Unroofed coronary sinus syndrome (UCSS) is a rare congenital heart disease, which has variable morphologic features and is strongly associated with persistent left superior vena cava (PLSVC). However, it is often difficult to visualize the left-to-right shunt pathway through the CS by transthoracic echocardiography (TTE).

A 37-year-old female was admitted to the hepatological surgery department of a hospital with complaint of subxiphoid pain that had started 1 wk prior. Physical examination revealed a grade 3/6 systolic murmur at the left margin of the sternum, between the 2^nd and 3^rd intercostal cartilage. The patient underwent echocardiography and was diagnosed with ostium primum atrial septal defect (ASD); thus, she was subsequently transferred to the cardiovascular surgery department. A second TTE evaluation before surgery showed type IV UCSS with secundum ASD. Right-heart contrast echocardiography (RHCE) showed that the right atrium and right ventricle were immediately filled with microbubbles, but no microbubble was observed in the CS. Meanwhile, negative filling was observed at the right atrium orifice of the CS and right atrium side of the secundum atrial septal. RHCE identified UCSS combined with secundum ASD but without PLSVC in this patient.

This rare case of UCSS highlights the value of TTE combined with RHCE in confirming UCSS with ASD or PLSVC.

Unroofed coronary sinus syndrome (UCSS) is a rare congenital heart disease, in which left atrial to right atrial shunt occurs through a partial or complete defect of the roof of the CS[1]. UCSS has variable morphologic features and the clinical syndrome of UCSS varies from symptomless to severe right heart failure, which is mainly determined by the size of the defect between the CS and other associated anomalies, such as persistent left superior vena cava (PLSVC) and atrial septal defect (ASD). UCSS is strongly associated with PLSVC in about 75% of cases[2], and UCSS in the terminal portion (Kirklin and Barratt-Boyes type IV) without PLSVC or other anomalies is classified as a type of ASD, which comprises less than 1% of all ASD cases[1]. However, it is often difficult to visualize the left-to-right shunt pathway through the CS by transthoracic echocardiography (TTE), which can lead to misdiagnosis or a missed diagnosis[3].

We present a rare case of UCSS combined with secundum ASD but without PLSVC, which was misdiagnosed as ostium primum ASD identified by TTE.

Pulmonary function tests showed that the diffusing capacity of the lung for carbon monoxide was mildly decreased (78%), but the forced expiratory volume in 1 s and ratio of forced expiratory volume to forced vital capacity remained normal.

Electrocardiogram (ECG) examination showed that the patient had sinus rhythm, a normal ECG axis, and incomplete right bundle branch block.

No genetic testing was performed.

No multidisciplinary expert consultation was conducted.

Type IV UCSS combined with secundum ASD.

The patient underwent repair surgery for the CS roof defect, secundum ASD closure, and tricuspid annuloplasty. During the operation, obvious broadening of the CS with partial defect of the roof of the CS (3.0 cm × 2.1 cm) and secundum ASD near the oval foramen (1.1 cm) were detected (Figures 2A and 2B). When perfused through the CS, the perfusate reflowed to both the left atrium and right atrium. The moderate-to-severe tricuspid valve regurgitation was due to a significantly dilated tricuspid annulus.

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Figure 2 Imaging during the operation. A: Obvious broadening of the coronary sinus (CS) with a partial defect of the CS roof in the terminal portion (3.0 cm × 2.1 cm) was seen upon incision of the right atrium; B: The defect of the CS in the terminal portion was repaired.

The patient was in good condition and no complications occurred after surgery. The patient was discharged from the hospital about 2 wk after surgery. TTE before discharge showed no shunt through the UCSS or ASD from the left atrium to right atrium, mild tricuspid valve regurgitation (velocity 223 cm/s, PG 20 mmHg), and normal PASP (25 mmHg) (Figures 3A-3D). At the 6-mo follow-up visit, the patient was in good condition.

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Figure 3 Transthoracic echocardiography at 1 wk after surgery. A: The repaired atrial septum was continuous and complete on apical four-chamber view (arrow); B: The repaired coronary sinus (CS) roof was continuous and complete on apical four-chamber view (arrow); C: There was no shunt from the left atrium to right atrium on apical four-chamber view (arrow); D: Trace tricuspid regurgitation (Vmax = 223 cm/s, pressure gradient = 20 mmHg, pulmonary artery systolic pressure = 25 mmHg). RA: Right atrium; RV: Right ventricle; LA: Left atrium; LV: Left ventricle; CS: Coronary sinus.

UCSS is a rare congenital heart disease characterized by communication between the CS and the left atrium through the partial or complete absence of the CS roof. According to the location of the absence, UCSS is classified into the following four morphological types: Completely unroofed with PLSVC (type I); completely unroofed without PLSVC (type II); partially unroofed in the midsection (type III); and partially unroofed in the terminal portion (type IV)[1,4].

In general, UCSS is strongly associated with a PLSVC, which remains the most common association[2]. Moreover, it can also be associated with other congenital heart abnormalities, such as cor triatriatum, canal defects, tetralogy of Fallot, abnormal atrioventricular connection, pulmonary atresia or stenosis, and anomalous pulmonary venous return[5].

TTE is the most widely used noninvasive technique for the diagnosis of UCSS; although posterior structures such as the pulmonary veins or CS may not be seen well in some patients. RHCE using agitated saline or glucose injection through the left arm vein may help indicate PLSVC, the most common association which is characterized by microbubbles in the CS prior to its appearance in the right atrium.

However, it is not easy to determine the type of UCSS due to difficulties in detecting the exact location of the unroofed portion. In the present case, the defect of CS was partially unroofed in the terminal portion (type IV); this UCSS type was misdiagnosed at the first TTE because the location of the defect was near the endocardial cushions on apical four-chamber view, which was mistaken for a defect of the ostium primum ASD. On the second TTE, the defect of the CS in the terminal portion and normal endocardial cushions were detected on apical four-chamber view by scanning backward. Moreover, the CS was significantly dilated and the CS roof structure was not always seen while a shunt from the left atrium was passed through the dilated CS to the right atrium. All evidence led to the diagnosis of UCSS. Meanwhile, a small shunt through the secundum ASD was detected, with the exception of an atrial-level UCSS shunt.

In the present case, RHCE worked in two ways. When injected through the left arm vein, microbubbles first entered the right atrium but no microbubble appeared in the CS, indicating that there was no PLSVC. Moreover, negative filling was observed at the right atrium orifice of the CS and right atrium side of the secundum atrial septal during RHCE, confirming the diagnosis of UCSS and secundum ASD. Although TTE of suitable image sections is the first-line examination to evaluate UCSS, it should be more frequently used in combination with RHCE in these cases.

We highlight a rare case of type IV UCSS combined with secundum ASD but without PLSVC, which was misdiagnosed as ostium primum ASD identified by TTE. TTE combined with RHCE is of value in confirming UCSS with or without ASD and PLSVC.