Cardio Physiology Flashcards
What is automaticity
The intrinsic ability of the heart to spontaneously depolarise and trigger action potentials that are spread across all of the myocardium to trigger the heart muscle to contract.
2 components of myocardium
Nodal cells
Contractile cells
Name the nodal cells
SA node
AV node
AV bundle (Bundle of His)
Bundle branches (L&R)
Purkinje fibers
Name the contractile cells
Actin
Myosin
Troponin
Tropomyosin
Sarcoplasmic reticulum
Who sets the sinus rhythm and how many bpm
SA node. 60-80bpm
Action potential from SA node goes to…. and what happens as a result
Bachman’s bundle: Depolarises the LA
Internodal branches: Depolarise RA
The SA bundle sends action potential to the rest of Right atrium via the
Internodal pathway
Where does the internodal branch converge?
AV node
What is the importance of AV node
Acts as a gateway between atria and interventricular septum
What is the importance of AV node delay
Want to give time for the atria to contract before the ventricles contract
How is AV node delay created?
Has fewer gap junctions than other nodal cells
Have a smaller diameter (slower conduction speed)
Cardiac conduction system
- SA node
- AV node
- Bundle of His
- L/R Bundle branches
- Purkinje fibers
What are intercalated discs?
Gap junctions(protons move across the nodal cells to contractile cells) + Desmosomes (connect the actual cardiac cells together).
Nodal cell resting potential
-60mV
Contractile cell resting potential
-90mV
Stage 0 of the cardiac action potential
Rapid upstroke and depolarisation
Voltage gated Na+ channels open-depolarisation
Stage 1 of the cardiac action potential
Initial repolarisation
Inactivation of voltage-gated Na+ channels. Voltage-gated K+ channels begin to open.
Causes initial repolarisation
Stage 2 of the cardiac action potential
Plateau
Ca2+ channels open up more slowly than K+ channels. Ca2+ influx through the voltage-gated Ca2+ channels balances K+ efflux (plateau period).
Ca2+ influx triggers Ca2+ release from the sarcoplasmic reticulum and myocyte contraction
Stage 3 of the cardiac action potential
Rapid repolarisation
Massive K+ efflux due to opening of voltage-gated slow delayed-rectifier K+ channels and closure of voltage-gated Ca2+ channels- Rapid repolarisation
Stage 4 of the cardiac action potential
Resting potential
High K+ permeability through K+ channels
Maintaining resting potential (approx -90mV)
Na+ inflow, K+ outflow
H zone what is it?
Distance between thin filaments on the same sarcomere
What consists of one sarcomere
Z disc - Z disc
What consists in the thin filament
Actin
Troponin
Tropomyosin
How many binding sites does troponin have and what are they?
3
Troponin C- Ca
Troponin I-Actin
Troponin T- Tropomyosin
What is the Z disc
The functional unit of muscle fibre
What does Titin do?
Link thick filament to the Z disc
M line what does it do?
Connects titin to thick filamet
What protein connects actin to sarcolemma?
Dystrophin
What does Limb lead 1 show activity of?
High lateral wall of LV
What does Limb lead 2+3 show activity of?
Inferior wall of the heart
What does aVR show activity of?
RV + Basal septum
What does aVL show activity of?
High lateral wall of LV
What does aVF show activity of?
Inferior wall of the heart
Where would you place V1
right 4th intercostal space, parasternal space
Where would you place V2
Left 4th intercostal space (parasternal line)
Where would you place V3
Between V2 + V4
Where would you place V4
left 5th intercostal space, mid clavicular line
Where would you place V5
Left 5th intercostal space, anterior axillary line
Where would you place V6
Left 5th intercostal space, mid axillary line
What is happening to the R wave as you go through V1-V6
Getting bigger
What is happening to the S wave as you go through V1-V6
Getting smaller
What do V1-V3 tell us about the activity?
RV
What limb leads tell us about the right ventricle
V1-V3
aVR
What does V2-V3 tell us about the activity of?
Basal septum
What limb leads tell us about the basal septum
V2-V3
aVR
What limb leads tell us about the anterior wall of the heart
V2-V4
What does V2-V4 tell us about the activity of?
Anterior wall of heart
What does V5-V6 tell us about the activity of?
LV
What limb leads tell us about the LV
V5-V6
Limb lead 1
aVL
How long should PR interval be?
<0.2 secs
How long should QRS wave be?
>0.12 secs
What is the Electrocardiogram?
NOT a DIRECT RECORD of the changes in membrane potential across individual cardiac muscle cells.
But instead it is a measure of the currents generated in the EXTRACELLULAR FLUID by the changes co-occurring in many cardiac cells
What is a P Wave?
Atrial depolarisation - seen in every lead apart from aVR
What is the PR Interval?
Time taken for atria to depolarise and electrical activation to get through AV node
What is the QRS complex?
Ventricular depolarisation, still called QRS even if Q and/or S are missing depending on what lead you are looking at
What is the ST Segment?
Interval between depolarisation & repolarisation
What is the T wave?
Ventricular repolarisation
What is Tachycardia?
Increased heart rate
What is Bradycardia?
Decreased heart rate
What is Dextrocardia?
Heart on right side of chest instead of left
What happens to the ST segment in an Acute Anterolateral Myocardial Infarction?
ST segments are raised in anterior (V3-V4) and lateral (V5-V6) leads
What happens to the ST segment in an Acute Inferior Myocardial infarction?
ST segments are raised in inferior (II, III, aVF) leads
Why is atrial repolarisation usually not evident on an ECG?
since it occurs at the same time as the QRS complex so is hidden
How does the impulse generate the ECG?
Electrical impulses in the heart move in 3 dimensions
- ECG only measure voltage in 1 dimension
- If an impulse is towards the electrode it looks big
- If an impulse is away from the electrode it looks small or even negative
- The impulse from the atria is smaller since the atria are smaller than the ventricles thus less myocytes
What are the 12 leads on a 12 lead ECG?
Standard limb leads (I, II & III)
Augmented leads (aVR, aVL & aVF)
The precordial leads (V1 - V6)
When reading an ECG, what are the times represented by the small squares and the big squares?
When reading an ECG, the graph shows changes in voltage over time, each small square across represents 40ms & each big square across represents 0.2s
Are P waves positive?
In a normal ECG the p waves are POSITIVE in EVERY LEAD (apart from the aVR)
What is the first phase of the cardiac cycle?
Mid-late ventricular diastole
What is the second phase of the cardiac cycle?
Isovolumetric contraction
What is the third phase of the cardiac cycle?
Mid-late ventricular systole
What is the fourth phase of the cardiac cycle?
Isovolumetric relaxation
How does blood flow passively into the ventricles in phase 1 of the cardiac cycle?
Atria fills with blood but mitral/tricuspid valve. the myocardium is relaxed as its not contracting and so papillary muscles aren’t anchoring valves through chordae tendinea. Results in valve being slight open and blood go down to ventricles.
What happens during mid-late ventricular diastole
Atrial p >Ventricular p
Arterial p > Ventricular p
Mitral + Tricuspid: open
Aortic + Pulmonic: closed
ECG: P wave
What happens during isovolumetric contraction
Atrial p < Ventricular p
Arterial p > Ventricular p
Mitral + Tricuspid: close (s1)
Aortic + Pulmonic: closed
ECG: QRS complex
What happens during mid-late ventricular systole
Atrial p > Ventricular p
Arterial p < Ventricular p
Mitral + Tricuspid: closed
Aortic + Pulmonic: open
ECG: QRS complex
What happens during isovolumetric relaxation
Atrial p < Ventricular p
Arterial p > Ventricular p
Mitral + Tricuspid: closed (s2)
Aortic + Pulmonic: closed
ECG: T wave
What is isovolumetric contraction?
Ventricular contraction when all valves are closed. This increases ventricular pressure but as the valves are closed the volume remains unchanged.
What produces the first heart sound?
Closing of the mitral valve.
What causes the mitral valve to close?
When the ventricular pressure is greater than the atrial pressure and the arterial pressure s greater than
and the ventricular pressure.
Describe systole.
A wave of depolarisation arrives, and Ca2+ channels open.
LVp>LAp and the mitral valve closes.
LVp rises, isovolumetric contraction,
LVp>aortic p.
The aortic valve opens and ejection begins.
Describe systole.
A wave of depolarisation arrives, and Ca2+ channels open.
LVp>LAp and the mitral valve closes.
LVp rises, isovolumetric contraction,
LVp>aortic p.
The aortic valve opens and ejection begins.
What produces the second heart sound?
Closing of the aortic valve.
Describe diastole.
LVp decreases and there is a phase of reduced ejection.
LVp is less than aortic pressure and the aortic valve closes isovolumetric ventricular relaxation.
LVp is less than LAp and the mitral valve opens - ventricles fill with blood.
Atria contract - atrial booster.
LVp > LAp and mitral valve close.
What is the duration of systole?
0.3s.
What is the duration of diastole?
0.5s.
What is end systolic volume?
The volume of blood remaining in the LV following systole.
Define preload.
The volume of blood in the ventricles just before contraction (EDV).
Define afterload.
The pressure against which the heart must work to eject blood in systole.
Define contractility.
The inherent strength and vigour of the heart’s contraction during systole.
Define elasticity.
Myocardial ability to recover it’s original shape after systolic stress.
Define compliance.
How easily a chamber of the heart expands when it is filled with blood (C=ΔV/ΔP).
Define diastolic distensibility.
The pressure is required to fill the ventricle to the same diastolic volume.
Define resistance.
A force that must be overcome to push blood through the circulatory system.
What is the basic principle of Starling’s law of the heart?
Increased EDV = increased SV.
Explain Starling’s law.
The greater the EDV, the greater the sarcomeres are stretched and the more forceful the contraction.
With relation to Starling’s law, what is the effect of an increased venous return?
EDV will increase and so SV increases and so Cardiac output also increases as CO=SVxHR.
Give the equation for stroke volume.
SV=EDV-ESV.
Give the equation for cardiac output.
CO=SVxHR.
Define cardiac output.
The volume of blood each ventricle pumps per unit time.
Give the equation for mean arterial pressure.
MAP = DP + 1/3(SP-DP).
(SP - systolic pressure, DP - diastolic pressure).
Give the equation for pulse pressure.
PP=SP-DP.
Give the equation for blood pressure.
BP=COxTPR.
What is Poiseuille’s equation?
What is Ohm’s law?
F=ΔP/R.
What are the principal vessels of resistance?
Arterioles
What do arterioles respond to?
Blood pressure changes. Local, neural and hormonal factors.
Name 2 local factors that result in vasoconstriction
Endothelin, internal BP.
Name 5 local factors that result in vasodilation.
Hypoxia, NO, K+ (accumulate from AP), CO2, H+, adenosine.
What neural factors result in vasoconstriction?
Sympathetic nerves that release noradrenaline.