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)
What does the QRS complex represent?
Ventricular activation/depolarisation
what is the Q part of QRS complex?
downward (negative) deflection preceding an R wave
what is the R part of QRS complex?
deflection upwards (positive) is called an R wave, irrespective of whether, or not, it is proceeded by a Q wave
what is the S part of QRS complex?
downward (negative) deflection following an R wave
What is the normal duration of a QRS complex?
100ms or less
what causes the Q wave in the heart?
starts in the interventricular septum and spreads from left to right causing the small
what causes the R wave in the heart?
subsequently the main free walls of the ventricles depolarize causing a tall
what causes the S wave in the heart?
, the ventricles at the base of the heart depolarize, producing a small
What does the T wave represent?
Ventricular repolarisation
What is the T wave?
It is an upward (positive) deflection because the wave of repolarization is spreading away from the recording electrode
Where is V1 placed?
4th intercostal space RH side
Where is V2 placed?
4th intercostal space LH side
Where is V3 placed?
5th intercostal space mid clavicular line
Where is V4 placed?
halfway between lead 2+4 on the rib between them
Where is V5 placed?
5th intercostal space on the anterior axillary line
Where is V6 placed?
5th intercostal space mid axillary line
What is the PR interval?and std duration?
AV node delay
0.12-0.2s
What is the QT interval?
depolarisation and repolarisation of ventricles
how do you work out HR on a normal ECG?
HR = 300/no. of large squares between beats
Name the 6 steps to analysing an ECG
- Verify patient details
- Check date and time ECG was taken
- Check calibration of ECG paper
- Determine axis
- Workout rhythm:
- Is electrical activity present?
- Regular or irregular?
- Heart rate?
- P waves present?
- PR interval?
- Each P wave followed by QRS?
- QRS duration normal? - Look at individual leads for voltage criteria changes OR any ST or T wave changes
