ECG Flashcards
Route of electrical discharge in the heart:
SA node -> AV node -> Bundle of His -> R/L bundle branch -> Purkinje fibres
What part of the heart rhythm is associated with the P wave?
Depolarisation of the atria
What part of the heart rhythm is associated with the QRS wave?
Depolarisation of the ventricles
What part of the heart rhythm is associated with the T wave?
REpolarisation of the ventricles
What is the standard ECG calibration (speed)?
25mm/s
If the machine is calibrated at 25mm/s, and a large square is 5mm long, how much time does a large square correspond to?
0.2 seconds = 200 milliseconds
If the machine is calibrated at 25mm/s, and a small square is 5mm long, how much time does a small square correspond to?
0.04 seconds = 40 milliseconds
- How many large squares are there in one second?
- How many large squares are there in one minute?
- How can you use this to calculate HR?
- 5
- 300 (5x60)
- Divide 300 by the number of large squares between successive R waves
E.g. 3 large squares between R waves –> 300/3 i.e. HR=100bpm
- What is the PR interval?
- How is it measured on the ECG strip (i.e. start and end)?
- How long is it usually:
i. In squares?
ii. In milliseconds?
- time taken for excitation to spread from the SA node into the ventricular muscle
- From beginning of P wave to beginning of QRS (think PR should be called PQ interval)
- i. 3-5 small squares
ii. 120ms - 200ms
- What is the QRS interval?
- How is it measured on the ECG strip (i.e. start and end)?
- How long is it usually:
i. In squares?
ii. In milliseconds?
- How long it takes for excitation to spread through ventricles
- From start of Q wave to end of S wave
3.
i. No more than 3 squares
ii. 120ms
How long is a QT interval?
Less than 450ms
What is the calibration (mV/cm) of an ECG machine?
1 mV (millivolt) should move the stylus 1 cm vertically
- Calibration signal of 1mV:1cm should be included in every ECG
- How many electrodes are there (and where do they go?)
- Mnemonic for limb electrodes
- Where to place electrodes
- There are 10 electrodes (4 on limbs and 6 on chest)
- Starting on R arm -> Riding Your Green Bike (Red, Yellow, Green, Black)
3.
» V1 - 4th intercostal space (ICS) at the right border of the sternum
» V2 - 4th ICS at the left border of the sternum
» V3 - Midway between placement of V2 and V4
» V4 - 5th ICS at the midclavicular line
» V5 - Anterior axillary line on the same horizontal level as V4
» V6 - Mid-axillary line on the same horizontal level as V4 and V5
What plane do the limb leads assess?
Vertical place
What plane do the chest leads assess?
Horizontal place
