What are the potential causes and management of a soft systolic murmur heard in the lower left area of the chest?

Soft Systolic Murmur at Lower Left Sternal Border

A soft systolic murmur at the lower left sternal border most commonly represents tricuspid regurgitation, a ventricular septal defect, or a flow murmur across the right ventricular outflow tract, and requires echocardiography if there are any associated abnormal findings or if the patient has cardiovascular risk factors. 1

Primary Differential Diagnoses by Location

Tricuspid Regurgitation

• The most common pathological cause at the lower left sternal border is tricuspid regurgitation (TR), particularly in the context of right heart pathology. 1
• In injection drug users presenting with fever, petechiae, Osler's nodes, and Janeway lesions, a right heart murmur in early to midsystole at the lower left sternal border likely represents TR without pulmonary hypertension. 1
• The murmur typically increases with inspiration (Carvallo's sign) due to increased venous return to the right heart. 1

Ventricular Septal Defect (VSD)

• VSD produces a pansystolic murmur at the lower left sternal border with high sensitivity on physical examination (100% detection rate in one study). 2
• The murmur reflects continuous flow between chambers with widely different pressures throughout systole. 3

Right Ventricular Outflow Obstruction

• Pulmonic stenosis produces an ejection sound heard only in the pulmonic area and left sternal border during expiration. 1
• Intraventricular pressure gradients (including across the moderator band) can cause systolic murmurs at the lower left sternal border but are poorly detected on physical examination (only 18% sensitivity). 2, 4

Critical Associated Findings That Change Management

Findings Requiring Echocardiography

• Fixed splitting of the second heart sound during inspiration and expiration with a grade 2/6 midsystolic murmur suggests atrial septal defect. 1
• Any murmur grade ≥3/6 warrants echocardiography regardless of other findings. 5
• Left ventricular failure, history of thromboembolism, or abnormal electrocardiogram/chest X-ray mandate echocardiographic evaluation. 1, 5

Dynamic Auscultation Maneuvers

• Systolic murmurs that increase after ventricular premature beats or during long cycle lengths in atrial fibrillation suggest significant valvular disease. 5
• Murmurs that increase with standing and decrease with squatting suggest mitral valve prolapse rather than right-sided pathology. 3

Diagnostic Approach Algorithm

Step 1: Assess Murmur Characteristics

• Grade the intensity (1-6 scale) - grade ≥3/6 requires echocardiography. 5
• Determine timing: early systolic, midsystolic, late systolic, or pansystolic. 1
• Assess radiation pattern and location of maximal intensity. 1

Step 2: Evaluate Associated Cardiac Findings

• Check for splitting of S2 (fixed vs. physiologic vs. reversed). 1
• Listen for additional sounds (clicks, S3, S4, ejection sounds). 6
• Palpate for displaced or prominent apical impulse suggesting ventricular hypertrophy. 6

Step 3: Perform Dynamic Maneuvers

• Assess respiratory variation (inspiration increases right-sided murmurs). 1
• Evaluate response to Valsalva, standing, and squatting if mitral pathology suspected. 3

Step 4: Risk Stratification

• Echocardiography is mandatory for any patient with suspected significant heart disease based on murmur characteristics, associated symptoms, or abnormal ancillary findings. 5, 2
• Physical examination alone has limited accuracy for determining the exact cause, particularly when multiple lesions are present (only 55% accuracy for combined valve disease). 2

Common Pitfalls to Avoid

• Do not assume a soft murmur is benign without considering the clinical context - severe aortic stenosis can present with a soft murmur when left ventricular ejection fraction is severely diminished. 2
• Physical examination missed significant heart disease completely in 2% of patients in one study, emphasizing the need for echocardiography when clinical suspicion exists. 2
• Mitral valve prolapse with click-murmur may be misdiagnosed as a benign flow murmur if the ejection click is not recognized. 3
• Combined aortic and mitral valve disease is frequently missed on physical examination (only 55% sensitivity). 2