Hemitricuspid Dysplasia in Association with Ventricular Septal Defect

Abstract

The tricuspid valve essentially consists of a straight septal leaflet and a curved mural leaflet that includes the anterior and posterior leaflets. A plane bisecting the septal and anterior leaflets divides the chordopapillary support of the tricuspid valve into 2 groups. One group is related to the bulbar and adjacent perimembranous and sinus components of the interventricular septum. The other is related to the trabecular septum and the adjacent free wall. We report our surgical findings in 5 patients who had dysplasia of the leaflets and chordopapillary support related to the bulbar, perimembranous, and sinus portions of the interventricular septum, in conjunction with a perimembranous ventricular septal defect. Phylogenic, ontogenic, and surgical implications of this association are discussed.

The tricuspid valve, as seen by the surgeon through the right atrium, is divisible into left- and right-hand sides by a mid-tricuspid plane, which bisects the septal and anterior leaflets (Fig. 1). ^1,2 The left side of the tricuspid valve consists of the left half of the anterior leaflet, the left half of the septal leaflet, and the commissural tissue in between. We report the cases of 5 patients in whom there was dysplasia of this side of the tricuspid valve in association with a perimembranous-type ventricular septal defect.

Fig. 1 Transventricular view of the tricuspid valve. The dotted mid-tricuspid line divides the tricuspid valve into left and right halves. Leftward-pointing arrowheads direct attention to the bulbar chordal support, and rightward-pointing arrowheads mark the trabecular chordal support of the septal leaflet.

Case Reports

Patient 1

A 3-year-old boy presented with a perimembranous ventricular septal defect, the presence of which was confirmed by echocardiography and cardiac catheterization. At surgery on 3 February 1996, the patient's heart was found to be displaced to the left. The origin of the right coronary artery and its proximal 2 cm were easily seen. They were exposed in the atrioventricular groove, which was deep and devoid of fat. A right atriotomy revealed a ventricular septal defect, 5 × 5 mm, beneath the anteroseptal commissure. The defect was surrounded by sclerosed endocardium, which was in continuity with similar tissue that formed the rim of a nonobstructive os infundibulum. The left halves of the anterior and septal leaflets and the related chordopapillary support could not be identified. The defect was closed with a Dacron patch. The boy's postoperative recovery was uneventful.

Patient 2

A 4-year-old boy presented with a ventricular septal defect. At surgery on 4 March 1996, the right atrioventricular groove was found to be deep and devoid of fat, resulting in clear visibility of the proximal segment of the right coronary artery. The perimembranous ventricular septal defect was situated beneath the anteroseptal commissure. The defect was 5 × 5 mm, with a substantial rim of thickened endocardium all around (Fig. 2A). The left halves of the anterior and septal leaflets had been replaced by thickened endocardium at the annulus, and there was no chordopapillary support (Fig. 2B). The defect was closed by approximating the thickened redundant endocardial edges with 2 sutures reinforced by pledgets. The patient's postoperative course was uneventful.

Fig. 2 A) Transatrial surgical view of the ventricular septal defect between the deficient anterior and septal leaflets.

B) Only the anterior and septal papillary muscles from the trabecular septum provide chordal support to these leaflets.

IVC = inferior vena cava; SVC = superior vena cava

Patient 3

A 3-year-old boy presented with echocardiographic evidence of a perimembranous ventricular septal defect with minor tricuspid incompetence. At surgery on 3 November 1997, a 5 × 5-mm ventricular septal defect with a rim of thickened endocardium was found beneath the junction of the anterior and septal leaflets. The left halves of the anterior and septal leaflets and the related chordopapillary support were missing. The anterior papillary muscle supplied ¹ chorda to the septal leaflet (Fig. 3). The rest of the chordal support to the septal leaflet originated from the trabecular septum. The ventricular septal defect was closed with a Dacron patch. The child's postoperative recovery was uneventful.

Fig. 3 Transatrial surgical view of the patched ventricular septal defect (VSD) situated between the anterior and septal leaflets. One chorda connects the anterior papillary muscle to the septal leaflet.

Patient 4

An 18-month-old boy presented with echocardiographic evidence of a ventricular septal defect. At surgery on 21 March 1997, atrial-appendage-like tissue was found surrounding the acute margin of the heart. A right atriotomy revealed a prominent valve of the inferior vena cava. The coronary sinus was at the bottom of a shallow, saucer-like depression in the sub-Eustachian sinus. A large ventricular septal defect was situated at the junction of the septal and anterior leaflets. The left halves and the related chordopapillary support of the anterior and septal leaflets could not be identified. The right halves of these leaflets were intact, with normal trabecular chordal support.

The ventricular septal defect was closed with a polytetrafluoroethylene patch. When the left ventricle was filled, the perimembranous tissue around the patch was observed to be bulging into the right ventricle in the region where the left halves of the anterior and septal leaflets should have been. This tissue protrusion was aiding in the closure of the tricuspid valve (Fig. 4). The boy's postoperative course was uneventful, except for problems related to preexisting sequelae of postnatal cerebral asphyxia.

Fig. 4 The ventricular septal patch and the surrounding membranous tissue form a bulge between the deficient anterior and septal leaflets, helping to make the valve competent.

Patient 5

A 34-year-old man who had been diagnosed with ventricular septal defect at the age of 5 years presented at our institution with multiple cardiac problems, consisting of gross congestive heart failure, ventricular septal defect, aortic leakage into both ventricles, tricuspid regurgitation, severe pulmonary hypertension, and infective endocarditis. At surgery on 26 March 1998, we found the heart to be greatly enlarged. The right atrioventricular cleft was deep, and the proximal right coronary artery was easily seen. An oblique aortotomy revealed a severely dilated annulus and a tricuspid aortic valve with poorly coapting leaflets. The right coronary cusp was muscularized and was prolapsing through a perimembranous ventricular septal defect that had thick margins of sclerosed endocardium. The septal defect was closed with sutures reinforced by pledgets. There was a 1-cm-wide incomplete subaortic membrane, which we excised. The aortic valve was also excised and replaced with a Starr-Edwards silastic ball valve (size 11A, model 1260; Baxter Health Care Corp., Edwards CVS Division; Santa Ana, Calif). The patient's initial recovery was satisfactory; however, he had persistent cardiac failure and died 2 months after surgery.

A postmortem examination of the right ventricle revealed no residual ventricular septal defect (Fig. 5). The bulbar segment of the anterior leaflet was poorly formed, with no bulbar chordopapillary support. The septal leaflet was also deficient, with only 1 true bulbar chorda. There was 1 false bulbar chorda, which indicated to us that it had not found its leaflet component during prenatal development. There was no continuity between the anterior and septal leaflets.

Fig. 5 The sutured ventricular septal defect (arrowhead) is situated between the deficient septal leaflet and the anterior leaflet, which is devoid of bulbar papillary support. There is a gap between these leaflets.

Discussion

Bifocal Chordopapillary Support

The tricuspid valve can be considered to consist of a straight septal leaflet and a curved mural leaflet. The mural leaflet encompasses the classic anterior and posterior leaflets with their related scallops. ^1–3 The papillary muscles of the valve are usually designated as the conus, anterior, posterior, and septal groups; these muscles exhibit wide variations and are as unique to each heart as a fingerprint is to a person. ¹ We have suggested an approach through the right atrium for intraoperative evaluation of the tricuspid valve. ³ A mid-tricuspid plane that bisects the anterior and septal leaflets divides the leaflets and chordopapillary support visually into left and right sides, corresponding to the left and right hands of the surgeon. The chordae tendineae of these 2 sides of the valve are perpendicular to one another. ^1,2

The Left Half

To the left of the mid-tricuspid plane, the left halves of the anterior and septal leaflets can be identified with intervening septomural commissural leaflet tissue that may contain 1 or 2 scallops. ^1,3 This half of the anterior leaflet is supported by chordopapillary support from the conus papillary muscle: a derivative of the bulbar septum. However, the number, size, and configuration of this conus or bulbar papillary support vary. Sometimes, direct chordae tendineae replace the papillary muscles.

The chordopapillary supports of the left half of the septal leaflet are anchored to the trabecula septomarginalis (a derivative of the bulbar musculature) and septum between it and the annulus of the tricuspid valve, or solely to the latter. This support consists of a variable number of papillary muscles and direct chordae tendineae.

Between the anterior and septal leaflets, there is usually continuity of leaflet tissue, of various widths, with chordae tendineae from the membranous and perimembranous septum. Rarely, otherwise normal hearts manifest a discontinuity of leaflet tissue in this region (Fig. 6). On either side of the gap are varying degrees of dysplasia of the related leaflet tissue and chordopapillary support. Thus, the chordopapillary support of the left half of the valve is related mainly to the bulbar and adjacent sinus and membranous segments of the interventricular septum.

Fig. 6 A gap between the anterior and the septal leaflets is present in an otherwise normal heart. In this instance, the anterior leaflet has adequate conal chordopapillary support, but the septal leaflet is devoid of bulbar chordopapillary support.

The Right Half

The right halves of the anterior and septal leaflets and the leaflet tissue in between are supported by various configurations of chordopapillary support related to the trabecular part of the interventricular septum ¹ and the adjacent free wall. Anterior, posterior, and septal papillary muscles, direct chordae tendineae, or a combination of these, may be identifiable; however, 2 or more groups may be fused. Rarely, a single common papillary muscle is present. ¹

Hemitricuspid Valve Dysplasia

In our 5 patients, there was dysplasia of the leaflets and the chordopapillary support of the left half of the tricuspid valve, as well as a perimembranous ventricular septal defect. This type of ventricular septal defect is caused by a failure of the bulbar, ⁴ membranous, and sinus parts of the interventricular septum to join in the perimembranous region. The developmental defect in the tricuspid valve is not related to the attempted closure of the ventricular septal defect, because the dysplasia encompasses not only the leaflets but also the chordae tendineae and the papillary muscles. In these patients, the deficiency was not detected during preoperative echocardiography. Echocardiographic techniques need to be further refined to display the chordopapillary apparatus in greater detail.

Phylogenic Considerations

The phylogeny of the tricuspid valve provides clues to its human ontogeny. ⁵

In the crocodile, the venous atrioventricular valve has a straight septal leaflet and a curved mural leaflet extending from the bulbar septum superiorly and from the trabecular septum inferiorly. The bulbar segments of both the leaflets are membranous. In birds, the curved mural leaflet is membranous toward the bulbar septum. There is no septal leaflet.

In the echidna, which is an egg-laying mammal, the bulbar segment of the septal leaflet is missing. Occasionally in human beings, a deficiency of the leaflet tissue is seen in this location in an otherwise normal heart (Fig. 1).

Phylogeny suggests that the cranial segments of the septal and mural leaflets of the venous atrioventricular valves are embryologically different from the caudal segments. Human ontogeny of the tricuspid valve ^6,7 needs to be viewed from this perspective.

Surgical Considerations

An appreciation of the variability of the tricuspid valve is necessary when performing surgery to close ventricular septal defects. Closure of the defect was simple in our patients because of a substantial rim of thickened endocardium in the margins of the septal defect. (This endocardium might represent redundant leaflet tissue that was not used to form definitive leaflets.) However, care should be taken not to distort nature's compensation for the defective valve. In our 5 patients, dysplasia of the left side of the valve was not associated with tricuspid incompetence of clinical or echocardiographic importance, except in patient number 5. It is of interest to note that in birds, the venous atrioventricular valve is competent without a septal leaflet. In echidna, an incomplete septal leaflet is not associated with valvular incompetence. We should also be aware that other defects, such as the following, could coexist: malformation of the aortic sinuses, muscularization of the aortic leaflet, presence of a subaortic membrane, a deep right atrioventricular sulcus, an abnormally visible proximal segment of the right coronary artery, and an abnormal termination of the coronary sinus in the right atrium. This list suggests that the disturbed embryogenesis in such patients affects much more of the heart than just the bulbar musculature, the interventricular septum, and the tricuspid valve.