The P wave on the ECG represents atrial depolarization, which results in atrial contraction, or atrial systole.
The normal P wave morphology is upright in leads I, II, and aVF, but it is inverted in lead aVR. The P wave is typically biphasic in lead V1 (positive-negative), but when the negative terminal component of the P wave exceeds 0.04 seconds in duration (equivalent to one small box), it is abnormal.
P-Wave AxisIt is determined by measuring net positive or negative P-wave deflections on all six limb leads and calculating the net direction of electrical activity using the hexaxial reference system. Abnormal P-wave axis is defined as any value outside 0–75° (Figure 1) (31).
P wave duration is a marker of atrial conduction derived from ECG. Normal P wave can be considered to be less than 110 ms [12–14]. Prolonged P wave duration signifies conduction delay between right and left atrium due to impulse slowing or blockage, probably most often but not exclusively in the Bachmann bundle.
An abnormal EKG can mean many things. Sometimes an EKG abnormality is a normal variation of a heart's rhythm, which does not affect your health. Other times, an abnormal EKG can signal a medical emergency, such as a myocardial infarction (heart attack) or a dangerous arrhythmia.
On a hexaxial diagram (see figure 1): If the electrical axis falls between the values of -30° to +90° this is considered normal. If the electrical axis is between -30° to -90° this is considered left axis deviation. If the electrical axis is between +90° to +180° this is considered right axis deviation (RAD).
When everything is working smoothly, you have a normal sinus rhythm and your heart beats between 60 and 100 times per minute.
Normal intervalsNormal range 120 – 200 ms (3 – 5 small squares on ECG paper). QRS duration (measured from first deflection of QRS complex to end of QRS complex at isoelectric line). Normal range up to 120 ms (3 small squares on ECG paper).
In a normal EKG, the P-wave precedes the QRS complex. It looks like a small bump upwards from the baseline. The amplitude is normally 0.05 to 0.25mV (0.5 to 2.5 small boxes). Normal duration is 0.06-0.11 seconds (1.5 to 2.75 small boxes).
The P-R IntervalThe first measurement is known as the "P-R interval" and is measured from the beginning of the upslope of the P wave to the beginning of the QRS wave. This measurement should be 0.12-0.20 seconds, or 3-5 small squares in duration.
First, the standard 12-lead ECG is a 10-second strip. The bottom one or two lines will be a full “rhythm strip” of a specific lead, spanning the whole 10 seconds of the ECG. Other leads will span only about 2.5 seconds. Each ECG is divided by large boxes and small boxes to help measure times and distances.
