The Normal EKG

Eric J Milie D.O.

Sinus Rhythm

P wave before every QRS complex P waves upright in II, negative in

aVr Reproducibility of the R-R interval

Sinus Rhythm

Rate

<60bpm bradycardia >100bpm tachycardia Normal rate between 60 and 100

bpm If regular with <10% variation of R-

R interval, termed “sinus arrhythmia”

Determining Rate

EKG grid made of large and small boxes

One large box= 0.2ms One small box= 0.04ms

Determining Rate

Locate a QRS complex on a bold line (ie edge of large box)

If the next QRS complex is separated by one large box, the rate is 300, two boxes 150, three boxes 100, etc.

Example

Rate

If rhythm is irregular, may use the “six second rule” to estimate the rate

Count the number of QRS complexes present in span of 30 large boxes, then multiply by 10 for an estimated heart rate

Axis

Normal QRS in an adult between –30° and +105°

Axis determined by finding “isoelectric” lead

I, aVF most important for quick estimate

Axis

Intervals

Intervals

P-R interval: beginning of p-wave to beginning of QRS; normal 0.12-0.2ms (3-5 small blocks)

Q-T interval: initiation of QRS complex to termination of T wave. Normal QT is 0.4 +/- 0.05ms

QT normal if <1/2 of the R-R interval

QRS

QRS complex represents the depolarization through the ventricles

Normal QRS duration between 0.08 and 0.12ms (2-3 small blocks)

S-T segment

Distance from the termination of the QRS complex to the initiation of the T-wave

Important to note its configuration (depression or elevation)

J-point: where ST segment “takes off” from QRS

ST Elevation

T-wave

Should be of the same direction as the main deflection of QRS complexes in all leads

Positive in II, V3-V6 Negative in aVR Variable in other leads No greater than 5mm in limb leads

and 10mm in precoridal

Pathological Q waves

Significant Q-wave is >1mm wide OR >1/3the total vertical magnitude of the QRS

Must be present in contiguous leads for clinical significance

Small Q-waves common in I, ii, V5 and V6 and are considered “non-pathologic”

Localizing Injury

R wave progression

Transition from a mostly negative to a mostly positive QRS complex in the precordial leads should occur between V3 and V4

Before V3 “early transition” After V4 “poor R-wave

progression”

Poor R wave Progression