Coronary Sinus Behind the Right Atrium
Understanding the Anatomy
The term "sinus behind the right atrium" most likely refers to an enlarged or dilated coronary sinus, which is a venous structure that normally runs in the posterior atrioventricular groove behind the left atrium and drains into the right atrium. 1, 2
Clinical Significance
The significance depends on the underlying cause and associated anomalies:
Causes of Coronary Sinus Enlargement
- Persistent left superior vena cava (LSVC) is the most common cause of coronary sinus dilation, where systemic venous blood drains anomalously into the coronary sinus 3, 2
- Coronary sinus defects (partial or complete unroofing) can create communications between the coronary sinus and left atrium, resulting in right-to-left or left-to-right shunting 3, 4
- Isolated coronary sinus anomalies without associated shunts may be clinically benign 1, 2
Hemodynamic Consequences
- Right-to-left shunting can cause systemic desaturation and cyanosis, particularly with exertion 3
- Left-to-right shunting may lead to volume overload and right heart failure over time 4, 2
- Enlargement without shunting typically indicates anomalous systemic venous drainage but may be hemodynamically insignificant 2
Arrhythmia Risk
- Coronary sinus diverticula and malformations carry significant arrhythmia risk, with supraventricular tachycardia occurring in 40% of cases and sudden cardiac death reported in 18% of patients with coronary sinus diverticula 5
- These anomalies may be relevant in patients with persistent atrial fibrillation after pulmonary vein isolation 4
Diagnostic Evaluation
Coronary angiography using catheterization, CT, or CMR is recommended for detailed anatomical evaluation of coronary sinus anomalies. 6, 7
- Cardiac CT is generally preferred due to superior spatial and temporal resolution for delineating the coronary sinus anatomy and its relationship to surrounding structures 6, 1
- Contrast echocardiography can demonstrate shunting at the atrial level and assess coronary sinus size 3
- Cardiac catheterization provides hemodynamic assessment of shunt magnitude and direction 3
Management Approach
For Asymptomatic Patients Without Shunting
- Regular clinical follow-up with echocardiography every 3-5 years to monitor coronary sinus size and cardiac function is recommended 7
- Watchful waiting is appropriate when there is no evidence of hemodynamic compromise 7, 2
For Symptomatic Patients or Those With Shunting
- Surgical repair is indicated when there is significant left-to-right or right-to-left shunting causing symptoms or hemodynamic compromise 3
- Transcatheter closure may be considered in select cases with suitable anatomy and evidence of shunting 7
For Patients With Arrhythmias
- Catheter or surgical ablation should be strongly considered given the high mortality risk in untreated coronary sinus diverticula (100% mortality in one series of untreated patients) 5
- All patients with coronary sinus diverticula who were not treated with ablation eventually died in reported case series 5
Critical Pitfalls to Avoid
- Do not dismiss systemic desaturation as unexplained without considering coronary sinus defects with right-to-left shunting 3
- Do not misdiagnose as primum ASD when unroofed coronary sinus is present, as this requires different surgical approach 3
- Do not underestimate arrhythmia risk in patients with coronary sinus diverticula or malformations, as sudden cardiac death occurs in nearly 1 in 5 patients 5
- Recognize that normal stress testing does not exclude risk in coronary anomalies, though this primarily applies to anomalous coronary arteries rather than coronary sinus anomalies 6
Follow-up Recommendations
- Regular cardiac imaging to monitor coronary sinus size is recommended for all patients with identified anomalies 7
- Patients who develop symptoms require prompt re-evaluation with appropriate cardiac imaging 7
- Consider electrophysiology consultation for any patient with documented arrhythmias and coronary sinus anomalies 5