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QRS Complex Morphology


The QRS complex can present different morphologies, depending on the lead and the abnormalities present in the patient.

QRS polarity: Positive, Negative or Biphasic?

QRS complex polarity is important in order to determine the Electrocardiogram Heart Axis, when the QRS polarity in leads I and III allow us to quickly estimate whether it is normal or not.

Also, a predominantly negative QRS in precordial leads should spark a suspicion of abnormalities of the heart anterior wall.

But, when is a QRS complex Positive or Negative?

Positive QRS Complex

Positive QRS Complex: The largest positive wave amplitude (R or R') is larger than the largest negative wave amplitude (Q or S).

Negative QRS Complex

Negative QRS Complex: The largest positive wave amplitude (R or R') is smaller than the largest negative wave amplitude (Q or S).

Biphasic QRS Complex

Biphasic QRS Complex: The amplitudes of the largest positive and negative waves are similar.


Electrocardiographic meaning:

When the QRS is clearly positive it means that the electric impulse flows towards the lead; if QRS is negative the impulse flows away from the lead; if the QRS complex is biphasic it means the direction of the impulse is perpendicular to the lead.

QRS Complex Morphology

Some authors prefer to differentiate the diverse QRS complex morphologies by using capital letters for waves with great amplitude and lower-case letters for those ones with small amplitude.

In certain articles of My EKG, we used this nomenclature for a better understanding, as we consider it an easy way to differentiate the multiple morphologies QRS can present.

Rs QRS Complex Morphology

Rs: Tall R wave followed by a small S wave. On a normal Electrocardiogram we find it in precordial leads V4-V6 and in all limb leads, except aVR.

qRs QRS Complex Morphology

qRs: Small initial non-pathological Q wave, followed by a tall R wave and a small S wave. On a normal Electrocardiogram, it can be seen in leads V5-V6.

RS QRS Complex Morphology

RS: Tall R wave followed by a deep S wave, with similar amplitude (biphasic QRS). It is the characteristic morphology in V3.

rS QRS Complex Morphology

rS: Small R wave followed by a deep S wave. Normal morphology in leads V1-V2.

In Left Posterior Fascicular Block it is seen in lateral leads; in Left Anterior Fascicular Block, in inferior leads. It is commonly mistaken as a QS when the R wave is very small.

Qr QRS Complex Morphology

Qr: Deep Q wave followed by a small R wave. Normal morphology in aVR. When found in other leads, it is a sign of myocardial infarction (previous STEMI) in the corresponding heart area.

QS QRS Complex Morphology, necrosis

QS: A lone, deep negative wave. It is a sign of myocardial infarction in the region near to the Electrocardiogram leads, it should not be present on a normal EKG.

rSR' QRS Complex Morphology', Bloqueo de Rama Derecha

rSR': Small R wave, followed by a deep S wave and a second tall R wave. It is a characteristic sign of Right Bundle Branch Block and Incomplete Right bundle branch block. It is also present in the Brugada Syndrome.

Other morphologies: As you may well imagine, there are many more QRS Complex morphologies. We have mentioned only the more frequent and important but we may also come across wide R waves, rSr’, QR, qR, qRS, qrS, among others.

In the next article we will further explain Posterior and Right-Side Leads. Click on Next down below to stay with us.

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