Understanding some basic ECG disturbances Flashcards
What is bradycardia?
Heart rate <60
What is tachycardia?
Heart rate >100
What are some common cardiac arrhythmias?
- bradycardia
- tachycardia
- cardiac conduction abnormalities
- supraventricular arrhythmia
- ventricular arrhythmia
What is the PR interval?
P wave to start of QRS complex
What is a normal PR interval?
120 - 200 ms
What does the PR segments show?
Between atrial and ventricular depolarisation caused by AVN
What is the PR segment?
Between end of P wave and start of QRS complex
What is the ST segment?
Between the end of the QRS complex and start of T wave
What can the ST segment tell us about the heart?
Problems with coronary arteries
What is the normal QRS complex length?
<120 ms
What can cause ST segment elevation?
Blockage in coronary artery - MI
What is the ST interval?
Between the end of QRS complex and end of T wave
What is the QT interval?
Between the start of QRS complex and end of T wave
What can the QT interval be used for?
Some people are predisposed to arrhythmia and it is marked by long QT interval
What are the steps taken to analyse an ECG?
1 - correct reading? 2 - identify leads 3 - check calibration 4 - identify rhyhthm 5 - look at QRS axis 6 - look at p wave 7 - look at PR interval 8 - look at QRS complex 9 - position of ST segment 10 - calculate QT interval 11 -Look at T wave 12 - check
What is a normal QT interval?
380-420 ms
What does sinus tachycardia look like?
Normal rhythm just very fast (normally physiological response to something e.g. hypovolaemia, stress)
What does atrial fibrillation look like?
Dis-coordinated contraction of atria - don’t have one P wave but many little waves (fibrillation). Irregularly irregular QRS complex. Atrial and ventricular rate is fast
What is atrial flutter
More coordinated than fibrillation (around the AV valve continuously in the right atrium).
What does atrial flutter look like on an ECG?
Saw-toothed pattern P wave. Regular ventricular rhythm and rate is 150. Atria rate is high.
What are two types of SVT?
atrioventricular nodal reentry tachycardia (AVNRT) and atrioventricular re-entrant tachycardia (AVRT)
What does SVT look like on an ECG?
- Tachycardia
- No clear P wave
- Lots of QRS complexes that are narrow
What is AVNRT and why does it cause that ECG trace?
Impulse is going round and round the AVN so the P and QRS are simultaneous and only QRS is seen. P wave may be just after QRS complex
What is pre-excitation syndrome and what does it look like on the ECG?
P wave without iso-electric line - straight to QRS complex (which is slurred - called a delta wave). Caused by people having accessory pathways between the atria and ventricles so no property of AVN.
What is AVRT?
Can be caused by an accessory pathway. Rhythm down AVN and back up the accessory pathway to atria
Heart block - AV nodal block
1st degree
2nd degree
3rd degree - worst (complete heart block)
What is a 1st degree block and what does it cause in the ECG?
Too much of a pause before ventricular systole. Long PR interval. Caused by diseased AV node. Still 1:1 P wave to QRS.
What is a 2nd degree block and what does it cause in the ECG?
Some P waves don’t get to ventricles - impulse may be lost. Some P waves are not followed by QRS complex
What is Mobitz Type 1 (2nd degree block) and its appearance on ECG?
PR interval gradually increases and then a dropped beat. Once AVN cannot cope anymore, QRS is missed
What is Mobitz Type 2 (2nd degree block) and its appearance on ECG?
Some missing beats but no gradual P interval lengthening. Fixed PR interval then missing beat
What is a 3rd degree block and what does it cause in the ECG?
AV node doesn’t work so no conduction to ventricles. Ventricles fir on their own and so P and QRS are not associated - may occur regularly but independent. Look at P and QRS relationship to identify.
What does a bundle branch blockage look like on an ECG and which electrodes are used?
Seen in QRS complex.
QRS complex widens and morphology changes depending on which bundle branch is blocked and the lead. Look at chest leads
What does RBBB look like on an ECG?
Bunny ears and wide QRS
What does LBBB look like on an ECG?
Deep negative S wave and wide QRS
What does ventricular fibrillation look like?
Broad, irregular QRS complex (amplitude and rhythm)
What does ventricular tachyarrhythmia look like?
Rapid, regular, broad
What is Wolff-Parkinson-White Syndrome and what does it look like on an ECG?
Accessory pathway and short PR interval causing ventricular pre-excitation giving a delta wave. Can predispose to AVRT.
