P Wave determines the small positive deflection that can be seen in the isoelectric baseline occurring before the complex of QRS.

Sometimes abnormalities can be found in P Wave and PR segment morphology where clinical pathology timing can be significantly indicative. With an accurate understanding of the morphology of abnormal and normal P waves, one can also understand the crucial part of the interception of ECG or electrocardiogram. In a healthy human, this P wave originates at SA which means a sinoatrial node and then disperses into both the right and left atria. The left atrium depolarization is mainly responsible for the P wave early part and left atrium depolarization is generally responsible for the terminal and middle parts of this P wave.

Morphology of normal sinus P Wave

“P wave” is determined as "positive deflection" on ECGs or electrocardiograms and helps in the representation of the "atrial depolarization".

The duration of the P Wave that is determined to be of normal state is more than 0.12 s which is greater than 120 ms or the three small squares (litfl, 2022).

The normal sinus P wave must be upwards right that is leading I and II and also inverted in a VR.

Figure 1: Normal Sinus P Wave

The morphology of normal sinus P Wave can be determined by its smooth colour, Biphasic in V1, and it’s Monophasic in lead II.

The axis of the normal sinus P wave lies between 0° and +75°. The duration of the normal “sinus P wave” is greater than 20 s that is [".

P Wave’s Atrial Depolarization

In “P wave”, “atrial depolarization” progresses to almost in sequence, from right to left where the atrium is in the right is activated first then the atrium in the left. In the formation of the P wave the right and left atrial waveforms summate contribute greatly. In most of the leads, the left and right atrial waveforms move in the same direction which forms a "monophasic P wave" (Maršánová et al. 2019).

AV blocks are also associated with hypertrophic obstructive cardiomyopathy and sarcoidosis and amyloidosis [infiltrative conditions]. The common source of “ischemic disease” of the human heart is generally responsible for nearly 40% of cases of AV blocks.

Clinical significance of PR segments and P Wave

The proper ECGs interpretation mainly needs the ability to recognize both PR segments and normal P Wave and also the common abnormalities that denote diseases. The morphology and timing of PR segments and P Wave leading to pathology denotes the time difference between ventricular and atrial depolarization.

Pathology can be indicated if abnormalities in the PR segment are found. PR interval that shows less than 120 ms indicates electrical impulses that are travelling between ventricles and atria quickly (Peimankar et al. 2019). Electrical depolarization of human atria is represented mainly by the P Wave and in a healthy individual.

Figure 2: Atrial Hypertrophy [P Wave]

It originates at the node of the sinoatrial and then disperses into the right and left atria of that individual.

It is very essential for all healthcare workers like doctors, nurses, and clinicians, to properly interpret the ECGs that will further help to recognize heart blocks and pathology effectively. This process will also help the caregivers treat the patients in such a way that they can recover soon and become less prone to the same diseases in future.

Differences between P and QRS wave

AV or Atroventicular conduction is evaluated by the assessment of the relationship between the QRS and P Waves complexes. Generally, P Wave precedes each complex QRS wave by a fixed interval of PR segments that ranges from 120 to 200 ms.

The blocks of AV mainly represent the disturbance or delay in the impulse transmission from the human atria to the ventricles. This condition occurs because of functional or anatomical impairment in the system of the heart’s conduction (Wijaya et al. 2019). On the ECGs, P Wave is leading to pathology denotes the time difference between ventricular and atrial depolarization.

The QRS complex is the major spike found in the standard ECGs. It is the most obvious part of an electrocardiogram that is visible clearly. The depolarization of ventricles is represented by this QRS complex which shows the beginning of ventricular and systole contraction.

Applications of P Wave

  • P Wave is incorporated in ECGs means the electrocardiogram represents the electrical depolarization of the human heart’s atria.
  • P Wave is often determined as pressure or primary waves which are the 2 major “elastic body waves” (sciencedirect, 2019). These are also known as seismic waves in the matter of “seismology” and these “P waves” moves fast than the “seismic waves”.
  • In healthcare sectors, P waves are used for the identification of ECG interpretation d pathology of human heart atria. In ECGs, this P Wave helps the healthcare workers like nurses, doctors, and clinicians to determine and monitor the symptoms of abnormal heart function in the patients admitted to the healthcare ward.

Figure 3: Normal sinus rhythm for the heart on ECG

The healthcare team and cardiologist can quickly identify common abnormalities in ECG patterns by the electrocardiogram rhythm (ncbi. nlm.nih, 2021).

If any abnormalities in this rhythm or electrical conduction are detected on ECG then it decreased mortality and morbidity of patients in the ward.


The very first P Wave deflection normally appears between 120 to 200 ms before the first upside QRS complex deflection. On an electrocardiogram or ECG, it is the first defection occurs from the baseline voltage. The length between the QRS compound and the P Wave is represented by interval of PR segments. The timing between the onset of ventricular and atrial depolarization is also represented by the interval of PR segments. The interval of PA mainly reflects the time conduction from the node of the sinus to the AV node. Prolonged “PA interval” denotes the abnormalities in human heart atrial conduction and can provide the cardiologists of the healthcare workers with clues that there is a biatrial disease. The range of PA interval that is considered to be the normal range is from 20 to 60 ms.


Q1. What is the P wave?

The P wave is incorporated in the electrocardiogram or ECG complex that indicates the atrial depolarization in the human heart. In a healthy human, this P wave originates at SA which means a sinoatrial node and then disperses into both the right and left atria.

Q2. What do you understand by T and P QRS wave representation?

In the electrocardiogram, “P Wave” denotes “atrial depolarization”. On the other side, the QRS complexmainly in charge of “ventricular depolarization” and T wave is in charge of “ventricular repolarization”.

Q3. What condition can be found in a human heart during the P wave?

The first P wave mainly determines the atrial depolarization in a human heart. When the waves between the ventricles and atria open about 70% of blood in the atria fall through with the "aid of gravity" and as the ventricles get to expand the suction of blood is caused.

Q4. What are past references that clinicians must take from the patients concerned with the AV blocks?

The patients concerned with the AV blocks must have records of a history of heart disease, which includes both acquired and congenital. The records should also include present cardiac procedures and baseline exercise capacity. The symptoms like chest pain, sudden cardiac arrest, and Dyspnea can raise concerns.

Q5. What is the popper medication for preventing the conduction delay or disturbance in the human heart?

Medications like disopyramide, procainamide, and quinidine, can block all sodium channels and heart delay conduction. These medications can also delay the system of infra-Hisian conduction in the human body.



Maršánová, L., Němcová, A., Smíšek, R., Vítek, M., & Smital, L. (2019). Advanced P wave detection in ECG signals during pathology: evaluation in different arrhythmia contexts. Scientific reports, 9(1), 1-11. Retrieved from: https://www.nature.com/articles/s41598-019-55323-3

Peimankar, A., & Puthusserypady, S. (2019, May). An ensemble of deep recurrent neural networks for p-wave detection in the electrocardiogram. In ICASSP 2019-2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) (pp. 1284-1288). IEEE.

Wijaya, C., Harahap, M., Turnip, M., & Turnip, A. (2019, July). Abnormalities State Detection from P-Wave, QRS Complex, and T-Wave in Noisy ECG. In Journal of Physics: Conference Series (Vol. 1230, No. 1, p. 012015). IOP Publishing. Retrieved from: https://iopscience.iop.org/article/10.1088/1742-6596/1230/1/012015/pdf


litfl (2022). About “P-Wave”. Retrieved from: https://litfl.com/p-wave-ecg-library/ [Retrieved on: June 7 2022]

ncbi.nlm.nih, (2021). About “P-Wave”. Retrieved from: https://www.ncbi.nlm.nih.gov [Retrieved on: June 7 2022]

sciencedirect, 2019. About “P Wave”. Retrieved from: https://www.sciencedirect.com/topics/medicine-and-dentistry/p-wave [Retrieved on: June 7 2022]

Updated on 13-Oct-2022 11:19:47