Normal ECG Flashcards
Which leads have an inferior view of the heart?
2, 3, aVF
Which leads have a lateral view of the heart?
1, aVL, aVR, V5, V6
Which leads have an anterior view of the heart?
V3, V4
Which leads have a septal view of the heart?
V1, V2
Why can we consider all atrial and all ventrical cells to contract as groups?
cardiac myocytes are connected by gap junctions which allow rapid transmission of electrical impulses from cell to cell
Which direction does current flow?
from negative to positive
What direction is the current going if there is an upward deflection?
current moving towards electrode
What direction is the current going if there is a downward deflection?
current moving away from electrode
What directions do the deflections of depolarisation and repolarisation point?
the same direction
What is the natural pacemaker of the heart?
sinoatrial (SA) node
pacemaker cells spontaneously depolarise and initiate the heartbeat
Is depolarisation or repolarisation slower? How does this show on an ECG?
repolarisation is a slower process
deflection is wider and has a smaller amplitude
What 2 types of waves can an ECG record?
depolarisation
repolarisation
What does the P wave represent? What does it look like?
atrial depolarisation
dome-shaped + symmetrical
What does the QRS complex represent?
ventricular depolarisation
What does the T wave represent? What does it look like?
ventricular repolarisation
longer than P wave + asymmetrical
usually points same direction as QRS complex
What does the PR interval represent?
the time for wave of depolarisation to spread from SA node –> across atria –> through AV node –> ventricular muscle
measure from beginning of P wave to beginning of QRS
Why is having adequate PR interval important physiologically?
physiologic delay gives ventricles enough time to fill up with blood before they depolarise
What is a Q wave?
if the first deflection is down in the QRS complex, this is a Q wave
What is an R wave?
the first upwards deflection of the QRS complex
What is an S wave?
the downward deflection after an R wave
What does the ST segment represent?
interval between ventricular depolarisation and repolarisation
flat, isoelectric portion of ECG between S wave and T wave
What does the QT interval represent?
time taken for ventricular depolarisation an repolarisation
beginning of QRS to end of T wave
What are the limb leads? How can these be further classified?
limb leads = 1, 2, 3, aVR, aVL, aVF
bipolar leads = 1, 2, 3
augmented leads = aVR, aVL, aVF
What are the chest leads?
V1, V2, V3, V4, V5, V6
What is meant by axis?
overall direction of depolarisation in the frontal plane
What is a normal cardiac axis?
-30 to 90 degrees
What would be considered left axis deviation?
less than -30
What would be considered right axis deviation?
more than 90
How would a normal axis look on an ECG (leads 1 and 2)?
both pointing up
How would left axis deviation look on an ECG (leads 1 and 2)?
QRS complexes leaving each other (pointing away from each other)
How would right axis deviation look on an ECG (leads 1 and 2)?
QRS complexes reaching towards each other (pointing towards each other)
What plane do the chest leads look at the heart in?
horizontal plane
What area of the heart does the right coronary artery supply?
inferior (shown by leads 2, 3 and aVF)
What areas of the heart does the left anterior descending artery supply?
septal (shown by leads V1 and V2)
anterior (shown by leads V3 and V4)
What area of the heart does the circumflex artery supply?
lateral (shown by 1, aVL, V5, and V6)
How can you systematically assess an ECG?
Patient details
paper speed
calibration
rate
rhythm
axis
waves (P, QRS, T)
intervals (PR, ST, QT)
How much time does a little square represent on an ECG?
0.04 seconds
How much time does a big square represent on an ECG?
0.2 seconds
How can over-calibration show on an ECG?
QRS complexes between leads touching /overlapping
How can under-calibration show on an ECG?
very small calibration curve and QRS complexes
What is the standard paper speed for an ECG?
25 mm/sec
How does a too fast paper speed show on an ECG?
looks slow, QRS complexes far apart
How does a too slow paper speed show on an ECG?
looks fast, QRS complexes close together
