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Clinical Skills Blogspot

How to Analyse (read) an ECG

Proceed one step at a time analyse the following:

Identify

Ñ    Check patient details, date and time

Rate

Ñ    Rate =60/R-R interval

Rhythm

Ñ    Place a piece of paper on the ECG strip

Ñ    Mark a few peaks or troughs of the QRS complex with dots

Ñ    Move the piece of paper so that one of the dots is in line with either a peak or trough of the QRS

Ñ    See if the other dots align

Ñ    This will show if the rhythm is regular or irregular

P wave

Ñ    Height

< 2.5 millivolts (2.5 small squares)

Ñ    Width

< 0.11 seconds (slightly < 3 small squares)

Ñ    Shape:

Normal

Notched

Peaked

PR interval

Ñ    0.12-.20 milliseconds

QRS Complex

Ñ    Axis:

Draw 2 lines on a sheet of paper to represent lead I and lead III

Take lead I and add up the number of small squares above the base line and subtract from this the number of small squares below the base line

Plot this point onto lead I

Draw a perpendicular from this point

Similarly take lead III, add up the small squares above the baseline and subtract from this the number of small squares below the baseline

Plot this point onto lead III

Draw a perpendicular from this point

Join the point of intersection of leads I and III with the point of intersection of the two perpendiculars

This represents the axis

Quick method

If lead I is predominantly upgoing and lead III is predominantly downgoing, the leads are Leaving each other and it is Left axis deviation

If lead I is predominantly downgoing and lead III is predominantly upgoing the leads are Reaching for each other and it is Right axis deviation

Equiphasic Method    

If a lead has equal amounts of the QRS complex above and below the baseline, it is equiphasic and the axis would be at right angles to this lead

Ñ    Ventricular hypertrophy

LVH

Add R wave in V₁ with S wave in V₅ > 35 =LVH

RVH

R wave in V1 > 7 small squares (with inverted T)

Ñ    QRS Duration

< 120 milliseconds

Ñ    Analysis of the waves of the QRS complex and progression

Analyse

II, III and aVF together (inferior leads)

I, aVL, V₁ to V₆ together

Configuration

Note configuration of the waves

Progression

Note progression of waves in chest leads (V₁, V₂ small r, Q and R’, V₃ and V₄ equiphasic V5, V₆ small Q, R, S

ST Segment

Ñ    Normal

Ñ    Elevated

Ñ    Depressed

T wave

Ñ    Normal

Ñ    Inverted

U wave

Ñ    If present

QT interval

Ñ    Correct for heart rate QTc

QTc=QT / Ö RR

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