1 Electrophysiology of the Heart Flashcards
What is the view of the heart called when you open it in the chest?
Anatomical position of the heart
What arteries supply blood to the heart?
Coronary arteries
What is the LAD?
Your left anterior descending (LAD) artery is one of two branches of your left main coronary artery.
Anterior means the artery supplies blood to the front portion of your heart. It’s the biggest supplier of oxygenated blood to your heart’s lower left pumping chamber or ventricle.
Why are the coronary arteries on the surface of the heart?
So they are not affected by the heart’s contraction
How are the atrium and ventricles described as pumps?
Atrium = priming pump
Ventricles = main pump
How many pulmonary veins are there and what do they do?
There are 4 altogether = 2 from each lung
The blood is oxygenated in the lungs and returned to the heart by the pulmonary veins
What is the role the electrical signal?
Initiates and synchronizes the contraction of the atria and ventricles
Can the pump output be varied?
Yes, this is important if the blood flow needs to be changed depending on acitivty
What cells are electrically excitable?
Nerves and muscle cells (cardic muscle cells too)
What does the ATPase pump do?
Pumps 2K+ in and 3Na+ out of the cell using ATP as energy source because they are moving against conc grad
Inside of the cell becomes negatively charged
Define action potential
Depolarization followed by repolarization of cell membrane
What is the resting membrane potential of a cardiac cell v nerve cell?
Cardiac cell = -85-95mV
Nerve cell = -70mV
What is the difference between an atrial and ventricular action potential
VENTRICLE has a longer plateau phase because of the voltage-gated calcium channels
All cardiac cells have the plateau phase but the duration changes
What joins cardiac cells and what happens because of this?
Gap junctions are channels between the cells allowing cardiac AP to propagate from cell to cell through low reistance pathway
How is the heart contraction initiated and synchronized?
Signal starts from SA node and ripples outward across ATRIUM causing atriums to contract at same time
Fibrous tissues do not have gap junctions so electrical signal cannot cross to the ventricles = DELAY
AV node = embedded within fibrous tissue allows signal to be passed to Bundle of HIs, bundle branches and then purkinje fibres
Can the heart beat outside the body?
Yes, heart does not require nerve or hormonal input to beat
Because of autorhythmicity, some cells have prepotential/PACEMAKER potential to trigger AP
What is the heirarchy of pacemakers?
SA node = 90-100 bpm
AV node = 40-60 bpm
Bundle of His = 15-30bpm
What is overdrive suppression?
Fastest pacemaker normally drives the heart and suppresses other pacemakers
What is an ectopic beat and what is the location of that beat called?
Heartbeat generated outside the normal pacemaker
Ectopic focus/pacemaker = site that generates an ectopic beat
What are agents that alter heart rate called?
Chronotropic
What are positive chronotropic agents?
Adrenaline and noradrenaline = act on β-adrenergic receptors on heart
Increase heart rate
What are negative chronotropic agents?
Acetylcholine = acts on muscarinic cholinergic receptors on the heart
Slows heart rate
At rest what system controls heart rate?
Heart is under parasympathetic tone, which slows the natural rhythm of the heart
What system increases heart rate?
Sympathetic nervous system needed to adjust heart rate = NOT initiate it
How does ANS affect SA node? ***
What are the leads needed in an ECG?
12 leads = 3 bipolar limb leads, 3 augmented limp unipolar leads and 6 precordial unipolar leads
Leads 1-3
aVR, aVL and aVF
V1-V6
Difference between bipolar ad unipolar leads?***
In an ECG, bipolar leads (I, II, III) measure electrical activity between two points on the body, providing a view of the heart’s electrical impulses from different angles.
Unipolar leads (aVR, aVL, aVF, and chest leads V1-V6) measure voltage from a single point, offering a more localized perspective of heart activity.
Which leads measure vertical axis and which measure horizontal axis?
Vertical = bipolar limb and augmented limb
Horizontal axis = precordial /chest leads
How does the flow of electrical signal produce the recordings we see in the ECG?
P wave
Atrial depolarization
QRS complex
Ventricular depolarization
T wave
Ventricular repolarization
P-R interval
Time between atrial depolarization and ventricular depolarization
0.12-0.20 seconds if greater than 0.20s then AV conduction block
ST segment
Isoelectric period following QRS = time the entire ventricle is depolarized
Roughly corresponds to plateau phase of ventricular AP
What is ST segment important for?
Diagnosis of ventricular ischaemia or hypoxia
What can diagnose ventricular ischaemia or hypoxia?
ST segment
Q-T interval
Time for both ventricular depolarization and repolarization to occur
Rough estimate of duration of average ventricular AP
