The key to ECG interpretation is practice. The way to use this guide is
to print it out and use it on the wards or with a book of examples.
Some good testbooks are recommended in the
Things To Buy
Big square: 0.2s. Small square: 0.04s.
A system for looking at ECGs
300 divided by the number of big squares between R-R values.
regular? Irregular? Irregularly or regularly irregular?
Normal: QRS complexes are ↑ in I, II
Right deviation: ↓ in I
Left deviation: ↓ in II, III
less than 1 big square
less than 3 small squares
Predominant R waves in V1?
elevation or depression
Here are some common abnormalities that you would be expected to
recognise in finals, listed roughly in order of importance. Beware that
some of these are rules of the thumb, and that it is necessary to
practice interpretation to be any good at it.
A more comprehensve list can be found in the cardiovascular section of the Oxford Handbook.
Indicates myocardial infarction (MI). The leads in which the ST segment
is raised give an indication of the area of heart infracted and which
vessels are blocked:
ST elevation in II, III, VF
Right coronary artery
ST elevation in V3
Left anterior descending artery
ST elevation in V5 to V6
ST depression in V3 to V4
This is illustrated in the following diagram:
Indicates an old MI.
True Q waves must be 2 small squares deep, 1 small square wide.
Alternatively more than 1/3 of QRS height. Q waves can be normal in
leads I and AVR.
Long PR interval (>1 big square).
Mobitz type I:
(Wenckebach phenomenon): cycles of gradually increasing PR interval
until the QRS complex is dropped (i.e. a P wave not followed by a QRS
complex). The cycle then repeats.
Mobitz type II:
Randomly dropped, or regularly dropped QRS complexes.
Alternate conducted and non-conducted atrial beats:
Often 2:1, meaning 2 P waves to 1 QRS complex.
Third Degree (Complete)
No relationship between P waves and QRS complexes (although both are present).
No P waves
Irregularly irregular rhythm
Ventricular rate of about 150 usually
Between QRS complexes "sawtooth" complexes representing a fluttering atrial contraction
Broad QRS complexes
No P waves
A random appearing rhythm. Beware of mistaking it for VT.
Saddle shaped ST segment elevation in all leads without reciprocal ST depression
Tall R waves in V1-V3 and deep S waves in V4-V6 indicate
Tall R waves in V4-V6 and deep S waves in V1-V3 indicate
Bundle Branch Block
helps to recall the features of
bundle branch block. RR stands for "Right." M indicates a M shape in V1 (an RSR shape).
("LL") bundle branch block. W indicates an SRS pattern in V1 and a RSR pattern in V6.
Can be lethal so important to identify.
Tall tented T waves
increased PR interval
Wolf Parkinson White Syndrome
Wide and initially slurred QRS complex (delta wave) and a short PR interval.
Reverse tick (concave downwards) in all leads, T wave inversion.
Right Bundle Branch Block
Left axis deviation (Left Anterior Hemiblock)
1st degree HB (long PR interval)
NYU ECG guide