QRS polarity: Positive, Negative or Biphasic?
QRS complex polarity is important in order to determine the QRS 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 complex 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
When the amplitude of the largest positive wave (R or R') is larger than the amplitude of the deepest negative wave (Q or S).
Negative QRS Complex
When the amplitude of the largest positive wave (R or R') is smaller than the amplitude of the deepest negative wave (Q or S).
Biphasic QRS Complex
When the amplitudes of the largest positive and deepest negative waves are similar.
When the QRS complex is clearly positive, it means that the electric impulse flows towards the lead; if the QRS complex 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: 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: 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 and V6.
RS: tall R wave followed by a deep S wave, with similar amplitude (biphasic QRS). It is the characteristic morphology in lead sV3.
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.