📚 Question Bank

The orifice of the mitral valve is level with the left half of the sternum opposite the left 4th costal cartilage and is represented by a line approximately 3 cm long and descending to the right.

The base of the heart is formed mainly by the left atrium. Enlargement of the left atrium can cause hoarseness due to compression of the left recurrent laryngeal nerve.

The base of the heart is a quadrilateral directed posteriorly. It is made of:

• The left atrium mainly
• Small part of the right atrium
• Proximal parts of superior vena cava, inferior vena cava, and pulmonary veins
• The base of the heart lies at the level of T5-T8 vertebrae in the supine position.
• The apex of the heart is formed by the left ventricle in the 5th intercostal space.
• Surfaces of the heart:
• Sternocostal surface - Formed by the right atrium, right and left ventricles
• Diaphragmatic surface - Formed mainly by the left ventricle
• Left surface - Formed mainly of the left ventricle
• Right surface - Formed mainly of the right atrium

The region marked corresponds to the surface marking for the right atrium.

The costal margin, xiphoid process, and the mid-clavicular line are seen in this image. The examiner draws a laterally convex line that extends from a level below the 2nd costal cartilage (as clued in by the sternal angle) i.e., 3rd costal cartilage to about 3 spaces below i.e., the 6th costal cartilage. This line is about 1.2 cms lateral to the sternal edge. These suggest that the region marked corresponds to the surface marking for the right atrium.

The projection of the cardiac borders, of an average adult, onto the anterior thoracic wall forms a trapezoid. This can be mapped out using the percussion method by looking for cardiac dullness.

The varying heart borders and the corresponding surface markings are as follows:

• Upper border: Slopes gently from the second left costal cartilage to the third right costal cartilage. It corresponds to the left atrium.
• Right border: Convex to the right and runs from the third to the sixth right costal cartilages,
• 1–2
• cm lateral to the sternal edge. It corresponds to the right atrium.
• Inferior border or acute border: Runs leftwards from the 6th right costal cartilage to the cardiac apex which is located approximately 9 cm lateral to the midline, often in the left 5th intercostal space or level with the 5th or 6th rib. It corresponds to the right ventricle.
• Left border or obtuse border: Convex laterally on the left. It extends superomedially from the cardiac apex to meet the second left costal cartilage about 1 cm from the left sternal edge. It corresponds to the left ventricle.

The area posterior to the sternum is occupied by the right ventricle and hence is most likely to be injured in this case.

The convex anterosuperior surface of the right ventricle makes up a large part of the sternocostal aspect of the heart, and is separated from the thoracic wall only by the pericardium.

The structure being palpated by the resident is crista terminalis. It is present in the right atrium.

It is a muscular ridge that runs anteriorly along the atrial wall from the opening of the superior vena cava to the opening of the inferior vena cava. It corresponds externally to sulcus terminalis. It is the site of origin of pectinate muscles.

It divides the right atrium into a smooth posterior part and a rough anterior part. Both the vena cavae empty into the posterior smooth part.

The right border of the heart is formed of the right atrium. Borders of the heart:

• Right border: Right atrium
• Left border: Left ventricle mainly and to a slight extent by left atrial appendage
• Inferior border: Right ventricle mainly and a small contribution by the left ventricle
• Upper border: Left atrium, ascending aorta, and the pulmonary trunk.

The structure mentioned here is the foramen ovale through which blood passes from the right atrium to the left atrium as part of fetal circulation. It closes at delivery and later forms fossa ovalis. The floor of the fossa ovalis is formed by the septum primum.

Fossa ovalis is an oval-shaped depression in the septal wall of the right atrium just above the opening of inferior vena cava. Its floor is formed by the remnant of septum primum. The limbus of fossa ovalis is the prominent rim of the depression which represents the remnant of septum secundum.

The sinoatrial (SA) node is located at the upper part of the crista terminalis, at the junction of the superior vena cava opening to the right atrium. This is also the junction between the parts of the right atrium derived from sinus venosus and primitive atria.

The Atrioventricular (AV) node lies at the lower back section of the interatrial septum near the opening of the coronary sinus. It is located in the center of the Koch triangle.

The AV node is present in the center of the triangle of Koch. The posterior leaflet of the tricuspid valve does not form its boundary.

The triangle of Koch is found on the smooth posterior wall of the right atrium. It is bound by:

• The coronary sinus
• Tendon of Todaro
• The septal cusp of the tricuspid valve

The triangle of Koch can be seen in the image below bound by the dashed blue lines:

Sino-atrial (SA) node is not located at the right border of the ascending aorta.

It is located at the opening of the superior vena cava into the right atrium. It is called the 'pacemaker' of the heart. It is supplied by the atrial branches of the right coronary artery. It contains specialized nodal cardiac muscle which spontaneously produces an electrical impulse. The action potential of these cells does not have phase 1 or 2.

The aorta lies anterior to the transverse pericardial sinus.

The reflections of the serous pericardium are arranged as two tubes – one enclosing the aorta and the pulmonary trunk and the other enclosing the vena cavae and the four pulmonary veins.

Oblique pericardial sinus: The zone of reflection surrounding the veins is J-shaped and the cul-de-sac formed within the J is the oblique pericardial sinus. This lies posterior to the left atrium.

The image below shows the posterior view of the heart demonstrating the oblique and the transverse sinus.

Transverse pericardial sinus: It is a passage between the two 'tubes'. The aorta and the pulmonary trunk lie anterior and the superior vena cava and the atria lie posterior to it.

The pulmonary trunk divides into the right and left pulmonary arteries above the transverse sinus.

Clinical significance:

During cardiac surgery, the transverse pericardial sinus allows a surgeon to isolate the pulmonary trunk and ascending aorta and apply a temporary ligature or clamp.

Purkinje fibers are modified cardiac muscles.

The Purkinje network is subendocardial and the muscular excitation proceeds from endocardium to epicardium.

During surgery, a clamp is passed through the transverse sinus. This stops/diverts the blood flow from the aorta and pulmonary trunk.

The transverse pericardial sinus separates the arterial end of the heart tube from the venous end. Aorta and pulmonary trunk lie anterior to the sinus and the superior vena cava lies posterior to it. Therefore, during surgery, a clamp passed through the transverse sinus stops or diverts the blood flow from the aorta and pulmonary trunk.

Coronary dominance is determined by the posterior interventricular artery (PIVA).

In about 65 of the population, the PIVA is given by the right coronary artery and this is called the right cardiac dominance.

In 10 of the population, it is a branch of the left coronary artery alone, called the left cardiac dominance.

In the remaining 25 population, it is given by both (balanced dominance).

If the circumflex artery gives off the posterior interventricular artery, then the arterial supply is called left dominant.

In 65 of the population, the posterior interventricular artery (PIVA) is a branch of the right coronary artery and this is called the right dominance.

In 10 of the population, PIVA is given by the circumflex artery (a branch of the left coronary artery) and this is called the left dominance.

The right coronary artery does not give rise to the circumflex coronary artery.

The right coronary artery arises from the anterior aortic sinus (right coronary sinus) of the ascending aorta. It passes anteriorly and descends vertically in the coronary sulcus between the right atrium and the right ventricle. On reaching the inferior margin, it turns posteriorly and continues in the sulcus onto the diaphragmatic surface and the base of the heart.

The diameter of the right coronary artery is less than that of the left coronary artery. The right conal artery is, usually the first branch of the right coronary artery.

The circumflex coronary artery is a branch of the left coronary artery and is the exclusive supplier to the right bundle branch.

The circumflex artery is a branch of the left coronary artery, not the right coronary artery. Hence, blood supply through the circumflex artery won't be affected.

The branches of the right coronary artery are:

• Right conal artery - first branch of the right coronary artery
• Artery of the SA node
• Acute right marginal artery
• Posterior interventricular artery (in 65 population)
• Atrial and anterior and posterior ventricular branches

The anterior interventricular artery is a branch of the left coronary artery.

The left coronary artery arises from the left aortic sinus (left posterior sinus) of the ascending aorta. It passes between the pulmonary trunk and the left auricle and then runs in the coronary sulcus. It divides into its two terminal branches in the coronary sulcus. They are:

• Anterior interventricular branch - also called the left anterior descending artery (LAD).
• Circumflex branch - It gives a left marginal artery also called the obtuse marginal artery supplying the left ventricle.

The anterior two-thirds of the interventricular septum is supplied by the left coronary artery. Hence, this artery is most likely blocked.

The right coronary artery distribution supplies:

• Right atrium
• Right ventricle (except a small region to the right of the anterior interventricular groove)
• A variable part of the diaphragmatic aspect of the left ventricle
• Posteroinferior 1/3rd of the interventricular septum
• Part of the left atrium
• The conduction system, as far as the proximal parts of the right and left crura
• The left coronary artery distribution supplies:
• Left atrium
• Left ventricle
• A narrow strip of the right ventricle
• The anterior 2/3rd of the interventricular septum

The image shows a triangle of Koch marked with blue dotted lines. The arterial supply to the triangle of Koch is from the right coronary artery in the majority of the population.

The occlusion of the left anterior descending artery (LAD) will lead to the infarction of the anterior wall of the left ventricle.

The left anterior descending artery also called the anterior interventricular artery supplies the anterior 2/3rd of the interventricular septum and the adjacent anterior wall of the left ventricle.

Options A and D: The posterior interventricular artery supplies the posterior part of the interventricular septum and the inferior part of the right ventricle.

Option C: The left lateral surface of the heart is supplied by the circumflex artery.

Anterior cardiac vein does not open into the coronary sinus. It drains directly into the right atrium.

Tributaries of coronary sinus include the following:

• Great cardiac vein
• Middle cardiac vein
• Small cardiac vein
• Posterior cardiac vein
• Oblique vein of the left atrium

Thebsian vein/venae cordis minimae, anterior cardiac veins, and the right marginal vein drain directly into the right atrium.

The great cardiac vein lies in the anterior interventricular sulcus.

The great cardiac vein begins at the cardiac apex, and ascends in the anterior interventricular groove to the atrioventricular groove, which it follows, passing to the left and posteriorly to enter the coronary sinus at its origin.

The great cardiac vein accompanies the anterior interventricular artery (left anterior descending artery).

Coronary sinus ends in the right atrium.

Coronary sinus develops from the left horn of the sinus venosus and lies in the posterior part of the atrioventricular groove. The sinus opens into the right atrium between the opening of the inferior vena cava and the right atrioventricular orifice.

Venae cordis minimae drains directly into the nearest heart chamber (drains into all 4 chambers).

The middle cardiac vein is present in the posterior interventricular groove accompanying the posterior descending artery, and hence is most likely to be injured in this case.