Interpreting ECG's Flashcards
What is a normal PR interval, and when is it classed as prolonged?
A normal PR interval is 3-5 small boxes.
If it’s greater than 5 small boxes (AKA 1 large box) it is classed as prolonged.
Where does the PR interval start and end?
Start of P wave and just before Q wave starts
Where does the QRS complex start and end?
When is the QRS complex classed as prolonged?
Start of Q wave to the J point (part of the S wave where it returns to baseline).
Greater than 3 small boxes, classed as prolonged.
What are the 6 limb leads?
I, II, III, aVR, aVL, aVF
What are the 6 chest leads?
V1-V6
What happens during a heart block?
There is either no conduction/delayed conduction of impulses from atria to ventricles via AV node and Bundle of His
What are the different types of heartblock?
1st Degree 2nd Degree- (Mobitz type 1 & Mobitz type 2) 3rd Degree (AKA complete heartblock)
What are the causes of heartblock (atrioventricular conduction blocks)?
1* Acute myocardial infarction (due to AV conduction block usually affecting Right coronary artery)
2* Degenerative changes (old age, fibrous tissue replaces conducting tissue. Usually permanent, pacemaker needed)
What are the characteristics of 1st Degree heartblock?
PR interval is longer than 5 small boxes (0.2 seconds, each small box is 0.04 seconds)
What are the characteristics of 2nd Degree, Mobitz type 1 heart block?
PR intervals get longer, until there is a missing QRS complex.
Then cycle starts again.
In general, 2nd Degree heartblock is identified by missing QRS complex.
What are the characteristics of 2nd Degree heartblock, Mobitz type 2?
PR intervals stay the same length, but there is a missing QRS complex.
(HIGHLY LIKELY TO LEAD TO COMPLETE HEARTBLOCK)
What are the characteristics of 3rd Degree heartblock?
Atria and ventricles depolarise independently (as there is absolutely no AV conduction).
Ventricular escape rhythm (ventricular myocytes take over and make their own pace).
Wide QRS complexes.
Slow ventricular rate (30-40bpm-> dangerously low bp)
P-P intervals are normal. R-R intervals are much slower.
No relationship between P waves and QRS complex (PR intervals vary)
Requires urgent pacemaker.
What are the features of a bundle branch block?
Conduction delay in branches of Bundle of His.
P wave and PR interval is normal.
QRS complex is wider (>3 small squares) as ventricular depolarisation takes longer.
WiLLiaM- v1 looks like a W for Left bundle branch block, v6 looks like M
MaRRoW- v1 looks like a M for Right bundle branch block, v6 like W
What are the different types of abnormal rhythms?
Supraventricular (above ventricle) rhythms- SA node, Atrium, AV node
Ventricular rhythms- Ventricular myocyte contraction
How do supraventricular rhythms differ from ventricular rhythms?
Supraventricular rhythms will have normal QRS complexes, as regardless of where the impulse is generated, it will still travel down the same pathway across ventricles.
Ventricular rhythms do not go down the His-Purkyne System. A ventricular myocyte behaves like its own pacemaker and generates action potentials —> wide and bizarre QRS complexes
What are the features of atrial fibrillation?
Supraventricular rythmn
Multiple parts of the atria are depolarising rapidly —> Leads to chaotic, rapid impulses.
NO P WAVES- wavey baseline.
Lots of impulses to AV node, not all are conducted due to refractory period of AV node.
When they are conducted, the ventricles depolarise normally so QRS complex is normal. The R-R interval is irregular.
What are the haemodynamic effects of atrial fibrillation?
Atria don’t contract, they just quiver-> blood begins to stagnate, leading to clots.
Ventricles contract normally, but irregular rate —> irregular heart rate and pulse.
What are ventricular ectopic beats?
Ventricular myocyte produces its own impulse. The impulse doesn’t spread via the fast His-Purkyne system —-> slower depolarisation of the muscle——> wide, abnormally shaped QRS
(Look like villi)
What is Ventricular tachycardia?
More than three consecutive ventricular ectopic beats.
Fast, regular broad QRS complexes
What are the features of ventricular fibrillation?
Rapid and chaotic depolarisation of ventricles. Not co-ordinated, ventricles quiver rather than contract-> no cardiac output-> Cardiac arrest. ECG just looks like up and down scribbles.
Why do we need to look at all 12 leads when identifying damage to heart?
If there is a narrowing of coronary artery (due to ischaemia), or complete occlusion (leading to necrosis) only that part of the heart will be damaged.
Which leads face the inferior surface of the heart?
Leads II, III and aVF.
This area is supplied by the right coronary artery.
Which leads face the anterior (septal) surface of the heart?
V1-V4.
This area is supplied by LAD.
Which leads show the lateral surface of the heart?
I, aVL, V5, V6.
The lateral area is supplied by circumflex artery.
