ECG Basics
 

The Normal ECG Trace

 
 
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On this page:The ECG TraceECG Leads

Overview

    • Square Sizes

      The standard ECG is recorded at a speed of 25mm/sec and gain of 10mm/mV.
    • 40ms = 1mm = 1 small square
    • 200ms = 5mm = 1 large square
    • 0.1mV = 1mm = 1 small square

The ECG Trace

  • A normal ECG trace includes a P wave, a QRS complex and a T wave.
    • The ECG Trace

    • Look For

    • PQRST Complex

    • P wave - indicative of atrial depolarisation
    • QRS complex - indicative of ventricular depolarisation
    • T wave - indicative of ventricular repolarisation

    • Intervals

    • PR interval - the time between atrial depolarisation and ventricular depolarisation, suggestive of AV conduction time
    • QT interval - the time between ventricular depolarisation and repolarisation

ECG Leads

  • A standard 12-lead ECG includes bipolar limb leads, unipolar limb leads and chest leads.

    • Bipolar Limb Leads

    • Electrical potential difference is measured between two limb electrodes.
  • ElectrodesDirectionComplex
    IRA → LA0Lateral
    IIRA → LL+60Inferior
    IIILA → LL+120Inferior

    • Unipolar (Augmented) Limb Leads

    • Electrical potential difference is measured between one limb electrode and a combination of the other limb electrodes.
  • ElectrodesDirectionComplex
    aVLLA-30Lateral
    aVRRA-150Right atrial
    aVFLL+90Inferior

    • Unipolar Chest Leads

    • Electrical potential difference is measured between the chest electrode and the average of the limb electrodes.
  • Complex
    V1Right atrial
    V2Septal
    V3Anterior
    V4Anterior
    V5Lateral
    V6Lateral
 
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 Balci B. Tombstoning ST-elevation myocardial infarction. Current cardiology reviews. 2009 Nov 1;5(4):273-8. Baranchuk A, Enriquez A, Garcia-Niebla J, Bayes-Genis A, Villuendas R, de Luna AB. Differential diagnosis of rSr’pattern in leads V1-V2. Comprehensive review and proposed algorithm. Ann Noninvasive Electrocardiol. 2015 Jan 1;20(1):7-17.
Benjamin EJ, Levy D, Vaziri SM, D'Agostino RB, Belanger AJ, Wolf PA. Independent risk factors for atrial fibrillation in a population-based cohort: the Framingham Heart Study. Jama. 1994 Mar 16;271(11):840-4.
Brady WJ, Skiles J. Wide QRS complex tachycardia: ECG differential diagnosis. The American journal of emergency medicine. 1999 Jul 31;17(4):376-81.
 Chung EK. Appraisal of multifocal atrial tachycardia. British heart journal. 1971 Jul;33(4):500. Coppola G, Carita P, Corrado E, Borrelli A, Rotolo A, Guglielmo M, Nugara C, Ajello L, Santomauro M, Novo S. ST segment elevations: Always a marker of acute myocardial infarction?. indian heart journal. 2013 Aug 31;65(4):412-23. Edhouse J, Thakur RK, Khalil JM. ABC Of Clinical Electrocardiography: Conditions Affecting The Left Side Of The Heart.BMJ: British Medical Journal. 2002; 324: 1264-1267. Fuchs RM, Achuff SC, Grunwald L, Yin FC, Griffith LS. Electrocardiographic localization of coronary artery narrowings: studies during myocardial ischemia and infarction in patients with one-vessel disease. Circulation. 1982;66:1168-1176. H. Abdollah, J.A. Milliken. Recognition of electrocardiographic left arm/left leg lead reversal. Am J Cardiol, 80 (1997), p. 1247. Hanna EB, Glancy DL. ST-segment depression and T-wave inversion: classification, differential diagnosis, and caveats. Cleve Clin J Med. 2011;78:404-414. Harrigan RA, Jones K. ABC of clinical electrocardiography. Conditions affecting the right side of the heart. BMJ. 2002; 324(7347): 1201-4. Hayden GE, Brady WJ, Perron AD, Somers MP, Mattu A. Electrocardiographic T-wave inversion: differential diagnosis in the chest pain patient. The American journal of emergency medicine. 2002 May 31;20(3):252-62. Herring N, Paterson DJ. ECG diagnosis of acute ischaemia and infarction: past, present and future. QJM : monthly journal of the Association of Physicians. 2006; 99: 219-230. Ishikawa K, Pipberger HV. Critical evaluation of the twin peaked P wave (“Pseudo-P mitrale”) in orthogonal electrocardiograms. Journal of Electrocardiology. 1980;13:181-184.
Kandolin R, Lehtonen J, Kupari M. Cardiac sarcoidosis and giant cell myocarditis as causes of atrioventricular block in young and middle-aged adults. Circulation: Arrhythmia and Electrophysiology. 2011 Jun 1;4(3):303-9.
 Kastor JA. Multifocal atrial tachycardia. New England Journal of Medicine. 1990 Jun 14;322(24):1713-7. Katritsis DG, Camm AJ. Atrioventricular nodal reentrant tachycardia. Circulation. 2010 Aug 24;122(8):831-40. Khan, IA Clinical and therapeutic aspects of congenital and acquired long QT syndrome.Am J Med2002;112,58-66. Lewin RF, Sclarovsky S, Strasberg B, Arditti A, Erdberg A, Agmon J. Right axis deviation in acute myocardial infarction. Clinical significance, hospital evolution, and long-term follow-up. Chest. 1984 Apr;85(4):489-93.
Lynch R. ECG lead misplacement: A brief review of limb lead misplacement. African Journal of Emergency Medicine. 2014 Sep 30;4(3):130-9.
 McCord J, Borzak S. Multifocal atrial tachycardia. CHEST Journal. 1998 Jan 1;113(1):203-9. Mieghem CV, Sabbe M, Knockaert D. The Clinical Value of the ECG in Noncardiac Conditions. Chest. 2004; 125: 1561-1576. Nora Goldschlager, and Galen Wagner. Electrocardiogram interpretation. Journal of Electrocardiology, 2007-07-01, Volume 40, Issue 4, Pages 326-326.
Okada M, Yotsukura M, Shimada T, Ishikawa K. Clinical implications of isolated T wave inversion in adults: Electrocardiographic differentiation of the underlying cause of this phenomenon. Journal of the American College of Cardiology. 1994 Sep 1;24(3):739-45.
 Porela P, Kyto V, Nikus K, Eskola M, Airaksinen KE. PR depression is useful in the differential diagnosis of myopericarditis and ST elevation myocardial infarction. Annals of Noninvasive Electrocardiology. 2012 Apr 1;17(2):141-5. Rashford S. Acute Pleuritic Chest Pain. Australian Family Physician. 2001; 30(9). Rautaharju, P.M., Surawicz, B. and Gettes, L.S., 2009. 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. Journal of the American College of Cardiology, 53(11), pp.982-991. Riddle W. Misleading. The clinical implications of misplaced ECG leads. JEMS: a journal of emergency medical services. 2008 Sep;33(9):56-62. Salman S, Bajwa A, Gajic O, Afessa B. Paroxysmal atrial fibrillation in critically ill patients with sepsis. Journal of intensive care medicine. 2008 Apr 28. Seidenberg PH, Haynes J. Pericarditis: diagnosis, management, and return to play. Current sports medicine reports. 2006 Mar 1;5(2):74-9. Somers MP, Brady WJ, Perron AD, Mattu A. The prominant T wave: electrocardiographic differential diagnosis. The American journal of emergency medicine. 2002 May 31;20(3):243-51. Surawicz B, Childers R, Deal BJ, Gettes LS. 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. Journal of the American College of Cardiology. 2009 Mar 17;53(11):976-81. Vincent, GM Long QT syndrome.Cardiol Clin2000;18,309-325. W.M. Jackman, K.J. Friday, J.L. Anderson, E.M. Aliot, M. Clark, R. Lazzara. The long QT syndrome: a critical review, new clinical observations and a unifying hypothesis. Prog Cardiovasc Dis, 31 (1988), p. 115. Wellens HJ. Ventricular tachycardia: diagnosis of broad QRS complex tachycardia. Heart. 2001 Nov 1;86(5):579-85. Zema MJ, Kligfield P. ECG poor R-wave progression: review and synthesis. Archives of internal medicine. 1982 Jun 1;142(6):1145-8.
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