The ECG Flashcards
what does an ECG do?
monitors electrical activity of the heart
How is the electrical activity of the heart recorded?
by electrodes on the body surface
How does the body surface get potential?
Currents that flow when the membrane potential of myocardial tissue is changing ie depolarising/repolarising
Only large/small masses of cardiac tissue generate sufficient current and what are these masses?
larger eg atrial and ventricular muscle
Why does the L ventricle give a larger signal on an ECG?
as larger mass on LH side of heart as thicker wall
What does a flat line indicate on an ECG?
the heart has stopped
What is the Pd measured between and in what unit?
mV and distant sites
What is the reading called on an ECG?
the electrocardiograph
What is the paper print out of the results?
the electrocardiogram
describe the physics of the ECG?
action potential causes a separation of charge,( difference in Pd), produces electric dipole which is a vector, generates an electric field, which varies over time, due to direction constantly changing
What is the ECG lead?
the imaginary line, the lead axis, between two (or more) electrodes, it is not the wire that connects the electrode to the recording device (the electrocardiograph)
what is the ‘seeing electrode’?
one electrode acts as the recording (positive) electrode
what generates the upward deflection on the ECG?
when depolarization moves towards the recording electrode
what generates the downward deflection on the ECG?
When depolarization moves away from the recording electrode
When is there no deflection on the ECG and why?
o If there is no movement towards or away from the recording electrode, there is no deflection on the ECG (it is isopotential) ie flat line
heart has stopped
What are the 3 groups of leads the 12 lead ECG is composed off?
3 standard limb leads (I,II,III)
3 augmented Voltage leads
6 Chest Leads
Name the 3 std limb leads and what they are called?
I,II,III
bipolar
Name the 3 augmented voltage leads and what they are termed?
(aVR (right), aVL (left) and aVF (foot)
unipolar
Name the 6 chest leads and what they are termed?
V1-V6
Precordial Leads
What are the leads that give the vertical(or frontal/coronal) view of the heart?
leads I,II, III, aVR, aVL and aVF
What are the leads that give the horizontal/tranverse view of the heart?
V1-6
What is the P wave?
Atrial depolarisation spreading from SA node inferiorly and to the left
what is the movement of the depolarisation in the P wave?
moving towards the recording electrode (+ve) in lead II producing a (normally) upward deflection in this lead
What does the P wave duration represent and what is the normal value for this?
P wave duration in the normal ECG reflects the time for the depolarization of atrial muscle to be complete. less than 0.120 s (120 ms)
