FUNDAMENTALS
OF PHYSIOLOGY
AND ANATOMY
4BBY1060
Cardiovascular
Physiology & Anatomy
, LECTURE 8:
The cardiac pacemaker
All cardiac pacemaker tissues have
intrinsic activity, Therefore contracts
without external stimuli. If a pacemaker
fails to shoot an action potential, the
following node will take over. (from fastest
beating to slowest beating)
There primary pacemaker of the
heart is the SA node (sinoatrial).
(Top right)
Then it spreads down to
atrioventricular node (AV node).
Moved down towards the Bundle of
Hiss, that then branches through the septum
Then branches out towards Purkinje fibers
The cardiac pacemaker also has a slow diastolic depolarization (funny current),
from –70mV to –40mV when the action potential fires.
The steeper the rate of the funny current the faster the depolarization and
therefore the faster the heart rate.
o May be modified by:
Sympathetic stimulation (faster bpm), steeper gradient,
tachycardia
Parasympathetic stimulation (slower bpm), more gentle,
brachycardia
The ∑ of stimulations (in proportions) , tachycardia + brachycardia = bpm
Until 90bpm – vagus tone is in charge
To raise < 90bpm – you must activate the sympathetic tone
Spread of excitation
Conduction from SA to AV is slow, as there is no specialized path from one to the
other. Once there is a is a delay, known as the ‘AV pause’. This stops high rates
of excitation being conducted to the ventricles.
This serves to fill the ventricles, and conditions where the AV pause does
not occur are known as atrial fibrillation – could become lethal arrythmia
ECG – electrocardiogram explained
By using electrodes at each side of the heart we can measure an electrical
dipole. Must be thought in a 3D context as the electrical impulse moves down
the apex and then around the back of the heart.
Wave of positiveness – delay – wave of
negativeness
o + wave is upstroke of the action potential
spreading down towards apex of heart
o – wave is due to the repolarization
Must be set in Einthoven's Triangle
OF PHYSIOLOGY
AND ANATOMY
4BBY1060
Cardiovascular
Physiology & Anatomy
, LECTURE 8:
The cardiac pacemaker
All cardiac pacemaker tissues have
intrinsic activity, Therefore contracts
without external stimuli. If a pacemaker
fails to shoot an action potential, the
following node will take over. (from fastest
beating to slowest beating)
There primary pacemaker of the
heart is the SA node (sinoatrial).
(Top right)
Then it spreads down to
atrioventricular node (AV node).
Moved down towards the Bundle of
Hiss, that then branches through the septum
Then branches out towards Purkinje fibers
The cardiac pacemaker also has a slow diastolic depolarization (funny current),
from –70mV to –40mV when the action potential fires.
The steeper the rate of the funny current the faster the depolarization and
therefore the faster the heart rate.
o May be modified by:
Sympathetic stimulation (faster bpm), steeper gradient,
tachycardia
Parasympathetic stimulation (slower bpm), more gentle,
brachycardia
The ∑ of stimulations (in proportions) , tachycardia + brachycardia = bpm
Until 90bpm – vagus tone is in charge
To raise < 90bpm – you must activate the sympathetic tone
Spread of excitation
Conduction from SA to AV is slow, as there is no specialized path from one to the
other. Once there is a is a delay, known as the ‘AV pause’. This stops high rates
of excitation being conducted to the ventricles.
This serves to fill the ventricles, and conditions where the AV pause does
not occur are known as atrial fibrillation – could become lethal arrythmia
ECG – electrocardiogram explained
By using electrodes at each side of the heart we can measure an electrical
dipole. Must be thought in a 3D context as the electrical impulse moves down
the apex and then around the back of the heart.
Wave of positiveness – delay – wave of
negativeness
o + wave is upstroke of the action potential
spreading down towards apex of heart
o – wave is due to the repolarization
Must be set in Einthoven's Triangle
