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Pathophysiology of Heart and circulatory lecture notes 2022
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Summary Pathophysiology of Heart and Circulatory System (AB_1015)
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Lecture 1 – ECG and rhythm disorders (chapter 2)Excitation-contraction coupling = system that ensured that
cardiomyocytes can contract
- Making sure that the electoral signal gets everywhere
- Action potentials =
o Absolute refractory period = period during which
another action potential cannot occur
o Relative refractory period = immediately after
absolute
o Supranormal period = The heart has relaxed and can contract again to pump out the
blood.
- Action potentials are very long in the heart
o Because = you want the heart to fill with blood
(relax) and contract (push the blood towards the
aorta)
So that the cells do not get stimulated
directly after the previous stimulus
- Dependent on in and out flow of:
1. Sodium = go into the cell
Causes rapid depolarization
2. Calcium = go into the heart cell (calcium channels are slow)
Need to be high enough in the cytosol to initiate the contraction
Cells have an amplifier =
o The calcium coming into the cells from outside is not enough
to start a action potential
o When the calcium enters the cell = the SR (sarcoplasmic
reticulum) in the cell releases more calcium
o Now the calcium level is high enough = calcium binds to
myofilaments (are all connected in your heart, they are
inside cells)
= called calcium-induced calcium release
o Calcium reuptake in the SR --> the calcium is released from
the myofilaments for relaxation
3. Potassium = leaves the cell for repolarization (slow)
Action potential and ECG
- How the action potential goes:
1. Signal in Sinus node (SA node) = top of your
right atrium To the atrioventricular node (AV
node) = right under in the right atrium
2. Signal goes through the base of the heart =
Bundle of His (AV bundle)
3. Branches into the right and left bundle of his
4. Purkinje fibers
, - ECG =
o P-wave = spread of the depolarization wave through the atria
o PR-interval= conduction through the AV node --> the time for the action potential to
go from SA to AV node
o QRS = spread of the depolarization wave through the ventricles
= Biggest signal
Q peak = depolarization of the intraventricular septum (the wall in between
the atria)
Negative because the signal slightly moves in the opposite direction
of the lead = it moves from left to right
R-wave = depolarization of most of the heart wall in the ventricles
S-wave = final depolarization of the purkinje fibers at the base of the heart
o ST interval = heart contracts --> blood goes towards the arteries, into the body
o T-wave = repolarization of the ventricles --> heart relaxes
o 12 leads = 6 leads and 6 precordial leads
Arrhythmias = Disturbances of your normal rhythm
- Caused :
o Within cells
o Between cells
- Assessment of the ECG = following these 7 steps
and seeing if it is a normal or not normal heartbeat
o Rhythm disorders / frequency disorders =
Regular rhythm in rest (it is still abnormal but regular, so every heart beat is
the same) = bradycardia < 60 and tachycardia > 110
Bradycardia = occurs often when someone works out a lot = the
stroke volume increases = heart frequency is lower
o If you do not exercise a lot and your heart rate is <60 = that
is not normal
Tachycardia does not happen often
Irregular rhythm =
atrium fibrillation
o Older = fibrillation increases
Very common and gives an increased risk of a stroke
You can feel this from the pulse in someone’s arm =
it is uncomfortable
o Chaotic depolarization atrium = so conduction through AV
node not regular
RR intervals are irregular = the time between two
ventricle depolarization
Cause: Damage in atrium = chaotic pattern from SA
node to AV node
V
e
,ntricle fibrillation = Cannot pump blood normally into the body
anymore, which is why it is more dangerous
o It is relatively benign
o Filling ventricle is (for 80%) passively happening = passive
filling
Because the ventricles can relax very well
o Treatment: people with this get an ICD (implantable
cardioverter-defibrillator) = it is implanted and gives a shock
to the heart
Given to people with high risk (inherited i.e.)
, o Conduction times disorders
Atrioventricular conduction disorders = a group of disorders in which
conduction of atrial impulses to the ventricles is delayed or blocked:
o PR interval is affected
o AV block = A type of AV conduction disorder
Has multiple levels:
First degree: PR- interval longer (less severe)
Takes a bit longer for the signal to arrive to the ventricle
QRS wave disorders:
o Second degree: some signals are not passed on to the ventricle
Some P waves are not followed by a QRS complex
Treatment usually pace maker but people don’t want that
It often becomes third degree --> then they get a
pacemaker
o Third degree = severe!
No conduction through AV node and ventricles do not
contract
Other pacemaker cells take over the job to contract the
ventricles = Some of the other pacemakers are in our
ventricles (and some in our AV node, which you cannot use
because there is no conduction through the AV node)
Patients with this have very low heart rate
2 types = Partial VS total
Treatment for second and third-degree = pacemaker
o Two wires go into the wall of the right atrial wall = pulse is given to
the wall.
o It uses the heart rate to see whether it needs to set the pace
Long QT syndrome = long T wave
o QT time is longer than normal = beginning QRS until end T
wave
o Action potential of your cardiomyocytes are longer -->
mainly repolarization takes longer
o Due to:c
Mutations in ion channels (inherited) =
Mostly in potassium, but also in the calcium
channels
The closing of the channels is slower than normal
Risk =
o During exercise you shorten your QT time
o In people with this syndrome = this does not happen very
well and inconsistent
Some cells have normal action potentials and some
have very long
The ones with a longer action potential can turn on
the other cells again --> causing multiple
contractions = fibrillation
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