QRS complex on ECG is the graphic representation of ventricular depolarization.

1) What is a wave in QRS complex?

Wave is actually the deflection away from in reference to isoelectric line.

Deflection above in reference to isoelectric line is a positive wave.

Deflection below in reference to isoelectric line is a negative wave.

2) What is an isoelectric line?

Isoelectric line is the “TP” segment on the E.C.G ; the line between the end of “T” wave and start of “P” wave.

“PR” segment and “ST” segment cannot be called as isoelectric lines because in some pathologies they can be raised or depressed.

3) Factors determining the QRS complex:

Nomenclature of QRS depends upon:

a) Direction of deflection of wave:

Whether it is a positive deflection or negative deflection.

b) Position of wave within the complex:

Negative deflections coming before and after the positive deflection are given different names. If a negative deflection is coming before a positive deflection “R” wave is given a name “q” wave , if a negative deflection is coming after a positive deflection “R” wave it is given a name “s” wave.

c) Degree Of deflection:

i) Small deflection (wave): Represented by small letter e.g. “q” , “r” , ”s”.

ii) Large deflection (wave): Represented by a large letter e.g. “Q”, “R” ,”S”.

4)Rules for QRS complex:

a) Initial negative wave is always “q” or “Q” wave.

b) First positive wave is always “r” or “R” wave.

c) Negative wave after “R” or “r” wave is a whether “S” or “s” wave.

In QRS complexes the first positive wave is “R” wave and any wave coming before the “R” wave is a “q” wave and wave after the “R” is a “s” wave.

d) If there is a second positive deflection within the QRS complex it is called as R’ (R prime) and if there is second negative deflection after the R’ it is called as s’ (s prime) .

e) Small deflections are designated by small letters “s” , ”r” and large deflections are represented by large letters “R” “S” “Q” “R’” “S’”.

f) If the amplitude of the deflection is more than three small squares it is considered as large deflection and if it is less than 3 squares than it is considered as small deflection.

5) Triphasic QRS Complex:

Triphasic QRS complex is a complex when there are 3 waves present in the QRS complex. e.g. qRs , rSr’, RSR’.

6) Biphasic QRS complex:

Biphasic QRS complex is a complex when there are 2 waves present in a QRS complex. e.g. qR , QR, Qr, qr, Rs, rs, rS.

7) Monophasic QRS complex:

Monophasic QRS complex is a complex when there is only 1 wave present in a QRS complex

Note:To label a negative wave as “q” or “s” we must have a “R” wave.

Sometimes there is a QRS complex which does not have a positive deflection and has only a negative deflection, so we will label it as “QS” or “qs” depending upon the amplitude of a wave.

QRS complex is a name given to any wave complex produced by the ventricular depolarization it can have 1,2,3 waves and will call as Monophasic, Diphasic and Triphasic respectively.

QRS complex

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