ECG Flashcards
Method for going through an ECG
- Rate
- Rhythm
- Axis
- P waves
- PR interval
- Q and RS
- QT interval
- ST interval
- T waves
How to calculate the Rate
Either 300/Number of big squares within R-R int
Count the number of complexes x 6
(a rhyth strip is 10secs)
What are you looking for with the rhythm?
- Whether it’s irregular → An ectopic/arrhythmia
- Or whether it’s irregularly-irregular → Atrial fibrillation
What is the normal QRS axis distribution, and why do we look at the axis?
Normal axis distribution is between avL (-30) to aVF (90)
We look to rule out LAD and RAD to determine there is correct electrical spread within the heart.
What do you look at to determine normal axis spread on ECG
- Lead I and aVF are + deflected
* Lead II will also be extremely +
What would cause suspicion of LAD on ECG and how do you confirm it?
- Lead I + and aVF is -
This tells you your axis is between -90 to 0 somewhere. But it could still be between -30 and 0.
- check Lead II, if this is also negative, this confirms LAD
Summary:
Lead I and avL +
Lead II and aVF -
What would indicate RAD on ECG
- Lead I - and aVF +
What do you need to be thinking about with P waves?
- Are P waves present? (SA node activation)
- If so, are they followed by a QRS complex (sinus rhythm)
- Duration?
- Should be <3 little squares <0.12s
- Increaseed duration could indicate atrial hypertrophy
- Shape?
- Sawtooth = AF
- Fibrillation waves
- Flat line = no atrial activity at all
What do the little and big squares on ECG represent?
Each small square is 1 mm in length and represents 0.04 seconds.
Each larger square is 5 mm in length and represents 0.2 seconds.
What is normal for P waves on leads II, aVF and V1?
Lead II and aVF positive
V1 Biphasic
How long should the P-R interval be? What does anything larger then this suggest?
<0.2s (one big square)
this suggests atrioventricular (AV) block
What are the different types of AV block and can you describe them?
First Degree HB: PR interval >0.2s
Second Degree HB
- Mobitz Type I: The PR interval gets progressively longer until a QRS comlexes ‘drops off’
- Mobitz Type II: The PR interval is fixed but there is dropped beats
Third Degree HB/”complete Heart Block”: The P waves and QRS complexes are completely unrelated.
Whats Second degree HB, mobitz type 1 also called?
Wenckebach
Where is the Heart block occuring in relation to each type?
- First Degree: between SA node to AV node
- Second Degree
- Mobitz T1: AV node
- Mobitz T2: After AV node in bundle of His or Purkinje fibres
- Third Degree: anywhere from AV node down causing a complete blockage
What could a shortened PR interval indicate?
Simply, the P-wave is originating from somewhere closer to the AV node so the conduction takes less time (the SA node is not in a fixed place and some people’s atria are smaller than others!)
The atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall. This is an accessory pathway and can be associated with a delta wave
What is a broad QRS defined as and what does it indicated pathologically?
QRS >0.12s (3ss)
It means the electrical activity is moving through the myocardium instead of the purkinje fibres.
This could indicate a ventricular ectopic
BBB
Hyperkalaemia
Sodium-channel blockade
What are the main sodium channel blockers to look out for and what can they cause?
They can cause seizures and ventricular arrhythmias
- Tricyclic antidepressants (= most common)
- Antiarrhythmics (quinidine, procainamide)
- Local anaesthetics (bupivacaine, ropivacaine)
- Antimalarials (chloroquine, hydroxychloroquine)
- Dextropropoxyphene
- Propranolol
- Carbamazepine
- Quinine
What is a delta wave, and what else do you need to made the diagnosis of the pathology in question?
A sign that the ventricles are being activated earlier than normal from a point distant to the AV node. The early activation then spreads slowly across the myocardium causing the slurred upstroke of the QRS complex.
To diagnose WPW you need delta waves + tachyarrhythmias
What does a pathological Q wave indicate, what lead would you find it in?
A large Q wave, indicates a prior MI
Where should you have dominant S waves?
rS
aVR and V1
If you see R> s in leads aVR and V1 what does that indicate?
In aVR : tricyclic OD
In V1 : Posterior MI? RBBB?
What should you see in regards to the QRS complex in leads V1 to V4?
Progression of the R wave upwards
How to distiguish Left Ventricular Hypertrophy on ECG?
V2 + V5 = >7 small squares
Where would you see on ECG to indicate an inferior stemi?
Where would you see reciprocal change?
ST elevation in the inferior leads: II, III and aVF
progression of the Q in II, III and aVF
Reciprocal changes in I and aVL
Up to 40% of patients with an _____ STEMI will have a concomitant right ventricular infarction.
What is the significance of this?
Up to 40% of patients with an inferior STEMI will have a concomitant right ventricular infarction.
These patients may develop severe hypotension in response to nitrates as they are heavily dependent on preload. Be catious of GTN spray here.
What vessels are involved in an inferior STEMI or NSTEMI.
How would this produce a difference on ECG?
- 80% Right Coronary Artery (RCA)
- ST ele. in III > II
- 18% Left circumflex Artery (LCx)
- ST ele. in III < II
What would cause suspicion of a Posterior STEMI (20% of MI’s)
As the posterior myocardium is not directly visualised by the standard 12-lead ECG, reciprocal changes of STEMI are sought in the anteroseptal leads V1-3. Posterior MI is suggested by the following changes in V1-3:
- Horizontal ST depression of anteroseptal leads (reciprocal effect)
- Tall, broad R waves (>30ms)
- Upright T waves
- Dominant R wave (R/S ratio > 1) in V2
Posterior infarction is confirmed by the presence of ST elevation and Q waves in the posterior leads (V7-9).
Where would you see ST elevation for anterior/septal/lateral STEMI
- ST segment elevation with Q wave formation in the precordial leads (V1-6) ± the high lateral leads (I and aVL).
- Reciprocal ST depression in the inferior leads (mainly III and aVF).
Septal Leads: V1 - V2
Anterior Leads: V3 - V4
Lateral Leads: V5 - V6, I and aVL
What is the issue with NSTEMI’s on ECG
ST depression indicating an NSTEmI doesn’t correlate to specific leads like STEMI’s do
Anterior STEMI results from occlusion of the….
Left anterior descending (LAD)
Has the worst prognosis mainly due to a larger infarct size?
