First Look at the ECG Flashcards
What is an ECG?
Electrocardiogram used to record electrical activity of the heart
What does the P wave represent?
Atrial depolarisation
What is depolarisation?
Orderly passage of electrical current sequentially through the heart muscle, changing it, cell by cell, from the resting polarized state to the depolarized state until the entire heart is depolarized.
What does the PR interval represent?
Start of P wave - end of Q wave
Represents time taken for electrical activity to move between the atria and the ventricles
What does the QRS complex represent?
Depolarisation of the ventricles
What is the normal QRS range?
What is a narrow and broad QRS complex?
NARROW (< 0.12 seconds) or BROAD (> 0.12 seconds):
What does the ST segment represent?
Starts at the end of the S wave and ends at the beginning of the T wave
Represents the time between depolarisation and repolarisation of the ventricles (i.e. ventricular contraction)
What does the T wave represent?
Ventricular repolarisation
What does the PR interval represent?
The RR interval begins at the peak of one R wave and ends at the peak of the next R wave.
It represents the time between two QRS complexes.
What does the QT interval represent?
Time taken for the ventricles to depolarise and then repolarise
Normal range for QT interval
350 to 450 ms for adult men
360 to 460 ms for adult women
What does a small square on a ECG represent?
0.04 seconds
What does a large square on a ECG represent?
0.2 seconds
What does 5 large squares represent?
1 sec
What doe 300 large squares represent?
1 min
How can you calculate the heart rate in a patient with a regular heart rhythm?
Count the number of large squares present within one R-R interval.
Divide 300 by this number to calculate heart rate.
EG:
4 large squares in an R-R interval
300/4 = 75 beats per minute
How can you calculate heart rate in a patient with an irregular heart rhtym?
Count the number of complexes on the rhythm strip (each rhythm strip is typically 10 seconds long).
Multiply the number of complexes by 6 (giving you the average number of complexes in 1 minute).
How many electrodes are used in an ECG?
10 physical electrodes and 12 leads
6 on chest
4 on limb
What is an ECG lead?
Graphical representation of the heart’s electrical activity which is calculated by analysing data from several ECG electrodes.
What is the cardiac axis?
Describes the overall direction of electrical spread within the heart
ECG findings for normal cardiac axis
Lead II has the most positive deflection compared to leads I and III.
ECG findings for right axis deviation
Lead III has the most positive deflection and lead I should be negative.
Right axis deviation is associated with right ventricular hypertrophy.
ECG findings for left axis deviation
Lead I has the most positive deflection.
Leads II and III are negative.
Left axis deviation is associated with heart conduction abnormalities.
What do absent P waves suggest?
Irregular rhythm - may suggest AF
What can different types of P waves indicate?
Sawtooth baseline → flutter waves
Chaotic baseline → fibrillation waves
Flat line → no atrial activity at all
How long should a PR interval be and what does a prolonged one indicate?
The PR interval should be between 120-200 ms (3-5 small squares).
Prolonged PR interval (>0.2 seconds)
A prolonged PR interval suggests the presence of atrioventricular delay (AV block).
What does first degree heart block indicate?
First-degree heart block involves a fixed prolonged PR interval (>200 ms).
What is second degree AV heart block (type 1)?
AKA Mobitz type 1 AV block or Wenckebach phenomenon
Progressive prolongation of the PR interval until eventually the atrial impulse is not conducted and the QRS complex is dropped
AV nodal conduction resumes with the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself.
What happens in second degree AV heart block (type 2)?
AKA Mobtiz Type 2 AV block
What area and artery of the heart do the following leads represent?
I, aVL, V3-6
Area: Anterolateral
Artery: Left coronary artery
What area and artery of the heart do the following leads represent?
V1-4
Area: Anterior
Artery: Left anterior descending artery (LAD)
What area and artery of the heart do the following leads represent?
I, aVL, V5-6
Area: Lateral
Artery: Circumflex
What area and artery of the heart do the following leads represent?
II, III, aVF
Area: Inferior
Artery: Right Coronary Artery
What is a narrow QRS complex?
