Session 7.1 Flashcards
(26 cards)
How long should the PR interval be?
3-5 small boxes
Prolonged if more than 1 large box
How long should the QRS complex be?
Less than 3 small boxes
If more, prolonged
What is normal sinus rhythm?
Heart rate 60-100bpm P waves present Leads I and II, leads upright PR interval = 3-5 small boxes QRS complex = less than 3 small boxes
What lead do you use to interpret the rhythm?
Lead II rhythm strip at the bottom of the 12 lead ECG
What’s a heart block/AV conduction block and what are the causes?
Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of His
Causes
- acute myocardial infarction
- degenerative changes
What’s a first degree heart block?
PR interval prolonged more than 5 small boxes (0.2 seconds)
If long standing, don’t need to do anything about it.
What’s the different between mobitz type 1 and mobitz type 2 second degree heart block?
Type 1 = successively longer PR intervals until one QRS is dropped, then cycle starts again.
Type 2 = PR intervals do not lengthen, but suddenly dropped a QRS complex (higher risk of progression to complete heart block)
What’s a third degree heart block?
Complete failure of AV conduction
Atria and ventricles depolarise separately - ventricular pacemaker takes over as sinus control isn’t reaching ventricles
Usually get a wide QRS complex, inverted T waves, and urgent pacemaker insertion is required
Where can abnormal rhythms arise from?
Sinus node
Atrium
AV node
These are also called supraventrivcular rhythms (arise above the ventricles)
Also ventricular rhythms
What do ventricular rhythms cause?
Ventricular tachycardia
Wide and bizarre QRS complex
What it atrial fibrillation?
A supraventricular rhythm
Arises from multiple atrial foci
Rapid, chaotic impulses
No P waves, wavy baseline
Impulses reach AV node at rapid irregular rate and not all are conducted due to AV node refractory period
Ventricles depolarise normally = narrow QRS complex with irregular R-R intervals
What are the haemodynamic effects of atrial fibrillation?
Atrial conduction lost, they just quiver
Ventricles contract normally but at an irregular rate
Heart rate and pulse irregular
What’s the difference between regularly irregular and irregularly irregular?
Regularly irregular = weird but consistent
Irregularly irregular = weird but inconsistent
What is a ventricular ectopic beat?
Ectopic focus in ventricular muscle
Impulse doesn’t spread via his— purkinje system
Therefore much slower depolarisation of ventricular muscle
Therefore wide QRS complex, different in shape to usual QRS
How can a ventricular ectopic lead to ventricular tachycardia?
More than 3 consecutive ventricular ectopic = ventricular tachycardia
What is risky about ventricular tachycardia?
Can lead to ventricular fibrillation = causes cardiac arrest
What is ventricular fibrillation?
Abnormal, chaotic, fast, ventricular depolarisation
Impulses from number ectopic sites in ventricular muscle
No coordinates contraction = ventricles quiver
No cardiac output = cardiac arrest
What sequence do you go through when analysing an ECG?
1) regular or irregular
2) rate
3) p waves present
4) PR interval
5) QRS - narrow or broad
6) is every P followed by a QRS
7) Is every QRS preceded by a p wave
What are the ECG changes of ischaemia and myocardial infarction?
- coronary artery occlusion = ischaemia or infarction in area supplied by artery
- changes seen in leads facing affected area of ventricle
- look at PQRST in all 12 leads
- need to know which groups of leads look at different parts of the heart
What does partial narrowing of the lumen of arteries cause?
Sub endocardial ischaemia/injury
This area is further away from coronary arteries which lie on the surface of the heart
hence the most vulnerable region, involved first
What does complete occlusion of the lumen cause?
Full thickness injury
Including sub- epicardial region
What’s a STEMI?
- ST elevation myocardial infarction
- Due to complete occlusion of coronary artery by thrombus
- Full thickness of myocardium involved
- Sub epicardial injury causes ST segment elevation in leads facing affected area
What do pathological q waves indicate?
Muscle necrosis
Pathological if more than 1 small square wide and 2 small squares deep
How do unstable angina and severe ischaemia present on an ECG?
Same ECG changes seen in both unstable angina and NSTEMI
They are differentiated by a blood test = troponin present in NSTEMI
