What are the causes of an enlarged coronary sinus?

Causes of Enlarged Coronary Sinus

An enlarged coronary sinus is most commonly caused by persistent left superior vena cava (PLSVC) draining into it, followed by right atrial pressure overload conditions including pulmonary hypertension, right heart failure, and elevated right atrial pressure. 1, 2

Primary Causes

Congenital Anomalies

• Persistent Left Superior Vena Cava (PLSVC): This is the most common congenital cause of coronary sinus enlargement, where the left superior vena cava drains directly into the coronary sinus rather than the normal venous pathway 3, 1, 2

  • PLSVC causes marked dilatation of the coronary sinus due to increased blood flow volume 4, 5
  • This anomaly can be distinguished from other causes by measuring the coronary sinus eccentricity index (EI): an EI <0.8 is 100% sensitive and specific for PLSVC 1
  • Patients with PLSVC have significantly larger coronary sinus cross-sectional area compared to those with right atrial pressure overload 1

• Unroofed Coronary Sinus: This rare defect (<1% of atrial septal defects) involves partial or complete absence of the separation between the coronary sinus and left atrium 3

Acquired Hemodynamic Conditions

• Pulmonary Hypertension: Elevated pulmonary artery pressures lead to right heart strain and increased right atrial pressure, causing coronary sinus dilation 1, 6

• Right Atrial Pressure Overload (RAPO): Any condition elevating right atrial pressure can dilate the coronary sinus 1

  • Right ventricular failure
  • Tricuspid valve disease
  • Restrictive cardiomyopathy affecting the right heart
  • These conditions produce a coronary sinus with EI >0.8, distinguishing them from PLSVC 1

Clinical Significance and Complications

Hemodynamic Consequences

• Left Ventricular Inflow Obstruction: Marked coronary sinus enlargement can cause supramitral obstruction by compressing or displacing the mitral valve apparatus 4, 6, 5

  • This rare complication can mimic cor triatriatum clinically 6, 5
  • Presents with cardiac failure in infancy or early childhood when severe 6, 5
  • Echocardiography shows abnormal mitral inflow Doppler patterns 4
  • Cardiac catheterization reveals increased atrial "a" waves with gradient to left ventricular end-diastolic pressure 4

• Increased Left-to-Right Shunting: When associated with atrial septal defects, the elevated left atrial pressure from inflow obstruction increases shunt magnitude and worsens symptoms 5

Diagnostic Approach

Imaging Characteristics

• Echocardiography: Measure coronary sinus cross-sectional area and eccentricity index in parasternal long-axis view at end-diastole 1

  • EI = B/A (where A is widest diameter, B is perpendicular minor axis)
  • EI <0.8 indicates PLSVC; EI >0.8 indicates RAPO 1

• Confirmation of PLSVC: Use computed tomography or agitated saline injection in left antecubital vein 1

Associated Anomalies

• Anomalous pulmonary venous connections 3
• Atrial septal defects 5
• Mitral valve abnormalities 4

Common Pitfalls

• Misdiagnosis as Pulmonary Hypertension: Double-chambered right ventricle or dilated coronary sinus from RAPO may show elevated tricuspid regurgitant jet velocity, leading to incorrect diagnosis of primary pulmonary hypertension 7
• Overlooking Hemodynamic Significance: Not all dilated coronary sinuses cause symptoms, but when associated with left ventricular inflow obstruction, surgical correction (coronary sinus angioplasty) is safe and effective 4, 5