description of ECG waves and segments

Question 1

P wave

Answer 1

The P wave is produced by the depolarization of the atria. It indicates SA node function and is best seen on leads LII and V1, where it is normally upright.

Question 2

P-R INTERVAL

Answer 2

Normal: 0.12–0.20 sec. It is measured from the onset of the P wave to the beginning of the QRS complex.

Question 3

Q WAVE

Answer 3

The Q wave is the first negative (downward) deflection following the P wave and the P-R interval. Septal depolarization

Question 4

R WAVE

Answer 4

The R wave is the first positive (upward) deflection. It follows the Qwave, if there is one. It represents the depolarization of the left ventricle.

Question 5

S WAVE

Answer 5

The S wave is a negative deflection following the R wave and is usually the last portion of the QRS complex.

Question 6

QRS INTERVAL

Answer 6

From the beginning of the Q wave to the end of the S wave, it represents the time in which ventricular depolarization occurs. Normal: 0.04–0.10 sec. (<0.10)

Question 7

S-T INTERVAL

Answer 7

Measured from the end of the S wave to the end of the T wave; represents repolarization of the ventricles.

Question 8

T WAVE

Answer 8

T wave follows S wave and S-T segment—shows repolarization of the ventricles.

Question 9

P-R SEGMENT

Answer 9

Measured from end of P wave to beginning of QRS complex; normally isoelectric.

Question 10

S-T SEGMENT

Answer 10

Measured from end of S wave to beginning of T wave; normally isoelectric.

Question 11

QT INTERVAL

Answer 11

Measured from beginning of QRS complex to end of T wave