6. The ECG - calculating heart rate and intervals Flashcards Preview

ESA 2- Cardiovascular System > 6. The ECG - calculating heart rate and intervals > Flashcards

Flashcards in 6. The ECG - calculating heart rate and intervals Deck (19)
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What is normal ECG paper speed?

25 mm/sec


How many small and large squares are there in a second?

25 small squares = 1 sec
5 large squares = 1 sec


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)


How many large sqaures are there in 6 seconds and 1 min?

6 secs = 30 large squares
1 min = 300 large squares


How is heart rate (bpm) calculated for regular and irregular rhythms?

- 300/no. of squares of R-R interval

- no. of QRS in 6sec x 10


What is the normal range for the PR interval?

0.12 - 0.20 secs (3-5 small boxes)


What is the normal range for the QRS interval (width of QRS complex)?

< 0.12 secs (<3 small boxes)


What does the QT interval represent?

Ventricular depolarisation + repolarisation


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


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


What is sinus rhythm?

Normal rhythm of depolarisation initiated by sinoatrial node (as has fastest rate of depolarisation)


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)?


What is a sinus rhythm with rate <60bpm or >100bpm called?

sinus bradycardia or sinus tachycardia


What does a shorter R-R interval indicate?

faster heart rate


What does a wider QRS complex indicate?

ventricular depolarisations that aren't initiated by normal conductance mechanism


What does a longer P-R interval indicate?

slow conduction from atria to ventricles (1st degree heart block)


What does a raised or depressed ST segment indicate?

myocardial infarction or ischaemia (should be isoelectric)


What does a prolonged QT interval indicate?

prolonged repolarisation of ventricles, which can lead to arrhythmias as occur in long QT syndrome


What are the most common causes of 1st degree heart block?

- AV nodal disease
- enhanced vagal tone (e.g. in athletes)
- myocarditis (e.g. from Lyme disease)
- acute MI (esp. when inferior)
- electrolyte imbalances (hypokalaemia)
- medication