This document discusses the P wave on an electrocardiogram (ECG). It defines the P wave as representing atrial depolarization. It describes the normal characteristics of P waves including morphology, axis, duration and amplitude. It explains how right and left atrial depolarization summate to form the P wave. It discusses various abnormalities of P waves seen in conditions like atrial fibrillation, sinus arrest, right atrial enlargement and left atrial enlargement. It provides criteria for diagnosing enlargement of the right atrium or left atrium based on changes in the P wave.

1. P WAVE
Dr.G.VENKATA RAMANA
MBBS DNB FAMILY MEDICINE

2. P Wave Overview
• First positive deflection on the ECG
• Represents atrial depolarisation
• Characteristics of the Normal Sinus P Wave
• Morphology
• Smooth contour
• Monophasic in lead II
• Biphasic in V1
• Axis
• Normal P wave axis is between 0° and +75°
• P waves should be upright in leads I and II, inverted in aVR
• Duration
• < 0.12 s (<120ms or 3 small squares)
• Amplitude
• < 2.5 mm (0.25mV) in the limb leads
• < 1.5 mm (0.15mV) in the precordial leads
• Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF)
and lead V1, as the P waves are most prominent in these leads

3. The Atrial Waveform – Relationship to the P wave
• Atrial depolarisation proceeds sequentially from right to left, with the
right atrium activated before the left atrium
• The right and left atrial waveforms summate to form the P wave
• First 1/3 of the P wave  Right atrial activation
• Final 1/3 of the P wave  Left atrial activation
• Middle 1/3 of the P wave  Combination of the two
• In most leads (e.g. lead II), the right and left atrial waveforms move in
the same direction, forming a monophasic P wave
• However, in lead V1 the right and left atrial waveforms move in
opposite directions
• This produces a biphasic P wave with the initial positive deflection
corresponding to right atrial activation and the subsequent negative
deflection denoting left atrial activation

4. Normal P-wave Morphology – Lead II
• The right atrial depolarisation wave (brown) precedes
that of the left atrium (blue)
• The combined depolarisation wave, the P wave, is less
than 120 ms wide and less than 2.5 mm high

5. • Normal P-wave Morphology – Lead V1
• The P wave is typically biphasic in V1, with similar sizes
of the positive and negative deflections

6. • P WAVE
• Present or Absent
• If P waves absent
• Completely absent
• Intermittently absent
• Present but not obvious
• If P waves present look for
• Morphology
• Uniformity
• Amplitude
• Duration
• No of P waves per QRS complex

7. • P waves are completely absent
• Atrial fibrillation
• Sinus arrest or SA block (prolonged)
• Hyperkalemia
• P waves are present but not obvious
• AVNRT
• Third degree AV block
• P waves are intermittently absent
• Sinus arrest or SA block (intermittent)
• Are any P waves inverted?
• If ‘yes’, consider:
• Electrode misplacement
• Dextrocardia
• Retrograde atrial depolarization

8. Atrial fibrillation
• Irregular ventricular response
• Coarse fibrillatory waves are visible in V1
• “Sagging” ST segment depression is visible in V6, II, III and aVF, suggestive of digoxin effect

9. SINUS ARREST OR SA BLOCK
• Anatomical Basis
• The SA node consists of two main groups of cells:
• A central core of pacemaking cells (P cells) that produce
the sinus impulses
• An outer layer of transitional cells (T cells) that transmit
the sinus impulses out into the right atrium.
• Sinus node dysfunction can result from either:
• Failure of the P cells to produce an impulse
• This leads to sinus pauses and sinus arrest
• Failure of the T cells to transmit the impulse
• This leads to sino-atrial exit block

16. • Common P Wave Abnormalities
• P pulmonale (peaked P waves), seen with right atrial
enlargement
• P mitrale (bifid P waves), seen with left atrial
enlargement
• P wave inversion, seen with ectopic atrial and junctional
rhythms
• Variable P wave morphology, seen in multifocal atrial
rhythms

17. Right Atrial Enlargement
• In right atrial enlargement, right atrial depolarisation lasts
longer than normal and its waveform extends to the end
of left atrial depolarisation
• Although the amplitude of the right atrial depolarisation
current remains unchanged, its peak now falls on top of
that of the left atrial depolarisation wave
• The combination of these two waveforms produces a P
waves that is taller than normal (> 2.5 mm), although the
width remains unchanged (< 120 ms)
• Right atrial enlargement produces a peaked P wave (P
pulmonale) with amplitude:
• > 2.5 mm in the inferior leads (II, III and AVF)
• > 1.5 mm in V1 and V2

18. • Causes of right atrial enlargement
• Primary pulmonary hypertension
• Secondary pulmonary hypertension
chronic bronchitis
emphysema
massive pulmonary embolism
• Pulmonary stenosis
• Tricuspid stenosis

19. •Right atrial enlargement: P pulmonale
•P wave amplitude > 2.5mm in leads II, III and aVF

20. •Right atrial enlargement: P wave amplitude > 1.5 mm in V1 and V2

21. • P Pulmonale
• The presence of tall, peaked P waves in lead II is a sign
of right atrial enlargement, usually due to pulmonary
hypertension (e.g. cor pulmonale from chronic
respiratory disease)

22. • Left Atrial Enlargement
• In left atrial enlargement, left atrial depolarisation lasts longer than
normal but its amplitude remains unchanged
• Therefore, the height of the resultant P wave remains within normal
limits but its duration is longer than 120 ms
• A notch (broken line) near its peak may or may not be present (“P
mitrale”)
• ECG Criteria for Left Atrial Enlargement
• LAE produces a broad, bifid P wave in lead II (P mitrale) and enlarges
the terminal negative portion of the P wave in V1
• In lead II
• Bifid P wave with > 40 ms between the two peaks
• Total P wave duration > 110 ms
• In V1
• Biphasic P wave with terminal negative portion > 40 ms duration
• Biphasic P wave with terminal negative portion > 1mm deep

23. • P Mitrale
• The presence of broad, notched (bifid) P waves
in lead II is a sign of left atrial enlargement,
classically due to mitral stenosis

24. P waves with terminal portion > 1mm deep in V1

25. • Biatrial Enlargement
• Biatrial enlargement is diagnosed when criteria for both right and left
atrial enlargement are present on the same ECG
• The spectrum of P-wave changes in leads II and V1 with right, left
and bi-atrial enlargement:

26. • Inverted P Waves
• P-wave inversion indicates a non-sinus origin of the P waves
• Causes
• Dextrocardia
• Abnormal atrial depolarization
• Atrial ectopics
• AV junctional rhythms
• Ventricular tachycardia (retrogradely conducted)
• Ventricular ectopics (retrogradely conducted)

27. • Variable P-Wave Morphology
• The presence of multiple P wave morphologies indicates
multiple ectopic pacemakers within the atria and/or AV
junction
• If ≥ 3 different P wave morphologies are seen,
then multifocal atrial rhythm is diagnosed:

28. • If ≥ 3 different P wave morphologies are seen and the
rate is ≥ 100, then multifocal atrial
tachycardia (MAT) is diagnosed: