Normal ECG

Normal ECG characteristics

Rhythm: Regular (<10% variation at RR intervals)
Rate: 60-100 per minute



P wave duration: <120 msec
P wave amplitude: 0.2 mV in the frontal plane, 0.1 mV in the transverse plane
Sinus P waves: Upright in I, II, aVF, Inverted in aVR


PR interval: 120-200 msec


QRS duration: 60-110 msec (adults), 40-100 msec (4-16 years old), 30-90 msec (<4 years old)
Q wave:

• < 20 msec in leads V2-3, 
• < 30 msec and <0.1 mV in leads I, II, aVL, aVF, V4-6

R wave height: increases from V1 to V5 and then decreases in V6

• V1: 0-7 mm + R ≥ S
• V2: 1-10 mm + R ≥ 1.5x S
• V3: 2-20 mm
• Transition at V3-V4

R wave peak time: <35 msec in V1-2, <45 msec in V5-6
QRS axis: -30 to 90 degrees


ST segment:  < 0.5-1 mm of elevation


T waves:

• Height: < 2/3 of the size of the preceding R wave, 
• Axis: in the same direction of the predominant QRS deflection (QRS-T angle should be <45 degrees in frontal leads and < 60 degrees in precordial leads)

U waves:

• Height: about 10% of the preceding T wave or <1.5 mm
• Axis: In the same direction as the T wave

QTc (corrected): 390-450 msec (men), 390-460 msec (women)