P WAVE AND ITS ABNORMALITIES IN ECG

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: