Implantation of a Cardiac resynchronization therapy system in a patient with an unroofed coronary sinus

Abstract The unroofed coronary sinus (URCS) is a spectrum of cardiac anomalies in which part or all of the common wall between the coronary sinus and the left atrium is absent. Rarely, it is associated with coronary sinus atresia. The diagnosis of this lesion is important for the prognosis of the patient, especially in cases when cardiac interventions such as CRT implantation needs to be performed. It is found incidentally because of nonspecific clinical features. We report a case of a complete URCS and CS atresia during a computed tomographic investigation performed following prior impossibility of LV lead to be implanted.


| INTRODUC TI ON
Unroofed coronary sinus is a rare congenital cardiac anomaly in which there is partial (either focal or fenestrated) or complete absence of the roof of the coronary sinus, which results in a communication between the coronary sinus and the left atrium.
Unroofed coronary sinus is the rarest type of atrial septal defect.
It is often associated with persistent left superior vena cava and other forms of complex congenital heart disease, usually heterotaxia syndromes. 1 Although unroofed CS and CS atresia often remain silent due to nonspecific clinical features, the diagnosis is difficult but important as it can cause impediments during intravenous interventions such as CRT implantation, as it happened in our case.
Cardiac resynchronization therapy is an adjunct current therapy in patients with systolic heart failure and prolonged interventricular conduction 2 aiming to restore the normal synchronization between the two ventricles. This can be achieved by implantation of a pacing lead in a CS branch draining the free lateral wall of the LV. Unfavorable anatomy impairs a successful procedure.

| C A S E REP ORT
We present a 37-year-old Caucasian female referred to our hospital for cardiac resynchronization therapy due to left ventricle dysfunction. Due to lack of accessibility to cannulate the coronary sinus and the entire cardiac venous system, the patient was referred for surgical lead implantation (Figure 3). The morphological types have been classified into four groups: type I-completely unroofed with PLSVC; type II-completely unroofed without PLSVC; type III-partially unroofed mid portion; and finally type IV-partially unroofed terminal portion as illustrated in the present case. 3 Also, in our case, the unroofed CS is accompanied by coronary sinus ostial atresia.

| D ISCUSS I ON
The diagnosis of coronary sinus abnormalities is not straightforward. The coronary sinus dilatation can be easily visualized by transthoracic and trans-esophageal echocardiography. However, detection of defect between coronary sinus and left atrium by echocardiography can be quite challenging due to limited sonographic window. In our case, transthoracic echocardiography did not depict the coronary sinus defect. Moreover, the patient underwent previous cardiac surgeries that did not document coronary sinus atresia, neither unroofing of the coronary sinus. Omission of coronary atresia even after cardiac surgery has been previously reported in literature.
The clinical presentation depends on the size of the communication between coronary sinus and left atrium and the degree of left to right and right to left shunt. Often, they remain silent as in our case. When it is symptomatic, the symptoms may range from mild, nonspecific complaints to severe dyspnea with symptoms of rightsided heart failure from chronic right ventricular volume overload. In case of right to left shunt, a potential complication of brain abscess and emboli exists.
Most cases of CS atresia are associated with an alternative exit for coronary venous blood return, such as a PLSVC, large Thebesian vein, or CS canal defect. 4 In our case, there are collateral small venous pathways. However, no persistent left superior vein was present which can be used as an alternative path for LV lead implantation. In such cases, an optional treatment is surgical epimyocardial lead implantation.

| CON CLUS ION
A thorough knowledge of the cardiac venous anatomy prior to the procedure will facilitate the intervention process and increase the successful outcome.
Cardiac CT with its excellent spatial resolution allows for the accurate morphological evaluation of the structures of the heart.

CO N FLI C T O F I NTE R E S T
The authors declare no conflict of interest.