The heart of the newborn child: an anatomical study based upon

J. Anat. (1988), 159, pp. 93-1 1 1 93With 13 figuresPrinted in Great Britain

The heart of the newborn child: an anatomical study basedupon transverse serial sections*

ROBERT WALMSLEY AND W. S. MONKHOUSEt

Department of Anatomy and Experimental Pathology, Bute Medical Buildings, TheUniversity, St Andrews KYI 6 9TS and t Department of Human Morphology,

Nottingham University Medical School, Queen's Medical Centre,Nottingham NG7 2UH

(Accepted 30 September 1987)

INTRODUCTION

The relationships of the heart and great vessels in the infant are assuming an evergreater clinical significance as a result of the many diagnostic procedures and surgicaloperations now routinely performed. Also, in the context of sectional anatomy of thethorax, these relationships are becoming increasingly important with the advent ofmodem scanning methods which require a sound anatomical knowledge for theirinterpretation. This study presents a review of the cardiac anatomy of the newbornchild based mainly on observations made on thin transverse serial sections of thethorax.More than 25 years ago Walmsley (1958, 1960) described the position and

orientation of the adult human heart based on observations made on thick sections ofthe thoraces of cadavers cut in several different planes. In these communications a pleawas made that gross cardiac anatomy should always be considered with the heart insitu in the chest. It was considered then, as it is now, that this is the only manner thatallows the heart surfaces, the cusps of the valves and other cardiac structures to bedesignated by names that are precisely appropriate to them: it furthermore providesan understanding of the correct relationship to one another of heart chambers, valvesand great vessels. The general principle that determines the nomenclature used indescriptive human anatomy is that the body is in the erect posture with the head andpalms of the hands directed forwards, and while this principle is meticulouslyadopted in the terminology for other parts of the body, it is in many instancesdisregarded in descriptions of cardiac anatomy, as is evidenced by the NominaAnatomica (1983).

Physicians, surgeons and radiologists are concerned with the heart and great vesselsas they lie in situ in the thorax. This is evident in the works ofmany clinicians includingSilverman & Schlant (1974) and McAlpine (1975). In a more recent study on theclinical anatomy of the heart (Walmsley & Watson, 1978) both thick and thin sectionsof entire thoraces were used in the correlation of the form and position of the heartin the cadaver with that in the living person. In this work due consideration was givento the alterations that occur in the position of the heart with changes in posture andduring elevation and depression of the diaphragm. It was also recognised that thethoracic viscera in the embalmed cadaver usually lie about one vertebra higher than

* Reprint requests to Professor W. S. Monkhouse, Department of Anatomy, Royal College ofSurgeons in Ireland, St Stephen's Green, Dublin 2, Ireland.

R. WALMSLEY AND W. S. MONKHOUSEthey do in the erect living person. In an extensive work on cardiac anatomy Anderson& Becker (1980) likewise considered that the heart should be described as it lies in situin the body.

In some anatomical texts the heart is depicted and described as if it has beenremoved from the body and were being held in the hand with the apex directeddownwards and the atria lying above the ventricles. Such an erroneous orientation ofthe heart is even implied in the Nomina Anatomica (1983) where the interventricularsulcus on the diaphragmatic surface of the heart is designated the posterior sulcus: anappended footnote stating that 'this Sulcus is, of course, inferior in position, and notposterior' is unsatisfactory as an attempt to correct the implications of thisnomenclature.Another feature of the fetal and postnatal heart that should be stressed is that the

atrial and ventricular septa are in line with each other throughout life from the timeof their appearance in the embryo. The plane of the septa is indicated by a line thatextends from the most anterior (or ventral) part of the anterior interventricular sulcusto the posterior (or dorsal) attachment of the atrial septum (Walmsley, 1958; Cooper& O'Rahilly, 1971). In the10 mm human embryo the developing atrial and ventricularsepta lie in or near the median plane so that the heart is an almost symmetrical organwith the two right chambers which form the 'right heart' lying directly to the right ofthe two left chambers forming the 'left heart'. It is only at this stage in developmentthat the adjectives 'right' and 'left' (as applied to the cardiac chambers) are preciselycorrect even though the terms 'right heart' and 'left heart' are in common usage inclinical practice and in the cardiac literature.

Details of the rotation of the heart that occurs during embryonic and early fetal lifeare not considered in this study, but certain facts are relevant. The first is that arotation of the heart begins to occur shortly after the embryo is 10 mm in crown-rumplength so that the apical part of the anterior interventricular sulcus is displaced to theleft and the posterior attachment of the atrial septum passes to the right; this resultsin the right heart coming to lie not only to the right of the left heart but to anincreasing degree in front of it. When the fetus is about 100 mm long and 4 monthsold the plane of the atrial and ventricular septa has attained an angle of about 450 tothe median plane and this is the approximate angulation that is seen in all older fetaland adult thoraces where the heart has been sectioned in situ. These observations haveled to the generalisation that rotation of the heart occurs early in development and iscompleted in the first half of intrauterine life. The great importance of this angulationof the septa is that in the newborn child, as in the adult, the right heart chambers liealmost, if not actually, as much in front of the left chambers as they do to their rightside.

Observations made on sections cut in one plane cannot in themselves reveal all thefeatures of any organ in the body and for this reason sections of thoraces cut in planesother than the transverse are also included, as well as figures showing a dissection ofthe thorax and a section of an ex situ heart. By this means the heart is studied as it liesin situ within the thorax and the relationships it has to other intrathoracic structuresare revealed.

MATERIALS AND METHODS

The human material on which the observations in this investigation were made wasobtained from several hospitals more than 25 years ago. The material was collected assoon as was practicable after it became available and its preparation for sectioning wasbegun as soon as possible. Walmsley (1958) described a method by which transverse

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The heart of the newborn childsections, about 2-5 cm thick, of the thoraces of the newborn child were prepared, andin that same communication reference was made to observations on 0-2 mm thicksections of the chest of the newborn child although no photographs of them wereincluded. Observations made since then have shown that such 0-2 mm sections of theentire child thorax reveal more clearly many features of the in situ heart and greatvessels than can possibly be seen on the thicker 2 5 cm sections.For this study the thoraces of more than 20 newborn children were examined.

Sections were cut in both transverse and vertical planes at thicknesses varying between1 and 2 5 cm. Six thoraces, however, were used for the preparation of 0-2 mm thickserial sections. It was difficult to obtain a complete series of serial sections in whichboth heart and great vessels were free of blood clot, and therefore the figures includedin this study were all taken from one thorax that showed the fewest artefacts of itsviscera.The thin sections were prepared by a modification of the technique described by

Gough & Wentworth (1949) for making thin sections of entire organs in morbidanatomical studies. To obtain thin sections of the entire thoraces of larger fetuses andthe newborn child it was necessary to fix the entire body and to decalcify the bones ofthe thoracic cage. As much blood as possible was removed from the cardiovascularsystem. The perfusion of the vascular system with physiological saline was attemptedeither through an umbilical artery or a femoral artery; perfusion was continued untilthe effluent from an incised femoral vein appeared to be free of blood. Whenexsanguination was complete, perfusion was continued with a 5 % formaldehydesolution.

Specimens were then frozen for 48 hours at -25 °C after having marked in pencilthe skin over the upper border of the manubrium sterni and the cartilaginous xiphoidprocess. This was done in order to provide guides as to the position of that part of thethorax containing the heart and the roots of the great vessels. This block of tissue wasthen removed by cutting through the trunk with a bandsaw using the previously drawnpencil marks as guides, the length of the part of the thorax so excised being, in a fullterm fetus, about 5 cm. The specimen was then washed in running tap water overnightand as much remaining blood as possible was removed from the free surfaces.The tissue was then immersed in 4% formaldehyde solution for about five days to

ensure that fixation was adequate. Decalcification was carried out by immersion in8% nitric acid, changed daily, and after this the tissue was washed for at least fourdays in running water. The specimens were placed in a solution of gelatine as describedby Gough & Wentworth (1949) and thereafter their method for the preparation offrozen blocks was followed. The sections were cut on a MSE (Measuring and ScientificEquipment Ltd) large sledge microtome at 0-2 mm section thickness. All the thintransverse sections included in this work were cut serially from one specimen: these areillustrated in Figures 4, 5, 6, 7, 11, 12 and 13. The sections were unstained andmounted on sheets of Grade 1 Whatman's filter paper. The sections of fetal materialthat are included (Figs. 1, 2) were fixed in 4% formaldehyde solution, decalcifiedand embedded in paraffin wax in a vacuum incubator; 20,um sections were cut ona Leitz rotary microtome, mounted on glass plates and stained with Masson'strichrome.

Several linear measurements of the thoracic cage and intrathoracic structures weremade with a millimetre rule. These included the maximum internal transverse diameterof the thoracic cavity, the sternovertebral distance in the median plane, the maximumanteroposterior dimension of the pleural cavity and the maximum anteroposterior andtransverse dimensions of the heart. These were used to derive cardiothoracic ratiosand thoracic indices as described in the Observations.

95

R. WALMSLEY AND W. S. MONKHOUSE

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Fig. 1. Transverse section of the thorax of 180 mm human fetus passing through both atria (RA, LA)and both ventricles (RV, Lk). Atrial and ventricular septa are approximately in line at an angle ofabout 450 to the median plane. The oesophagus (0) and descending aorta (A) lie behind the leftatrium and in front of an ossifying vertebra. The moderator band (MB) traverses the cavity of theright ventricle. A broken oblique line indicates the vertical plane in which the thorax of Figure 2 wascut. x 2.

OBSERVATIONS

The figures are reproduced as if each section were viewed from above with theanterior surface directed upwards. The right side of the specimen is thus on thereader's right and the left side on the reader's left. This method of presentation issimilar to that of Eycleshymer & Schoemaker (1970) in the re-issue of their classicwork on cross sectional anatomy. The -authors are aware that cardiologists prefertransverse sections of the thorax to be presented with the posterior surface above andthe anterior surface below, as in Walmsley & Watson (1978), but in this anatomicalwork the sections are presented in the manner thought most appropriate for ananatomical journal.

Transverse sections of the thoraces of fetuses in the second half of intrauterine lifereveal that the normal heart has already rotated upon itself so that the atrial andventricular septa, which are nearly in line with each other, lie at an angle of about 450to the median plane (Fig. 1). It is this angulation of the septa that, having occurredmidway through fetal life, establishes that even at that age the in situ fetal heart showsmany of the basic features and relationships characteristic of the postnatal heart. Forexample, it illustrates the manner in which the right atrium forms the right surface ofthe heart whereas the right ventricle forms the greater part of the anterior surface andis certainly the most anterior heart chamber.

96

The heart of the newborn child

Fig. 2. Oblique vertical section of the thorax of 160 mm human fetus sectioned in the plane indicatedby the two parts of the broken line in Figure 1. It passes through the left atrium (LA) and left ventricle(LV) cutting through the left costal cartilages anteriorly and the right ribs posteriorly. The two cuspsof the left AV (mitral) valve are separated by the AV orifice. The flatness of the diaphragm (D) isevident and the liver (L) occupies the upper part of the abdominal cavity. A small part of the thymus(TH) lies above the heart. x 3.

Figure 1 also illustrates another basic feature of cardiac anatomy that will bestressed later and this concerns the dorsal attachment of the atrial septum, which isdisplaced farther and farther to the right and away from the median plane as serialtransverse sections of any post-midterm fetus, child or adult are traced cranially. Thisresults in the left atrium lying not only to the left and behind the right atrium but alsolying above it. In transverse sections of the thorax that pass through the lower or morecaudal part of the heart (Fig. 1) the left atrium is relatively small compared with theright atrium but as the heart sections are followed cranially the left atrium becomesrelatively larger (Fig. 6).The form of the thoracic cavity in older fetuses and young infants differs

considerably from that seen in older children and adults. In the newborn child the ribsare almost horizontal and do not have the obliquity or angulation that is such acharacteristic feature of their orientation in later childhood and in the adult. This isreflected in the flatness of the diaphragm which is attached to the costal cartilages ofthe thoracic outlet. In all older fetuses that have been examined, the flatness of thediaphragm is evident (Fig. 2); it lacks the dome-shaped form that is so characteristicof it after birth.Many vertical sections of fetal, child and adult thoraces have been prepared over

many years to demonstrate the right and left hearts but none of them shows theorientation of the left heart more clearly nor demonstrates in a more convincingmanner the relationship that the left atrium has to the left ventricle than Figure 2. Theorientation of the left heart seen in this specimen is entirely comparable to that seenin the hearts of older infants and adults.The flatness of the diaphragm, to which reference has already been made, is evident

in the newborn child after the anterior wall of the thorax has been removed (Fig. 3).Overlying the upper part of the heart and extending upwards into the root of the neckis the thymus, a dominant structure in the upper part of the chest. The manner inwhich the right and left lobes of the thymus, lying as they do between the two lungs,

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98 R. WALMSLEY AND W. S. MONKHOUSE

Fig. 3. Dissection showing the thorax of newborn child after removal of the anterior walls of thethoracic cage and abdomen. The thymus (TH), which appears to have three lobes in this specimen,overlaps the upper part of the heart and the adjacent great vessels. The diaphragm (D) is relativelyflat. x 1.

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Fig. 4. Transverse section of newborn child thorax at the level of the second costal cartilage. Thethymus (TH) is a prominent bilobed gland which is closely related to cardiovascular structures. Thepulmonary trunk (P) extends backwards from the conus arteriosus (CA) to its bifurcation. To theleft of the pulmonary trunk lies the left auricle and to its right the right auricle (RAU), ascendingaorta (A) and superior vena cava (SC). The ductus arteriosus (DA) lies between the left pulmonaryartery and the descending aorta (D). x 1.

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5 (b) 5 (c)Fig. 5 (a-c). Three Figures (actual size) of parts of transverse sections of newborn child at differentlevels showing the ductus arteriosus and the manner in which it joins the descending aorta. 5(a)shows the ductus (DA) descending between the left pulmonary artery (LP) and the anterolateralsurface of the aorta (A). 5(b) (0-8 mm below (a)) shows the ductus entering the aorta. 5(c) (3 mmbelow (b)) shows the increase in size of the aorta (A) below the entrance of the ductus. Sections havepassed through the intervertebral disc regions of the vertebral column (v). x 1.

embrace the cardiovascular structures is convincingly seen in transverse sections of theupper part of the child thorax (Fig. 4).

Several features regarding the great vessels in the superior mediastinum of thenewborn child (Fig. 4) show considerable differences from those seen in the upper partof the thorax of the adult. Some of these are of considerable interest to clinicians andthese include the angulation of the pulmonary trunk and the ascending aorta and therelative sizes of the ascending aorta and the superior vena cava (Fig. 4).

In all newborn fetuses that have been examined the pulmonary trunk extends almostdirectly backwards from the conus arteriosus (infundibulum) of the right ventricle toits bifurcation into right and left pulmonary arteries. The conus arteriosus lies in theanterior part of the mediastinum and the pulmonary trunk, in order to attain itsbackward inclination, forms almost a right angle to the ascending conus at its originfrom the conus. It can also be seen (Fig. 4) that whereas the left pulmonary arterypasses backwards to the hilum of the left lung at an angle of about 450 to the medianplane, the right pulmonary artery has a more direct course to the right lung as it passesbehind the ascending aorta and the superior vena cava. The ascending aorta passesalmost vertically upwards (Fig. 4) and, unlike that in the adult, shows no inclinationto the right as it ascends closely applied to the right side of the pulmonary trunk andanterior to the right pulmonary artery. Also, the ascending aorta is smaller in diameter

99

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6Fig. 6. Transverse section through newborn child thorax at the level of the fourth ribs (4R) whichshows all four chambers of the heart. The atrial septum separating the two atria (RA, LA) is theseptum primum and in it is a small ostium secundum. The septal cusp of the right AV valve (SC) isattached to the right side of the membranous ventricular septum. The anterior cusp of the left AVvalve (AC) projects into the left ventricle (LV). The descending aorta (A) lies behind the left atriuminto which both a right and a left pulmonary vein (PV) open. The right ventricle (RV) forms thegreater part of the anterior surface of the heart. x 1.

than the pulmonary trunk and this may be associated with the presence of the ductusarteriosus which connects the left pulmonary artery with the descending aorta.The superior vena cava in Figure 4 has been sectioned almost immediately above its

entrance into the sinus venarum of the right atrium and lies closely behind the rightauricle. The superior vena cava, draining as it does the relatively large upper part ofthe body, is a prominent vessel on account of its size compared with the smallerascending aorta. The close relationship that the superior vena cava, the pulmonarytrunk and the intermediate ascending aorta bear to each other is apparent in Figure4.The ductus arteriosus is displayed in parts of three transverse sections of the

newborn child thorax (Fig. 5) showing some of the features that are typical of thenormal ductus. In this series of sections it arises from the left pulmonary artery at itsorigin from the pulmonary trunk about 8 mm to the left of the median plane andpasses downwards between the left pulmonary artery and the descending aorta (Fig.5a). It is important to note that the ductus is related to the anterolateral wall of thedescending aorta and it is this wall of the aorta that the ductus perforates where thetwo vessels join each other (Fig. Sb). At the upper part of the junction of the twovessels (Fig. Sb) there is an apparent constriction between them but at a slightly lowerlevel there is no evidence of this and the two vessels are in free communication witheach other. In this series of serial sections the ductus is about 6 mm long. The greatestexternal diameter of the ductus is about 5 mm and this is slightly less than the diameter

100


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Fig. 7. Transverse section of newborn child thorax 2 5 mm higher than Figure 6. The membranouspart of the interventricular septum (M) lies between the two ventricles (RV, Lk). One cusp of theaortic valve lies between the membranous septum and the anterior cusp of the left AV valve (AC):the two principal cusps of this valve appear fused in this section because they are joined by acommissural cusp. The ostium secundum (arrow) lies between the right and left atria (RA, LA).x 1-5.

of the descending aorta immediately above the level at which the two vessels join (Fig.5 a). The narrow part of the aorta immediately above its junction with the ductusrepresents the aortic isthmus and, as it is of considerable pathological interest,reference will be made to it in the Discussion. Below the entrance of the ductus, theaorta increases in calibre and its external diameter is about 7 mm (Fig. Sc); noanatomical valvular mechanism has been observed at the junction of the twovessels.

Reference has already been made to the posterior attachment of the atrial septuminclining to the right as successive serial sections of the thorax are followed upwards;this results in the left atrium lying above the right atrium as well as lying to its left sideand behind it. A feature of human cardiac anatomy is that the pulmonary veins,usually two from each lung, enter the uppermost part of the left atrium. In thenewborn child the veins have an extremely short extrapulmonary course and openalmost directly into the left atrium (Fig. 6). It is obvious that the position of theposterior attachment of both the atrial septum primum and the septum secundum isin accordance with the right pulmonary veins passing unimpeded into the left atrium.It is unfortunate that the ostia of the pulmonary veins show a constriction at theiropenings into the atrium (Fig. 6) because it is well recognised that the pulmonary veinsare in free communication with the atrium and that there is no valvular mechanismassociated with them or their tributaries.

Figure 6 also displays the membranous part of the ventricular septum in whichventricular septal defects may occur. The membranous septum varies considerably insize but is seen to lie behind and above the muscular part of the ventricular septum,and on its right side gives an attachment to the septal cusp of the right AV valve. It

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8Fig. 8. Section through ex situ heart of newborn child to show continuity of the membranousventricular septum (M) with the right lateral wall of the ascending aorta (A). The septal cusp of thetricuspid valve (S) is attached to the right side of the membranous ventricular septum. Note themanner in which the anterior cusp of the left AV valve (AC) projects into the cavity of the leftventricle (LV). Right and left atria (RA, LA) lie above corresponding ventricles in this ex situ heart.x3.

is well recognised that owing to this attachment of the septal AV cusp the anterior andlower part of the membranous septum separates the two ventricles from each other,whereas the posterior and upper part intervenes between the left ventricle and the rightatrium and is appropriately designated the atrioventricular septum. In most sectionsof the newborn infant that have been examined, an interventricular part of themembranous septum was found to be present. This is not in accordance with the viewsexpressed by Allwork & Anderson (1979).As sections in this series are traced upwards, the anteroposterior length of the

membranous ventricular septum increases and its close relationship to the aortic valveis evident (Fig. 7). The upper and most anterior part of the cavity of the left ventriclelies between a muscular and membranous part of the ventricular septum in front andthe anterior cusp of the left atrioventricular valve behind (Fig. 7). It is this region ofthe ventricle that is designated the 'aortic vestibule' by anatomists but, on account ofthe blood flow, is customarily called by clinicians the left ventricular outflow tract.This leads directly upwards to the root of the aorta and this relationship of outflowtract to aorta may be seen in Figure 7 where the membranous septum and an aorticvalve cusp are included in the same section.

It has already been stated that sections of the thorax cut in one plane only cannotdisplay all the features of an anatomically complex organ such as the heart, and forthis reason a section of an ex situ heart of a newborn child has been included (Fig. 8)to show more convincingly the relationships of the membranous ventricular septumand the boundaries of the left ventricular outflow tract. This ex situ heart was cut inan oblique vertical plane at right angles to the ventricular septum and it illustrates how

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Fig. 9. Coronal section of the thorax of newborn child with the heart in situ viewed from the front.It shows the formation of the atrial septum by the septum primum (SI) and septum secundum (S2).The superior vena cava (SC) enters the upper part of the right atrium (RA) and the larger inferiorvena cava (IC) enters the lower part. The thin septum primum is deficient in its upper part (ostiumsecundum): overlying this on the right is the thicker septum secundum. Between the septa is theforamen ovale (arrow). The ascending aorta (A) lies above the two pulmonary arteries. x 2.

the membranous part of the ventricular septum becomes continuous with the rightanterolateral part of the aortic annulus that gives attachment to the anterior cusp ofthe aortic valve. The nomenclature advocated for the cusps of the aortic valve in theNomina Anatomica is not in accordance with the position of the cusps in the in situheart in the newborn child or in later postnatal life. The names of the aortic valvecusps and sinuses, and the position of origin of the two coronary arteries, is of suchanatomical and clinical interest that they are considered in some detail later (Figs. 11,12).Also illustrated in Figure 8 is the manner in which the anterior cusp of the left AV

valve separates the inflow atrioventricular tract of the left ventricle from its outflowtract. The portion of the muscular ventricular septum that participates in theformation of the left ventricular outflow tract is characteristically smooth-walled as itis throughout fetal and postnatal life. This section also shows that although the freewalls of the two ventricles are of almost the same thickness, the compact leftventricular myocardium is in striking contrast to the trabeculated structure of that ofthe right chamber.The formation of the atrial septum and the foramen ovale is well known and Figures

9 and 10 display several features of the septum in the newborn child. One of the mostimportant relationships in the heart of the fetus and the newborn child is the proximityof the fossa ovalis to the opening of the inferior vena cava into the right atrium. Thesingle cusped valve of the inferior vena caval opening is continuous with the anteriorlimb of the limbus fossa ovalis and it directs most of the blood from the inferior venacava towards the thin-walled floor of the fossa ovalis and the foramen ovale.Remnants of this valve cusp may be seen on the right side of the ostium of the inferiorvena cava in Figure 9.The right and left coronary arteries arise from two of the three aortic sinuses that

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Fig. 10. Oblique vertical section through the right atrium (RA) and ventricle (RV) of newborn childheart viewed after removal of its right side. The septum secundum (82) has an arched lower border,the limbus fossae ovalis, and overlies the right side of the septum primum (SI). The septum primumforms the floor of the fossa ovalis and is fenestrated in its upper part. x 2-2.

constitute the lowest part, or root, of the ascending aorta and it should be noted thatthe sinuses giving rise to these coronary arteries lie adjacent to the pulmonary trunk.In the Nomina Anatomica the cusps of the aortic valve are given names that would beappropriate to them only if an ex situ heart were held in the hand and rotated through450 so that the atrial and ventricular septa lay in a sagittal plane, but which arecertainly not in accordance with their positions in the in situ heart.

All observation7s that have been made on in situ normal human hearts after birthhave shown that one aortic cusp lies in front of the other two and may appropriatelybe named the anterior cusp, whereas the two that lie behind it may be called the rightposterior and left posterior. The guide to the position of the cusps in both in situ andex situ hearts is indicated by the origins of the right and left coronary arteries whichusually arise near the middle of the aortic sinuses at or just above the level of the freeedges of the relative aortic cusps. The right coronary artery arises from the anteriorsinus (Fig. 11) and the left coronary artery from the left posterior sinus (Fig. 12). Onaccount of this relationship the anterior sinus is customarily, and reasonably, calledby cardiologists the right coronary sinus, the left posterior sinus is called the leftcoronary sinus and the right posterior sinus is called the noncoronary sinus. The three

104

The heart of the newborn child 105

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Fig. Transverse section of the thorax of niewborn child at the level of the anteri'or parts of the

third ribs (3R). The right coronary artery (RC) arises from the anterior aortic sinus and passes

forward between the conus arteriosus (CA) and the right auricle (RAGU). The transverse pericardialsinus lies between the aorta (A) in front and the left atrium (LA) behind. x 1-2.

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12Fig. 12. Transverse section of the thorax of newborn child at the level of the anterior parts of thethird ribs (3R) 0-2 mm higher than Figure 11. The left coronary artery (LC) arises from the leftposterior aortic sinus and passes between the conus arteriosus (CA) and the left auricle (LA U). Theleft atrium (LA) lies behind the aorta (A) x 1-2.

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106 R. WALMSLEY AND W. S. MONKHOUSE

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13(b)Fig. 13 (a-b). Two transverse sections of the thorax of (a) newborn child and (b) adult man. (a)(actual size) is at the level of the fourth ribs and is the entire section from which Figure 6 shows themost anterior part of the thorax. (b) An adult thorax sectioned as the level of the fourth costalcartilages, reproduced x 044 so that the sternovertebral measurement is the same as that in (a)(55 mm) for ease of visual comparison. Both sections show all four chambers of the heart.

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Table 1. Cardiothoracic ratios in newborn and adult humans derivedfromFigure 13a, b

(Using maximum transverse and anteroposterior linear dimensions.)

Using transverse dimensionsNewborn child 0 57Adult 047

Using anteroposteriordimensionsNewborn child 0-66Adult 0-48

Table 2. Thoracic indices in the fetus, the newborn child and the adult

180 mm fetus (from Fig. 1) 0-80Newborn child (from Fig. 13 a) 0 79Adult (from Fig. 13 b) 0-76

cusps of the aortic valve are thus conveniently designated the right coronary, the leftcoronary and the noncoronary.

Figure 13 allows a direct comparison to be made between the internal form of thethoraces of a newborn child and of an adult man. The newborn thoracic cavitymeasures 55 mm from the posterior surface of the sternum to the anterior surface ofthe intervertebral disc; in the adult specimen this measurement is 125 mm but thephotograph of it was reduced in size so that its sternovertebral measurement is also55 mm. In both cases the angle of the line of the cardiac septa with the median sagittalplane is about 450, showing that there is no change between birth and the adultcondition.

Table 1 gives the cardiothoracic ratios in the specimens shown in Figure 13 a, b. Theratio is normally taken from transverse measurements of the heart width/thoracicwidth between internal aspects of the rib cage. In the newborn child it is 0 57 and inthe adult 0 47. For interest, the ratios derived from anteroposterior dimensions arealso included in Table 1. The anteroposterior internal thoracic measurement used wasthe maximum anteroposterior extent of the thoracic cavities. These ratios are in thenewborn child 0-66 and in the adult 0-48.The thoracic index is the greatest anteroposterior thoracic dimension expressed as

a proportion of the greatest transverse dimension at the same level and Table 2 showsthoracic indices in a 180 mm human fetus (Fig. 1) and in newborn and adult humanthoraces (Fig. 13 a, b). The indices are in the fetus 0-80, in the newborn child 0 79, andin the adult 0-76. It is noteworthy that the anterior projection of the vertebral bodieswould affect this index markedly if as the anteroposterior measurement thesternovertebral distance were taken; the indices would then be in the fetus 0-61, in thenewborn child 0-63, and in the adult 0-52.

DISCUSSION

The size of the transverse sections, reproduced at actual size in Figures 4, 5, 6 and13a, and the measurements of intrathoracic viscera are consistent with the childhaving a weight of about 3 kg. The general form of the heart is that of a blunt conewith a base (basis cordis) and an apex (apex cordis) but its exact form is, of course,

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R. WALMSLEY AND W. S. MONKHOUSEdependent on its functional state. Most illustrations show the heart in diastole, thephysiological state in which it is customarily described in anatomical works (Walmsley,1929).

All oblique vertical sections of older fetal (Fig. 2) and postpartum thoraces whichpass through the right or left heart invariably show that the heart lies much morenearly in the horizontal than in the vertical plane (Walmsley, 1958, 1960). For thisreason transverse sections of thoraces of infants cut about the level of the fourth costalcartilages (Figs. 6, 7) show all four chambers of the heart with the two atria lyingbehind and to the right of their respective ventricles. It is very noticeable in thesesections that the left atrium forms the greater part of the base of the heart and this isreflected by the extremely short extrapulmonary course of the pulmonary veins.

In a comprehensive anatomical study of the newborn child, Crelin (1969) hasemphasised the great differences that may occur in the size and weight of newbornchildren of the same gestational age though he was able, from his study of sixteenanatomically normal newborn infants of between8- and 91 months gestation, to createwhat he called an average newborn infant. In his atlas, consisting of reproductions ofdrawings of organs and dissections of infants, some thoracic specimens are reproducedat actual size, but in this atlas the heart is only about three quarters of the size foundin the present study. It should be recognised, though, that the definition of the termnewborn is important: Ringertz (1983) has described the considerable changes thatoccur in cardiac size during even the first 48 postnatal hours as a result of closure ofthe ductus arteriosus.The important relationship between the ductus arteriosus and the aorta is seen to

advantage in Figures 4 and 5. The ductus, having arisen from the root of the leftpulmonary artery, descends on the anterolateral side of the aorta before joining it.This is in accordance with the description given by Noback & Rehman (1941) in awork on dissections ofhuman fetuses and infants which did not, however, allow therelationship of the ductus to the aorta to be as convincingly displayed as in the presentwork. The ductus arteriosus in the newborn child is usually about 10 mm longalthough in the transverse sections in this study it is calculated to be only 6 mm long.This may be due to shrinkage occurring during preparation of tissues for sectioning.It is well recognised, however, that in newborn children the ductus shows greatvariation in its form, length and diameter and this receives considerable attention inworks on cardiovascular pathology (Edwards, 1960; Hudson, 1965). It should also beemphasised that whereas the ductus passes downwards to join the descending aorta,the ligamentum arteriosum in the postnatal thorax passes upwards and backwards tobe attached to the under surface of the arch of the aorta immediately beyond the originof the left subclavian artery.Evans (1964) has stated that during the first three postnatal months there is a slight

and gradual narrowing of the aortic isthmus (between the origin of the left subclavianartery and the junction with the ductus arteriosus) and that this disappears during thefourth month. In a critical work on the size and histological structure of the aorticisthmus in newborn children, van Meurs-van Woezik & Krediet (1982) stress thatthere is great variation in the degree of this narrowing which may be much less thanthat usually described. Such variation means that no deductions should be maderegarding the relative size of the larger vessels as seen in a single transverse section ofthe upper part of the thorax (Fig. 4) though it is nevertheless interesting to note thatin this section the pulmonary trunk is slightly wider than the ascending aorta which,in turn, is considerably larger than the descending aorta proximal to its junction withthe ductus arteriosus (Fig. 4). The increase in size of the aorta distal to this junctionis evident in other sections (Fig. 5). Although values for the diameters of the great

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The heart of the newborn child 109arteries are not presented in this work, they were entirely in accordance with thosedescribed in a recent detailed study (van Meurs-van Woezik, Debets & Klein,1987).The pathological changes that may occur in the aortic isthmus have been classified

by Ho & Anderson (1979) into two different types of obstructive lesions that mayoccur separately or together. The first, isthmic coarctation, is an abrupt curtain-likelesion that encircles the aorta in the region of the ductal-aortic junction and containstissue characteristic of the ductus arteriosus. The second pathological lesion is tubularor isthmal hypoplasia, considered by Bremer (1948) to be a persistence of thenarrowing normally present in the isthmus in fetal life.

Thoracic shape in the living person is often defined by means of the thoracic indexderived as described earlier. Scammon & Rucker (1921) hold that the index is anexpression of the relative depth of the chest. These measurements are customarilymade on the living person but as they take no account of the considerable variationin the amount of subcutaneous tissue, they cannot truly be compared with similarmeasurements made on dead infants who both before and after fixation have probablylain in the supine position. The distortion of the external thoracic form that occurs inthe newborn infant cadaver is evident in the transverse sections used in this studywhere the thorax has lost its customary rounded form and its entire posterior surfaceis flat (Fig. 13 a). Although this distortion affects the soft tissues of the body there isno evidence that it influences the rounded form of the thoracic cage which is associatedwith the horizontal orientation of the ribs at the time of birth. After birth the thoraxbecomes more elliptical owing to the change in the form of the ribs and their becomingmore obliquely orientated: these changes continue until about puberty (Gardner,Gray & O'Rahilly, 1969). The change in the orientation of the ribs with age is obviousin comparing radiographs of infants and older people, and it is equally apparent intransverse sections (Fig. 13) where in the infant (Fig. 13 a) only one rib is sectioned,whereas in the adult (Fig. 13 b) there are five ribs in the section.The values for thoracic indices in the present work (Table 2) are at variance with

those quoted by Trotter & Peterson (1966) who state that in the fetus the sagittaldistance is greater than the transverse, thus giving an index greater than 1 (not 0-8 asin Table 2). They also hold that at birth the value is about 0 9 (not 0-76 as in Table2). Unfortunately, Trotter & Peterson state neither their method of derivation of theindices nor the level at which they were taken. The thoracic index, when applied to theliving person, takes no account of the manner in which the bodies of the vertebrae andthe intervening discs project anteriorly into the thoracic cavity to give it a reniformappearance (Duckworth, 1904). This is very obvious in transverse sections of thethorax and it is clear that if the sternovertebral measurement were used for thethoracic index instead of the maximum anteroposterior dimension, the index wouldchange markedly as shown above. Therefore, if the thoracic index is to be used, themanner of its derivation must be clearly stated.Although it has been reported that, relative to total body weight, the weight of the

heart changes little after birth (Rakusan, 1984) the relationship of the size of the heartto that of the thoracic cavity changes. In this study the cardiothoracic ratio, calculatedfrom the linear transverse measurements (the recognised method), is 0-57 in thenewborn and 0 47 in the adult. These values fall well within the normal limits given byBakwin & Bakwin (1935). Interestingly, Cooper & O'Rahilly (1971) found in a studyon 17 mm CR human embryos that the ratio (from transverse measurements) was0-61. The ratios from anteroposterior measurements (Table 1) are not normallycalculated; they are 0-66 in the newborn and 0'48 in the adult.

Official anatomical nomenclature remains a problem. Williams & Warwick (1980)

R. WALMSLEY AND W. S. MONKHOUSEare conscious of the differences in cardiac terminology used by preclinical teachersand their clinical colleagues and in the section on the heart they state 'account will betaken not only of the official nomenclature... but in many instances, terms stemmingfrom widespread clinical practice will be given as alternatives'. In an earlier editionof the same textbook (Davies, 1967) the cusps of the aortic and pulmonary valves werenamed according to their position in the in situ heart; this terminology did notconform with the nomenclature of the then current Nomina Anatomica. The authorstrust that the approach adopted in this study might contribute to the adoption of ananatomical nomenclature for the heart that is acceptable to both anatomists andclinicians.

SUMMARY

This study of the newborn child heart is based mainly on observations made on thin(02 mm) serial transverse sections of an entire thorax. Several features of thecardiovascular system associated with the fetal circulation are discussed. Despiteconsiderable differences between the cardiac form in the newborn child and that inlater postnatal life, the orientation of the heart in the newborn child has alreadyattained many of its postnatal features. For example, it lies more nearly in thehorizontal than the vertical plane and the atrial and ventricular septa are in line witheach other at an angle of about 450 to the median plane. This angulation of the septadetermines that the right atrium and ventricle lie as much in front of the correspondingchambers of the left heart as they do to their right side. The cardiothoracic ratio andthoracic index are derived from a section through the thorax of the newborn child andthese values are compared with those from a section through an adult man. A majorpurpose of this communication is to make a plea that the nomenclature given to allcardiac structures, even in the newborn child, should be consistent with the heart insitu in the anatomical position.

The authors wish to express their thanks to Professor D. Brynmor Thomas of StAndrews for his kindness in making available to them the facilities of his Department.They also wish to thank Professor R. E. Coupland for much helpful discussion duringthe preparation of this work and for providing financial and secretarial support. Thesections of the thorax were prepared by Mr R. J. Stuart and the photographs are thework of Mr K. J. Thom, both of St Andrews, and to these technicians we extend ourthanks.

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