P wave abnormality in ECG l P wave interpretation

 

               Abnormalities of P wave

Normal P waves in ECG

 P wave is upright in most leads except AVR (most -ve) and V1 (biphasic).

 It is < 2.5mm (0.25mv) in height and < 2.5mm (0.10sec) in width

Absent P waves

ü      There are five conditions in which the P wave will be absent:

1.     Atrial fibrillation
numerous, small p waves with ragged/irregular baseline

2.     Atrial flutter
P waves are replaced by F waves giving corrugated/ saw-tooth appearance of baseline

3.     Junctional rhythm
P wave may precede, follow or buried in QRS due to simultaneous anterograde ventricular stimulation

4.     Ventricular tachycardia
 Difficult to identify P waves as they are buried under wide QRS

5.     Hyperkalaemia
P waves are either absent or with reduced amplitude in association with tall T waves and wide QRS

 

Inverted P waves

Normally atrial depolarisation occurs from above downward and thus P wave can be seen upright in II, III and Avf. But in certain conditions the activation of atria occurs retrogradely from below upward which leads to negative or inverted P waves in these inferior leads.

1.     Junctional rhythm
here P waves may just precede or follow QRS.

2.     By pass tracts
inverted  P waves are seen if the atria are activated retrogradely through an accessary pathway by passing the AV nodal pathway like in WPW syndrome.

Changing P wave morphology

If impulses arise from different foci other than SA node then it causes abnormal P wave morphology called as P’ (P prime). Can be seen in the following conditions:

Wandering pacemaker rhythm
Here the pacemaker wanders from one focus to other with a varying origin from SA-->atrium-->AV. Causing P waves of different morphology.

 Multifocal atrial tachycardia
due to multiple atrial foci atrial tachycardia occurs causing an abnormal P wave.

ü       Three types of P waves can be seen in above two rhythm:

1.     Ectopic P’ (atrial in origin and differ from sinus origin)

2.     Retrograde P’ (inverted and junctional in origin)

3.     Fusion beats (P waves having morphology in between sinus P & ectopic P’)

ü        WPM (wander pacemaker rhythm)  and MAT(multifocal atrial tachycardia) only differ in heart rate means that WPM has HR less than 100bpm while MAT has > 100bpm

 

Tall P wave

the normal P wave is < 2.5mm in its height and it is the sum of the right and left atrial depolarisation if we are having right atrial enlargement so the P wave get enlarged or Tall due to being superimposed on left atrium.

therefore, the Tall P wave is representative of the right atrial enlargement.

A tall P wave is also called as p pulmonale due to pulmonary HTN or p congenitale since it can be observed in congenital heart diseases.

 

 

 

Broad P wave

If the left atrium is enlarged, the deflection of the left atrium is further delayed after the right atrial deflection, resulting in a broad P wave exceeding 2.5 mm in width. Also, a notch appears on the P wave, between its right and left atrial components.

since it if often associated with mitral valve diseases so it is also called as p mitral or notched p wave and the terminal portion of the P wave will be enlarged.

A broad and notched P wave is representative of the left atrial enlargement.

Various causes of the left and right atrial enlargement: