CVS S2+3 - The Heart as a Pump & Congenital Heart Disease + DR Work

Question 1

What are the properties of cardiac muscle that allow the heart to pump? (TOB)

Answer 1

Striated

Branching

Central nuclei

Intercalated disks

Gap junctions - Electrical transmission

Adherens type junctions - Anchorage for actin

Question 2

Muscle cells in the heart are connected physically, but how else?

Answer 2

Electrically

Question 3

Electrical activity in one cardiac muscle cell of the heart leads to what? (in normal circumstances)

Answer 3

Activity in all cardiac muscle cells

Question 4

What are ‘pacemaker’ cells?

Answer 4

A small group of cells that generate action potentials in the heart to produce coordinated contraction

Question 5

How long is a cardiac action potential and what does this amount of time correspond to physically?

Answer 5

280ms

The length of systole

Question 6

Define ‘systole’

Answer 6

The period where the myocardium is contracting

Question 7

Define ‘diastole’

How long does it last typically?

Answer 7

The relaxation in between contraction of the heart, lasting about 700ms

Question 8

Is the length of systole and diastole variable?

Answer 8

Length of systole is fixed, however diastole is variable

Question 9

Describe how electrical excitation spreads through the heart during systole

Relate this to the physical events of systole

Answer 9

1. Sino-atrial (SA) node fires and AP which spreads over the atria (atrial systole), it reached the Atrioventricular (AV) node where it is delayed for 120ms
2. From the AVN, excitation spreads down the ventricular septum
3. Excitation spreads from inner (endocarial) to outer (epicardial) myocardial surfaces
4. Ventricles contract from the apex up, forcing blood out of the outflow valves

Question 10

How is ventricular muscle organised?

How does this facilitate the pumping of blood?

Answer 10

Organised in figure of 8 bands that squeeze the ventricular chambers simultaneously from apex upward

The apex contracts first and relaxes last to prevent back flow

Question 11

How do the left and right side of the heart differ?

Answer 11

Left has thicker myocardium (as it must pump blood around the body, not just the lungs)

Right side has the SA node, the main pacemaker

Question 12

Describe the sequence of pressure and volume changes over the course of one cardiac cycle beginning at the start of diastole

Hint: Long card, but it’s no use in small chunks

Answer 12

Early diastole:

• Ventricles relax and intraventricular (IV) pressure falls - Inflow valves (Mitral/Tricuspid) open
• Atria now distended from continuous venous return during systole
• Blood forced rapidly into ventricles (Rapid Filling) due to low IV pressure

NB: No atrial contraction yet!

Diastole Cont.:

• Ventricles fill at steadily decreasing rate
• Stops when IV and atrial pressures equalise
• At low heart rates, ventricles mostly full

Atrial systole:

• Small amount of extra blood forces into ventricles by contraction as atrial pressure rises
• IV pressure rises as result

Ventricular systole:

• As IV pressure rises blood tends to flow into the atria turbulently, closing the inflow valves
• Then delay of 100-150ms
• Ventricles contract isovolumetrically, raising pressure rapidly
• Outflow valves open
• Rapid ejection period where arterial and intraventricular pressures rise to max

End of Ventricular systole:

• IV pressure falls below arterial pressue
• Arterial pressure closes outflow valves
• IV pressure falls below atrial pressure

Repeat!

Question 13

When do the heart’s outflow valves open and close

What causes them to open and close?

Answer 13

Open in systole

Open due to Intraventricular pressure being higher than arterial

Close at the end of systole

Close due to arterial pressure being higher than intraventricular pressure (causing a backflow of blood)

Question 14

When do the heart’s inflow valves open and close?

What causes them to open and close?

Answer 14

Open in early diastole

Open due to atrial pressure being higher than ventricular pressure

Close at the start of ventricular systole

Close due to ventricular pressure being higher than atrial pressure (causing a backflow of blood)

Question 15

What is the origin of the 1st heart sound?

What does it sound like?

Answer 15

AV valves close causing oscillations in a variety of structures

A mixed sound with crescendo-descendo quality - ‘lup’

Question 16

What is the origin of the 2nd heart sound?

What does it sound like?

Answer 16

AS the semi-lunar valves close oscillations are induced in a variety of structures, including the column of blood in the arteries

Sound is shorter duration, higher frequency and lower intensity than the 1st sound - ‘dup’

Question 17

When might the 3rd and 4th heart sounds be heard?

Answer 17

3rd may be heard early in diastole

4th sometimes associated with atrial contraction

Question 18

What is a heart murmur?

What causes them?

Answer 18

Additional or distorted heart sounds

Caused by turbulent blood flow (E.g. in exercise or stenotic valves)

Question 19

What is depicted in this diagram?

Label the Axes

What is represented by the red, blue and grey lines?

Select from A, B, C or D:

• Where valves open and close
• Where the 1st and 2nd heart sounds are produced

Answer 19

Pressure in the left atrium, left ventricle and aorta over the course of one cardiac cycle

Y = Time (s)

X = Pressure

Red = Left ventricular pressure

Blue = Aortic pressure

Grey = Left atrial pressure

A = Mitral valve closes, 1st heart sound

B = Aorta opens

C = Aorta closes, 2nd heart sound

D = Mitral valve opens

Question 20

What is the incidence rate for congenital heart disease?

Answer 20

6-8 per 1000 births

Question 21

What are the most common two heart defects?

Answer 21

Ventricular septal defects (VSDs)

Followed by Atrial septal defects (ASDs)

Question 22

What are the 5 Acyanotic defects we need to consider?

Answer 22

ASD

Patent foramen ovale

VSD

Patent ductus arteriosus

Coarctation of the Aorta

Question 23

Why are the acyanotic defects acyanotic?

Answer 23

They do not result in lower than normal oxygen concentration in the blood leaving the left ventricle

Question 24

What is ASD?

What is the incidence rate?

Answer 24

An acyanotic defect

An opening in the septum of the two atria which persists following birth

Allows left to right flow (higher pressure in left atrium) hence acyanotic

67 in 100,000 live births

Question 25

Where in the atrial septum does ASD occur?

Include examples of two sites where it might occur

Answer 25

Can occur almost anywhere

Most common is the foramen ovale (ostium secundum ASD)

Ostium primum ASD occurs in the inferior septum and is less common

Question 26

What is the foramen ovale?

Answer 26

An opening in the atrial septum that exists prenatally to allow right to left shunting of oxygenated blood

Question 27

What haemodynamic effects does left to right shunting of blood in ASD have?

Answer 27

Increased pulmonary resistance

Pulmonary hypertension (rarely)

Eventual right heart failure (rarely)

If pulmonary resistance increases to the degree that right atrial pressure increases past left atrial pressure the shunt direction will reverse (Eisenmenger syndrome)

Question 28

What is a patent foramen ovale?

How common is it?

Answer 28

A form of ASD that is clinically silent

This is due to higher left atrial pressure closing the flap valve in the septum

Occurs in 20% of the population

Question 29

Patent foramen ovale can lead to paradoxical embolism, explain how

Answer 29

Allows venous embolisms into the left side of the heart if right atrial pressure increases (even transiently)

Question 30

What is ventricular septal defect? (VSD)

Where does VSD most commonly occur?

Answer 30

An acyanotic defect

An opening in the interventricular septum

Most commonly occurs in the membranous portion of the septum

Question 31

In VSD, which direction is blood shunted?

What are the other haemodynamic effects of VSD?

Answer 31

Left to right due to higher pressure in the left ventricle

Pulmonary venous congestion

Eventual pulmonary hypertension

Question 32

What would you heart upon ascultation of a newborn with patent ductus arteriosus?

Answer 32

A mechanical murmur constantly through systole/diastole

Question 33

What is coarctation of the aorta?

Answer 33

An acyanotic defect

A narrowing of the aortic lumen in the region of the ligamemtum arteriosum (former ductus arteriosus)

Question 34

What effects does aortic coarctation have on the body?

Answer 34

Increases afterload on the left ventricle that can lead to left ventricular hypertrophy

Vessels of the head and upper limbs supplied by branches of the aorta that are proximal to the coarctation therefore blood supply to head + arms not compromised

Blood flow to the rest of the body is reduced

Question 35

Aortic coarctation ranges from mild to severe, what is the symptomatic difference?

Answer 35

Mild:

Defect might only be detected in later life

Severe:

An infant might present with the symptoms of heart failure shortly after birth

Question 36

What are the signs for aortic coarctation that you might pick up during a physical exam?

Answer 36

Femoral pulses will be weak and delayed

Upper body hypertension

Question 37

What are the 4 cyanotic defects we need to consider?

Answer 37

Tetralogy of Fallot

Tricuspid Atresia

Transposition of the great arteries

Hypoplastic left heart

Question 38

What is tetralogy of Fallot?

Answer 38

Cyanotic defect

A group of 4 lesions occuring together as a result of a single developmental defect which places the outflow portion of the interventricular septum too far anterior and cephelad

The 4 lesions are:

• VSD
• Overriding Aorta
• Pulmonary stenosis (variable degree)
• Right ventricular hypertrophy (variable degree)

Question 39

In tetralogy of fallot, what causes the right ventricular hypertrophy?

Answer 39

Caused by pulmonary stenosis as the right ventricle must operate at a higher pressure as a result of this

This causes the RV hypertrophy

Question 40

In which direction does blood flow through the VSD present in tetralogy of fallot?

Explain why

Answer 40

Right to left shunt, hence cyanotic defect:

• This is because of the pressure in the right ventricle is higher than in the LV due to pulmonary stenosis
• Aortic valve has a biventricular connection (over-riding aorta)

Question 41

What does the severity of the shunt in tetralogy of fallot depend on?

When do mild cases present versus severe cases?

Answer 41

The degree of pulmonary stenosis determines the magnitude of the shunt

Mild cases may present in adulthood

Severe cases will present with cyanosis in infancy

Question 42

What is tricuspid atresia?

Answer 42

A cyanotic condition in which there is lack of development of the tricuspid valve resulting in lack of blood flow from the right atria to the right ventricle

Question 43

How can someone with tricuspid atresia survive past birth?

Answer 43

There must be a complete right to left shunt in the atria:

• Patent foramen ovale
• Atrial septal defect

And a left to right shunt in the ventricles or vessels:

• VSD
• Patent ductus arteriosus

Question 44

What is transposition of the great arteries?

Answer 44

Connection of the right ventricle to the aorta and the left ventricle to the pulmonary trunk

Resulting in two unnconnected parallel circulations

Question 45

In what situations may someone with transposition of the great arteries survive?

Answer 45

The condition untreated is incompatible with life

A shunt must be made after birth to sustain life until surgical correction can be made to allow the pateint to survive

Question 46

What is hypoplastic left heart?

How is it compensated for?

Answer 46

A cyanotic condition in which the left ventricle and aorta are severely underdeveloped

To compensate an ASD or patent foramen ovale must be present

A patent ductus arteriosus forms a fight to left shunt to allow systemic circulation

Question 47

Can a pateint with hypoplastic left heart survive with just endogenous compensation?

Answer 47

No, requires surgical intervention to correct

Question 48

What are some variations of the coronary artery?

Answer 48

Can arise from a common trunk

Can be three CAs (additional posterior)

May exist as a double structure (two RCAs for example)

Question 49

What is dominance in reference to cardiac blood supply?

Give percentages of people in which each type of dominance is found

Answer 49

Dominance is determined by which coronary artery supplies the posterior interventricular artery (a.k.a. posterior descending artery)

Right dominant: 70%

Left dominant: 10%

Co-dominant: 20%

Question 50

From which vessels does blood flow into the right atrium?

Where do these vessels enter the right atrium?

Answer 50

Superior and inferior vena cavae

The coronary sinus

Superior vena cavae enters the superior portion of the atrium

Inferior VC and coronary sinus enter from the posterior portion of the atrium

Question 51

The right atrium is divided into two spaces, describe the structure of each space’s walls

What defines the border between them and where is it located?

What are the walls of these spaces derived from embryologically?

Answer 51

Sinus of the vena cavae:

Smooth, thin walls

Posterior to the crista terminalis

Derived from the right horn of the sinus venosus

Atrium proper:

Walls are covered in ridges (muscli pectinati) that fan out from the crista terminalis

Anterior to the crista terminalis

Includes the right auricle

Derived from the primitve atrium

Two spaces divided by:

Crista terminalis interiorly

Sulcus terminalis cordis exteriorly

Question 52

Discounting the structure of the walls and vessel openings of the right atrium, what other important structures may be found there?

Describe their location in the atrium and embryological derivation or importance (if applicable)

Answer 52

Valves of the Inferior vena cavae and coronary artery:

Associated with their respective valves

Not of any use to an adult, direct blood toward the foramen ovale in the embryo

The interatrial septum:

Can been seen in the posterior of the right atrium

Fossa ovales and its prominant margin, the limbus of the fossa ovales:

Just above the orifice of the inferior vena cavae on the interatrial septum

Fossa ovales marks the location of the embryonic foramen ovale

Right atrioventricular orifice:

Seen on the right of the atrium facing anterior and medially

Question 53

The left atrium is divided into two spaces, What are they called and what is their structure analogous to?

What are the walls of these spaces derived from embryologically?

What defines the border between them and where is it located?

Answer 53

Posterior inflow portion:

Analogous in structure to the sinus of the vena cavae in the right atrium

Derived from the proximal portions of the pulmonary veins

Anterior half:

Analogous in structure to the right atrium proper (includes the left auricle)

Derived from the primitive atrium

Nothing clearly separates the two components

Question 54

Discounting the structure of the walls of the left atrium, what other structures or important sites may be found here?

Answer 54

Interatrial septum:

Part of the anterior wall

Valve of the foramen ovale:

Found on the interatrial septum

Prevented blood from passing left to right in the embryo

Pulmonary vein inflows:

Posterior wall recieves the inflows of the 4 pulmonary veins

Question 55

Why are the walls of the ventricles differnt thickness?

Answer 55

The left ventricular wall is thicker than the right as it must support systemic circulation

The right ventricle must only support pulmonary circulation

Question 56

Describe the structure of the pulmonary and aortic valves

Hint: Describe the general structure and point out any differences as you go along

Answer 56

Consist of three semi-lunar cusps

Left and right common

3rd cusp posterior in the aorta, anterior in the pulmonary

Superior edge of each cusp has a central nodule and lateral lunula

Each cusp forms a pocket like sinus

In the aorta, the left and right coronary arteries originate from the left and right sinuses

Question 57

Describe the structure of the mitral and tricuspid valves (including their associated structures in the ventricles)

Answer 57

Found in the atrioventricular orifices

Consist of:

• Cusps

Anterior and posterior cusps in the mitral

Anterior, posterior and septal in the tricuspid

Each cusps has an associated papillary muscle:

Named according to the cusp they anchor (eg. Right septal papillary muscle)

These project from the walls of the ventricle

Chordae tendineae:

Connect the papillary muscles and the cusps

Question 58

What is the function of the papillary muscles and the chordae tendineae?

Answer 58

Anchor the mitral and tricuspid valve cusps to prevent their inversion into the atria during ventricular systole