British HeartJournal, I970, 32, 7I4-7I6.

Cor triatrium dexter

D. Verel, J. Pilcher, and D. M. HynesFrom The Cardio-Thoracic Unit, Northern General Hospital, Sheffield S5 7AU

A case of cor triatrium dexter is described in which the patient had been independently assessed intwo cardiological centres as having a form of Ebstein's anomaly. The differential diognosis isdiscussed.

Septation of the right atrium to form a triatrialheart is a rare anomaly. Most cases have beenrecorded at necropsy, either as an incidentalfinding in an otherwise normal heart, or inassociation with severe congenital heartdisease. In most cases the additional partitionis due to the persistence of the foetal Eusta-chian and Thebesian valves which form aseptum across the lower part of the atrium.This may vary from a substantial sheet oftissue shown at angiocardiography (Kjellberget al., 1959) to a reticulum of the typedescribed by Chiari (I897). Cor triatrium hasalso been used to describe a grossly dilatedcoronary sinus entering the right atrium by adilated orifice. Dilatation of this magnitudemay be due to the presence of a left superiorvena cava, or to anomalous pulmonary veinsentering the coronary sinus (Hudson, 1965).Other cardiac defects may be found in associa-tion with either defect.We have been unable to find a clinical

account of isolated cor triatrium dexter. Sincethe differendial diagnosis may be of some im-portance, the following case is reported.

Case reportThe patient was a slightly obese woman aged 2Iyears. Two years previously heart disease had beendiagnosed for the first time when the clinical, radio-logical,and electrocardiographic findings suggesteda mild degree of Ebstein's anomaly. Investigationwas delayed by her marriage and an uneventfulpregnancy, during which she moved into theSheffield region. She was referred for advice asshe complained of slight dyspnoea on exertion.On examination she was not dyspnoeic at rest

or on moderate exercise. There was no clubbingor central cyanosis. At times there was slightperipheral cyanosis but this appeared to be physio-logical and due to the cold. The apex beat was

normal in character but displaced to the fifthspace in the anterior axillary line. The heartsounds were normal, with a soft pansystolic mur-mur audible from the left sternal edge to the apex.The electrocardiogram showed a well-marked

RSR' pattern most clearly seen in leads II, aVF,and V2 to V5. The T waves were biphasic in mostof these leads.The outline of the heart on the PA radiograph

was enlarged (Fig. ia), being somewhat like thatof Ebstein's anomaly, with clear lung fields. How-ever, the atrial shadow on the right border ex-tended only to the seventh thoracic vertebra. Onthe lateral and left anterior oblique'films, the heartshadow overlay the spine at the level of the tenthrib (Fig. ib). The shape of this projection wasunusual. It was thought initially to be due to anabnormality of the left atrium or ventricle. Afterangiocardiography, however, it became evidentthat it was the shadow of the backward projectionof the right atrium.

Cardiac catheterization revealed normal intra-cardiac pressures on the right side of the heart(pulmonary arterial I3/5, right ventricular I3/0,right atrial 3/0 mm. Hg). Oximetry did not showany abnormality, arterial saturation being 96 percent and the venous saturations ranging from 68per cent in superior vena cava to 75 per cent ininferior vena cava and 73 per cent in main pul-monary artery. Angiocardiography from the mainpulmonary artery showed a normal pulmonaryartery tree, left atrium, left ventricle, and aortawith no evidence of left-to-right shunt.

Angiocardiographic injection into the superiorvena cava (Fig. 2a, b) showed that immediatelybelow the entry of the vena azygos, the superiorvena cava widened into a flask-shaped chambersituated behind the main chamber of the rightatrium. This flask-shaped chamber extendedmedially to the left margin of the spine, but didnot reach to the lower limit or to the right borderof the heart shadow. The inferior vena cavaappeared to communicate with the lower extrem-ity of the posterior chamber (Fig. 2b). From thischamber the blood passed forward to fill the an-

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(a) (b)FIG. I(a) Postero-anterior radiograph of the chest showing globular enlargement of the heart.The outline suggested mild Ebstein's anomaly. (b) Left lateral radiograph of the chest withbarium showing apparent enlargement of the left ventricle. This projection of the heart overthe shadow of the spine proved to be due to the large right atrium.

terior part of the right atrium (Fig. 2a, b) whichformed the right border of the heart shadow. Theright ventricle was rotated clockwise by the largeatrium and formed the left border of the heart(Fig. 2c). From the right ventricle contrastmedium passed through an anatomically normalheart as described above.The intracardiac electrocardiogram and intra-

cardiac pressure were simultaneously recordedthrough a 9F NIH angiocardiographic catheterusing 5 per cent sodium bicarbonate as electro-lyte (Stentiford, I968). A normal change in QRSpattern was recorded at the tricuspid valve, and anormal change in axis of the P wave was found asthe catheter was drawn up the right atrium. Nosignificant pressure gradient was found at thearea of transition from the main right atrial cham-ber to the posterior chamber.

DiscussionThe anatomy revealed by cardiac catheteriza-tion in this patient appears to correspond tothe form of cor triatrium dexter associatedwith an anomaly of the Eustachian andThebesian valves. These valves are formedduring atrial development when the sinusvenosus and parts of the pulmonary veinsare incorporated into the atrial walls.

The left horn and transverse portion of thesinus venosus become the oblique vein of theleft atrium and coronary sinus, respectively.Simultaneously the atria grow rapidly result-ing in the incorporation of the right horn ofthe sinus venosus into the right atrium. Thisarea is represented in the right atrium by thesmooth-walled sinus venarum. The openingof the sinus venosus is initially guarded by avalvular fold. At 3 months the right half ofthis fold nearly divides the atrium into twochambers. As the heart develops the fold be-comes greatly diminished in size. Its cephalicportion becomes the crista terminalis and thecaudal portion develops into the folds orvalves which guard the inferior vena cava andcoronary sinus, i.e. the Eustachian valve. Itseems likely that the cor triatrium dexter inthis patient is due to a persistence of the wholeor part of the primitive valve of the sinusvenosus. The not infrequent reports of casesin which this anomaly has been described asan incidental finding at necropsy suggestthat it is of no great significance (Yater, I929).This conclusion is supported by the absenceof any pressure gradient between the twoatria and by the normal pressures found on

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7I6 Verel, Pilcher, and Hynes

(a) (b) (c)

FIG. 2 (a) and (b) Antero-posterior and lateral films taken one second afterinjection of contrast medium into the superior vena cava. The posterior chamber of the rightatrium is well outlined. The vena azygos can be seen filled retrogradely. The inferior venacava in the antero-posterior projection can be seen to rise above the lower limit of the anterioratrium to enter the same chamber as the superior vena cava. (c) Postero-anterior filmI second after a and b shows a large right atrium and right atrial appendage filled. Theright ventricle has opacified. The outline of the superior vena cava and vena azygos is stillvisible. The right border of the heart is formed by the anterior division of the right atrium,the left border of the heart by the right ventricle.

the right side of the heart and normal leftheart anatomy.

This patient was assessed clinically in tworegional cardiological centres. In both a diag-nosis of Ebstein's anomaly was made on thebasis of the physical signs, postero-anteriorchest radiograph, and electrocardiogram. Theunusual appearance shown on the left lateraland left anterior oblique film, however, sug-

gested that some other lesion was present.In view of the relatively poor prognosis inEbstein's anomaly and the probable normaloutlook in the patient described, this casereport appeared justified.

ReferencesChiari, H. (I897). Ueber Netzbildungen im rechten

Vorhofe des Herzens. Beitrage zur pathologischenanatomie und zur allgemeinen Pathologie, 22, I.

Hudson, R. E. B. (I965). Cardiovascular Pathology.Arnold, London.

Kjellberg, S. R., Mannheimer, E., Rudhe, U., andJonsson, B. (1959). Diagnosis of Congenital HeartDisease, 2nd ed. Year Book Publishers, Chicago.

Stentiford, N. H. (I968). Increasing the safety ofselective angiocardiography. Clinical Radiology, I9,I92.

Yater, W. M. (I929). Variations and anomalies of thevenous valves of the right atrium of the humanheart. Archives of Pathology, 7, 4I8.

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