RIGHT atrial membranes arise from resorption failure of the sinus venosus valve. 1,2Most right atrial membranes are attributed to the degree of persistence of valve tissue and are associated with congenital defects. A case in which a right atrial membrane interferes with passage of a pulmonary artery catheter is presented.

An 81-yr-old man (105 kg, 180 cm) presented for a coronary artery bypass grafting procedure. Preoperative cardiac catheterization revealed severe three-vessel occlusive coronary artery disease. Left ventricular function was estimated to be normal, with an ejection fraction of 60%. Cardiac output was 4.8 l/min, with an index of 2.1. Pulmonary artery pressure, measured via  the femoral vein to the inferior vena cava route, was normal. Results of a physical examination were remarkable only for a plethoric purplish red face, which the patient has had for many years. Results of other laboratory tests and of chest radiography were noncontributory.

On the morning of surgery, the patient was brought to the operating room, routine monitors were placed, intravenous access was obtained, and a radial arterial catheter was inserted. General anesthesia was induced, and an endotracheal tube was inserted without difficulty. The right internal jugular vein was identified, and an 18-gauge catheter was inserted. Catheter position was verified by blood aspiration and by pressure transduction to rule out arterial insertion. A wire was passed through the catheter but met with resistance at a depth of 15–20 cm. Several attempts to reposition the wire, including reinsertion of the catheter by several experienced operators from the anesthesia and surgery team, were also met with resistance.

A right-sided subclavian approach was attempted, but, again, it was met with the same resistance at similar depths. Subsequently, the left subclavian vein was cannulated after a wire was passed without resistance. Multiple attempts to float a pulmonary artery catheter were unsuccessful, without sight of a right ventricular pressure trace. The catheter was left at a depth of 20 cm, and preparation for surgery continued.

Transesophageal echocardiography was performed. The transesophageal echocardiography revealed a long right atrial membrane that extended from the lower portion of the interatrial septum, above the tricuspid valve, which divided the right atrial lumen into anterolateral and posteromedial chambers (fig. 1) . The membrane appeared to be mobile in its center but fixed by its margins. A microbubble imaging contrast test performed by injecting agitated saline via  the central line side port showed filling of the posteromedial portion first and a rapid propagation into the anterolateral portion via  what appeared to be a single opening in the membrane close to the interatrial septum.

Fig. 1. Transesophageal echocardiographic view of the left atrium (LA), right atrium (RA), right atrial membrane (RAM), and right ventricle (RV) in partial view.

Fig. 1. Transesophageal echocardiographic view of the left atrium (LA), right atrium (RA), right atrial membrane (RAM), and right ventricle (RV) in partial view.

Close modal

No right-to-left shunts in the form of an atrial septal defect or a patent foramen ovale were shown. Results of the rest of the transesophageal echocardiography examination were normal. After the patient’s chest was opened, the surgeon noted that the venous system draining into the right atrium was exceptionally dilated.

Because of these findings, the right atrium was opened during the cardiopulmonary bypass period of the procedure, and the membrane was identified and resected. The transesophageal echocardiography findings were confirmed, and a diagnosis of Cor Triatriatum Dexter was made. The rest of the operation was uneventful, and the patient was weaned from the cardiopulmonary bypass machine without difficulty. The pulmonary artery catheter was floated into position without difficulty after cardiopulmonary bypass. The patient was taken to the intensive care unit, and he was extubated several hours later. He was discharged from the hospital on the ninth postoperative day.

Right atrial membranes represent embryonic remnants from the fetal development of the valve between the sinus venosus and the primitive common atrium. During the fourth week of human embryonic development, the common atrium is separated from the sinus venosus by a bileaflet valve, known as the valve of the sinus venosus or as the sinoatrial valve. As the primitive common atrium divides, the left leaflet of the sinoatrial valve is incorporated into the right surface of the interatrial septum and becomes part of the septum secundum. The right leaflet of the sinoatrial valve resorbs between the ninth and fifteenth weeks of gestation and leaves behind the Eustachian valve of the inferior vena cava and the Thebesian valve of the coronary sinus. During this time, the sinus venosus gives rise to the superior and inferior vena cava and to the coronary sinus.

In the adult heart, the remnant of the right leaflet can be traced to a small fold near the opening of the inferior vena cava. Failure of complete resorption of the right leaflet of the sinoatrial valve leads to a scale of anatomic findings, with or without physiologic implications, depending on the degree of persistence of leaflet tissue and accompanying defects. 1In the mild form, a large eustachian valve can be identified near the orifice of the inferior vena cava. This valve remnant has a free-floating edge in the right atrium, and it is a relatively common incidental finding during transesophageal echocardiography. 2A more developed valve remnant can be fenestrated and form a perforated veil, known as the Chiari network. 1The extreme case of a persistent sinoatrial right leaflet completely divides the right atrium into an anterolateral and posteromedial portion, and is therefore known as Cor Triatriatum Dexter. 3Such a membrane usually has a single fenestration close to the interatrial septum. A right atrial membrane was first noted in 1876 by Lauenstein, 4but the term Cor Triatriatum Dextrum was mentioned first in 1963 by Doucette. 5 

The incidence of Cor Triatriatum Dexter comprises approximately 0.025% of the cases of congenital heart disease, but it has an unclear definition because it can be found in different anatomic degrees, with varying physiologic and symptomatologic presentations. It is unclear why a well-developed membrane that divides the right atrium in two and possibly creates a grade chronic obstruction to flow, as described in this case report, presents incidentally with so few symptoms, compared with other symptomatic membranes found in adulthood 1,3or in childhood that cause heart failure and cyanosis. 6 

The function of the Eustachian valve in fetal life is to divert blood flow from the inferior vena cava via  the foramen ovale to the left atrium. When Cor Triatriatum Dexter is present, it often is accompanied by a patent foramen ovale or by an atrial septal defect, which diverts some of the right atrial blood, in a right-to-left shunt, to the left atrium, potentially causing cyanosis.

The current case is characterized by a well-developed, anatomically impressive membrane; yet, because of membrane fenestration, there was little flow obstruction, and because of an absent patent foramen ovale and atrial septal defect, there was no flow diversion or shunt, which allowed the patient to lead a normal life, without significant symptoms related to the right atrial membrane. In rare instances, a right atrial membrane was reported to cause such significant obstruction to flow that the presenting symptoms were of tricuspid atresia, and the tricuspid valve and the right ventricle were underdeveloped. Other cases reported a membrane that prolapsed through the tricuspid valve into the right ventricle, and even through the pulmonic valve. 7–9The diagnosis of right atrial membranes is best made by use of two-dimensional echocardiography, 1,3,10and, when found, recommendations for resection are probably related to symptoms resulting from the membrane.

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