The P wave on the

ECG Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...

represents atrial depolarization, which results in atrial contraction, or

atrial systole The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following ...

Physiology

The P wave is a summation wave generated by the depolarization front as it transits the atria. Normally the right atrium depolarizes slightly earlier than left atrium since the depolarization wave originates in the

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approxima ...

, in the high right atrium and then travels to and through the left atrium. The depolarization front is carried through the atria along semi-specialized conduction pathways including Bachmann's bundle resulting in uniform shaped waves. Depolarization originating elsewhere in the atria (atrial ectopics) result in P waves with a different morphology from normal.

Pathology

Peaked P waves (> 0.25 mV) suggest right atrial enlargement,

cor pulmonale Pulmonary heart disease, also known as cor pulmonale, is the enlargement and failure of the right ventricle of the heart as a response to increased vascular resistance (such as from pulmonic stenosis) or high blood pressure in the lungs. Chroni ...

, (''P pulmonale'' rhythm), but have a low predictive value (~20%). A P wave with increased amplitude can indicate

hypokalemia Hypokalemia is a low level of potassium (K+) in the blood serum. Mild low potassium does not typically cause symptoms. Symptoms may include feeling tired, leg cramps, weakness, and constipation. Low potassium also increases the risk of an abno ...

. It can also indicate right atrial enlargement. A P wave with decreased amplitude can indicate

hyperkalemia Hyperkalemia is an elevated level of potassium (K+) in the blood. Normal potassium levels are between 3.5 and 5.0mmol/L (3.5 and 5.0mEq/L) with levels above 5.5mmol/L defined as hyperkalemia. Typically hyperkalemia does not cause symptoms. Occasi ...

De-P wave morphology (CardioNetworks ECGpedia)

Bifid P waves (known as ''P mitrale'') indicate left-atrial abnormality - e.g. dilatation or hypertrophy. If at least three different shaped P waves can be seen in a given ECG lead tracing, this implies that even if one of them arises from the SA node, at least two others are arising elsewhere. This is taken as evidence of multiple (i.e. at least two)

ectopic foci An ectopic pacemaker, also known as ectopic focus or ectopic foci, is an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the heart. It is thus a cardiac pacemaker that is ectopic, producin ...

, and is called multifocal (or more correctly, multiform) atrial rhythm if the rate is ≤100) or

multifocal atrial tachycardia Multifocal (or multiform) atrial tachycardia (MAT) is an abnormal heart rhythm, specifically a type of supraventricular tachycardia, that is particularly common in older people and is associated with exacerbations of chronic obstructive pulmona ...

if the rate is over 100. This appears particularly commonly in exacerbations of

chronic obstructive lung disease Chronic obstructive pulmonary disease (COPD) is a type of progressive Obstructive lung disease, lung disease characterized by long-term respiratory symptoms and airflow limitation. The main symptoms include shortness of breath and a cough, which ...

. If the baseline has a totally irregular form, this suggests fibrillatory waves of atrial fibrillation or possibly artefact; a saw tooth shaped baseline suggests the flutter waves of

atrial flutter Atrial flutter (AFL) is a common abnormal heart rhythm that starts in the atrial chambers of the heart. When it first occurs, it is usually associated with a fast heart rate and is classified as a type of supraventricular tachycardia. Atrial f ...

. With either of these rhythms, if the ventricular rate is fast, the fibrillatory or flutter waves can easily be misinterpreted as P waves. Absence of the P wave with a flat baseline may indicate: * Fine atrial fibrillation *

Sinoatrial arrest Sinoatrial arrest is a medical condition wherein the sinoatrial node of the heart transiently ceases to generate the electrical impulses that normally stimulate the myocardial tissues to contract and thus the heart to beat. It is defined as lasti ...

(with a secondary

escape rhythm In cardiology, a ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of the Ventricle (heart), ventricles of the heart; normally the heart rhythm is begun in the Atrium (heart), atria of the heart ...

) If P waves are not clearly delineated in the surface ECG, a

Lewis lead A Lewis Lead (also called the S5 lead) is a modified ECG lead used to detect atrial flutter waves when atrial flutter is suspected clinically, based on signs and symptoms, but is not definitely demonstrated on the standard 12 lead ECG. In order to ...

may be used to better visualize P waves.

Atrial repolarization

This occurs a mean of 320 ms after the end of the P wave, with a duration of 2-3 times that of the P wave and a polarity always opposite to that of the P wave. It is represented on the surface ECG by a so-called Ta wave. The clinical relevance of this is that, although a normal phenomenon, the nadir of the Ta wave can occur just after the QRS complex and cause ST depression similar to (and easily mistaken with) that occurring with disease states such as cardiac ischaemia.

* Electrocardiography *

PR interval In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization ...

QRS complex The QRS complex is the combination of three of the graphical deflections seen on a typical electrocardiogram (ECG or EKG). It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the ri ...

* QT interval *

ST segment In electrocardiography, the ST segment connects the QRS complex and the T wave and has a duration of 0.005 to 0.150 sec (5 to 150 ms). It starts at the J point (junction between the QRS complex and ST segment) and ends at the beginning of the ...

T wave In electrocardiography, the T wave represents the repolarization of the ventricles. The interval from the beginning of the QRS complex to the apex of the T wave is referred to as the ''absolute refractory period''. The last half of the T wave ...

U wave The 'U' wave is a wave on an electrocardiogram (ECG). It comes after the T wave of ventricular repolarization and may not always be observed as a result of its small size. 'U' waves are thought to represent repolarization of the Purkinje fibers. ...

References

{{Cardiovascular physiology Cardiac electrophysiology

Physiology

Pathology

Atrial repolarization

Related pages

References