S6L1 - Interpreting ECGs Flashcards
Define depolarisation
Change within cell of electrical charge distribution leading to a less negative charge within the cell
Define Repolarisation
Change within the cell of electric charge distribution leading to more negative charge inside the cell.
Define resting membrane potential
Electrical imbalance between the inside and outside of the cell due to separation of charges across the cell membrane. Measure in mV
What is the function of specialised myocytes?
These are pacemaker cells, and have an intrinsic rhythm. Set the cardiac rate and rhythm by spontaneously generating AP that initiate the cardiac cycle.
Where are the primary pacemaker cells located?
In the sinoatrial node. Where the superior veins Cavan empties into the right atrium.
How are cardiac cells electrically connected?
Through gap junctions. Allows unidirectional propagation of action potential.
What is excitation-contraction coupling?
Depolarisation wave causing coordinated contraction of the atria and ventricles
Where is the atrioventricular node located?
In the inter-atrial septum near the tricuspid valve (bottom left of right atrium)
What happens at the AV node?
Impulse is delayed by 120-200ms in order to delay ventricular contraction.
What is the bundle of his?
Fast conducting electrical fibres that start in the atria, goes through the annulus fibrosus and travels down the ventricles through the septum.
What is the annulus fibrosis?
The fibrous skeleton of the heart that anchors the myocardium and cardiac vessels. It is an electrical insulator between the atria and the ventricles. Consists of 4 fibrous rings.
What does the bundle of his divide into?
The righ bundle branch and the left bundle branch within the interventricular septum.
Where does the RBB and the LBB terminate?
Terminate at the apex of the heart into the purkinje fibres which continue t conduct the depolarisation wave through the ventricles up to the base of the ventricles.
What is the difference between a wave and a deflection?
A wave has one deflection, a complex has more than one
What is the function of the right leg electrode?
The grounding electrode. Does not contribute to any views of the heart.
How many electrode are there?
10
4 on limbs
6 on chest
How many leads are there?
12 leads.
Describe the classic limb leads 1, 2 and 3
Bipolar, have negative and positive electrodes.
Describe limb lead 1
Voltage difference between the electrode on the RA and LA. LA is positive electrode.
Describe limb lead 2
Voltage difference between electrode RA and LL. LL is positive electrode
Describe limb lead 3
Voltage difference between the LA and LL electrodes. LL is positive electrode.
What are augmented limb leads?
Uni polar - only have a positive electrode AVL = left arm AVR = right arm AVF = left leg. Use same electrodes as limb leads.
How are limb leads viewed?
Limb leads are viewed from positive to negative
Describe the function of the precordial chest leads
Have horizontal views of the heart. Are unipolar.
What does the p wave represent?
Represents the depolarisation of the atria. Upwards deflection from lead 2 as depolarisation is travelling towards the LL electrode.
What is represented by the R wave?
A upwards
