What is the P wave on electrocardiography (ECG)?

Answer

The P wave represents atrial depolarization. The normal P wave morphology is upright in leads I, II, and aVF, but it is inverted in lead aVR. The P wave is typically biphasic in lead V1 (positive-negative), but when the negative terminal component of the P wave exceeds 0.04 seconds in duration (equivalent to one small box), it is abnormal.

Left atrial enlargement should be suspected when the P wave duration is increased; it is associated with being more than one small box deep (>1 mm²) in lead V1 and a bifid P wave in lead II with a duration that is longer than 110 seconds.^[19] Right atrial enlargement is associated with a peaked P wave taller than 2.5 mm in the inferior leads and more than 1.5 mm tall in leads V1 and V2.^[20]

Did this answer your question?

Yes No

Additional feedback? (Optional)

Thank you for your feedback!

Bayes de Luna A. Basic Electrocardiography: Normal and Abnormal ECG Patterns. Malden, MA: Wiley-Blackwell; 2007.
Goldberger AL. Clinical Electrocardiography: A Simplified Approach. 7th ed. Philadelphia, PA: Mosby-Elsevier; 2006.
Baltazar RF. Basic and Bedside Electrocardiography. 1st ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009.
[Guideline] Wagner GS, Macfarlane P, Wellens H, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part VI: acute ischemia/infarction: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2009 Mar 17. 53 (11):1003-11. [Medline].
Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Philadelphia, PA: Elsevier Saunders; 2012. 126-65.
[Guideline] Mason JW, Hancock EW, Gettes LS, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. Recommendations for the standardization and interpretation of the electrocardiogram: part II: electrocardiography diagnostic statement list a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2007 Mar 13. 49 (10):1128-35. [Medline].
Galvani A. De Viribus Electricitatis in Motu Musculari. Commentarius [Latin]. Bologna, Italy: Ex Typographia Instituti Scientiarium; 1791. 7363-418.
Matteucci C. [Sur un phenomene physiologique produit par les muscles en contraction] [French]. Ann Chim Phys. 1842. 6:339-41.
Kolliker A, Muller H. [Nachweis der negativen schwankung des muskelstromes am naturlich sich contrahieden muskel verhandl] [German]. J Phys Med Gesellsch. 1856. 6:494.
Lippmann G. [Relations entre les phenomenes electriques et capillaries] [French]. Ann Chim Phys. 1875. 5:494.
Waller AD. A demonstration on man of electromotive changes accompanying the heart's beat. J Physiol. 1887 Oct. 8 (5):229-34. [Medline].
Einthoven W. [Un nouveau galvanometre] [French]. Arch Neerl Sci Exactes Nat. 1901. 6:625-33.
Wilson FN, Johnston FD, Macleod AG, Barker PS. Electrocardiograms that represent the potential variations of a single electrode. Am Heart J. 1934. 9(4):447-58.
Goldberger E. A simple, indifferent, electrocardiographic electrode of zero potential and a technique of obtaining augmented, unipolar, extremity leads. Am Heart J. 1942 Apr. 23(4):483-92.
[Guideline] Schlant RC, Adolph RJ, DiMarco JP, et al. Guidelines for electrocardiography. A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Committee on Electrocardiography). Circulation. 1992 Mar. 85 (3):1221-8. [Medline].
[Guideline] Kligfield P, Gettes LS, Bailey JJ, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. Recommendations for the standardization and interpretation of the electrocardiogram. Part I: The electrocardiogram and its technology. A scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Heart Rhythm. 2007 Mar. 4 (3):394-412. [Medline].
Rajaganeshan R, Ludlam CL, Francis DP, Parasramka SV, Sutton R. Accuracy in ECG lead placement among technicians, nurses, general physicians and cardiologists. Int J Clin Pract. 2008 Jan. 62 (1):65-70. [Medline].
Schijvenaars BJ, Kors JA, van Herpen G, Kornreich F, van Bemmel JH. Effect of electrode positioning on ECG interpretation by computer. J Electrocardiol. 1997 Jul. 30 (3):247-56. [Medline].
Edhouse J, Thakur RK, Khalil JM. ABC of clinical electrocardiography. Conditions affecting the left side of the heart. BMJ. 2002 May 25. 324 (7348):1264-7. [Medline].
Harrigan RA, Jones K. ABC of clinical electrocardiography. Conditions affecting the right side of the heart. BMJ. 2002 May 18. 324 (7347):1201-4. [Medline].
[Guideline] O'Gara PT, Kushner FG, Ascheim DD, et al, for the American College of Emergency Physicians, Society for Cardiovascular Angiography and Interventions. 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol. 2013 Jan 29. 61 (4):e78-140. [Medline].
Thygesen K, Alpert JS, White HD, for the Joint ESC/ACCF/AHA/WHF Task Force for the Redefinition of Myocardial Infarction. Universal definition of myocardial infarction. Eur Heart J. 2007 Oct. 28 (20):2525-38. [Medline].
[Guideline] Rautaharju PM, Surawicz B, Gettes LS, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part IV: the ST segment, T and U waves, and the QT interval: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2009 Mar 17. 53 (11):982-91. [Medline].
[Guideline] Priori SG, Blomstrom-Lundqvist C, Mazzanti A, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: The Task Force for the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death of the European Society of Cardiology (ESC). Endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC). Eur Heart J. 2015 Nov 1. 36 (41):2793-867. [Medline].
Roden DM. Clinical practice. Long-QT syndrome. N Engl J Med. 2008 Jan 10. 358 (2):169-76. [Medline].
[Guideline] Hancock EW, Deal BJ, Mirvis DM, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part V: electrocardiogram changes associated with cardiac chamber hypertrophy: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology. Circulation. 2009 Mar 17. 119 (10):e251-61. [Medline].
Gami AS, Holly TA, Rosenthal JE. Electrocardiographic poor R-wave progression: analysis of multiple criteria reveals little usefulness. Am Heart J. 2004 Jul. 148 (1):80-5. [Medline].
Einthoven W. [Le telecardiogramme] [French]. Arch Int de Physiol. 1906. 4:132-64.
Bouzas-Mosquera A, Peteiro J, Broullon FJ, et al. Incremental value of exercise echocardiography over exercise electrocardiography in a chest pain unit. Eur J Intern Med. 2015 Nov. 26 (9):720-5. [Medline].
Triggiani AI, Valenzano A, Ciliberti MA, et al. Heart rate variability is reduced in underweight and overweight healthy adult women. Clin Physiol Funct Imaging. 2017 Mar. 37 (2):162-7. [Medline].
[Guideline] Hauk L. ECG, echocardiography, or MPI for cardiac screening: guidance from the ACP. Am Fam Physician. 2015 Sep 15. 92 (6):531. [Medline].
[Guideline] Amsterdam EA, Wenger NK, Brindis RG, et al, for the ACC/AHA Task Force Members. 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2014 Dec 23. 130 (25):e344-426. [Medline].
[Guideline] Surawicz B, Childers R, Deal BJ, et al, for the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology, et al. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2009 Mar 17. 53 (11):976-81. [Medline].
Funk M, Fennie KP, Stephens KE, et al, for the PULSE Site Investigators. Association of implementation of practice standards for electrocardiographic monitoring with Nurses' knowledge, quality of care, and patient outcomes: findings from the Practical Use of the Latest Standards of Electrocardiography (PULSE) Trial. Circ Cardiovasc Qual Outcomes. 2017 Feb. 10 (2):53. [Medline].
Breen C, Bond R, Finlay D. A clinical decision support tool to assist with the interpretation of the 12-lead electrocardiogram. Health Informatics J. 2017 Jan 1. 1460458216683534. [Medline].
Hartman ND, Wheaton NB, Williamson K, Quattromani EN, Branzetti JB, Aldeen AZ. A novel tool for assessment of emergency medicine resident skill in determining diagnosis and management for emergent electrocardiograms: a multicenter study. J Emerg Med. 2016 Dec. 51 (6):697-704. [Medline].
Yeo TJ, Sharma S. Using the 12-lead electrocardiogram in the care of athletic patients. Cardiol Clin. 2016 Nov. 34 (4):543-55. [Medline].
Huitema AA, Zhu T, Alemayehu M, Lavi S. Diagnostic accuracy of ST-segment elevation myocardial infarction by various healthcare providers. Int J Cardiol. 2014 Dec 20. 177 (3):825-9. [Medline].
Sibbald M, Davies EG, Dorian P, Yu EH. Electrocardiographic interpretation skills of cardiology residents: are they competent?. Can J Cardiol. 2014 Dec. 30 (12):1721-4. [Medline].
Drezner JA. Standardised criteria for ECG interpretation in athletes: a practical tool. Br J Sports Med. 2012 Nov. 46 suppl 1:i6-8. [Medline].
Gregg RE, Deluca DC, Chien CH, Helfenbein ED, Ariet M. Automated serial ECG comparison improves computerized interpretation of 12-lead ECG. J Electrocardiol. 2012 Nov-Dec. 45 (6):561-5. [Medline].
Farooqi KM, Ceresnak SR, Freeman K, Pass RH. Electrocardiograms transmitted via facsimile may not allow accurate interval interpretation. Pacing Clin Electrophysiol. 2011 Oct. 34 (10):1283-7. [Medline].
Uberoi A, Stein R, Perez MV, et al. Interpretation of the electrocardiogram of young athletes. Circulation. 2011 Aug 9. 124 (6):746-57. [Medline].
Magnani JW, Johnson VM, Sullivan LM, et al. P-wave indices: derivation of reference values from the Framingham Heart Study. Ann Noninvasive Electrocardiol. 2010 Oct. 15 (4):344-52. [Medline].
Clark EN, Sejersten M, Clemmensen P, Macfarlane PW. Automated electrocardiogram interpretation programs versus cardiologists' triage decision making based on teletransmitted data in patients with suspected acute coronary syndrome. Am J Cardiol. 2010 Dec 15. 106 (12):1696-702. [Medline].

Media Gallery

I, II and III represent the original three leads used by Einthoven. These describe the electrical vector between the right and left arms, right arm and left leg, and left arm and left leg, respectively. R, L, and F represent the augmented limb leads aVR, aVL, and aVF. They are calculated as follows: aVR = (I+II)/2 , aVL = (I-III)/2, aVF = (II+III)/2.
The hexagonal reference system is the standard method of determining the axis of electrical activation of the heart. As an example, depolarization that is parallel with lead II would yield a value of 60º, whereas a depolarization vector in the opposite direction would be -120º. Image courtesy of Wikipedia.
Proper placement of the precordial leads for standard 12-lead electrocardiography.
The hexagonal reference system is the standard method of determining the axis of electrical activation of the heart. As an example, depolarization parallel with lead II would yield a value of 60º, whereas a depolarization vector in the opposite direction would be -120º.
Electrocardiogram waves, intervals, and segments.
On standard calibration, each large box has sides of 0.5 cm. On the horizontal axis, each large box represents 0.2 seconds, and each smaller box represents 0.04 seconds. On the vertical axis, each small box is 1 mm in height; 10 mm = 1 mV.
Heart rates associated with each of the large boxes in the following order are 300, 150, 100, 75, 60, 50, 43, 37, 33 beats per minute (bpm).
Heart rate boxes.
ST depression.
ST elevation.
ST morphology.
Electrocardiographic axis. Normal axis is between -30º and 90º; left axis deviation (LAD) is between -30º and - 90º; right axis deviation (RAD) is between 90º and 180º; extreme axis deviation (EAD) (left or right) is between -90º and -180º.
R-wave progression.
A 12-lead electrocardiogram is divided into the following four main contiguous lead groups: inferior, lateral, septal, and anterior.
Typical normal 12-Lead electrocardiogram. Courtesy of Dr Bob McGraw, Queen’s University Technical Skills Program and Department of Emergency Medicine (https://meds.queensu.ca/central/assets/modules/ECG/index.html).

of 15

What is the P wave on electrocardiography (ECG)?

Answer

Related Questions:

About

Membership

Apps

WebMD Network

Editions

What to Read Next on Medscape

What is the P wave on electrocardiography (ECG)?

Answer

Related Questions:

References

Tables

Contributor Information and Disclosures

Find Us On

About

Membership

Apps

WebMD Network

Editions

What to Read Next on Medscape

Related Conditions and Diseases

Medscape Consult

News & Perspective

Tools

Slideshow

Most Popular Articles

Recommended