Pathophysiology of Heart and circulatory lecture notes 2022

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