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Straddling Right Atrioventricular Valves
in Atrioventricular Discordance
ANTON E. BECKER, M.D., SIEW YEN Ho, M.D., GILDA CARUSO, M.D.,
SIMCHA MILO, M.D., AND ROBERT H. ANDERSON, M.D.
SUMMARY Four hearts are described in which the right atrioventricular valve, draining a morphologically
right atrium, straddled and overrode a septum between a right-sided chamber of left ventricular morphology
and a left-sided chamber of right ventricular morphology. The degree of override varied between the straddling
valve and was committed by 20-45% to the morphologically right ventricle. The ventriculoarterial connections
in the hearts were discordant in one, double outlet from the morphologically right ventricle in two and single
outlet via an aorta from the morphologically right ventricle with pulmonary atresia in the other. The straddling
valve in one of the cases with double outlet had a dual orifice. Pulmonary stenosis was present in three cases,
and pulmonary atresia in the fourth. Study of the conduction system in three of the hearts revealed subtle but
important differences from the pattern expected in atrioventricular discordance. Each case had an anterior
atrioventricular node and penetrating bundle, but the connection thus formed was more lateral than usual, and
in the case with ventriculoarterial discordance, the nonbranching bundle was unrelated to the pulmonary outflow tract. A sling of conduction tissue between the anterior node and the regular node was found in the case
with single outlet and pulmonary atresia.
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STRADDLING VALVES have usually been
described either in hearts in which they connect the
right atrium to both the right and left ventricles, with
the ventricles normally related'14 or in which they connect the left atrium to both normally related ventricles.5 6 More rarely, the left atrioventricular
(tricuspid) valve may straddle a septum between a
larger right-sided chamber of left ventricular
morphology and a left-sided smaller chamber of right
ventricular morphology. These hearts are intermediate in morphology between congenitally corrected transposition and "single ventricle with inverted outlet chamber."2 Another type of straddling
valve, a right-sided atrioventricular (mitral) valve
straddling a septum in the setting of atrioventricular
discordance, is exceedingly rare; we know of only
three cases that have been described.7' 8
We have encountered four such hearts with various
arterial connections. Presence of the straddling valve
markedly influences surgical correction of hearts with
atrioventricular discordance,8 and examination of the
conduction systems of three of the hearts studied
revealed subtle but important differences from the anticipated pattern usually seen in atrioventricular discordance.9' 10 The findings in these hearts with straddling mitral valves and atrioventricular discordance
are the subject of this report.
Materials and Methods
The hearts were from patients who had been
attended at the Binnen Gasthuis, University of
Amsterdam; the Hospital for Sick Children, London;
the Brompton Hospital, London; and the Royal Infirmary, Edinburgh. The clinical findings were nonspecific and the surgical results not relevant to this
paper because our major interest was the cardiac
morphology. The patients had died at the ages of 3
days, 3 months, 7 years and 29 years, respectively.
Each heart was carefully studied to determine
the segmental arrangement and the degree of override
of the straddling valve. To do this the annulus of the
valve was viewed from the right atrium and the
amount of annulus committed to each ventricular
chamber was determined. In three hearts, blocks were
then removed for study of the conduction system by
the method of Smith et al.1" In the two smaller hearts
the entire right atrioventricular orifice was removed
and sectioned as a single block of tissue. In a third,
larger heart with double outlet arterial connection
only the anterior and posterior junctions of the ventricular septum with the atria were removed as
separate blocks of tissue.
Autopsy Findings
In each case the basic malformation was situs
solitus and atrioventricular discordance with straddling of the right atrioventricular valve across an
anterior ventricular septal defect (table 1, figs. 1-5).
The degree of override of the straddling valve was 45%
to the morphologically right ventricle in cases 2 and 4
and 20% to the morphologically right ventricle in
cases 1 and 3. The overriding part of the valve was
tethered by an anomalous anterior papillary muscle
that was attached to the trabecula septomarginalis in
the morphologically right ventricle in cases 1-3. The
posteromedial papillary muscle in these cases was present in the hypoplastic morphologically left ventricle.
From the Department of Pathology, Wilhelmina Gasthuis,
Amsterdam, The Netherlands, and the Departments of Pediatrics
and Surgery, Cardiothoracic Institute, Brompton Hospital, London, United Kingdom.
Dr. Milo was a visiting fellow from the Chaim Sheba Medical
Centre, Tel Aviv, Israel.
Dr. Anderson is supported by the Joseph Levy Foundation and
the British Heart Foundation.
Address for correspondence: Dr. A. E. Becker, Department of
Pathology, Wilhelmina Gasthuis, Eerste Helmerstraat 104, Amsterdam, The Netherlands.
Received December 11, 1978; revision accepted November 30,
1979.
Circulation 61, No. 6, 1980.
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VOL 61, No 6, JUNE 1980
TABLE 1. Autopsy Findings in Four Cases with Sitas Solitus, Atrioventricular Discordance and Straddling Right Atrioventricular
Valve
% of overriding of MV to
morph RV
Size of morph LV compared
with morph RV
Morphology of straddling
atrioventricular valve
Case 1
Case 2
Case 3
Case 4
20%
45%
20%
45%
2:3
Anomalous ant. PM
attached to TSM
1:2
2:3
Anomalous ant. PM Dual orifice
attached to TSM
"parachute" ant.
orifice to TSM
3:5
Keyhold valve
attached by chordae
to infundibullar
septum and TSM
Ventriculoarterial connection
Aortic position
Pulmonary outflow tract
Discordant
Anterior, left-sided
Stenotic ("squeeze"
+ tissue tag)
ASD
PDA
DORV
Single outlet
Anterior to
Anterior, right-sided
pulmonary remnant
Atretic
Stenotic (squeeze +
valve stenosis
ASD
ASD
PDA
Ebstein's anomaly
LAVV
DORV
Anterior, left-sided
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Stenotic (squeeze +
valve stenosis)
ASD
Associated anomalies
Acquired incompetence, both AV
valves
Anterior connection Not studied
Anterior connection "'Sling"
Conduction tissues
Abbreviations: RV right ventricle; PM papillary muscle; TSM =trabecula septomarginalis; Ant. anterior; DORV
double outlet right ventricle; ASD = atrial septal defect; PDA = persistent ductus arteriosus; AV = atrioventricular; LAVV =
left atrioventricular valve; morph = morphologic.
=
In case 3 the straddling valve also had a dual orifice
(fig. 4). The orifice presenting to the morphologically
right ventricle was tethered in parachute fashion to the
anomalous papillary muscle. In case 4 the overriding
part of the valve was deformed and keyhole-like (fig.
5). The superior edge of the keyhole was attached to
the infundibular septum and the inferior edge was attached by short chordae to the trabecula septomarginalis. The part of the valve remaining in the
morphologically left ventricle was attached to the posteromedial papillary muscle. In all four hearts the
morphologically left ventricle was smaller than the
=
right, the discrepancy in size being most marked in
the cases with 45% override. The ventricular chambers
were arranged in superoinferior fashion in each case,
with the morphologically left ventricle the inferior
chamber. The ventricular septum was therefore
horizontally positioned. In all cases it extended
posteriorly to the crux, where its position was marked
externally by the posterior descending coronary
artery. Its anterior component ran toward the right
margin of the heart and was marked externally by an
anterior descending branch from the right coronary
artery (morphologically, a left coronary artery). The
Append
FIGURE 1. The angiogram obtained from case 1 and the specimen cut in matching fashion. (A) The right
atrial injection filling the appendage (append), with splitting of the stream of contrast through the right
atrioventricular valve (RA VV). Retrospective comparison with the specimen (B) showed that this splitting
was the consequence of the RA VV. The asterisk marks the stenotic outflow tract from the morphologically
(morph) left ventricle (LV). RV= right ventricle.
STRADDLING MITRAL VALVE IN AV DISCORDANCE/Becker et al.
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FIGURE 2. Further photographs of case 1. (A) The ventricular septal defect after removal of the overriding
part of the straddling right valve (arrows) as viewed from the right atrium. (B) The view from the left-sided
morphologically right ventricle (RV). To prepare figure 2B, the infundibular septum has been divided
(asterisks) so that the stenotic outflow tract from the morphologically left ventricle (L V) can be visualized.
Note the fibrous tissue tag herniating into this outflow tract from the partiallyformed interventricular membranous septum. RA VV - right atrioventricular valve.
ventricular septal defect in all hearts involved
predominantly the anterior part of the septum, but extended posteriorly to the crux.
The ventriculoarterial connection varied. Case 1
had arterial discordance, with the pulmonary outflow
a)
W
tract arising from the morphologically left ventricle
and wedged between the overriding part of the right
atrioventricular valve and the left atrioventricular
valve. It was stenotic, and the narrowing was exacerbated by a subvalvar tissue tag herniated from a par-
b)
FIGURE 3. Photographs of the autopsy specimen from case 2. (A) The opened right atrioventricular orifice
viewed from behind and slightly from beneath. Note the straddling valve (RA VV). The position of the sling
of conduction tissue has been marked. The sections obtained at sites a-a, b-b, c-c and d-d are shown infigure
9. (B) The straddling portion of the right valve as viewed from the morphologically right ventricle. Note the
small size of the left valve (A VV), the attachment of the straddling valve to the trabecula septomarginalis
(TSM) and the atretic pulmonary artery (pulm art). LV = left ventricle; RV right ventricle.
=
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a)
b)
VOL 61, No 6, JUNE 1980
K.
FIGURE 4. (A) The straddling right valve from case 3, showing its dual orifice. (B) The attachment of the
valve to the annulus in the morphologically left ventricle (L V) has been removed to demonstrate the site of
the anterior penetrating bundle (dotted lines). RA VV = right atrioventricular valve.
b) 'S'\
FIGURE 5. Photographs of the straddling valve in case 4. (A) The valve viewed by opening the right annulus from behind. The valve is committed by 45% to the morphologically right ventricle (RV). (B) View
from the morphologically right ventricle (left sided). Note the "keyhole" appearance of the straddling portion of the valve attached superiorly to the infundibular septum. Note also the right diaphragmatic obstruction to the pulmonary outflow tract from the R V. (There is double outlet from this ventricle.)
A V - atrioventricular valve, RA VV - right atrioventricular valve.
STRADDLING MITRAL VALVE IN AV DISCORDANCE/BeCker et al.
Straddling Mitral
Valve (cut away)
RihtAtrium-
1137
tially formed interventricular membranous septum
(fig. 2). Case 2 had pulmonary atresia, with the aorta
arising entirely from the morphologically right ventricle (fig. 3).
Cases 3 and 4 both exhibited double outlet from the
morphologically right ventricle. In both, the aorta was
anterior, but was to the left in case 4; it was slightly to
the right of the pulmonary trunk in case 3. A bilateral
infundibulum was present in both hearts and both had
subpulmonary infundibular obstruction with the outflow tract wedged between the straddling part of the
right-sided mitral valve and the left-sided tricuspid
valve. This produced a circular diaphragmatic obstruction (fig. 5). Additional pulmonary valvar stenosis was present in both hearts.
Conduction Tissues
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The conduction tissues were studied histologically
in cases 1-3. The findings were essentially the same in
cases 1 and 3. The regular atrioventricular node was
normally positioned at the apex of the "triangle of
Koch" formed between the insertion of the com-
FIGURE 6. Photograph illustrating the blocks removedfor
histologic examination in case I. Block A contains the
regular node, which fails to make contact with the ventricular myocardium. Sections through a-a and b-b are
shown in figure 7. Block B contains the anterior node and
the penetrating bundle. The sections a-a, b-b and c-c make
up figure 8.
FIGURE 7. Photomicrographs of the sections through the regular node in case 1 (see figure 6). The node
does not make contact with the ventricular myocardium. A V = atrioventricular. Elastic van Gieson stain;
magnification (A) X 12, (B) X 6.5.
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FIGURE 8. Photomicrographs of the anterior conduction system found in case 1 (see figure 6). The bundle
branches (fig. 8C) are inverted. Elastic van Gieson stain; magnification (A) X 12, (B) X 17, (C) X 30.
missure of the venous valves to the central fibrous
body and the septal attachment of the right atrioventricular valve. The node did not make any contact with
the underlying ventricular tissues (figs. 6 and 7).
An anterior node, located at the acute point of the
atrioventricular junction (figs. 6 and 8) gave rise to a
penetrating bundle. This bundle descended directly
onto the anterior limb of the ventricular septum and
was unrelated to the pulmonary outflow tract in the
case with arterial discordance. Having descended
STRADDLING MITRAL VALVE IN AV DISCORDANCE/Becker et al.
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FIGUREI 9. Photomicrographs of the sling of conduction tissue found in case 2 (seefigure 3 for position of the sections). Both
anterior (fig. 9A) and regular (fig. 9D) nodes give rise to penetrating bundles. Figures 9B and C show the anterior and posterior
limbs of the sling. Masson trichrome stain; magnifications X 4.
along the anterior rim of the septal defect, the bundle
branched in mirror-image fashion, the left bundle
branch entering the inferior morphologically left ventricle and the cord-like right bundle branch passing
into the left-sided morphologically right ventricle
(fig. 8).
In the other case with pulmonary atresia the
anterior node, penetrating bundle and bundle
branches were disposed in similar fashion. However,
in this case a bundle of conduction tissue extended
along the crest of the ventricular septum and ascended
its posterior limb to penetrate the annulus and make
contact with the regular atrioventricular node (fig. 9).
Thus, there was a sling of conduction tissue in this
heart (fig. 3). This heart also had better alignment
between the atrial and ventricular septa than the
others.
Discussion
Although the presence of atrioventricular discordance potentially "corrects" the effect of arterial discordance, the segmental arrangement of corrected
transposition is usually "uncorrected" by associated
malformations.12 14 Of the associated malformations,
ventricular septal defects, pulmonary stenosis and
Ebstein's malformation of the left atrioventricular
valve are well recognized.12 Straddling or overriding
atrioventricular valves are less common but important
because they make problems in accurate diagnosis and
because they present a major challenge to the surgeon,
who ideally should be aware of their existence before
surgery.8 Straddling of the left (tricuspid) valve in the
setting of atrioventricular discordance is becoming
recognized with increasing frequency,8 14, 16 but as far
as we know a straddling right (mitral) valve has been
described only three times before.7' 8
With increasing sophistication of angiographic'7
and echocardiographic'8 investigations, diagnosis of
straddling and overriding atrioventricular valves may
be made with increasing frequency. Thus, the
significance of the straddling valve is related to surgical correction. As shown by the experience of Tabry
et al.,8 palliative procedures may be necessary in the
presence of straddling valves. However, in older
patients it may be possible to perform more "corrective" procedures, and several options are then
available: first, a modified Fontan procedure, as in our
case 3; second, sacrifice of the straddling valve with
valve replacement and closure of the ventricular septal
defect;8 or finally, a septation procedure in the
morphologically right ventricle, giving back to the left
ventricle the overriding portion of the right valve. In
all these options the demonstrated disposition of the
conduction tissues and their subtle but important
variation from the anticipated pattern in atrioventricular discordance8 10 are of major significance.
In corrected transposition the penetrating atrioventricular bundle is an anterior structure and the extensive nonbranching atrioventricular bundle is intimately related to the pulmonary outflow tract.9 In all
the hearts we studied the penetrating bundle was
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anterior, but the connecting anterior node was placed
more laterally in the right atrioventricular orifice than
anticipated in the "standard" variety of corrected
transposition. This was related to the more lateral
position of the anterior part of the septum. Because of
this, the nonbranching atrioventricular bundle in the
case with arterial discordance could descend directly
onto the septum without encircling the pulmonary
outflow tract. In any case, with double outlet right
ventricle the bundle would not be expected to be
related to the outflow tract because the left ventricle
has no direct outlet. Nonetheless, the connecting node
was again more lateral than normal and was the only
node present.
Similarly, in the case with pulmonary atresia the
conduction tissues took origin more laterally in the
right atrioventricular orifice than in other hearts of
this type that we have examined.9 However, this case
was complicated by the presence of a sling of conduction tissue encircling the septal crest. We have encountered such slings previously in the presence of
atrioventricular discordance, and Wenink19 recently
reviewed other reported examples of this unusual finding. In the present case, as in our other cases, there
was good alignment between the atrial septum and the
inlet portion of the ventricular septum, a feature lacking in the other two hearts, which had only an anterior
connection. This finding reinforces our concept that
the presence of a posterior node in atrioventricular
discordance relates to the alignment of the atrial and
ventricular septal structures.9' 20
When considering these variations in the light of the
surgical options, the more lateral position of the anterior node would be of significance during either
valve replacement" or closure of the right valve during
a modified Fontan procedure. Its lateral position,
however, would place the anterior conduction system
in relatively safe position should the septation option
be attempted through the morphologically right ventricle, the latter perhaps the best option from an
anatomic standpoint. However, the presence of a sling
of conduction tissue, as in our case 3, could jeopardize
a septation procedure because the patch would require
insertion between the atrioventricular valves at the
crux, the precise site of the posterior penetrating bundle. Intraoperative mapping2' is therefore advisable to
exclude this possibility, particularly when good septal
alignment at the crux increases the likelihood of a
sling.
The fact that surgical correction of these cases
could involve a septation procedure, together with the
decreasing size of the left ventricular chamber and increasing commitment of the straddling valve to the
right ventricular chamber, brings up the whole relationship of hearts with straddling valves to univentricular hearts. Quero-Jimenez et al.5 described hearts
with straddling of the mitral valve and double inlet to
a chamber of right ventricular morphology. If the
hearts we describe are similar, as seems likely, then
similar hearts may be found with effectively double inlet ventricle and minimal overriding of the mitral
valve above the left ventricular type positioned to the
VOL 61, No 6, JUNE 1980
right.22 Of course, the hearts we describe are biventricular with atrioventricular discordance and
superoinferior ventricles. But in the setting of a univentricular heart of left ventricular type, it is generally
accepted that the criterion for inclusion as a single
ventricle is the presence of double inlet.23
Hearts are still classified as single ventricle when
there is double inlet despite the presence of minimal
straddling of one valve.24 25 When, in a continuum of
transfer of a straddling valve from one chamber to
another, does the atrioventricular connection change
from discordance (or concordance) to double inlet?
We suggest that in terms of the atrioventricular connection, the change in this continuum occurs at its
midpoint. Therefore, if hearts similar to those we
describe were found in which the straddling valve was
committed primarily to the left-sided morphologically
right ventricular chamber, we would categorize the
atrioventricular connection as double inlet and the
hearts as univentricular.
Acknowledgment
We are greatly indebted to several clinical colleagues involved in
the study of these patients for permitting us to describe these results,
in particular Dr. T. G. Losekoot and Dr. C. Marcelletti of the
University of Amsterdam; Prof. F. J. Macartney of the Hospital for
Sick Children, London; Drs. M. C. Joseph, E. A. Shinebourne and
G. A. H. Miller and Mr. J. C. R. Lincoln of the Brompton Hospital,
London, and Drs. R. M. Marquis, J. Irving and K. Grigor of the
Royal Infirmary, Edinburgh. We also thank Marsha Schenker,
Noelle de Freitas and Joan Otto for their help in the preparation of
the manuscript.
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Straddling right atrioventricular valves in atrioventricular discordance.
A E Becker, S Y Ho, G Caruso, S Milo and R H Anderson
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Circulation. 1980;61:1133-1141
doi: 10.1161/01.CIR.61.6.1133
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