How do you differentiate the murmur of a Ventricular Septal Defect (VSD) from Mitral Regurgitation (MR)?

From the Guidelines

To differentiate between a Ventricular Septal Defect (VSD) murmur and Mitral Regurgitation (MR) murmur, focus on their distinct characteristics during cardiac auscultation, with the most recent guidelines suggesting specific maneuvers and findings to aid in differentiation 1.

Key Differentiating Features

• A VSD murmur is typically harsh, holosystolic, and loudest at the left lower sternal border (4th-5th intercostal space), often with a palpable thrill, radiating toward the right sternal border rather than the axilla.
• An MR murmur is also holosystolic but is usually blowing in quality and heard best at the cardiac apex (5th intercostal space, mid-clavicular line), with radiation to the left axilla.

Diagnostic Maneuvers

• Having the patient lean forward in expiration may accentuate an MR murmur.
• Transient arterial occlusion by bilateral cuff inflation can augment murmurs of MR and VSD, as noted in guidelines 1.

Associated Findings

• VSD may present with signs of right ventricular overload in large defects.
• MR often has an enlarged point of maximal impulse and may be accompanied by an S3 gallop.

Underlying Pathophysiology

• VSD involves blood flowing from the left to right ventricle through a septal opening.
• MR results from blood regurgitating from the left ventricle into the left atrium due to mitral valve dysfunction, with recent studies highlighting its significance in heart failure 1.

Clinical Considerations

• The severity of MR is related to the magnitude of the regurgitant volume, leading to LV dilation and increases in left atrial pressure and volume, as discussed in recent guidelines 1.
• Differentiating between athletic training-induced LV dilation and that caused by severe MR is crucial, with LVEDD measurements >60 mm suggesting severe MR 1.

From the Research

Differentiating Murmurs of VSD and Mitral Regurgitation

To differentiate the murmur of a Ventricular Septal Defect (VSD) from Mitral Regurgitation (MR), several factors should be considered:

• Location and Radiation of the Murmur: The murmur of VSD is typically heard best at the left lower sternal border and may radiate to the right of the sternum 2. In contrast, the murmur of MR is usually heard best at the apex and radiates to the axilla.
• Timing and Duration: VSD murmurs are typically pansystolic, starting from the onset of systole and continuing until its end 2. MR murmurs can also be pansystolic but may vary in timing depending on the severity and cause of the regurgitation.
• Intensity and Pitch: The intensity of the murmur can vary with the size of the defect in VSD and the severity of regurgitation in MR. A louder murmur is often associated with a larger defect or more significant regurgitation.
• Associated Signs: Patients with VSD may exhibit signs of increased pulmonary blood flow, such as a prominent left parasternal heave, and possibly signs of heart failure if the defect is large 3, 4. Those with MR might show signs of left ventricular volume overload, including an enlarged cardiac silhouette on chest X-ray and possible signs of pulmonary congestion.
• Diagnostic Tests: Echocardiography is crucial for diagnosing both conditions, providing detailed information about the anatomy of the defect or the valve, the direction of blood flow, and the presence of any associated lesions 3, 5. Cardiac catheterization may be used in certain cases to assess hemodynamics, especially if there's concern about pulmonary vascular resistance or to guide interventions.

Clinical Considerations

• Symptoms: While both conditions can be asymptomatic, especially if mild, symptoms such as shortness of breath, fatigue, and failure to thrive in children can indicate significant disease 2, 6.
• Treatment Approach: The management of VSD and MR differs significantly. Small VSDs may close spontaneously or be monitored, while larger defects often require surgical closure 3. MR management depends on the cause and severity, ranging from medical therapy for asymptomatic patients with mild regurgitation to surgical repair or replacement of the mitral valve for those with severe symptoms or significant left ventricular dysfunction.

Diagnostic Challenges

Diagnosing and differentiating between VSD and MR can be challenging, especially in adults, due to the variability in clinical presentation and the potential for co-existing cardiac anomalies or acquired heart diseases 6. A comprehensive diagnostic approach, including detailed clinical examination, echocardiography, and sometimes cardiac catheterization, is essential for accurate diagnosis and appropriate management planning.