ECG Basics Flashcards
Rate =
300/N large squares in one R-R interval
OR
N QRS complexes on rhythm strip x6
1 small square =
0.04 seconds
1 large square =
0.2 seconds
1 second =
5 big squares
Normal QRS =
3 small squares (<0.12 seconds)
Normal P-R interval
3 to 5 small squares (0.12 to 0.20 seconds)
Normal QTc interval
<0.44 seconds in men (11 small squares)
<0.47 seconds in women (11-12 small squares)
Left axis deviation:
Look at leads I + II
Left axis deviation = R waves leaving each other
Right axis deviation:
Look at leads I + II
Right axis deviation. = R waves reaching towards each other
What is poor R wave progression?
R wave should be small in V1 and get progressively larger through to V6.
An R wave that remains small/doesn’t grow in V3 and V4 = ‘poor R wave progression’
A dominant/large R wave in V1 might indicate RBBB
What does a NEW LBBB with ACS symptoms indicate?
STEMI with proximal LAD occlusion
Signs of LBBB on ECG: (2 important/obvious + 3 others)
“WiLLiaM”
1. W shape in V1
2. M shape in V6
3. Broad QRS (delayed overall conduction time to LV)
4. Tall R waves in lateral leads
5. Deep S waves in right precordial leads (V1-V3)
Signs of RBBB on ECG: (2 obvious + 2 others)
“MaRRoW”
1. M shaped complexes in V1
2. W shaped complexes in V6
3. Wide slurred S wave in lateral leads (I, aVL, V5-V6)
4. Broad QRS
Inferior leads:
II, III, aVF
Lateral leads:
I, aVL, V5, V6
Anterior leads
V1, V2, V3, V4
Second degree heart block: Mobitz I
AKA Wenckebach
Progressive prolongation of the PR interval until a P wave occurs without a resulting QRS complex
Second degree heart block: Mobitz type II
Constant PR interval but some P waves are not conducted (i.e. followed by a QRS.
Increased risk of progression to complete AV block + asystole
2:1 AV Block
Only alternate waves are followed by a QRS
Can be due to type I or II 2nd degree heart block
Third degree heart block
No relationship between P and QRS complexes
What is an escape rhythm?
If the normal cardiac pacemaker (SA node) fails or operates abnormally slowly, cardiac depolarisation may be initiated from a subsidary pacemaker in the atrial myocardium, AV node conducting fibres or ventricular myocardium.
These pacemaker cells are found at various sites throughout the conducting system, with each site capable to independently sustaining a heart rhythm.
Under normal circumstances subsidiary pacemakers are supressed by the more rapid impulses from above (i.e. sinus rhythm). Junctional and ventricular escape rhythms arise when the rate of the supra-ventricular impulses arriving at the AV node or ventricle in less than the intrinsic rate of the ectopic pacemaker.
What is an agonal rhythm?
Occurs in dying patients, often seen in the later stages of an unsuccessful resuscitation.
Characteristics: slow, irregular, wide ventricular complexes, often varying in morphology.
Unlikely to produce a pulse
Characteristics of AF: (4)
Tachycardic
Irregularly irregular
No p waves
Narrow QRS
Define the following:
- Recurrent AF
- Paroxysmal AF
- Persistent AF
Recurrent = more than 2 episodes
Paroxysmal = self-terminating episode lasting <7 days
Persistent = not self-terminating, duration >7 days
First line tx in AF:
Rate control monotherapy with a beta-blocker or CCB
When might you use digoxin monotherapy in AF?
If the patient does very litte/no exercise or other rate limiting drugs are ruled out due to co-morbidities/personal preference
Second line AF tx:
Dual therapy with any two of: beta-blocker, diltiazem or digoxin
What is wolff-parkinson white?
The presence of a congenital accessory pathway and episodes of tachyarrhythmias.
Associated with a small risk of sudden cardiac death.
ECG features of wolff-parkinson white: (3)
- Sinus rhythm with a short PR interval (<3 small sqs)
- Broad QRS with a slurred upstroke to the QRS complex (= delta wave)
- Negative delta wave in aVL simulating Q waves of a lateral infarction (referred to as ‘pseudo-infarction’ pattern)
Atrial flutter
Monomorphic ventricular tachycardia:
Most common VT
Associated with MI
Supra-ventricular tachycardia
ECG changes seen in PE:
- Sinus tachycardia (most common)
- Complete or incomplete RBBB
- Right ventricular strain pattern (TWI in V1-4 +/- II, III, aVF)
- P pulmonale (peaked P wave in lead II)
What is p pulmonale?
Peaked P wave in lead II (>2.5mm)
Sign of right atrial enlargement, sometimes seen in a PE
What is right ventricular strain pattern?
TWI in right precordial leads (V1-4) +/- inferior leads (II, III, aVF).
Associated with high pulmonary artery pressures in PE.
6 stage approach:
- Is there any electrical activity?
- What is the ventricular rate?
- Is the QRS rhythm regular or irregular?
- Is the QRS narrow or broad?
- Is there atrial activity present?
- Is the atrial activty related to the ventricular activity and if so, how?
Ventricular tachycardia - 3 ECG features:
- Regular
- Broad QRS
- Tachycardic
Most commonly a re-entry VT
Toursades de Pointes:
- 2 ECG features
- Causes (2)
- Tx
- Polymorphic VT, QRS complexes “twist” around the isoelectric line
- Most commonly caused by MI, can occur due to QT prolonging agents
- Wait for it to self-terminate, protect the cardiac membrane with IV Mg, rate control with isoprenaline, defibrillate if unstable
Ventricular fibrillation:
- ECG features
No identifiable P waves, QRS complexes or T waves
Rate 150-500 bpm
Amplitude will decrease with duration (coarse -> fine VF)
Prolonged VF will degenerate into asystole
What is electrical alternans?
Electrical alternans refers to a beat-to-beat variation in the QRS complex height, with alternating taller and shorter QRS complexes. It is thought to be due to the heart swinging backwards and forwards within a fluid-filled (in a pericardial effusion).
