Anatomy 3 & 4 Flashcards

1
Q

Where does the mediastinum extend from?

A

Superior thoracic aperture superiorly to the diaphragm inferiorly

Sternum anteriorly to the thoracic vertebrae posteriorly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the mediastinum contain?

A

Heart and pericardium (the fibrous sac around the heart)
Great vessels that enter and leave the heart
Veins that drain the chest wall
Trachea and main bronchi
Oesophagus
Nerves (somatic and autonomic)
Lymphatics
Thymus gland

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Where does the line between the superior and inferior compartments in the mediastinum run from?

A

Run from the sternal angle anteriorly to the T4/T5 junction posteriorly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the inferior mediastinum divided into?

A

● The anterior mediastinum lies between the posterior aspect of the sternum and the anterior aspect of the pericardial sac. It is a narrow space that contains the thymus gland in children and its remnant in adults.

● The middle mediastinum contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta.

● The posterior mediastinum lies between the posterior aspect of the pericardial sac and the vertebrae.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the main contents of the superior mediastinum?

A

● arch of the aorta and its three branches
● superior vena cava and its tributaries - the left and right brachiocephalic veins
● trachea
● oesophagus
● phrenic nerves (left and right) and vagus nerves (left and right)
● thoracic duct
● thymus gland

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the 3 parts of the aorta?

A

● The ascending aorta is the short, first part. It gives rise to the coronary arteries, which supply the myocardium.

● The arch of the aorta curves posteriorly. It lies in the superior mediastinum.

● The descending (thoracic) aorta descends through the posterior mediastinum
and into the abdomen posterior to the diaphragm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the 3 major branches that the arch of the aorta give rise to?

A

● First, the brachiocephalic trunk. It bifurcates into the right common carotid artery which supplies the right side of the head and neck, including the brain, and the right subclavian artery which supplies the right upper limb.

● Second, the left common carotid artery, which supplies the left side of the head, neck, and brain.

● Third, the left subclavian artery, which supplies the left upper limb.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does the arch of the aorta contain?

A

Contains aortic bodies where chemoreceptors are located.

These receptors constantly monitor arterial oxygen and carbon dioxide.

This visceral sensory information travels back to the CNS along the path of the vagus nerve and results in reflex responses that regulate ventilation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the ligamentum arteriosum?

A

The ligamentum arteriosum is a fibrous, cord-like connection between the pulmonary trunk and the arch of the aorta.

It is the remnant of the ductus arteriosus, a foetal circulatory shunt. In the foetus, gas exchange occurs at the placenta, not in the lungs.

The ductus arteriosus diverts most of the blood entering the pulmonary trunk directly to the aortic arch (only a small amount of blood circulates through the foetal lungs; enough for them to develop).

When a baby starts to use their lungs at birth, the ductus arteriosus closes, and blood in the pulmonary trunk enters the lungs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What two veins carry deoxygenated blood to the right atrium?

A

● The superior vena cava (SVC) returns blood to the heart from the head, neck,
and upper limbs. The SVC and its tributaries lie in the superior mediastinum.

● The SVC is formed by the union of the left and right brachiocephalic veins (brachium = arm; cephalic = head).
● The union of the internal jugular vein (which drains the head and neck) and the subclavian vein (which drains the upper limb) forms each brachiocephalic vein.

● The inferior vena cava (IVC) returns blood to the heart from all regions inferior to the diaphragm (abdomen, pelvis, and lower limbs). The thoracic part of the IVC is very short - as soon as it enters the thorax (the inferior mediastinum) through the diaphragm it enters the right atrium.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does the trachea do?

A

The trachea conducts air to and from the left and right main bronchi. It is semi-rigid due to C-shaped, incomplete rings of cartilage in its walls.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where does the trachea extend from and terminate?

A

● It extends from the larynx in the midline of the neck into the superior mediastinum and is palpable just superior to the suprasternal notch.

● It terminates at the level of the sternal angle (and junction between the T4 and T5 vertebrae) by bifurcating into the left and right main bronchi.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the oesophagus?

A

The oesophagus is a muscular tube that extends from the pharynx in the midline of the neck to the stomach.

‘Waves’ of contractions of smooth muscle in the oesophageal wall move swallowed food and fluid distally (peristalsis).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the position of the oesophagus?

A

In the superior mediastinum, the oesophagus lies in the midline of the thorax, posterior to the trachea.

It descends into the posterior mediastinum, and we will learn more about the oesophagus when we look at the posterior mediastinum.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the phrenic nerves formed from?

A

The left and right phrenic nerves, formed by fibres from the C3, C4 and C5 spinal nerves, innervate the diaphragm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the phrenic nerves and where are they found?

A

They are somatic nerves and contain motor and sensory fibres.

They descend through the neck and enter the thorax through the superior thoracic aperture.

They course over the pericardium and pierce the diaphragm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the vagus nerves?

A

The left and right vagus nerves (CN X) arise from the brainstem and contain somatic sensory, somatic motor and parasympathetic fibres. They innervate structures of the thorax and abdomen, in addition to the head and neck.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Where are the vagus nerves found?

A

They descend through the neck alongside the internal carotid artery and internal jugular vein and enter the thorax via the superior thoracic aperture.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What do the vagus nerves give rise to?

A

They each give rise to a recurrent laryngeal nerve (RLN), which ascend back up into the neck to innervate the muscles of the larynx.

● The left recurrent laryngeal nerve loops under the arch of the aorta before ascending back up the left side of the neck (alongside the trachea) to the larynx.

● The right recurrent laryngeal nerve descends anterior to the right subclavian artery and then loops under the inferior border of the artery before ascending back up the right side of the neck (between the trachea and oesophagus) to the larynx.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where do the vagus nerves descend into?

A

Into the thorax posterior to the root of the lung

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What do the vagus nerves contribute?

A

They contribute parasympathetic fibres to the heart, lungs, and oesophagus.

● They traverse the diaphragm and convey parasympathetic fibres to most of the
abdominal viscera.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the thoracic duct?

A

The thoracic duct is a major channel for lymphatic drainage from most regions of the body.

It ascends through the posterior mediastinum and into the superior mediastinum, where it empties into the venous system at the union of the left internal jugular vein and left subclavian vein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the thymus gland?

A

The thymus is a lymphoid organ. It lies anteriorly in the superior mediastinum.

It is important in children, but atrophies with age, eventually becoming fatty.

We will not see the thymus in the cadavers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the pericardium?

A

The pericardium is a tough, fibrous sac that encloses the heart like a loose-fitting bag; it is loose to allow for the movement of the heart within it.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What two layers is the pericardium composed of?

A

● a tough, outer fibrous layer that is attached superiorly to the great vessels and inferiorly to the central tendon of the diaphragm

● a thin, inner serous layer which has two parts: the parietal layer lines the inner aspect of the fibrous pericardium, and the visceral layer covers the surface of the heart.

The two layers are continuous with each other.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the narrow space between the two layers of serous pericardium?

A

Pericardial cavity

It contains a small amount of pericardial fluid that lubricates the serous membranes and allows them to slide over each other with movements of the heart.

The left and right phrenic nerves give rise to sensory branches that innervate the fibrous pericardium.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the apex?

A

‘Point’ of the heart, which projects to the left of the sternum towards the left lung

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are the surfaces of the heart?

A

● base – it ‘faces’ posteriorly, so is also called the posterior surface.

● inferior surface – it lies on the central tendon of the diaphragm, so is also called
the diaphragmatic surface.

● anterior surface – it ‘faces’ the sternum and ribs, so is also called the sternocostal surface.

● The left and right sides of the heart ‘face’ the lungs and are referred to as the pulmonary surfaces.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What do the heart surfaces correspond to?

A

● Base / posterior surface = left atrium, part of the right atrium
● Inferior / diaphragmatic surface = left ventricle, part of the right ventricle
● Anterior / sternocostal surface = right ventricle
● Left pulmonary surface = left ventricle
● Right pulmonary surface = right atrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the apex formed by?

A

The apex is formed by the left ventricle.

It lies at the left 5th intercostal space in the midclavicular line and the apex beat is palpable here.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What do the borders of the heart correspond to?

A

● Right border = right atrium
● Left border = left ventricle
● Inferior border = right ventricle and part of the left ventricle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Where are the borders of the heart located?

A

● Right border = lies lateral to the right sternal edge, from the right 3rd costal cartilage to the right 6th costal cartilage.

● Left border = extends from the left 2nd intercostal space to the left 5th intercostal space in the midclavicular line (i.e. the apex).

● Superior border = lies along the line connecting the superior extents of the right and left borders (i.e. from the right 3rd costal cartilage to the left 2nd intercostal space).

● Inferior border = lies along the line connecting the inferior end of the right border with the apex (mostly formed by the right ventricle).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What are auricles (auricular appendages)?

A

So named because of their ear-like appearance

They are outpouchings from the walls of the right and left atria.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is coronary circulation?

A

The arteries and veins that supply the heart are visible on its external surface.

The major arteries lie in grooves on the external surface called sulci (singular = sulcus; Latin for groove or furrow).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is Patent ductus arteriosus (PDA)?

A

The ductus arteriosus usually closes immediately after birth. In some infants, the ductus arteriosus does not close and remains open (patent).

After birth, the pressure in the aorta exceeds the pressure in the pulmonary trunk, hence blood flows through a patent ductus arteriosus from the aorta into the pulmonary trunk.

Over time, increased flow through the pulmonary vessels can lead to pulmonary hypertension (high pressure in the vessels of the lungs) which strains the right side of the heart.

36
Q

Explain the Clinical relevance of Hoarseness of the voice and lung cancer?

A

Cancer at the apex of the lung may involve the recurrent laryngeal nerve, which supplies most of the muscles of the larynx.

Nerve injury results in weakness or paralysis of the ipsilateral intrinsic laryngeal muscles, which move the larynx and the vocal cords (we will look at the larynx in detail in sessions 7 and 8).

Hoarseness results as the patient can no longer fully adduct their vocal cords.

37
Q

Explain the pathology of the pericardium?

A

The pericardial space allows the heart to move within the pericardial sac with each contraction. Pericardial effusion is an increase in fluid volume in the pericardial space.

Pericardial effusion may result from inflammation of the pericardium (a condition called pericarditis) or an accumulation of blood (due to trauma).

Rapid fluid accumulation in the pericardial space can be rapidly fatal because the fibrous pericardium cannot stretch and so the heart is compressed and unable to fill properly - a condition called cardiac tamponade

38
Q

Where do the coronary arteries arise from?

A

Ascending aorta

39
Q

Where do the cardiac veins return blood?

A

Return venous blood to the coronary sinus, which enters the right atrium

40
Q

What branches does the right coronary artery supply?

A

● Branches to the sinoatrial node and atrioventricular node supply these major
components of the electrical conducting system of the heart.

● The right marginal artery supplies the inferior border of the heart.

● The posterior interventricular artery (PIV) is the continuation of the right coronary artery on the inferior (diaphragmatic) surface of the heart. It runs in the posterior interventricular sulcus and supplies both ventricles.

41
Q

What are the two terminal branches of the left coronary artery?

A

● Anterior interventricular artery (or the left anterior descending; ‘LAD’).
● Circumflex artery (abbreviated to ‘Cx’).

42
Q

What territories do the main branches of the left coronary artery supply?

A

● The anterior interventricular artery (LAD) runs in the anterior interventricular sulcus towards the apex. It supplies both ventricles.

● One or two diagonal branches arise from the LAD.

● The circumflex artery runs around the heart onto the inferior/diaphragmatic surface. It supplies the left atrium, part of the right ventricle
and the left ventricle.

● The left marginal artery arises from the circumflex and supplies the left
ventricle.

43
Q

What does the origin of the posterior interventricular artery determine?

A

Determines if an individual has a right dominant or a left dominant coronary circulation.

● Most people have a right dominant circulation; the PIV arises from the right coronary. In these people, both the right and left coronary arteries supply the left ventricle.

● In those with a left-dominant circulation, the PIV arises from the circumflex artery; the left coronary artery supplies the entire left ventricle.

44
Q

Why is the origin of posterior interventricular artery important in clinical practice?

A

In someone with a right-dominant circulation, occlusion of the left main stem would impair blood flow to part of, but not the entire left ventricle.

In someone with a left-dominant coronary circulation, blockage of the left main stem occludes blood flow to the entire left ventricle.

45
Q

What do the valves inside the heart ensure?

A

Ensure unidirectional flow of blood through the chambers of the heart

46
Q

Where does the atrium receive deoxygenated blood from?

A

Via the superior and inferior venae cavae,
and from the heart via the coronary sinus

47
Q

What are the main features of the right atrium?

A

● interatrial septum which separates it from the left atrium

● fossa ovalis – a depression in the interatrial septum. It is the remnant of the
foetal foramen ovale. In the foetus the foramen ovale shunts oxygenated blood
from the right atrium to the left atrium, hence bypassing the lungs.

● crista terminalis – a muscular ridge that separates the smooth-walled posterior
part of the atrium from the anterior part, which has a ridged, muscular wall. The ridges are pectinate muscles and extend into the right auricle. The parts of the right atrium on either side of the crista have different embryological origins.

48
Q

Where does blood flow into the right ventricle from?

A

Blood flows into the right ventricle via the right atrioventricular valve, also called the tricuspid valve.

The flow of blood is mostly passive, but the right atrium does contract to empty fully.

49
Q

Where does the right ventricle pump blood into?

A

Pulmonary trunk, which bifurcates into a left and right pulmonary artery

50
Q

What is the purpose of the pulmonary valve?

A

The pulmonary valve at the entrance of the pulmonary trunk prevents backflow of blood into the right ventricle.

51
Q

Why is the wall of the right ventricle thicker than that of the right atrium?

A

As contraction of the right ventricle propels blood into the pulmonary trunk, the wall of the right ventricle is thicker than that of the right atrium.

52
Q

What are the internal features of the right ventricle?

A

● interventricular septum which separates it from the left ventricle

● trabeculae carneae – muscular ridges on the internal wall

● papillary muscles – modified regions of trabeculae carneae, which project into the lumen of the ventricle

● chordae tendineae – fibrous cords which connect the tips of the papillary muscles to the tricuspid valve

● moderator band – a modified region of the trabeculae carneae which connects
the interventricular septum to one of the papillary muscles.

53
Q

Where does the left atrium receive blood from?

A

Receives oxygenated blood from the lungs via the pulmonary veins (two from each lung)

54
Q

What structure do the walls of the left atrium have?

A

It has a thinner wall compared to the ventricles and internally has a smooth-walled posterior part and an anterior part bearing pectinate muscles.

Again, this reflects the left atrium’s development from two different embryological structures.

55
Q

Where does blood flow into the left ventricle from?

A

Via the left atrioventricular valve, also called the mitral valve.

The flow of blood is mostly passive, but the left atrium does contract to empty fully.

56
Q

Where does the left ventricle pump blood into?

A

Aorta

57
Q

What are the first branches from the aorta?

A

Coronary arteries

58
Q

What does the aortic value do?

A

The aortic valve at the entrance to the aorta prevents backflow of blood into the left ventricle.

59
Q

Why is the wall of the left ventricle thicker than the right ventricle?

A

Because contraction of the left ventricle propels blood into the systemic circulation, the wall of the left ventricle is thicker than that of the right ventricle

60
Q

What is it called when the ventricles contract?

A

Ventricular systole

61
Q

What happens to the valves during ventricular contraction?

A

The tricuspid and mitral valves close during ventricular contraction and prevent regurgitation of blood back into the atria, ensuring that blood can only flow out the ventricles via the great vessels (the pulmonary trunk and aorta).

62
Q

What do the papillary muscles and chordae tendineae do?

A

The papillary muscles and chordae tendineae are crucial for normal functioning of the atrioventricular valves.

These structures do not close the valves, but instead allow the closed valves to resist the pressure generated inside the ventricles during contraction and prevent them from being forced open.

63
Q

What happens to the valve cusps when pressure rises in the ventricles?

A

As pressure rises in the ventricles, the valve cusps, which project into the ventricle, start to close passively.

When the ventricles contract, the papillary muscles also contract. The papillary muscles tense the cords, which in turn ‘pull’ on the valve cusps and prevent them everting into the atria.

64
Q

What are the semilunar values?

A

The aortic and pulmonary valves are called semilunar valves, as their cusps are semi-circular (half-moon) shaped.

They prevent the backflow of blood from the aorta and pulmonary trunk into the left and right ventricles, respectively, that would otherwise occur at the end of ventricular contraction.

65
Q

How many cusps does each semilunar valve have?

A

Each semilunar valve has three semi-circular cusps.

Each cusp is attached to the inner wall of the vessel, with a free edge that projects into the vessel lumen. Each cusp forms a pocket, or sinus, between its free edge and the vessel wall.

66
Q

What happens to the valve cusps during ventricular systole?

A

When blood is forcefully propelled from the ventricles during ventricular systole, the valve cusps are ‘flattened’ onto the vessel wall and blood flows through the valve unimpeded.

At the end of ventricular systole, pressure in the ventricles drops. Once pressure in the ventricle is less than that in the vessel (aorta or pulmonary trunk), blood in the vessel starts to flow back towards the heart.

As it flows back, blood is immediately ‘caught’ in the valve cusps. The sinuses rapidly fill with blood and the cusps balloon out into the lumen.

The free edges of the three valve cusps contact each other in the lumen and close the valve orifice.

67
Q

In the aorta where do the coronary arteries arise from?

A

Two of the three aortic sinuses, hence the coronary arteries fill during ventricular relaxation (diastole).

68
Q

What are the auscultatory areas for each valve?

A

● Aortic valve = 2nd intercostal space, just to the right of the sternum.

● Pulmonary valve = 2nd intercostal space, just to the left of the sternum.

● Tricuspid valve = 5th intercostal space, just to the left of the sternum.

● Mitral valve = left 5th intercostal space, midclavicular line.

69
Q

What is the ‘pacemaker’ of the heart?

A

Sinoatrial node (SA), spontaneously generates electrical impulses

70
Q

Where is the SA node found?

A

It is located at the superior end of the crista terminalis.

71
Q

What is the rate of impulses the SA node generates?

A

70 per minute approx

72
Q

What do impulses from the SA node stimulate?

A

Stimulates contraction of the atria
Impulses are conducted to the atrioventricular (AV) node

73
Q

Where is the AV node located?

A

Inferior end of the interatrial septum

74
Q

What is the atrioventricular bundle (Bundle of His)?

A

Conducting fibres

The atrioventricular bundle divides into two groups of fibres - the right and left bundle branches.

75
Q

What do the bundle branches give rise to?

A

Purkinje fibres that enter the myocardium of the left and right ventricles, respectively, and stimulate contraction.

76
Q

What is the SA node supplied by?

A

RCA in approximately 60% of people and by the
LCA in approximately 40% of people.

77
Q

What is the AV node supplied by?

A

The AV node is usually supplied by the posterior interventricular artery. In most people, the PIV arises from the RCA.

● In most people, the LCA supplies the Bundle of His.

78
Q

What can occlusion of the coronary arteries lead to?

A

Can result in conduction abnormalities,
in addition to myocardial ischaemia.

79
Q

What is the heart innervated by?

A

The heart is innervated by sympathetic and parasympathetic fibres.
These fibres act upon the SA node and can change the rate and force of myocardial contraction.

● Sympathetic stimulation increases the heart rate and force of contraction.
● Parasympathetic stimulation slows the heart rate and force of contraction.

The heart is also innervated by visceral afferent fibre

80
Q

What are the visceral afferent fibres?

A

Visceral afferent fibres convey sensory information from the heart back to the CNS.

Usually, this sensory information doesn’t reach our conscious perception. However, if the myocardium is ischaemic, this visceral sensory information is relayed back to our conscious perception and may be perceived as pain, burning, tightness or pressure in the chest.

Typically, the pain cannot be pinpointed, but is felt generally in the chest, the left side of the neck and / or the left arm. This is called referred pain.

81
Q

What is myocardial infarction?

A

This is the death of a region of myocardium secondary to occlusion (blockage) of the coronary vessel that supplies it.

Most commonly, it is caused by atherosclerosis within the coronary arteries. A fatty plaque in a coronary artery may grow until it narrows the vessel lumen (stenosis) and severely restricts blood flowing through it.

A fatty plaque may shear from the vessel wall, causing a clot to form in the lumen, which occludes blood flow.

82
Q

Explain valve dysfunction?

A

The AV and semilunar valves may become narrowed (stenosis) or incompetent.
Incompetent valves allow regurgitation of blood back into the preceding chamber. Both result in turbulent blood flow that produce murmurs on auscultation.

Valve dysfunction may be congenital (i.e. the patient is born with it) or acquired. For example, an AV valve may become dysfunctional if a myocardial infarct involves the associated papillary muscles.

83
Q

What is cardiomyopathy?

A

Cardiomyopathies are diseases of myocardium, and most are inherited.

There are different types – some cause the myocardium to thin, whereas others result in the myocardium becoming thick and stiff.

This affects the heart’s ability to pump efficiently and can lead to heart failure. Unfortunately, some cardiomyopathies have no obvious symptoms and are a cause of sudden cardiac death in otherwise healthy, young people.

84
Q

Explain conducting system abnormalities?

A

Myocardial infarction can cause conduction disturbances if the vessels that supply the conducting system are affected.

Sometimes patients may have no symptoms and the abnormality is picked up on ECG. Some conducting system abnormalities are life-threatening, but can be managed if they are detected, for example, by fitting a pacemaker or an internal cardiac defibrillator (ICD).

85
Q

What is heart failure?

A

Heart failure occurs when the heart does not pump efficiently. There are many possible causes, including dysfunction of one or more of the heart valves, or an ability of the myocardium to contract properly (e.g. due to damage by myocardial infarction or cardiomyopathy).

Signs and symptoms of heart failure include tiredness, shortness of breath and leg swelling.

86
Q

Explain cardiac arrest

A

Cardiac arrest is the cessation of cardiac contraction. Sometimes there is still detectable electrical activity, but the heart does not contract in response.

Myocardial infarction and conducting system abnormalities are two causes of cardiac arrest, but there are many more.