**2. Surgical anatomy of the heart**

which forms the distal end of the developing heart tube. The dorsal aorta on the right usually

The first arch disappears and the 2nd persists as stapedial artery which is not of clinical significance. The third arch forms the internal carotid artery on both the sides and is called the carotid arch. The 4th arch on the right forms the right subclavian artery as far as the origin of the internal mammary branch and the left 4th arch forms the arch of aorta between the left carotid artery and the termination of ductus arteriosus. The 5 th arch disappears on both sides. The proximal part of the right 6th arch forms the right pulmonary artery and the distal part disappears. The proximal part of the left 6th arch forms the left pulmonary artery and the distal

Double aortic arch which is the commonest arch anomaly causing trachea and oesophageal compression occurs as a result of persistence of dorsal aorta. The recurrent laryngeal nerve loops around the 6th arch and hence goes around the ductus arteriosus on the left side and the subclavian artery on the right side. Persistence of the ductus arteriosus results in patent ductus arteriosus (PDA) and its excessive resorption can result in coarctation of aorta or stenosis of

disappears and the dorsal aorta on the left forms the descending aorta.

part persists as the ductus arteriosus.(figure 2)

224 Principles and Practice of Cardiothoracic Surgery

**Figure 2.** Development of aortic arches

left pulmonary artery. [5]

The heart is enclosed in a pericardial sac. The pericardial cavity is the space between the inner lining of the fibrous pericardium and the surface of the heart.There are two recesses in the pericardial cavity lined by serous pericardium, the first is the transverse sinus behind the great arteries in front of the atria and is in free communication with the pericardial cavity on either side. The second is the oblique sinus, a blind ending cavity behind the left atrium.

The cardiac mass is 1/3rd to the right and 2/3rd to the left of midline. The ventricle is a three sided pyramid with diaphragmatic, anterior and left surfaces. The right sided margin is the acute margin and the left is the obtuse margin [7].

#### **2.1. The morphological right atrium**

The right atrium has 3 components-the appendage, venous sinus and the vestibule. (figure 3)The junction between the appendage and the venous sinus is marked by the prominent terminal groove. The groove internally corresponds to the crista terminalis, from which the pectinate muscle originates. The extensive array of pectinate muscles serves as one of the markers of the morphologic right atrium. Parallel and posterior to the groove is the second deeper groove between the right atrium and the right pulmonary veins. Dissection into this deep interatrial groove (Waterston's or Sondergaard's groove) permits incisions to be made into the left atrium (the *classic posterior approach* to the left atrium).

The sinus node lies in the subepicardial position at the cranial part of the terminal groove, and is a spindle-shaped structure which lies lateral to the superior cavoatrial junction. The artery to the sinus node arises from right coronary artery (55%) or cirumflex coronary artery (45%).

The septum between the right and left atria is formed by the floor of the oval fossa and its adjacent anteroinferior muscular rim. The superior rim or the septum secundum is formed by deep interatrial fold extending between the systemic and the pulmonary veins. Larger part of the anterior atrial wall is related to the aortic root (the torus aorticus). It is important to realize that the true atrial septum is rather small and it is easy to go outside the heart when attempting to gain access to the left atrium through the septal approach. Because of the infolding of the interatrial groove, access to the left atrium can be gained by approaching through the right atrium and incising superiorly within the fossa *(The septal superior approach*). [8]

The triangle of Koch which contains the atrioventricular (AV) node is an area of major surgical significance. The triangle is demarcated by the (a) the tendon of Todaro, (b) the attachment of the septal leaflet and (c) the orifice of the coronary sinus. The tendon of Todaro is formed by the fusion of the valve guarding the IVC (the Eustachian valve) and the coronary sinus (the Thebesian valve). This inserts into the central fibrous body and runs in the tissue separating the oval fossa from the mouth of the coronary sinus The trabeculated diverticulum found posterior to the coronary sinus is called the post-Eustachian sinus of Keith.

The node lies in the atrial muscle above the hinge point of the septal leaflet, and the bundle which arises from the node penetrates the interventricular septum at the apex of the triangle of Koch.

The central fibrous body is actually the area where the membranous septum and leaflets of the atrioventricular and the aortic valves join in fibrous continuity.

#### **2.2. The morphological left atrium**

Like the right atrium, the left atrium has a (a) venous sinus (b) appendage and (c) vestibule. The differences however are

The outlet component of the right ventricle is a complete muscular structure - the infundibu‐

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The muscular shelf separating the tricuspid and the pulmonary valve is the supraventricular crest. Much of the crest is no more than the infolded inner heart curve and incisions and sutures deep in this area can jeopardize the right coronary artery. The distal part of the crest is continuous with the sub-pulmonary infundibulum, the presence of which permits the

The crest is cradled between two limbs of the prominent right ventricular trabecula called the

The inferior limb gives rise to the medial papillary muscle (of Lancisi) and a line drawn from this muscle to the apex of the triangle of Koch marks the position of the atrioventricular

The body runs to the apex, and gives rise to the moderator band and the anterior papillary

pulmonary valve to be removed and used as autograft during the Ross procedure.

septomarginal trabeculation, which has a superior limb, an inferior limb and a body.

The superior limb runs up to the attachment of the pulmonary valve.

lum- which supports the pulmonary valve.

**Figure 3.** Right atrium and ventricle

conduction axis.

muscle.


Among these the confinement of the pectinate muscles within the appendage is the most reliable differentiating factor between the morphological right and left atrium.

#### **2.3. The morphologic right ventricle**

It has three components- the inlet, trabecular and outlet parts.

The inlet portion is limited by the tricuspid valve and its tension apparatus

The trabecular component extends to the apex, where it is thin and it is vulnerable to perfo‐ ration by cardiac catheters and pacemaker electrodes.

**Figure 3.** Right atrium and ventricle

The septum between the right and left atria is formed by the floor of the oval fossa and its adjacent anteroinferior muscular rim. The superior rim or the septum secundum is formed by deep interatrial fold extending between the systemic and the pulmonary veins. Larger part of the anterior atrial wall is related to the aortic root (the torus aorticus). It is important to realize that the true atrial septum is rather small and it is easy to go outside the heart when attempting to gain access to the left atrium through the septal approach. Because of the infolding of the interatrial groove, access to the left atrium can be gained by approaching through the right

The triangle of Koch which contains the atrioventricular (AV) node is an area of major surgical significance. The triangle is demarcated by the (a) the tendon of Todaro, (b) the attachment of the septal leaflet and (c) the orifice of the coronary sinus. The tendon of Todaro is formed by the fusion of the valve guarding the IVC (the Eustachian valve) and the coronary sinus (the Thebesian valve). This inserts into the central fibrous body and runs in the tissue separating the oval fossa from the mouth of the coronary sinus The trabeculated diverticulum found

The node lies in the atrial muscle above the hinge point of the septal leaflet, and the bundle which arises from the node penetrates the interventricular septum at the apex of the triangle

The central fibrous body is actually the area where the membranous septum and leaflets of the

Like the right atrium, the left atrium has a (a) venous sinus (b) appendage and (c) vestibule.

**c.** The pectinate muscles are confined within the appendage and do not extend around the

**d.** The appendage is long, tubular and finger like with a narrow end unlike the broad

Among these the confinement of the pectinate muscles within the appendage is the most

The trabecular component extends to the apex, where it is thin and it is vulnerable to perfo‐

**a.** The venous component of the left atrium is considerably larger than the appendage

**b.** the junction between them is NOT marked by a terminal groove or crest.

reliable differentiating factor between the morphological right and left atrium.

The inlet portion is limited by the tricuspid valve and its tension apparatus

atrium and incising superiorly within the fossa *(The septal superior approach*). [8]

posterior to the coronary sinus is called the post-Eustachian sinus of Keith.

atrioventricular and the aortic valves join in fibrous continuity.

**2.2. The morphological left atrium**

226 Principles and Practice of Cardiothoracic Surgery

triangular appendage of the right atrium

It has three components- the inlet, trabecular and outlet parts.

ration by cardiac catheters and pacemaker electrodes.

**2.3. The morphologic right ventricle**

The differences however are

vestibule

of Koch.

The outlet component of the right ventricle is a complete muscular structure - the infundibu‐ lum- which supports the pulmonary valve.

The muscular shelf separating the tricuspid and the pulmonary valve is the supraventricular crest. Much of the crest is no more than the infolded inner heart curve and incisions and sutures deep in this area can jeopardize the right coronary artery. The distal part of the crest is continuous with the sub-pulmonary infundibulum, the presence of which permits the pulmonary valve to be removed and used as autograft during the Ross procedure.

The crest is cradled between two limbs of the prominent right ventricular trabecula called the septomarginal trabeculation, which has a superior limb, an inferior limb and a body.

The superior limb runs up to the attachment of the pulmonary valve.

The inferior limb gives rise to the medial papillary muscle (of Lancisi) and a line drawn from this muscle to the apex of the triangle of Koch marks the position of the atrioventricular conduction axis.

The body runs to the apex, and gives rise to the moderator band and the anterior papillary muscle.

The coarseness of the apical trabeculation is the most constant feature of the right ventricle. The other differences are the direct septal attachment of the tension apparatus of the atrio‐ ventricular valve, which is usually tricuspid in nature.

posterior descending artery (90%) at the crux which supplies the diaphragmatic surface. The LCA gives rise to the anterior interventricular (left anterior descending) and the circumflex branches. The anterior interventricular artery gives rise to the diagonal branches to the obtuse surface of the heart and the septal perforating branches. The circumflex artery gives rise to the

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The Great cardiac vein runs along the left anterior descending artery and encircles the mitral orifice, and at its left margin receives the oblique vein of the LA and forms the coronary sinus. The coronary sinus lies between the left atrium and left ventricle before joining the right atrium.

The Middle cardiac vein runs along the posterior descending artery and the small cardiac veins accompany the right coronary artery. The Thebesian valve guards the orifice of the coronary

The heart develops from the mesoderm from fusion of vascular channels which forms the heart tube. The heart starts beating from the time the embryo is 22 days old. Even from the beginning there is a polarity and the peristaltic type of motion of the tube starts from the venous end and ends in the arterial end. This sequential contraction ensures that even in the absence of valves there is very little regurgitation of the blood, and an ECG similar to the adult ECG is recognized at the end of 1st month. It is believed that this primitive heart tube persists as the remnant of conduction tissue and the myocardium grows around this to form the atrium and the ventricle. The conduction system is one of the most primitive structures in the heart which forms even

There is a circle of conduction tissue at the atrioventricular junction, which as the atrioven‐ tricular valves form and the great arteries are assigned to the respective ventricles gradually becomes restricted.The only area of electrical continuity between the atrium and the ventricles is the AV node and the penetrating bundle where the muscular septum comes in contact with the AV junction. This establishes connection with the Purkinje network in the ventricular

This sequence of events occurs in the usual d-looping of the heart.If there is l-looping of the heart as in congenitally corrected transposition, where the right atrium joins the left ventricle, which then gives rise to the pulmonary artery and the left atrium joins the right ventricle which gives rise to aorta, the bundle can be extremely elongated bringing it under the pulmonary valve anteriorly. The conduction system is vulnerable to injury during surgery and otherwise Both congenital and spontaneous heart blocks can occur at the rate of 2% per annum in this

myocardium, to ensure sequential contraction of atrium and ventricles. (figure 4)

The Coronary veins accompany the artery and drain into the coronary sinus.

**3. Conductiion system and its surgical significance**

obtuse marginal branches of the heart. [10]

sinus.

**3.1. The development**

condition. [11]

before the heart tube starts looping.

#### **2.4. The morphologic left ventricle**

The inlet component is limited by the mitral valve and its tension apparatus. The mitral valve has two leaflets, the aortic or the anterior leaflet which is in fibrous continuity with the aortic valve, which is short and square and the other leaflet which is connected to the wall of the left atrioventricular junction is called the mural or the posterior leaflet.

The leaflets do not have direct septal attachment unlike the right ventricle but instead attach through anterolateral and posteromedial papillary muscles.

The apical myocardium is thin like the RV. The septum is not completely muscular unlike RV, and it has a small membranous part which forms the subaortic outflow tract.

The muscular septal surface is characteristically smooth and the left bundle lies below the membranous septum corresponding to the zone of apposition between the right coronary and non-coronary leaflets.

The semilunar valves of the aortic and pulmonary valves are similar, the distal portion forms the sinotubular junction and the proximal part takes origin from the ventricular structure. The overall arrangement is like the crown, rather than forming an annulus. [9]

The aorta and pulmonary artery form the vascular pedicle. The aorta gives rise to the brachio‐ cephalic or innominate artery, the left common carotid artery and the left subclavian artery. The pulmonary artery arises anteriorly and courses posteriorly, and is a short vessel giving rise to the right and left pulmonary arteries. The left pulmonary artery lies superior to the left bronchi in front of the descending aorta. The right pulmonary artery is anterior to the left main bronchus and has a long mediastinal course beneath the aortic arch and behind the superior vena cava to reach the hilum of the right lung. Sometimes a early branching large upper lobar branch can be mistaken for the right pulmonary artery.

The coronary arteries arise from the aortic sinuses. According to Leiden convention the position is described in terms of an observer from the non-coronary sinus, the right hand of the person is called the sinus 1 and gives rise to the right coronary artery and left hand facing sinus is called the sinus 2 and gives rise to left coronary artery. The coronary artery arises beneath the sinotubular junction, and when it is displaced more than 1 cm from the ST junction it is considered abnormal which occurs in 3.5% of hearts.

The left coronary artery has a single orifice,while in 50% there are two orifices in the right sinus, one gives rise to the main RCA and the smaller orifice gives rise to the infundibular or sinus nodal artery. It is important while giving ostial cardioplegia for stopping the heart to perform cardiac surgeries to instill into the smaller orifices to protect the sinus node.

The epicardial course of the coronary arteries follows the atrioventricular and interventricular grooves. The RCA gives to the acute marginal branches, the sinus nodal artery (55%), and posterior descending artery (90%) at the crux which supplies the diaphragmatic surface. The LCA gives rise to the anterior interventricular (left anterior descending) and the circumflex branches. The anterior interventricular artery gives rise to the diagonal branches to the obtuse surface of the heart and the septal perforating branches. The circumflex artery gives rise to the obtuse marginal branches of the heart. [10]

The Coronary veins accompany the artery and drain into the coronary sinus.

The Great cardiac vein runs along the left anterior descending artery and encircles the mitral orifice, and at its left margin receives the oblique vein of the LA and forms the coronary sinus. The coronary sinus lies between the left atrium and left ventricle before joining the right atrium.

The Middle cardiac vein runs along the posterior descending artery and the small cardiac veins accompany the right coronary artery. The Thebesian valve guards the orifice of the coronary sinus.
