Week 5 Flashcards
What is an ECG?
Electrocardiogram
Test to check rhythm and electrical activity of heart
What is a cardiac impulse?
the wave of cardiac excitation passing from the sinoatrial node to the atrioventricular node and along the bundle of His and initiating the cardiac cycle broadly
What are the parts of the cardiac conduction system?
SA node, AV node, bundle of His, bundle branches, and Purkinje fibers
Describe cardiac conduction system
Signal from sinoatrial node moves slowly to Atrioventricular node as ventricles begin to fill
From there signal moves through bundle of His, bundle branches, to Purkinje fibers which stimulate ventricles for ejection
Outline the properties of the ECG paper (speed, square size)
Speed: 25 mm/s
Large squares: .2 second, .5 mV
Small squares: .04 second, 0.1mV
What is positive/negative deflection?
Positive - energy coming towards the lead
Negative - energy travelling away from the lead
How many electrodes do you use for the ECG?
10
Leads are a misnomer (often called 12 lead ECG) - leads are not the cables, but the line between where you put the electrodeand where you are looking for
Describe Einthoven’s triangle
Right arm, left arm, left leg
aVR, aaVL, aVF
What is a chest lead vs limb lead?
Chest leads look at heart on horizontal transverse plane
Limb leads look at heart on coronal plane
What is the P wave? How long should it last? Where should it be positive (1) / negative (1) on ECG?
First positive deflection
Atrial depolarisation
Should no be more than 0.12 seconds
Positive in lead II (negative in AVR)
What is the T wave? What can changes indicate?
Rapid phase of ventricular repolarisation
Peaked or flattened can reflect changes in potassium, metabolic process
What is your QRS complex related to?
Ventricular depolarisation
If larger than 0.12 suggests defect in intraventricular conduction
Direction determine ‘electrical axis’
What is the PR interval?
Represents time for transmission of signal from atria to ventricles through AV node
0.12-.20 second duration (3-5 small squares)
What is the electrical axis? What is normal?
Direction of the mean vector of the wave of ventricular depolarisation in the limb leads
Lead 1 is arbitrarily defined as 0 degrees
Normal axis between -30 and +90 degrees
Define abnormal electrical axis readings
beyond -30 = left axis deviation
beyond 90 = right axis deviation
What is the ST segment?
In isoelectric line between QRS and T wave
Plateau phase of repolarisation
Should not deviate above/below isoelectric line by more than 1mm
Deviation = likely damage
STEMI!
What is the QT interval?
Measures polarisation process
Prolonged (>440ms in men, >460ms women)
Prolonged due to inherited conditions, drugs
Prolonged can cause arrhythmia
What is the structure for reading ECGs? (5)
Name / age of patient / current condition
Check heart rate
Check rhythm is regular (are R waves coming regularly)
P wave - duration and shape
T wave - should be positive in I, II, aVL, aVF, V2-6
How to check heart rate on ECG?
1 large square = 300 bpm
count number of squares between R waves (300 divided by this number)
What are the criteria for sinus rhythm? (3)
Positive 1, 2, aVF AND
Negative aVR AND
Each QRS preceded by P
What is left ventricle hypertrophy? How can you see it on ECG?
enlargement and thickening (hypertrophy) of the walls of your heart’s main pumping chamber (left ventricle)
Large QRS complex - various systems to add up
What are the changes on ECG during myocardial infarction?
ST elevation during STEMI
Maybe no changes during non-STEMI (or slight T inversion)
Pathological Q waves are long term effect
What are the clinical signs of shock?
Pale, sweaty, dizzy, cold/clammy skin
What is blood pressure? What maintains it? (4)
Pressure exerted by the circulating blood against the walls of the arteries Maintained by: 1. contraction of left ventricle 2. resistance of small blood vessels 3. elasticity of arterial walls 4. volume / viscosity of blood
What are the UK parameters for optimal, normal and high-normal blood pressure?
less than 120/80
less than 130/85
130-139/85-89
What are the parameters for grade 1-3 hypertension?
Grade 1 - 140-159 / 90-99
Grade 2 - 160-179 / 100-109
Grade 3 - More than 180 / 110
What is blood pressure homeostasis?
Maintenance of steady state of blood pressure
What are the three factors that control blood pressure?
Contraction of left ventricle
Resistance of small blood vessels
Volume of the blood
Why do we need blood pressure?
To move blood through vascular system
What are the characteristics that contribute to blood pressure stability? (3)
The mechanism that contribute to BP stability are:
powerful (it has rapid and slow components)
highly redundant (if something happens, there is back-up)
Able to cope/adjust (e.g physical activity, threats, trauma)
What is cardiac output? How do you calculate it?
amount of blood pumped out by the heart per minute (=Stroke volume x Heart rate)
What are the markers of low BP? (3)
low stroke volume, slow or very fast heart rate, or reduced peripheral vascular resistance
What are the markers of high BP? (2)
High stroke volume
High peripheral vascular resistance
How do you calculate vascular resistance?
Poiseuille’s law
Resistance = 8 x length of blood vessel x viscosity divided by pi x the radius of blood vessel ^4
What is the distribution of blood volume?
Arteries 13%
Capillaries 6%
Veins 81%
Blood pressure regulation - which four systems work together?
CVS, Renal, nervous, endocrine
What is the most important factor in regulation of blood pressure?
Salt
Describe role of renal system in BP regulation
RAAS system responds to low blood pressure and stimulates increase
Kidney filters more than 170 L of plasma every day, filtering 23,000mmol of sodium
Types / percentages of Na absorption on nephron - what is being absorbed? (4 sections with approximate percents of absorption of sodium)
Proximal tubule: Na+/H+ exchanger = 60% absorption
Thick ascending limb of Henle: Na-K-2Cl co-transporter= 30%
Distal convoluted tubule: Na-Cl co-transporter = 7%
Cortical collecting tubule: ENaC = 2%
Describe (simply) the RAAS system? location, purpose, main elements
xxx
Drugs that act on different stages of the RAAS system?
ACE inhibitors (between Angiotensin I and II) Beta blockers and renin inhibitors (between angiotensinogen and angiotensin I)
What is malignant hypertension?
extremely high blood pressure that develops rapidly and causes some type of organ damage.
What is the role of the sympathetic nervous system on BP?
Short-term variations (stress, exercise, changes in posture)
What is pressure naturesis?
central component of the feedback system for long-term control of BP
When pressure is very high, kidney will lose salt
What was the result of renal sympathetic dennervation?
Blocking sympathetic nerve pathways helped to lower blood pressure if those resistant to treatment. Research ongoing
What are baroreceptors? What happens if you put pressure on the neck?
Pressure receptors
The carotid sinus and aortic arch sense high pressure and the hear and pulmonary artery sense low pressure
Cause bradycardia and low blood pressure
Describe (simply) the activity of endocrine control of BP
hormonal mechanism for the regulation of blood pressure by managing blood volume
Why don’t you give epinephrine during shock?
Worsens the vasoconstriction, tissues aren’t getting enough blood
What is atrial natriuretic peptide? What does it do (3)? and why?
It increases excretion via kidneys - 3 methods:
- Reducing water reabsorption in collecting ducts
- Relaxes renal arterioles
- Inhibits sodium reabsorption in DCT
Starts these processes in response to stimulation of atrial receptors
In what order will you organs shut down with high BP? (2 early)
Skin, kidney, etc.
What is convection?
Mass movement of fluid caused by pressure difference
Describe Darcy’s Law of flow states
Flow is equal to the pressure drop divided by resistance to flow
Relationship between blood flow and cardiac output
They are equal
How does heart beat? (source, 4 steps)
Generates its own electrical activity (does not need external nerves)
Starts at SA node, spread out via gap junctions
Spreads to AV node, delays conduction to allow ventricles to fill
Depolarisation rapidly through bundle of His into ventricles
How does the heart beat? (from what part of the heart)
From apex (bottom) to base (line between atria and ventricles)
What are the general principles of the cardiac cycle?
- Electrical activity conducted from SA node to atria and then ventricles causing CONTRACTIONS, CHAMBER PRESSURE CHANGES, MOVEMENT OF BLOOD
- Blood flows from high pressure to low pressure (unless blocked)
- Valves open / close depending on pressure change
- Left and right side are doing the same thing but pressure on the right is lower
Movement of blood through right side of the heart (describe path, valves) - 6
Blood returns from superior and inferior vena cava Enters right atrium Flows throw tricuspid valve Gathers in right ventricle pushed through pulmonary semilunar valve into pulmonary arteries to lungs
Movement of blood through left side of the heart (describe path, valves) - 6
Blood from lungs is sent to heart by pulmonary veins Enters left atrium Flows through mitral (bicuspid) valve Gathers in left ventricle pushed through aortic semilunar valve into aorta to systemic circulation
Describe process of cardiac cycle (where is blood going, what is happening?) - 4 phases
- ventricular filling
- isovolumetric contraction
- ejection
- isovolumetric relaxation
What is ejection fraction? What are normal values and what does a lower value indicate?
Ensures blood that is coming into ventricles is being ejected
SV / EDV
Normal value is 2/3rd or more; lower indicates heart failure
Describe the pressure changes as blood moves into/through right atrium
Pressure is going up in the right atrium during diastole, until so high the tricuspid valve opens
Blood moves from the atrium to ventricle, tricuspid closes
Blood leaves ventricle as atrium starts filling again
Repeats
Why do you look at the jugular? What does normal look like?
Low at SCM, pulse may be visible put should not be elevated
Jugular pressure can indicate if pressure in right atrium is too high, possible right sided heart failure
Describe the 4 basic heart sounds and what you are hearing
S1 - lubb - tricuspid / mitral valves close - beginning of systole
S2 - dupp - aortic / pulmonary valves close - beginning of diastole
S3 - occasional - turbulent blood flow into ventricles (common in young people)
S4 - pathological in adults - forceful atrial contraction against stiff ventricle