CVS S2+3 - The Heart as a Pump & Congenital Heart Disease + DR Work Flashcards
This deck Does not test L.O. 2.1 from this session (Describe the basic structure of the heart)
What are the properties of cardiac muscle that allow the heart to pump? (TOB)
Striated
Branching
Central nuclei
Intercalated disks
Gap junctions - Electrical transmission
Adherens type junctions - Anchorage for actin
Muscle cells in the heart are connected physically, but how else?
Electrically
Electrical activity in one cardiac muscle cell of the heart leads to what? (in normal circumstances)
Activity in all cardiac muscle cells
What are ‘pacemaker’ cells?
A small group of cells that generate action potentials in the heart to produce coordinated contraction
How long is a cardiac action potential and what does this amount of time correspond to physically?
280ms
The length of systole
Define ‘systole’
The period where the myocardium is contracting
Define ‘diastole’
How long does it last typically?
The relaxation in between contraction of the heart, lasting about 700ms
Is the length of systole and diastole variable?
Length of systole is fixed, however diastole is variable
Describe how electrical excitation spreads through the heart during systole
Relate this to the physical events of systole
- 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
- From the AVN, excitation spreads down the ventricular septum
- Excitation spreads from inner (endocarial) to outer (epicardial) myocardial surfaces
- Ventricles contract from the apex up, forcing blood out of the outflow valves
How is ventricular muscle organised?
How does this facilitate the pumping of blood?
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
How do the left and right side of the heart differ?
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
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
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!
When do the heart’s outflow valves open and close
What causes them to open and close?
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)
When do the heart’s inflow valves open and close?
What causes them to open and close?
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)
What is the origin of the 1st heart sound?
What does it sound like?
AV valves close causing oscillations in a variety of structures
A mixed sound with crescendo-descendo quality - ‘lup’
What is the origin of the 2nd heart sound?
What does it sound like?
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’
When might the 3rd and 4th heart sounds be heard?
3rd may be heard early in diastole
4th sometimes associated with atrial contraction
What is a heart murmur?
What causes them?
Additional or distorted heart sounds
Caused by turbulent blood flow (E.g. in exercise or stenotic valves)
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
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
What is the incidence rate for congenital heart disease?
6-8 per 1000 births
What are the most common two heart defects?
Ventricular septal defects (VSDs)
Followed by Atrial septal defects (ASDs)
What are the 5 Acyanotic defects we need to consider?
ASD
Patent foramen ovale
VSD
Patent ductus arteriosus
Coarctation of the Aorta
Why are the acyanotic defects acyanotic?
They do not result in lower than normal oxygen concentration in the blood leaving the left ventricle
What is ASD?
What is the incidence rate?
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
Where in the atrial septum does ASD occur?
Include examples of two sites where it might occur
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
What is the foramen ovale?
An opening in the atrial septum that exists prenatally to allow right to left shunting of oxygenated blood
What haemodynamic effects does left to right shunting of blood in ASD have?
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)
What is a patent foramen ovale?
How common is it?
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
Patent foramen ovale can lead to paradoxical embolism, explain how
Allows venous embolisms into the left side of the heart if right atrial pressure increases (even transiently)
What is ventricular septal defect? (VSD)
Where does VSD most commonly occur?
An acyanotic defect
An opening in the interventricular septum
Most commonly occurs in the membranous portion of the septum
In VSD, which direction is blood shunted?
What are the other haemodynamic effects of VSD?
Left to right due to higher pressure in the left ventricle
Pulmonary venous congestion
Eventual pulmonary hypertension
What would you heart upon ascultation of a newborn with patent ductus arteriosus?
A mechanical murmur constantly through systole/diastole
What is coarctation of the aorta?
An acyanotic defect
A narrowing of the aortic lumen in the region of the ligamemtum arteriosum (former ductus arteriosus)
What effects does aortic coarctation have on the body?
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
Aortic coarctation ranges from mild to severe, what is the symptomatic difference?
Mild:
Defect might only be detected in later life
Severe:
An infant might present with the symptoms of heart failure shortly after birth
What are the signs for aortic coarctation that you might pick up during a physical exam?
Femoral pulses will be weak and delayed
Upper body hypertension
What are the 4 cyanotic defects we need to consider?
Tetralogy of Fallot
Tricuspid Atresia
Transposition of the great arteries
Hypoplastic left heart
What is tetralogy of Fallot?
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)
In tetralogy of fallot, what causes the right ventricular hypertrophy?
Caused by pulmonary stenosis as the right ventricle must operate at a higher pressure as a result of this
This causes the RV hypertrophy
In which direction does blood flow through the VSD present in tetralogy of fallot?
Explain why
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)
What does the severity of the shunt in tetralogy of fallot depend on?
When do mild cases present versus severe cases?
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
What is tricuspid atresia?
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
How can someone with tricuspid atresia survive past birth?
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
What is transposition of the great arteries?
Connection of the right ventricle to the aorta and the left ventricle to the pulmonary trunk
Resulting in two unnconnected parallel circulations
In what situations may someone with transposition of the great arteries survive?
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
What is hypoplastic left heart?
How is it compensated for?
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
Can a pateint with hypoplastic left heart survive with just endogenous compensation?
No, requires surgical intervention to correct
What are some variations of the coronary artery?
Can arise from a common trunk
Can be three CAs (additional posterior)
May exist as a double structure (two RCAs for example)
What is dominance in reference to cardiac blood supply?
Give percentages of people in which each type of dominance is found
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%
From which vessels does blood flow into the right atrium?
Where do these vessels enter the right atrium?
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
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?
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
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)
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
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?
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
Discounting the structure of the walls of the left atrium, what other structures or important sites may be found here?
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
Why are the walls of the ventricles differnt thickness?
The left ventricular wall is thicker than the right as it must support systemic circulation
The right ventricle must only support pulmonary circulation
Describe the structure of the pulmonary and aortic valves
Hint: Describe the general structure and point out any differences as you go along
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
Describe the structure of the mitral and tricuspid valves (including their associated structures in the ventricles)
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
What is the function of the papillary muscles and the chordae tendineae?
Anchor the mitral and tricuspid valve cusps to prevent their inversion into the atria during ventricular systole
