The electrocardiogram (abbreviated as ECG or EKG) represents an electrical tracing of the heart and is recorded non-invasively from the surface of the body. The word ECG derives from the German language. In German, it is elektro-kardiographie. In 1902, the Dutch physician Einthovan invented ECG, and his tremendous input in the clinical studies for about ten years led to full recognition of the clinical potential of the technique. Many arrhythmias and EKG changes associated with angina and atherosclerosis were identified by 1910. William Einthoven was named the "father of electrocardiography" and was awarded Nobel Prize in Medicine in 1924 for his hard work that laid the foundation of the most fundamental technique of investigating heart disorders. ECG was soon recognized as a robust screening and a clinical diagnostic tool, and today it is used globally in almost every healthcare setting.
ECG is a non-invasive diagnostic modality that has a substantial clinical impact on investigating the severity of cardiovascular diseases. ECG is increasingly being used for monitoring of patients on antiarrhythmics and other drugs, as an integral part of preoperative assessment of patients undergoing non-cardiac surgery, and for screening individuals in high-risk occupations and those who are participating in sports. Also, EKG serves as a research tool for surveillance and experimental trials of drugs with recognized cardiac effects. Cardiovascular disease, as the number one cause of death, puts a great emphasis on health-care providers to develop skills and knowledge in interpreting ECGs to provide the best care promptly. Many health-care providers find the advanced interpretation of ECG findings a complicated task. Errors in the analysis can lead to misdiagnosis resulting in delaying the appropriate treatment. This activity seeks to provide a general understanding of the ECG mechanisms, interpretation techniques, and commonly encountered ECG findings.
A basic understanding of cardiac anatomy and coronary distribution is essential to understand the electrocardiographic findings.
The heart is a vital organ of the body and occupies the space in the central chest between the lungs. Together with the blood vessels and blood, it constitutes the circulatory system of the body. The heart is a muscular organ comprised of four chambers that includes two atria (right and left) opening into right and left ventricles via tricuspid and mitral valves, respectively. A wall of muscle called septum separates all the four chambers. The heart receives deoxygenated blood from the whole body via superior and inferior vena cava, which first enters the right atrium. From here, it transits through the right ventricle and then passes into the lungs via right and left pulmonary arteries, where it is oxygenated. The oxygenated blood from the lungs pours into the left atrium through the right and left pulmonary veins, and from here, it is pumped by the left ventricle into the aorta to the rest of the body. The heart derives its blood supply from the coronary arteries that branch off from the aorta. The right and left coronary arteries lie on the surface of the heart. With considerable heterogeneity among the general population, different regions of the heart receive vascular supply by the various branches of the coronary arteries. This anatomic distribution is significant because these cardiac regions are assessed by a 12-lead ECG to help localize and diagnose ischemic or infarcted areas. Written below are the following regions supplied by the different coronary arteries.
The heart is a mechanical pump whose activity is governed by the electrical conduction system. It is essential to have a good understanding of the physiology of the cardiac cells as this will help the reader appreciate how the heart works and the implications of findings on the ECG. The heart is made up of specialized cardiac muscle, which is striated and organized into sarcomeres. These muscle fibers contain a single central nucleus, numerous mitochondria, and myoglobin molecules. Extensive branching of the cardiac muscle fibers and their end to end connection with each other through intercalated discs make them contract in a wave-like fashion. This mechanical work of pumping blood to the whole body occurs in a synchronized manner and is under the control of the cardiac conduction system. It is comprised of two types of cells, pacemaker and non-pacemaker cells. Pacemaker cells are located primarily in the SA and AV node, and it is the SA node, which drives the rate and rhythm of the heart. The AV node gets suppressed by the more rapid pace of the SA node.  The specialized function associated with the pacemaker cells is their spontaneous depolarization with no true resting potential. When spontaneous depolarization reaches the threshold voltage, it triggers a rapid depolarization followed by repolarization. The non-pacemaker cells mainly comprise the atrial and ventricular cardiac muscle cells and Purkinje fibers of the conduction system. They consist of true resting membrane potential, and upon initiation of an action potential, rapid depolarization is triggered, followed by a plateau phase and subsequent repolarization. Action potentials are generated by ion conductance via the opening and closing of the ion channels. Knowing which ECG leads corresponds to specific arteries helps in localizing the obstruction in acute ST-elevation MI or an age-indeterminate Q-wave infarction by observing predictable patterns on the ECG.
The evolution of EKG from a string galvanometer to the modern-day advanced computerized machine has led to its use as a diagnostic and screening tool, making it the gold standard for diagnosing various cardiac diseases.
Owing to its widespread use in the field of medicine, the EKG has several indications listed below:
There are no absolute contraindications for EKG. The relative contraindications to its use include:
The American College of Cardiology (ACC), in conjunction with American Heart Association (AHA) and the Heart Rhythm Society (HRS), has formulated guidelines and also set technical standards for ECG equipment . With advancements, most of the EKG machines are digital and can autogenerate preliminary findings based on the morphology criteria.
The conventional ECG machine consists of 12 leads, which divide into two groups, i.e., limb leads and precordial leads. Limb leads are further categorized as standard bipolar limb leads I, II and III, and augmented unipolar leads aVL, aVF, and aVR. The precordial leads include V1 to V6. The limb leads view the heart in a vertical plane, and the precordial leads record the electrical activity of the heart in the horizontal plane. The ECG represents a graphic recording of the electrical cardiac activity tracing on the electrocardiograph paper. The fundamental principles behind the recording of an ECG is an electromagnetic force, current or vector that has both magnitude and direction. When a current of depolarization travels towards the electrode, it gets recorded as a positive deflection, and when it moves away from the electrode, it appears as a negative deflection.
These concepts are easily applied to the heart while recording the ECG. There are several types of ECG monitoring equipment available, including continuous ECG monitoring, hardwire cardiac monitoring, telemetry, ambulatory electrocardiography, transtelephonic monitoring, and wireless mobile cardiac monitoring systems, etc. Furthermore, a duo of ECG and electronic stethoscope has been designed into a portable, handheld device that can review ECG rhythms and intervals at the bedside for analysis. With the evolution of technology, there are electronic wristwatches that can also provide monitoring of the heart rate and rhythm and have proven to be of value in detecting atrial fibrillation. The accuracy of these devices, however, may be somewhat inferior when compared to a 12-lead ECG; and when prompted for abnormal findings, these require confirmation by standardized clinical testing available in the Cardiology office.
The equipment for performing a conventional 12-lead ECG includes:
The medical personnel that can perform the ECG procedure includes a doctor, nurse, or a qualified technician. Usually, it is performed by the technicians either in the clinics or hospitals and then interpreted by physicians. Often, these findings are confirmed by a cardiologist in a hospital-based setting.
ECG merely requires special preparation. Before the procedure, a brief history regarding drugs and allergy to adhesive gel is necessary. The temperature of the room must be kept optimal to avoid shivering. The patient should be in a gown, and electrode sites identified. For good contact between body surface and electrodes, it is advised to shave the chest hair and then apply the electrocardiographic adhesive gel for electrodes. Any metallic object like jewelry or watch requires removal, if possible. Limb and precordial leads should be accurately placed to avoid vector misinterpretation. The patient must lie down and relax before recording the standard 10-second strip.
ECG machines are designed to record changes in the electrical activity by drawing a trace on a moving electrocardiograph paper. The electrocardiograph moves at a speed of 25mm/sec. Time is plotted on the x-axis and voltage on the y-axis. In the x-axis, 1 second is divided into five large squares, each of which represents 0.2 sec. Each large square is further divided into five small squares of 0.04 sec each. The EKG machine is calibrated in such a way that an increase of voltage by one mVolt should move the stylus by 1 cm. The conventional 12-lead EKG consisting of six limbs and six precordial leads is organized into ten wires. The limb leads include I, II, III, aVL, aVR, and aVF and named as RA, LA, RL, and LL. The limb leads are color-coded to avoid misplacement (red- right arm, yellow- left arm, green- left leg, and black- right leg). The precordial leads V1 to V6 are attached to the surface of the chest. For the correct location, the "Angle of Louis" method is an option, and the exact placement is as follows:
ECG is a safe, non-invasive, painless test with no major risks or complications. An allergic reaction or skin sensitivity to the adhesive gel can occur and usually resolves as soon as the electrode patches are removed, and in most cases, do not require any treatment. Artifacts and distortions pose serious diagnostic difficulties and may result in an inaccurate interpretation of the ECGs that may potentially result in an adverse therapeutic intervention.
The goal of the ECG interpretation is the ability to determine whether the ECG waves and intervals are normal or pathological. Electrical signal interpretation gives a good approximation of heart pathology. A standard 12 lead ECG is shown in [Figure 1]. The best way to interpret an ECG is to read it systematically:
ECG monitoring goals from simple heart rate and essential rhythm monitoring have been expanded significantly to the interpretation of complex arrhythmias, myocardial infarction, and other ECG abnormalities. The rapid detection of myocardial infarction has reduced the door-to-balloon time for reperfusion therapy substantially. Nurses' skills regarding assessment and comprehensive knowledge of the dysrhythmias can prevent stroke in atrial fibrillation and improve patient outcomes from the emergency department presentation through discharge and follow-up. Cardiology board-certified pharmacists can make appropriate medication recommendations for several medications, in particular, antiarrhythmics, based on ECG readings and patient history, working in conjunction with the cardiologist.
ECG outcomes in management are noticeable from observation to the critical care floors. An interaction among physicians, nurses, patient care assistants, pharmacists, and ECG technicians is critical to provide the most effective patient care. Interprofessional collaboration and teamwork in the hospital setting prevents significant medical errors by multiple checkpoints and also ensures timely emergency care in cardiac emergencies. For better outcomes, excellent professional ethics, evaluating patients satisfaction, and proficiency of the staff in evaluating ECGs are mandatory. There should be effective communication with appropriate role clarity, shared policies, and strategies to improve system-related issues. [Level V]
Continuous EKG monitoring is one of the current technologies being used in the emergency department, intensive, post-anesthesia, and cardiac care units, and often, nurses are the first care responders in these hospital settings. The first interaction of the EKG view puts great responsibility on the nurses in managing technical aspects of the EKG monitoring and also decision-making on the clinical grounds with information received from the monitor. The current practice involved is that nurses initially interpret the EKG and gather data and timely notify the physician-in-charge, to ensure an appropriate management plan.
Among the healthcare providers in a hospital setting, especially in intensive and cardiac care units where round the clock monitoring of critical patients is required, nurses play a very crucial role in cardiac monitoring. It is the responsibility of the nurse to assess the patient's clinical condition, monitor, and make sure that an excellent quality of care is delivered. The nurses' should monitor the continuous EKG monitoring very carefully and have competency in initial interpretation. Their knowledge about correct EKG leads placement, analysis, and providing thrombolytic treatment in acute coronary syndrome patients have significant implications in reducing morbidity and mortality.
|||Fye WB, A history of the origin, evolution, and impact of electrocardiography. The American journal of cardiology. 1994 May 15; [PubMed PMID: 8184849]|
|||Rundo F,Conoci S,Ortis A,Battiato S, An Advanced Bio-Inspired PhotoPlethysmoGraphy (PPG) and ECG Pattern Recognition System for Medical Assessment. Sensors (Basel, Switzerland). 2018 Jan 30; [PubMed PMID: 29385774]|
|||Surawicz B,Childers R,Deal BJ,Gettes LS,Bailey JJ,Gorgels A,Hancock EW,Josephson M,Kligfield P,Kors JA,Macfarlane P,Mason JW,Mirvis DM,Okin P,Pahlm O,Rautaharju PM,van Herpen G,Wagner GS,Wellens H, 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. Circulation. 2009 Mar 17; [PubMed PMID: 19228822]|
|||Klabunde RE, Cardiac electrophysiology: normal and ischemic ionic currents and the ECG. Advances in physiology education. 2017 Mar 1; [PubMed PMID: 28143820]|
|||Fakhri Y,Sejersten M,Schoos MM,Melgaard J,Graff C,Wagner GS,Clemmensen P,Kastrup J, Algorithm for the automatic computation of the modified Anderson-Wilkins acuteness score of ischemia from the pre-hospital ECG in ST-segment elevation myocardial infarction. Journal of electrocardiology. 2017 Jan - Feb; [PubMed PMID: 27889057]|
|||Ikawa A,Asai T,Kusakawa S, New EKG changes in rheumatic carditis. Japanese circulation journal. 1979 May; [PubMed PMID: 470109]|
|||Yilmaz S,Cakar MA,Vatan MB,Kilic H,Keser N, ECG Changes Due to Hypothermia Developed After Drowning: Case Report. Turkish journal of emergency medicine. 2014 Mar; [PubMed PMID: 27331164]|
|||Locati ET,Bagliani G,Testoni A,Lunati M,Padeletti L, Role of Surface Electrocardiograms in Patients with Cardiac Implantable Electronic Devices. Cardiac electrophysiology clinics. 2018 Jun; [PubMed PMID: 29784482]|
|||Alborzi Z,Zangouri V,Paydar S,Ghahramani Z,Shafa M,Ziaeian B,Radpey MR,Amirian A,Khodaei S, Diagnosing Myocardial Contusion after Blunt Chest Trauma. The journal of Tehran Heart Center. 2016 Apr 13; [PubMed PMID: 27928254]|
|||Saleh A,Shabana A,El Amrousy D,Zoair A, Predictive value of P-wave and QT interval dispersion in children with congenital heart disease and pulmonary arterial hypertension for the occurrence of arrhythmias. Journal of the Saudi Heart Association. 2019 Apr; [PubMed PMID: 30618481]|
|||El-Sherif N,Turitto G, Electrolyte disorders and arrhythmogenesis. Cardiology journal. 2011; [PubMed PMID: 21660912]|
|||Drezner JA,Sharma S,Baggish A,Papadakis M,Wilson MG,Prutkin JM,Gerche A,Ackerman MJ,Borjesson M,Salerno JC,Asif IM,Owens DS,Chung EH,Emery MS,Froelicher VF,Heidbuchel H,Adamuz C,Asplund CA,Cohen G,Harmon KG,Marek JC,Molossi S,Niebauer J,Pelto HF,Perez MV,Riding NR,Saarel T,Schmied CM,Shipon DM,Stein R,Vetter VL,Pelliccia A,Corrado D, International criteria for electrocardiographic interpretation in athletes: Consensus statement. British journal of sports medicine. 2017 May; [PubMed PMID: 28258178]|
|||Kligfield P,Gettes LS,Bailey JJ,Childers R,Deal BJ,Hancock EW,van Herpen G,Kors JA,Macfarlane P,Mirvis DM,Pahlm O,Rautaharju P,Wagner GS, 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; [PubMed PMID: 17341413]|
|||Wasserlauf J,You C,Patel R,Valys A,Albert D,Passman R, Smartwatch Performance for the Detection and Quantification of Atrial Fibrillation. Circulation. Arrhythmia and electrophysiology. 2019 Jun; [PubMed PMID: 31113234]|
|||Yang XL,Liu GZ,Tong YH,Yan H,Xu Z,Chen Q,Liu X,Zhang HH,Wang HB,Tan SH, The history, hotspots, and trends of electrocardiogram. Journal of geriatric cardiology : JGC. 2015 Jul; [PubMed PMID: 26345622]|
|||Chaubey VK,Chhabra L, Spodick's sign: a helpful electrocardiographic clue to the diagnosis of acute pericarditis. The Permanente journal. 2014 Winter [PubMed PMID: 24626086]|
|||Takla G,Petre JH,Doyle DJ,Horibe M,Gopakumaran B, The problem of artifacts in patient monitor data during surgery: a clinical and methodological review. Anesthesia and analgesia. 2006 Nov; [PubMed PMID: 17056954]|
|||Harrigan RA,Chan TC,Brady WJ, Electrocardiographic electrode misplacement, misconnection, and artifact. The Journal of emergency medicine. 2012 Dec; [PubMed PMID: 22929906]|
|||Mangalmurti S,Seabury SA,Chandra A,Lakdawalla D,Oetgen WJ,Jena AB, Medical professional liability risk among US cardiologists. American heart journal. 2014 May; [PubMed PMID: 24766979]|
|||Becker DE, Fundamentals of electrocardiography interpretation. Anesthesia progress. 2006 Summer; [PubMed PMID: 16863387]|
|||Atwood D,Wadlund DL, ECG Interpretation Using the CRISP Method: A Guide for Nurses. AORN journal. 2015 Oct; [PubMed PMID: 26411823]|
|||Spodick DH,Frisella M,Apiyassawat S, QRS axis validation in clinical electrocardiography. The American journal of cardiology. 2008 Jan 15; [PubMed PMID: 18178420]|
|||Reeves WC, ECG criteria for right atrial enlargement. Archives of internal medicine. 1983 Nov; [PubMed PMID: 6227299]|
|||Batra MK,Khan A,Farooq F,Masood T,Karim M, Assessment of electrocardiographic criteria of left atrial enlargement. Asian cardiovascular [PubMed PMID: 29587523]|
|||Nikus K,Pérez-Riera AR,Konttila K,Barbosa-Barros R, Electrocardiographic recognition of right ventricular hypertrophy. Journal of electrocardiology. 2018 Jan - Feb; [PubMed PMID: 29046220]|
|||NOTH PH,MYERS GB,KLEIN HA, The precordial electrocardiogram in left ventricular hypertrophy; a study of autopsied cases. Proceedings [of the] annual meeting. Central Society for Clinical Research (U.S.). 1947; [PubMed PMID: 20272816]|
|||Baranchuk A,Bayés de Luna A, The P-wave morphology: what does it tell us? Herzschrittmachertherapie [PubMed PMID: 26264481]|
|||PIPBERGER HV,TANENBAUM HL, [The P wave, P-R interval, and Q-T ratio of the normal orthogonal electrocardiogram]. Circulation. 1958 Dec; [PubMed PMID: 13608848]|
|||Aro AL,Anttonen O,Kerola T,Junttila MJ,Tikkanen JT,Rissanen HA,Reunanen A,Huikuri HV, Prognostic significance of prolonged PR interval in the general population. European heart journal. 2014 Jan; [PubMed PMID: 23677846]|
|||Delewi R,Ijff G,van de Hoef TP,Hirsch A,Robbers LF,Nijveldt R,van der Laan AM,van der Vleuten PA,Lucas C,Tijssen JG,van Rossum AC,Zijlstra F,Piek JJ, Pathological Q waves in myocardial infarction in patients treated by primary PCI. JACC. Cardiovascular imaging. 2013 Mar; [PubMed PMID: 23433932]|
|||Zema MJ,Kligfield P, ECG poor R-wave progression: review and synthesis. Archives of internal medicine. 1982 Jun; [PubMed PMID: 6212033]|
|||Channer K,Morris F, ABC of clinical electrocardiography: Myocardial ischaemia. BMJ (Clinical research ed.). 2002 Apr 27; [PubMed PMID: 11976247]|
|||Brady WJ, ST segment and T wave abnormalities not caused by acute coronary syndromes. Emergency medicine clinics of North America. 2006 Feb; [PubMed PMID: 16308114]|
|||de Bliek EC, ST elevation: Differential diagnosis and caveats. A comprehensive review to help distinguish ST elevation myocardial infarction from nonischemic etiologies of ST elevation. Turkish journal of emergency medicine. 2018 Mar; [PubMed PMID: 29942875]|
|||Chhabra L,Spodick DH, Brugada pattern masquerading as ST-segment elevation myocardial infarction in flecainide toxicity. Indian heart journal. 2012 Jul-Aug [PubMed PMID: 22929826]|
|||Khalid N,Chhabra L,Kluger J, PYREXIA-INDUCED BRUGADA PHENOCOPY. Journal of Ayub Medical College, Abbottabad : JAMC. 2015 Jan-Mar [PubMed PMID: 26182783]|
|||Chhabra L,Spodick DH, Electrocardiography in pericarditis and ST-elevation myocardial infarction: timing of observation is critical. The American journal of medicine. 2014 May [PubMed PMID: 24758877]|
|||Chhabra L,Chaubey VK,Spodick DH, Diagnostic criteria for acute pericarditis need closer attention. Pacing and clinical electrophysiology : PACE. 2014 May [PubMed PMID: 24628079]|
|||Chhabra L,Spodick DH, Persistent J-ST elevation: a sign of persistent perimyocardial irritation. Heart (British Cardiac Society). 2014 Aug [PubMed PMID: 24829368]|
|||Chhabra L,Mujtaba M,Spodick DH, Regional pericarditis or an alternate diagnosis? Case reports in medicine. 2014 [PubMed PMID: 25053949]|
|||[PubMed PMID: 22890314]|
|||Morris NP,Body R, The De Winter ECG pattern: morphology and accuracy for diagnosing acute coronary occlusion: systematic review. European journal of emergency medicine : official journal of the European Society for Emergency Medicine. 2017 Aug; [PubMed PMID: 28362646]|
|||Okin PM,Devereux RB,Kors JA,van Herpen G,Crow RS,Fabsitz RR,Howard BV, Computerized ST depression analysis improves prediction of all-cause and cardiovascular mortality: the strong heart study. Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc. 2001 Apr; [PubMed PMID: 11333167]|
|||Tse G,Chan YW,Keung W,Yan BP, Electrophysiological mechanisms of long and short QT syndromes. International journal of cardiology. Heart [PubMed PMID: 28382321]|
|||Rudic B,Schimpf R,Borggrefe M, Short QT Syndrome - Review of Diagnosis and Treatment. Arrhythmia [PubMed PMID: 26835070]|
|||Levis JT, ECG Diagnosis: Hypothermia. The Permanente journal. 2010 Fall; [PubMed PMID: 20844708]|
|||Wang J,Yang B,Chen H,Ju W,Chen K,Zhang F,Cao K,Chen M, Epsilon waves detected by various electrocardiographic recording methods: in patients with arrhythmogenic right ventricular cardiomyopathy. Texas Heart Institute journal. 2010; [PubMed PMID: 20844612]|
|||Jacob L, Nurse-led clinics for atrial fibrillation: managing risk factors. British journal of nursing (Mark Allen Publishing). 2017 Dec 14; [PubMed PMID: 29240471]|
|||Drew BJ,Califf RM,Funk M,Kaufman ES,Krucoff MW,Laks MM,Macfarlane PW,Sommargren C,Swiryn S,Van Hare GF, Practice standards for electrocardiographic monitoring in hospital settings: an American Heart Association scientific statement from the Councils on Cardiovascular Nursing, Clinical Cardiology, and Cardiovascular Disease in the Young: endorsed by the International Society of Computerized Electrocardiology and the American Association of Critical-Care Nurses. Circulation. 2004 Oct 26; [PubMed PMID: 15505110]|
|||Quinn T, The role of nurses in improving emergency cardiac care. Nursing standard (Royal College of Nursing (Great Britain) : 1987). 2005 Aug 10-16; [PubMed PMID: 16117268]|
|||Adams TL,Orchard C,Houghton P,Ogrin R, The metamorphosis of a collaborative team: from creation to operation. Journal of interprofessional care. 2014 Jul; [PubMed PMID: 24593331]|
|||Funk M,Fennie KP,Stephens KE,May JL,Winkler CG,Drew BJ, 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. Circulation. Cardiovascular quality and outcomes. 2017 Feb; [PubMed PMID: 28174175]|
|||Tootill DM, Thrombolytic therapy: nursing strategies for successful patient outcomes. Progress in cardiovascular nursing. 1995 Winter; [PubMed PMID: 7770439]|