Lecture 13 - Cardiac Cycle Flashcards
What chamber of the heart pumps deoxygenated blood to the lungs?
Right Ventricle
blood moves through the pulmonary artery away from heart to the lungs
What chamber of the heart should have thicker walls in a healthy patient?
The left ventricle
It needs to be more muscular to push blood through the body
How to calculate mean ABP?
Mean = diastolic pressure + (1/3) pulse pressure
How to calculate pulse pressure?
Systolic pressure - diastolic pressure
What is the pathway for conduction starting at the SA node?
SA node —> AV Node —> Bundle of His —> Right and Left Bundle Br.
Contractile cells do what in the heart and are the (most or least) numerous?
Are responsible for contraction and are the most numerous (~99% of heart cells)
What are conducting cells?
Cells responsible for electrical conduction in the heart.
e.g. SA node, AV node, bundle of His, bundle branches, purkinje fibres
PEA
Pulseless electrical activity
ECG shows signals but heart rate is 0
Asytole
What does this look like on the ECG? What else might we call it?
Flat line
Ventricular fibrilation look like what on an ECG?
Squiggles on the ECG screen
How much do atria contribute to cardiac output?
20%
AV block
What does it look like on an ECG?
Arrhythmia between the atria and the ventricle.
Will show a p wave without the presence of a QRS complex following
Ectopic pacemaker
When another area of the heart becomes the pacemaker
Chronotropy
autonomic effects on:
Influencing heart rate
Dromotropy
autonomic effects on:
Cardiac conduction
speed of beats
Apparently doesn’t always lead to an increase in heart rate if the effect is minute
Inotropy
Autonomic effects on:
Cardiac contractility
How hard it’s squeezing
Standardized lead placement
3 leads
White on the right front
Black on the left front
Red on the left hind
Smoke over fire to remember black and red
P wave
what action in the heart does this wave portray?
Atrial depolarization
QRS complex
what action in the heart causes this complex?
Ventricular depolarization
T wave
what action in the heart does this wave portray?
Ventricular repolarization
QT interval
What events would the mark the start and end of this interval?
time from start of ventricular depolarization to the end of ventricular repolarization
Heart rate calculation from ECG
hint: two variations exist depending on what strip you are reading
if 25mm/s strip 1500/R wave
if 50mm/s strip 3000/R wave
R waves (count the number of squares between R’s on the 2 different QRS complexes
Stroke volume
Blood volume ejected with one ventricular contraction
End diastolic volume - end systolic volume
Cardiac output
Total volume of blood ejected over time (expressed as ml or L/min)
SV x HR
What would happen if the mitral valve is leaky?
Blood backs up into the atria. Stroke volume will be decreased.
(Mitral valve is between left atrium and ventricle)
Frank Starling relationship
As the amount of blood that enters the heart increases, the heart naturally pumps harder to push out that extra blood.
Cardiac output correlates with end diastolic volume
As venous return increases cardiac output increases
Curvilinear relationship
4 Auscultation areas in dog
- Mitral valve (left AV) - left 5th intercostal space (beneath elbow)
- Aortic valve - left 4th intercostal space (level with shoulder) For hearing S2
- Pulmonic valve - Left 3rd intercostal space at sternal border (axilla)
- Tricuspid valve (right AV) - Right 3rd to 4th intercostal space at costal chondral junction
Causes of heart murmurs:
Leaky valves, stenosis valves, septal defects, decreased blood viscosity (e.g. anemia)
4 Descriptors of heart murmurs
Timing, intensity, location, quality
Baroreceptor reflex
Keeps blood pressure stable by adjusting heart rate based on sensing stretch in the carotid sinus
Patent ductus arteriosus
The patent ductus is a shunt needed for fetal hearts since they do not use their lungs. This shunt should close shortly after birth, when it does not it causes leakage of blood.
4 Auscultation areas in horses
- Mitral valve - left 5th intercostal space (1/3 distance from point of elbow to point of shoulder, caudal edge of triceps)
- Pulmonic valve - Left 3rd intercostal space (rostral dorsal to mitral valve)
- Aortic valve - left 4th intercostal space (under triceps)
- Tricuspid valve - Right 4th intercostal space (halfway between elbow and point of shoulder)
What happens to blood pressure when PDA is clamped?
Sharply increases
S1 heart sound
what sound does it make, where does it come from
Lub - AV valves close
S2 heart sound
What sound does it make and where does it come from
Dub - Aortic/Pulmonic valves close
Which type of adrenergic receptors lead to vasoconstriction?
Alpha adrenergic receptors
found on vascular smooth muscle
multiple vascular beds
What would happen to blood pressure if a neurotransmitter bound to an alpha adrenergic receptor?
Increase
A-1 causes vasoconstriction
What type of adrenergic receptor causes vasodilation?
Beta adrenergic receptors
Found in skeletal muscle
What would happen to blood pressure if a neurotransmitter bound to a beta adrenergic receptor?
Decrease
Beta receptors lead to vasodilation thus decreasing blood pressure
What type of muscles are found in arterioles?
Smooth
What would happen if the SA node is knocked out?
The next most excitable group of cells takes over
Where do normal conduction pathways begin in the heart?
SA node
Starting at the left ventricle, what is the movement of blood -also naming the major arteries which take blood from and send blood to the heart?
Left ventricle –>aorta –> body –> vena cava –> right atrium –> right ventricle –> lungs –> left atrium –> left ventricle
