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Journal of the Anatomical Society of India

Cardiac Anatomy - Viewed through the Eyes of Clinicians

Author(s): Mahendrakar M.

Vol. 53, No. 2 (2004-07 - 2004-12)

Seth G.S. Medical College & K.E.M. Hospital, Parel, Mumbai.

Abstract:

Anatomy is the basis of Medicine and Surgery. There is an unfortunate hiatus between the Anatomy, which the students learn in the preclinical year and that which is later encountered in the laboratory, wards and operation theatres. Here these facts are emphasized, that how an anatomist would dissect the heart and name various structures and how a pathologist would dissect the heart and use the terminology of the various structures as per the requirement of clinicians.

Clinicians would distinguish right and left ventricles on the basis of apical trabeculations and valves, while an anatomist would differentiate on the basis of ventricular wall thickness and chamber shape which do not necessarily exist in malformed hearts. Such facts which students are expected to carry with them during their graduate and postgraduate study need to be emphasized early in their formative years.

Key words: Anatomical terminology, cardiac position, visceral sidedness, morphologic atrium, morphologic ventricle, auricle.

Role of an Anatomist:

Anatomy is a dynamic and exciting discipline. The aim of an Anatomist is to provide the preclinical students better understanding of Human Anatomy. More importantly it should be of value to students and to practitioners throughout their professional life. Also, knowledge of anatomy is required by students entering professional courses allied to medicine. Therefore, the terminology employed should be that which is most frequently used in clinical practice,Message & Anderson (1996).

The Clinicians evaluate the heart from a diagnostic and therapeutic point of view. But from Anatomist point of view, the method should aim at a systematic study which covers all the structural, functional and developmental details.

Unifying Concepts of Cardiac Anatomy:

The heart is considered of having three segments - atriums, ventricles and great arteries. Each of which is partitioned in two components - right sided and left sided. Atrioventricular valves connect atriums to ventricles and semilunar valves connect ventricles to great arteries.

The clinicians follow a sequential segmental method for evaluation of the heart, Damjanov & Linder (1996). The evaluation commences with determination of cardiac position and visceral sidedness. Following which right sided and left sided structures at each level are evaluated, from the stand point of their morphology, relative position, connections to proximal and distal segments, shunts, obstructions and valvular regurgitations.

Cardiac position - In the chest the heart can be positioned on left side which is normal, right side or midline. Determined by the direction of the ventricular apex, the position can be leftwards - levocardia, rightwards - dextrocardia or inferior directed - mesocardia. The heart can be displaced by adjacent structures as well and the position is then termed as levoposition, dextroposition or mesoposition. Visceral sidedness - The three systems in the body cardiovascular, respiratory and gastro-intestinal system are asymmetric, so sidedness or handedness occur and require to be evaluated separately.

Cardiac sidedness is determined by the position of the morphologic right atrium, determined by the size and shape of the auricular appendage (vide Table II and Fig. 1A). It is not decided by direction of ventricular apex, position of ventricles or of great arteries or by sidedness of noncardiac viscera. Pulmonary sidedness is determined by the position of the morphologic right and left lungs. Gastro-intestinal sidedness is determined by position of the liver and inferior vena cava, which is usually opposite that of stomach, pancreas, spleen, abdominal aorta.

Sidedness may be normal - Situs Solitus, its mirror image - Situs Inversus, Isomeric or indeterminate - Situs Ambiguus and when all the three systems are mirror image of normal - Situs Inversus Totalis, Damjanov & Linder (1996). Right isomerism is bilateral right sided symmetry while left isomerism is bilateral left sided symmetry. Thus in right isomerism there is bilateral morphologic right atrium and the spleen is absent - asplenia syndrome. Table I evaluates sidedness of the three systems of the body.

Dissection of the Heart - There are several methods of dissecting the heart, some better adopted than others to display certain features, to preserve abnormalities, to provide adequate samples for microscopic sections or for teaching purposes, Ferrer (1977), Romanes (1998) & Silver (1983). The prosector should proceed systematically with a chosen method and open the heart by a method that will best display its features with the least destruction of valves, vessels and the conduction system. The following method of dissection can be easily applied to congenitally malformed heart as well as anatomically normal heart, Ferrer (1977)

Fig. 1

Missing ImageMissing Image

A - Large pyramidal right auricular appendage
B - Small fingerlike left auricular appendage

Fig. 2

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A - Showing first three cuts opening the right side of the heart.
B - Showing next three cuts opening the left side of the heart

Table - I: Visceral sidedness or handedness

  Situs Solitus Situs Inversus Situs Ambiguus
Right Isomerism Left Isomerism
Gastrointestinal system Liver on right side
Spleen on left side
Liver on left side
Spleen on right side
Liver midline
Asplenia
Liver midline
Polysplenia
Cardiovascular system Morphologice
Right Atrium on right side
Morphologic
right artium on left side
Bilateral morphologic Bilateral morphologic
  Morphologic
Left Atrium on left side
Morphologic
Left Atrium on right side
Right Atrium Left Atrium
Respiratory system Morphologic
Right lung on right side
Morphologic
Right lung on left side
Bilateral morphologic Bilateral morphologic
  Morphologic
Left lung on left side
Morphologic
Left lung on right side
Right lung Left lung

1st Cut - The right atrium is opened by cutting obliquely from the inferior vena cava to the tip of the right auricular appendage (Fig. 2A).

2nd Cut - The right ventricle is opened by cutting through the tricuspid valve ring along the inferior margin of the heart to the apex (Fig. 2A).

3rd Cut - The pulmonary outflow tract is opened by a cut on the sternocostal surface which starts from the 2nd cut at the apex and going through the pulmonary orifice to the pulmonary trunk. The cut is made near the interventricular septum so, that the anterior papillary muscle is preserved (Fig. 2A).

4th Cut - The left atrium is opened by cut through the right and left inferior pulmonary veins (Fig. 2B).

5th Cut - The left ventricle is opened by cutting through the center of 4th cut along the left margin to the apex (Fig. 2B).

6th Cut - There are two methods to open left ventricle out flow tract. First method - the left ventricle out flow tract is opened by a cut on the sternocostal surface extending from the apex parallel and close to the interventricular septum through the aortic orifice (Fig. 2B). In this technique the left coronary artery is cut but the mitral valve is saved. In the second method the left ventricle out flow tract is reached by incising through the septal leaflet of the mitral valve. In this technique the mitral valve morphology is disturbed but the left coronary artery is saved.

Morphology of Cardiac Segments - The anatomical criteria of distinguishing morphologic right atrium and left atrium are connections of caval veins, identification of limb of the oval fossa and the shape of auricular appendage. Refer Table II.

Table - II: Morphologic Atrium

Morphologic right atrium Morphologic left atrium
-Large pyramidal appendage -Small fingerlike appendage
-Limbus fossa ovalis -Ostium secundum
-Crista terminalis -No Crista terminalis
-Pectinate muscles -No pectinate muscles
-Receives caval veins -Receives pulmonary veins and coronary sinus

The right auricular appendage is large pyramidal in shape with a broad base and an apex (Fig. 1A). The left auricular appendage is small fingerlike with narrow base and a wider and scalloped margin (Fig. 1B). Atrioventricular valves travel with their respective ventricles. A morphologic tricuspid valve is joined to a morphologic right ventricle whereas mitral valve is connected to morphologic left ventricle. Refer Table III.

Table - III: Morphologic atriventricular valves

Morphologic Tricuspid valve Morphologic Mitral valve
-Low septal annular attachment -High septal annular attachment
-Septal cordal attachments -No septal cordal attachments
-Triangular orifice -Elliptical orifice
-Three leaflets and commisures -Two leaflets and commisures
-Three papillary muscles -Two large papilary muscles
-Empties into right ventricle -Empties into left ventricle

Thus if both atrioventricular valves join the left ventricle they both exhibit mitral morphology. The anatomic features that distinguished between morphologic right and left ventricles are the nature of the apical trabeculations, the morphology of the atrioventricular valve and the state of continuity between the atrioventricular and semilunar valves. The difference in ventricular wall thickness and chamber shape do not necessarily exist in malformed or diseased heart (Refer Table IV).

Fig. 3:

Missing ImageMissing Image

A - Interior of right ventricle showing large coarse apical trabeculations.
B - Interior of left ventricle showing small fine compact apical trabeculations

Fig. 4:

Missing Image

Right ventricle outflow tract.
Conus part with pulmonary valve
C = Conus. SL = Semilunar valve, AV = Atrioventruclar valve

Table - IV: Morphologic ventricle

Morphologic right ventricle Morphologic left ventricle
-Receives tricuspid valve -Receives mitral valve
-Tricuspid-pulmonary valve -Mitral-aortic valve continuity discontinuity
-Muscular outflow tract -Muscular-valvular outflow tract
-Septal and parietal bands -No septal and parietal bands
-Large apical trabeculations -Small apical trabeculations
-Coarse septal surface -Smooth upper septal sufrace

Right ventricle has large apical trabeculations and a coarse septal surface (Fig. 3A), while left ventricle has small apical trabeculations and a smooth upper septal surface (Fig. 3B). Conus cordis forms the outflow tract of the ventricle which separates the semilunar valve from the atrioventricular valves. This conus is present only in right ventricle in human. Absence of conus in left ventricle makes the mitral valve continuous with aortic valve and the conus musculature separates the tricuspid from the pulmonary valve (Fig. 4). High septal annular attachment of mitral valve and low septal annular attachment of tricuspid valve results in membranous septum, separating right atrium and left ventricle.

The semilunar valve is named after the artery into which it empties and not the ventricle from which it arises.

Conclusion:

Development is increasing at an unprecedented rate. The past decade has witnessed revolution in research, diagnosis and therapy. A torrent of new findings and techniques have revolutionized clinical medicine. Medical education and role of anatomy instruction within it are continuously changing, as the educational models and health care management evolves. Therefore an Anatomist requires to keep pace with the development.

Nomenclature and method of evaluation of the heart according to the clinicians - Pathologists, Paediatricians, Paediatric surgeons, Cardiothoracic surgeons, Cardiologists & Radiologists is uniform, but only the Anatomist differ. Also by accepting the uniform terminology, an Anatomist can get valuable input by taking part in multidiscipline discussion.

Ultimately, the teachers of anatomy failed because we did not present the new anatomy; which was dictated by new technology i.e. CT scan, MRI, sonogram. Rather, we left this important work to the radiologist. We did not embrace the technological triumph and, as a result, "we lost", quoted by John E.Skandalakis, (M.D., Ph.D., F.A.C.S.) in the Journal 'The American Surgeon' Vol.65 No.2, Feb 1999.

Acknowledgement:

Author wish to thank Dr. Pradeep Vaideshwar from the Department of Pathology and Dr. K. Shyamkishore from the Department of Anatomy, Seth G.S. Medical College and K.E.M Hospital, Parel, Mumbai 400012. for their helpful assistance.

References:

  1. Damjanov, I., Linder, J.: Anderson's Pathology In : Congenital Heart Disease. 10th Edn.; Vol - 1. Mosby. United States of America, London. pp 1339-1396. (1996).
  2. Ferrer - Brown, G.: A Colour Atlas of cardiac Pathology. In : Removal and Examination of the Heart, The Normal Adult Heart. 1st Edn.; Wolfe Medical Publications Ltd. London. pp 823 (1977).
  3. Message, M.A., Anderson, R.H. (1996) : Towards a New Terminology for Clinical Anatomy, With Special Reference to the Heart. Clinical Anatomy. 9(5): 317-329.
  4. Romanes, G. J.: Cunninghams Manual of Practical Anatomy. In : The Cavity of Thorax. 15th Edn; Vol 2. Oxford University Press. Oxford, New York, Tokyo, pp16-77 (1998).
  5. Silver, M.D.: Cardiovascular Pathology. In : Gross Examination and Structure of the Heart. 1st Edn.; Vol 1. Churchill Livingstone Inc. New York, London. pp 1-30. (1983)
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