Einthoven 's triangle - Wikipedia Einthoven 's triangle Graphical representation of Einthoven 's triangle Einthoven 's triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis. The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed. It is named after Willem Einthoven, who theorized its existence. Einthoven used these measuring points, by immersing the hands and foot in pails of salt water, as the contacts for his string galvanometer, the first practical ECG machine. Lead placements Lead I -- This axis goes from shoulder to shoulder, with the negative electrode placed on the right shoulder and the positive electrode placed on the left shoulder. This results in a 0 degree angle of orientation. I = L A − R A ( displaystyle I = LA - RA ) Lead II -- This axis goes from the right arm to the left leg, with the negative electrode on the shoulder and the positive one on the leg. This results in a + 60 degree angle of orientation. I I = L L − R A ( displaystyle II = LL - RA ) Lead III -- This axis goes from the left shoulder ( negative electrode ) to the right or left leg ( positive electrode ). This results in a + 120 degree angle of orientation. I I I = L L − L A ( displaystyle III = LL - LA ) Electrodes may be placed distally or proximally on the limb without affecting the recording. The leg electrode acts as a grounding lead, and either the right or left leg can be used as a grounding lead without an effect on the ECG results. Each lead measures the electric field created by the heart during the depolarization and repolarization of myocytes. The electric field can be represented as a vector that changes continuously and can be measured by recording the voltage difference between electrodes. Using Einthoven 's triangle to identify lead misplacements Though Einthoven 's triangle is no longer used in contemporary ECGs, Einthoven 's triangle can be helpful in the identification in incorrect placement of leads. ( Incorrect placement of leads can lead to error in the recording, which can ultimately lead to misdiagnosis. ) If the arm electrodes are reversed, lead I changes polarity, causing lead II and lead III to switch. If the right arm electrode is reversed with the leg 's electrode, lead II changes polarity, causing lead I to become lead III, and vice versa. Reversal of the left arm and leg causes a change in polarity of lead III and switching of leads I and II. References Jump up ^ Lippincott Williams & Wilkins ( 1 August 2009 ). ECG Facts Made Incredibly Quick !. Lippincott Williams & Wilkins. p. 5. ISBN 978 - 1 - 60547 - 476 - 2. Jump up ^ Understanding Electrocardiography. Elsevier Health Sciences. 2003. p. 4. ISBN 0 - 323 - 01905 - 6. Jump up ^ Silverman, M.E. ( 1992 - 10 - 01 ). `` Willem Einthoven -- the father of electrocardiography ''. Clinical Cardiology. 15 ( 10 ) : 785 -- 787. ISSN 0160 - 9289. PMID 1395193. ^ Jump up to : The Only EKG Book You 'll Ever Need. Lippincott Williams & Wilkins. 2003. p. 40. ISBN 0 - 7817 - 4176 - 9. Jump up ^ Klabunde, Richard E ( 2005 - 01 - 01 ). Cardiovascular Physiology Concepts. Lippincott Williams & Wilkins. pp. 34 -- 35. ISBN 9780781750301. ^ Jump up to : Abi - Saleh, Bernard ; Omar, Bassam ( 2010 - 01 - 01 ). `` Einthoven 's triangle transparency : a practical method to explain limb lead configuration following single lead misplacements ''. Reviews in Cardiovascular Medicine. 11 ( 1 ) : 33 -- 38. ISSN 1530 - 6550. PMID 20495514. Jump up ^ Richardson, Daniel R. ; Randall, David Clark ; Speck, Dexter F. ( 1998 - 03 - 13 ). Cardiopulmonary System Structure and Function. Hayes Barton Press. pp. 99 -- 101. ISBN 9781889325309. This cardiovascular system article is a stub. You can help Wikipedia by expanding it. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Einthoven%27s_triangle&oldid=797650972 '' Categories : Cardiac electrophysiology Dutch inventions Cardiovascular system stubs Talk About Wikipedia Add links This page was last edited on 28 August 2017, at 12 : 38. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where is the positive electrode placed in lead iii
Answer: right or left leg