Flashcards in 6. The ECG - calculating heart rate and intervals Deck (19):
1
What is normal ECG paper speed?
25 mm/sec
2
How many small and large squares are there in a second?
25 small squares = 1 sec
5 large squares = 1 sec
3
How long does 1 small or large square last?
1 small square = 0.04 sec (40 ms)
1 large square = 0.2 sec (200 ms)
4
How many large sqaures are there in 6 seconds and 1 min?
6 secs = 30 large squares
1 min = 300 large squares
5
How is heart rate (bpm) calculated for regular and irregular rhythms?
Regular
- 300/no. of squares of R-R interval
Irregular
- no. of QRS in 6sec x 10
6
What is the normal range for the PR interval?
0.12 - 0.20 secs (3-5 small boxes)
7
What is the normal range for the QRS interval (width of QRS complex)?
< 0.12 secs (<3 small boxes)
8
What does the QT interval represent?
Ventricular depolarisation + repolarisation
9
Why is QT interval usually corrected for changes in heart rate?
QT interval gets shorter with increasing heart rate (shorter diastole) - can mask problems so must be corrected for HR to assess this accurately
10
What is the upper limit for corrected QT interval?
0.45 secs (11-12 small boxes) in adult males
0.47 secs (11-12 small boxes) in adult females
11
What is sinus rhythm?
Normal rhythm of depolarisation initiated by sinoatrial node (as has fastest rate of depolarisation)
12
How is normality of sinus rhythm assessed?
1 - is the rhythm regular? (use rhythm strip and paper)
2 - is heart rate normal (60-100 bpm)?
3 - are P waves present and preceding every QRS?
4- are P waves upright in leads I and II?
5 - is PR interval normal (0.12-0.20 secs/3-5 small boxes)?
6 - is QRS width normal (<0.12 secs/<3 small boxes)?
13
What is a sinus rhythm with rate <60bpm or >100bpm called?
sinus bradycardia or sinus tachycardia
14
What does a shorter R-R interval indicate?
faster heart rate
15
What does a wider QRS complex indicate?
ventricular depolarisations that aren't initiated by normal conductance mechanism
16
What does a longer P-R interval indicate?
slow conduction from atria to ventricles (1st degree heart block)
17
What does a raised or depressed ST segment indicate?
myocardial infarction or ischaemia (should be isoelectric)
18
What does a prolonged QT interval indicate?
prolonged repolarisation of ventricles, which can lead to arrhythmias as occur in long QT syndrome
19