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ECGs for acute block – a suggested approach:
Information to check on every ECG:
Identifying information: name/unit number
Date/time
Voltage (10mm/mV)
Speed (25mm/s)
Rate:
Remember 1 small square is 0.04s, 1 large square is 0.2s, 5 large squares is 1
second
(one small square is 1mm)
300/number large squares between R-R (eg if there are 5 large squares
between complexes then the rate is 60/min)
Rhythm:
Is it regular or irregular?
Easiest way to tell is to use scrap paper to mark R waves and check they are
regular.
Are there P-waves?
(if no then atrial fibrillation, SVT or ventricular rhythm)
Is each P followed by a QRS?
If no then 2nd or 3rd degree heart block present
Normal PR interval 0.12-0.2s (3-5 small squares):
If prolonged PR interval but constant then 1st degree heart block:
If progressive prolongation of PR interval, then a P wave with no subsequent
QRS then it is Mobitz type 1 2nd degree heart block (Wenkebach):
If PR interval is constant but there are P waves with no subsequent QRS then
it is Mobitz type 2 2nd degree heart block:
2nd degree heart block can also be regular 2:1, 3:1, 4:1 block etc
Higher grade blocks are more dangerous (more at risk of asystole)
If there is no relationship between the P waves and QRS complexes then it is
3rd degree (or complete) heart block:
Is each QRS preceded by a P wave?
If no – atrial fibrillation, ectopic beats, junctional escape rhythms
Axis:
I and II positive = normal axis
I positive, II & III negative = left axis deviation [“Leaving”]
I negative, II & III positive = right axis deviation [“towaRds”]
QRS:
Normal QRS <0.12s (3 small squares) width
Wide QRS = either a beat arising from the ventricle (ectopic, escape rhythm,
VT) or a conduction defect – usually bundle branch block
Left bundle branch block [WiLLiaM]
Right bundle branch block [MaRRoW]
LVH criteria
V4, V5, V6 R wave = >25mm
R wave in V5 or V6 plus S wave in V1 = >35mm
ST segments:
ST elevation: STEMI, left bundle branch block, (pericarditis if global)
STEMI criteria if:
2mm in 2 consecutive chest leads, or
1mm in 2 limb leads
ST depression: ischaemia, posterior MI, NSTEMI, digoxin
T-wave:
Tall – hyperkalaemia, LBBB
Flat – ischaemia, hypokalaemia
Inverted - ischaemia
How to tell which area of the heart is ischaemic/infarcted:
ST changes
Area of heart
Coronary artery
V1 – V6
Anterior
LAD
V1 - V4
Septal
LAD
I, aVL, V5, V6
Lateral
Circumflex
II, III, aVF
Inferior
RCA/circumflex
V7-9
Posterior
Circumflex
Other resources:
ECG made easy, Hampton.
Making sense of the ECG. Houghton & Gray (and they have a self assessment
book)
ECGs by example, Jenkins & Gerred
Online resources: (FOAM!)
Overview at foamedstudent.com
Dr Smith’s ECG blog: http://hqmeded-ecg.blogspot.com.au/
Amal Mattu’s ECG blog: http://ekgumem.tumblr.com/
Learn the heart: http://www.learntheheart.com/ecg-review/ecg-quiz/
Ecglibrary.com