Heart Coverings and Coronary Circulation

Question 1

What region of the mediastinum houses the heart?

Answer 1

Middle mediastinum

Question 2

Describe the position of the heart in the thoracic cavity according to external landmarks.

Answer 2

• Top boundary: Sternal angle (T4/5)
• Bottom boundary: Xiphisternal joint (T9)
• Left limit: Left midclavicular line

Question 3

What are the 4 compartments of the mediastinum? What are the boundaries of the mediastinum? What is contained in the mediastinum.

Answer 3

The 4 compartments of the mediastinum are the superior, anterior, posterior and middle mediastinum.

Boundaries:
* 1st rib (superior border)
* rib cage (anterior border)
* thoracic vertebrae (posterior border)
* diaphragm (inferior border)

The mediastinum contains the extrapulmonary organs (i.e. non-lung) of the thoracic cavity.

Question 4

Which compartments of the mediastinum form the inferior mediastinum?

Answer 4

Inferior mediastinum:
* anterior, middle and posterior mediastinum

The border between the superior and inferior mediastinum is at the level of the sternal angle.

Question 5

Name the 5 contents of the middle mediastinum.

Answer 5

1. Heart
2. Roots of great vessels (aorta, pulmonary trunk, pulmonary arteries, pulmonary veins, superior and inferior vena cava)
3. Neurovasculature of the heart (inside pericardium)
4. Neurovasculature outside the pericardium
5. Primary bronchi (respiratory system)

Question 6

Neurovasculature inside the pericardium (middle mediastinum) consists of…

Neurovasculature outside the pericardium (middle mediastinum) consists of…

Answer 6

Inside: coronary circulation, cardiac plexus

Outside: phrenic nerve, pericardiacophrenic arteries and veins

Question 7

Describe the layers of the pericardium and pericardial cavity.

Answer 7

• Fibrous pericardium: external, dense connective tissue envelope of the heart
• Serous pericardium: continuous double layer (parietal and visceral) that encloses the pericardial cavity
• Parietal layer of the serous pericardium adheres to the fibrous pericardium

Question 8

What is the difference between epicardial and pericardial fat?

Answer 8

Epicardial fat: lies directly on the heart, below the visceral pericardium

Pericardial fat: lies on the external surface of the fibrous pericardium

Question 9

What are the pericardial sinuses? Where are they located? Name the two sinuses.

Answer 9

Anatomical landmarks where the visceral serous pericardium reflects onto parietal serous pericardium (where the two layers are continuous).

They form “cul-de-sac “ within the pericardial cavity where the fibrous pericardium is anchored to the great vessels.

• Oblique sinus (posterior to the heart
• Transverse sinus (posterior to the aorta and pulmonary trunk)

Question 10

The pericardial cavity is normally filled with…

Answer 10

a few mL of serous fluid (to ease gliding of the beating heart against surrounding tissues).

Question 11

What is a pericardial effusion?

Answer 11

Buildup of excess fluid in the pericardial cavity (i.e. between the parietal and visceral layer of the serous pericardium).

If slow, the fibrous pericardium will stretch in response to this buildup!

Question 12

What is a cardiac tamponade? What happens if it goes untreated?

Answer 12

A cardiac tamponade results from a large or rapid pericardial effusion. Fluid buildup in the pericardial cavity compresses the heart and limits its ability to pump blood effectively. In response, the heart rate accelerates to maintain the volume of blood pumped.
However, if untreated, the increasing pressure around the heart may prevent it from filling with blood and cause it to stop beating altogether (cardiac arrest).

Question 13

What is the treatment for a cardiac tamponade?

Answer 13

Pericardiocentesis (needle is used to remove excess fluid from pericardial cavity).

Question 14

Why doesn’t the heart have symmetrical views anteriorly and posteriorly?

Answer 14

In anatomical position, the heart is rotated (around the longitudinal axis) towards the left. Its apex is also tilted towards the left and anteriorly.

Understand the posterior and anterior views of the heart!

Question 15

What surfaces of the heart occupy the following:
- base
- anterior surface
- left pulmonary surface
- right pulmonary surface
- diaphragmatic surface

Answer 15

Base: mostly left atrium
Anterior surface: mostly right ventricle
Left pulmonary surface: left ventricle
Right pulmonary surface: right atrium
Diaphragmatic surface: mostly left ventricle

Question 16

What are the sulci of the heart (explain)?

Answer 16

The sulci are shallow grooves on the surface of the heart created by the muscular walls of the four chambers of the heart. They house coronary circulation (paired arteries and veins) and variable amounts of fat.

Question 17

Name and describe the 2 sulci of the heart.

Answer 17

Atrioventricular sulcus: ring around the heart, between atria and ventricles

Interventricular sulcus: between the left and right ventricles, anterior to posterior

Question 18

Like all other tissues, the heart needs its own blood supply, which is provided by…

Answer 18

the right and left coronary arteries, the first two branches of the aorta.

Question 19

In the aorta, what is the location of the openings to the coronary arteries?

Answer 19

In sinuses created by the aortic valve cusps.

Right coronary artery: right aortic valve cusp
Left coronary artery: left aortic valve cusp

Question 20

When the aortic valve is open, the coronary arteries…

When the aortic valve closes, …

Answer 20

When the aortic valve is open, the coronary arteries are sealed off by the cusps.

When the aortic valve closes, the coronary arteries open and the aortic valve sinuses fill with blood, which then travels into the coronary arteries.

Question 21

Where does the right coronary artery emerge? What is its position relative to the atrioventricular sulcus?

Answer 21

It emerges at the anterior/right base of the aorta. It runs to the right of the atrioventricular sulcus, around to the posterior surface.

Question 22

What are the 3 main branches of the right coronary artery? What parts of the heart do they supply?

Answer 22

1. Sinoatrial nodal: supplies sinoatrial node and right atrium
2. Right marginal: supplies most of the right ventricle
3. Posterior interventricular: supplies posterior ventricles and posterior interventricular septum (muscle wall) (1/3)

Question 23

Where does the left coronary artery emerge? What is its position relative to the pulmonary trunk?

Answer 23

It emerges at the posterior/left base of the aorta. It runs posterior to the pulmonary trunk.

Question 24

What are the 2 main branches of the left coronary artery?

Answer 24

1. Anterior interventricular
2. Circumflex

Left marginal is a branch of the circumflex!

Question 25

What parts of the heart are supplied by the following arteries (branches of LCA):

• Anterior interventricular
• Circumflex
• Left marginal

Answer 25

Anterior interventricular: runs towards apex in anterior interventricular sulcus, supplying the anterior ventricles and anterior interventricular septum (2/3).

Circumflex: Supplies left atrium

Left marginal: Branch of circumflex, supplies most of the left ventricle.

Question 26

Where do two important anatomoses commonly form?

Answer 26

• Between the ends of the right coronary artery and circumflex
• Between the anterior and posterior interventricular arteries

Question 27

What is heart dominance and how is it determined?

Answer 27

The coronary arteries are variable! Heart dominance describes which coronary artery gives rise to the posterior interventricular artery (PIVA) and supplies the posterior interventricular septum.

Question 28

What is coronary artery disease and what can it lead to?

Answer 28

Over time, plaque deposits build up on the internal walls of coronary arteries (atherosclerosis). This leads to the narrowing of the lumen (stenosis) and can cause local ischemia of heart muscle. This in turn can result in heart tissue necrosis, i.e. a myocardial infarct.

Question 29

Define the following terms:
* atherosclerosis
* stenosis
* ischemia
* myocardial infarct

Answer 29

Atherosclerosis: Thickening of arteries caused by plaque buildup on internal walls.
Stenosis: Narrowing of the blood vessel lumen.
Ischemia: Lack of blood supply to a tissue.
Myocardial infarct: Heart attack, heart tissue necrosis due to ischemia.

Question 30

How are less severe blockages of coronary arteries treated?

Answer 30

Percutaneous coronary intervention (angioplasty), which will help maintain the patency of the affected artery.

A catheter with a small ballon on its tip is threaded through the blood vessel. The balloon is inflated to compress the plaque and a mesh wire stent is inserted to keep the artery open.

Question 31

How are severe blockages of coronary arteries treated?

Answer 31

Coronary artery bypass graft (CABG), which circumvents the blockage and restores blood flow.

A healthy blood vessel is taken from another part of the body and used to create a new pathway for blood to flow around the obstruction.

Question 32

Why is it important to understand heart dominance when performing a coronary artery bypass graft (CABG)?

Answer 32

Knowing the dominance helps the surgeon prioritize which vessels need grafting to ensure adequate blood supply to all essential regions.

In a codominant heart, a blockage will affect the posterior interventricular artery less!

Question 33

Heart tissues are drained by a network of veins paired with the coronary arteries, usually in the sulci. Where do most of these veins join and where do they drain?

Answer 33

Most of these veins join the coronary sinus before draining into the right atrium.

Question 34

What is the coronary sinus?

Answer 34

It is a swelling in the atrioventricular sulcus that collects venous blood from great, middle and small cardiac veins. It is located on the posterior side of the heart. It opens directly into the right atrium near the inferior vena cava.

Question 35

Describe the great cardiac vein.

Answer 35

• Runs with anterior interventricular artery and then with the circumflex, onto the posterior heart.
• Drains anterior ventricles and left atrium into the coronary sinus.

Question 36

Describe the middle cardiac vein.

Answer 36

• Runs with posterior interventricular artery
• Drains the posterior interventricular septum into the coronary sinus

Question 37

Describe the small cardiac vein.

Answer 37

• Runs with the right marginal artery, then with the right coronary artery onto the posterior heart
• Drains the right atrium and right ventricle

Question 38

Describe the anterior cardiac veins (3)

Answer 38

• Run with local branches of the right coronary artery
• Open directly into the right atrium (not coronary sinus)
• Drain anterior right ventricle

Question 39

What are the first 2 branches of the aorta?

Answer 39

Right and left coronary arteries (located right at the base of the aorta).