Anatomy of the Mediastinum

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Questions and Answers

What is the most anterior structure of the heart?

Aorta

Right ventricle (correct)

Pulmonary artery

Left ventricle

What is the term for the superior aspect of the heart at the valve plane?

Apex of the heart

Right lateral margin

Base of the heart (correct)

Left lateral margin

Where is the apical impulse typically located?

Sixth intercostal space

Seventh intercostal space

Fifth intercostal space (correct)

Fourth intercostal space

What is the significance of a PMI >2.5 cm?

Evidence of left ventricular hypertrophy Signup and view all the answers

What is the location of the cardiac apex?

Inferolaterally Signup and view all the answers

What is the term for the point of maximal impulse?

PMI Signup and view all the answers

What is the location of the thoracic duct in relation to the heart?

Posterior to the heart Signup and view all the answers

What is the location of the inferior border of the right ventricle?

Below the junction of the sternum and the xiphoid process Signup and view all the answers

What occurs when the pressure in the left ventricle exceeds the pressure in the aorta?

The aortic valve opens Signup and view all the answers

What is the normal correlation between maximal left ventricular pressure and systolic blood pressure?

Maximal left ventricular pressure corresponds to systolic blood pressure Signup and view all the answers

What produces the first heart sound, S1?

Closure of the mitral and tricuspid valves Signup and view all the answers

What is the result of the aortic valve closing?

The second heart sound, S2, is produced Signup and view all the answers

In which condition may an audible opening snap (OS) be heard?

Mitral stenosis Signup and view all the answers

What may produce a third heart sound, S3, in children and young adults?

Rapid deceleration of the column of blood against the ventricular wall Signup and view all the answers

What is the significance of a fourth heart sound, S4?

It marks atrial contraction Signup and view all the answers

When does the tricuspid valve close?

During systole Signup and view all the answers

What is the term used to describe the mitral and tricuspid valves due to their location?

Atrioventricular (AV) valves Signup and view all the answers

What is the shape of the valve leaflets of the aortic and pulmonic valves?

Half-moon Signup and view all the answers

What is the significance of an S3 sound in a healthy adult?

It is correlated with diastolic heart failure Signup and view all the answers

What occurs during ventricular relaxation?

Blood flows from atrium to ventricle Signup and view all the answers

What is the cardiac cycle?

The complete movement of the heart from the beginning of one heartbeat to the beginning of the next one Signup and view all the answers

During systole, which valve is open and which valve is closed?

Aortic valve is open, mitral valve is closed Signup and view all the answers

What corresponds to an abrupt deceleration of inflow across the mitral valve?

S3 Signup and view all the answers

What corresponds to increased left ventricular end diastolic stiffness which decreases compliance?

S4 Signup and view all the answers

What is the primary cause of the second heart sound, S2?

Closure of the aortic and pulmonic valves Signup and view all the answers

During which phase of respiration does the right ventricular ejection period increase?

Inspiration Signup and view all the answers

Which of the following factors contributes to the 'hangout time' that delays P2?

Distensibility of the pulmonary vascular bed Signup and view all the answers

Which component of the S2 is normally louder?

A2 Signup and view all the answers

Where is the mitral sound of S1 best heard?

The cardiac apex Signup and view all the answers

What is the result of the increased right heart filling time during inspiration?

Increased right ventricular stroke volume and duration of right ventricular ejection Signup and view all the answers

Where is the P2 component of the S2 best auscultated?

The second and third left intercostal spaces Signup and view all the answers

What is the result of the faster right ventricular ejection period during expiration?

A2 and P2 fuse into a single sound Signup and view all the answers

What is the characteristic of a stenotic valve?

Abnormally narrowed orifice Signup and view all the answers

What is the location on the chest wall where you auscultate the pulmonic valve?

Left second and third intercostal spaces close to the sternum Signup and view all the answers

What is the term used to describe the murmur produced by blood leaking backward in a retrograde direction?

Regurgitant murmur Signup and view all the answers

What is the typical origin of sounds at the cardiac apex?

Mitral valve Signup and view all the answers

What is the term used to describe the characteristic sound of turbulent blood flow?

Murmur Signup and view all the answers

At which location on the chest wall do you auscultate the tricuspid valve?

Lower left sternal border Signup and view all the answers

What is the effect of increased blood volume in a dilated right ventricle on preload?

Increases preload Signup and view all the answers

Which of the following decreases myocardial contractility?

Impaired blood flow or oxygen delivery to the myocardium Signup and view all the answers

What is the primary source of resistance to ventricular contraction?

All of the above Signup and view all the answers

What is the term for the pathologic increase in preload?

Volume overload Signup and view all the answers

What is the result of pathologic increases in preload and afterload?

Clinical heart failure Signup and view all the answers

What is the effect of exhalation on right ventricular preload?

Decreases preload Signup and view all the answers

What is the normal range of times that the sinus node automatically discharges an impulse in one minute?

60 to 100 times Signup and view all the answers

What is the percentage of ventricular volume ejected during each heartbeat in a normal heart?

60% Signup and view all the answers

What is the term for the load that stretches the cardiac muscle before contraction?

Preload Signup and view all the answers

What is the result of increasing venous return to the right heart?

Increased right ventricular preload Signup and view all the answers

What is the term for the classification of heart failure based on the ejection fraction?

Heart failure with reduced ejection fraction Signup and view all the answers

What is the pathway of the electrical impulse in the heart?

Sinus node to AV node to bundle of His to ventricular myocardium Signup and view all the answers

What is the product of heart rate and stroke volume?

Cardiac output Signup and view all the answers

What is the muscle that the electrical conduction system stimulates and coordinates the contraction of?

Cardiac muscle Signup and view all the answers

Study Notes

Mediastinum Structure

Located centrally in the thoracic cavity
Bordered by lungs on either side, sternum anteriorly, and thoracic vertebral bodies posteriorly
Houses heart, great vessels, esophagus, trachea, thoracic duct, and thoracic lymph nodes

Heart Structure

Right ventricle (RV) is the most anterior structure of the heart
RV forms a wedge-like structure behind and to the left of the sternum
Inferior border of RV lies below the junction of the sternum and the xiphoid process
RV narrows superiorly and joins the pulmonary artery at the level of the sternal angle
Left ventricle (LV) forms the left lateral margin of the heart
Tapered inferior tip of LV is the cardiac apex
Cardiac apex produces the apical impulse

Clinical Importance

Point of maximal impulse (PMI) locates the left border of the heart
PMI is normally found in the fifth intercostal space at or just medial to the left midclavicular line
PMI >2.5 cm is evidence of left ventricular hypertrophy (LVH)
Displacement of PMI lateral to the midclavicular line or >10 cm lateral to the midsternal line occurs in LVH and ventricular dilatation
In chronic obstructive pulmonary disease (COPD), the most prominent palpable impulse may be in the xiphoid or epigastric area due to right ventricular hypertrophy

Aorta and Vena Cavae

Aorta curves upward from the left ventricle to the level of the sternal angle
Aorta arches posteriorly to the left and then downward
Superior and inferior venae cavae channel venous blood from the upper and lower portions of the body into the right atrium

Cardiac Chambers, Valves, and Blood Flow

The cardiac chambers include the left and right atria, and the left and right ventricles.
The valves include the mitral, tricuspid, aortic, and pulmonic valves.
The mitral and tricuspid valves are also known as atrioventricular (AV) valves.
The aortic and pulmonic valves are also known as semilunar valves.
Blood flows from the atria to the ventricles through the open AV valves during diastole.
Blood flows from the ventricles to the aorta and pulmonary artery through the open aortic and pulmonic valves during systole.

Heart Sounds

The heart sounds of S1 and S2 arise from the vibrations of the valve leaflets, adjacent cardiac structures, and the flow of blood.
S1 corresponds to the closure of the mitral and tricuspid valves.
S2 corresponds to the closure of the aortic and pulmonic valves.
S3 corresponds to an abrupt deceleration of inflow across the mitral valve.
S4 corresponds to increased left ventricular end diastolic stiffness which decreases compliance.

Cardiac Cycle

The cardiac cycle describes the complete movement of the heart and includes the period from the beginning of one heartbeat to the beginning of the next one.
Systole is the period of ventricular contraction when the left ventricle ejects blood into the aorta.
Diastole is the period of ventricular relaxation when the ventricle fills with blood from the atrium.
During systole, the aortic valve is open, and the mitral valve is closed.
During diastole, the aortic valve is closed, and the mitral valve is open.

Valve Function

The mitral valve opens during diastole, allowing blood to flow from the left atrium to the left ventricle.
The mitral valve closes during systole, preventing blood from regurgitating back into the left atrium.
The aortic valve opens during systole, allowing blood to flow from the left ventricle into the aorta.
The aortic valve closes during diastole, preventing blood from regurgitating back into the left ventricle.

Pathological Heart Sounds

An S3 gallop often indicates pathology in older adults.
An S4 marks atrial contraction and can reflect a pathologic ventricular stiffness, as seen in hypertension or an acute myocardial infarction.

Heart Sounds

Right ventricular and pulmonary arterial pressures are significantly lower than corresponding pressures on the left side of the heart.

Right-Sided Cardiac Events

Right-sided cardiac events usually occur slightly later than those on the left side.
During inspiration, right heart filling time is increased, which increases right ventricular stroke volume and the duration of right ventricular ejection.

Splitting of S2

The second heart sound, S2, is caused primarily by closure of the aortic and pulmonic valves.
S2 has two components: A2 (aortic valve closure) and P2 (pulmonic valve closure).
During inspiration, S2 splits into its two audible components due to delayed closure of the pulmonic valve, P2.
During expiration, A2 and P2 fuse into a single sound, S2.
A2 is normally louder due to high pressure in the aorta and is heard throughout the precordium.
P2 is relatively soft due to lower pressure in the pulmonary artery and is best auscultated near its anatomic location, the second and third left intercostal spaces close to the sternum.

Splitting of S1

S1 also has two components: an earlier mitral sound and a later tricuspid sound.
The mitral sound can be heard throughout the precordium and is loudest at the cardiac apex.
The softer tricuspid component is heard best at the lower left sternal border.
Splitting of S1 does not vary with respiration.
The earlier louder mitral component may mask the tricuspid sound, so splitting is not always detectable.

Heart Murmurs

Heart murmurs are distinct sounds produced by the heart, characterized by their pitch and longer duration.
They are caused by turbulent blood flow and often indicate valvular heart disease.

Types of Heart Murmurs

Stenotic murmurs occur when a valve has an abnormally narrowed orifice, obstructing blood flow (e.g., aortic stenosis).
Regurgitant murmurs occur when a valve closes abnormally, allowing blood to leak backward in a retrograde direction.

Auscultation of Heart Sounds and Murmurs

The location on the chest wall where heart sounds and murmurs are auscultated helps identify the valve or chamber where they originate.

Chest Wall Location and Valve Association

Right second intercostal space or cardiac apex: Aortic valve
Left second and third intercostal spaces close to the sternum: Pulmonic valve
At or near the lower left sternal border: Tricuspid valve
At and around the cardiac apex: Mitral valve

Electrical Conduction System

The electrical conduction system stimulates and coordinates the contraction of cardiac muscle.
The sinus node, a group of specialized cardiac cells, acts as the cardiac pacemaker, automatically discharging an impulse 60-100 times per minute.

Impulse Conduction

The impulse travels through both atria to the AV node, a specialized group of cells located low in the atrial septum.
The impulse is delayed at the AV node before passing down the bundle of His and its branches to the ventricular myocardium.
Muscular contraction follows: first the atria, then the ventricles.

Cardiac Output and Stroke Volume

Cardiac output is the volume of blood ejected from each ventricle in 1 minute.
Cardiac output is the product of heart rate and stroke volume.
Stroke volume is the volume of blood ejected with each heartbeat.
Stroke volume is dependent on preload, myocardial contractility, and afterload.

Ejection Fraction

The ejection fraction (EF) is the percentage of ventricular volume ejected during each heartbeat.
The normal EF is 60%.
Heart failure is classified into two distinct clinical entities based on the EF: heart failure with preserved EF and heart failure with reduced EF.

Preload, Myocardial Contractility, and Afterload

Preload refers to the load that stretches the cardiac muscle before contraction.
Right ventricular preload is the volume of blood in the RV at the end of diastole.
Physiologic causes of increased right ventricular preload include inspiration and increased volume of blood flow from exercising muscles.
Causes of decreased right ventricular preload include exhalation, dehydration, and pooling of blood in the capillary bed or the venous system.
Myocardial contractility refers to the ability of the cardiac muscle to shorten when given a load.
Contractility increases with sympathetic nervous system stimulation and decreases with impaired blood flow or oxygen delivery to the myocardium.
Afterload refers to the degree of vascular resistance to ventricular contraction.
Sources of afterload include the tone in the walls of the aorta, the large arteries, and the peripheral vascular tree, as well as the volume of blood already in the aorta.

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Description

Explore the mediastinum, a compartment in the thoracic cavity, and its contents, including the heart, blood vessels, and other vital structures.