction between the first and second heart sounds.
Types of Systolic Murmurs by Timing
Systolic murmurs are classified based on when they occur during systole, each with distinct clinical implications:
Midsystolic Murmurs
- These are the most common systolic murmurs, beginning after S1 and ending before S2 with a crescendo-decrescendo pattern 1
- Most innocent murmurs in children and young adults are midsystolic, originating from aortic or pulmonic outflow tracts 1
- Pathologic causes include valvular stenosis (aortic or pulmonic), where intensity depends on blood flow velocity across the narrowed area 1
- Echocardiography is often necessary to distinguish a prominent benign midsystolic murmur (grade 3) from true valvular aortic stenosis 1
- Functional mitral or tricuspid regurgitation can also produce midsystolic murmurs 1, 2
Holosystolic (Pansystolic) Murmurs
- These begin with S1 and continue through systole until S2, indicating continuous regurgitant flow throughout ventricular contraction 2
- This pattern represents chronic mitral regurgitation with an established pressure gradient between left ventricle and left atrium 2
- The continuous nature throughout systole is a red flag for pathology 2
Early Systolic Murmurs
- These begin with S1 but end in midsystole, making them less common than other systolic murmurs 1
- Often due to tricuspid regurgitation without pulmonary hypertension 1
- Acute mitral regurgitation (such as papillary muscle rupture or acute chordal rupture) characteristically produces an early systolic murmur 1, 2
- Also occur with large ventricular septal defects with pulmonary hypertension or small muscular VSDs 1
Late Systolic Murmurs
- These are soft or moderately loud, high-pitched murmurs at the left ventricular apex that start well after ejection and end before or at S2 1
- Classic for mitral valve prolapse, often accompanied by midsystolic clicks 1, 2
- Can occur without clicks and may be due to apical tethering and malcoaptation of mitral leaflets 1
- Standing causes these murmurs to lengthen and intensify, unlike most other murmurs which diminish 1, 2
Key Clinical Distinctions
Red Flags for Pathologic Murmurs
- Any diastolic murmur is pathologic and warrants workup 3
- Holosystolic murmurs indicate significant regurgitation 2
- Grade 3 or higher intensity 4
- Harsh quality or abnormal S2 4
- Maximal intensity at upper left sternal border 4
- Systolic click present 4
Dynamic Auscultation Maneuvers
- Handgrip exercise increases mitral regurgitation murmur intensity 1, 2
- Left-sided murmurs are louder during expiration 1, 2
- Valsalva maneuver decreases most murmurs except hypertrophic cardiomyopathy (which becomes louder) and mitral valve prolapse (which becomes longer and louder) 1
- Standing diminishes most murmurs but increases those from HCM and MVP 1, 2
Clinical Approach
The clinical examination by an experienced clinician has 96% sensitivity and 95% specificity for distinguishing innocent from pathologic murmurs 5. However, echocardiography provides definitive diagnosis when pathology is suspected 4, 5.