QRS complex: Difference between revisions
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{{for|other uses of the term "S wave"|S-wave}} |
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[[File:SinusRhythmLabels.svg|right|thumb|Schematic representation of normal ECG]] |
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[[File:Rapid Axis Vector.svg|thumb|Diagram showing how the polarity of the QRS complex in leads I, II, and III can be used to estimate the heart's electrical axis in the frontal plane.]] |
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The '''QRS complex''' is a name for the combination of three of the graphical deflections seen on a typical [[electrocardiography|the '''[[P wave (electrocardiography)|P wave]]'''. An '''R wave''' follows as an upward deflection, and the '''S wave''' is any downward deflection after the R wave. The '''[[T wave]]''' follows the S wave, and in some cases, an additional '''[[U wave]]''' follows the T wave. |
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==Formation== |
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{{See also|Electrical conduction system of the heart}} |
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Depolarization of the heart [[ventricle (heart)|ventricles]] occurs almost simultaneously, via the [[bundle of His]] and [[Purkinje fibers]]. If they are working efficiently, the QRS complex is {{nowrap|80 to 120 [[millisecond|ms]]}} in duration. This is represented by three small squares or less at the standard paper speed of 25 mm/s. |
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==Clinical significance== |
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Any abnormality of conduction takes longer and causes "widened" QRS complexes. In [[bundle branch block]], there can be an abnormal second upward deflection within the QRS complex. In this case, such a second upward deflection is referred to as R' (pronounced "R prime"). This would be described as an RSR' pattern. |
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Ventricles contain more muscle mass than the atria. Therefore, the QRS complex is considerably larger than the P wave. The QRS complex is often used to determine the [[Electrocardiogram#Axis|axis]] of the electrocardiogram, although it is also possible to determine a separate P wave axis. |
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The duration, amplitude, and morphology of the QRS complex are useful in diagnosing [[cardiac arrhythmias]], [[conduction abnormalities]], [[ventricular hypertrophy]], [[myocardial infarction]], [[electrolyte derangement]]s, and other disease states. |
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==Components== |
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[[File:QRS complex.png|right|thumb|Schematic representation of the QRS complex.]] |
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{| class="wikitable" |
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! Parameter !! Normal value !! Value comments !! Clinical significance |
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|- |
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| '''QRS duration''' || 0.06–0.10 s<ref name=Yanowitz>[http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson3/index.html III. Characteristics of the Normal ECG] Frank G. Yanowitz, MD. Professor of Medicine. University of Utah School of Medicine. Retrieved on April 14, 2010</ref> || Shorter in children and in [[tachycardia]]<ref name=uppsala>Compendium for interpretation of ECG at Uppsala Institution for Clinical Physiology. Year 2010</ref> || Prolonged duration indicates e.g. [[hyperkalemia]].<ref>[http://www.umm.edu/altmed/drugs/potassium-gluconate-104100.htm Complementary and Alternative Medicine Index (CAM)] {{webarchive |url=https://web.archive.org/web/20090904214055/http://www.umm.edu/altmed/drugs/potassium-gluconate-104100.htm |date=September 4, 2009 }}</ref> or [[bundle branch block]] |
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|- |
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| '''QRS amplitude''' |
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* S amplitude in V1 + R amplitude in V5 < 3.5 [[millivolt]] (mV)<ref name=uppsala/> |
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* R+S in a [[precordial lead]] < 4.5 mV<ref name=uppsala/> |
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* R in V5 or V6 < 2.6 mV |
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| Increased amplitude indicates [[cardiac hypertrophy]] |
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|- |
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| '''Ventricular <br>activation <br>time (VAT)''' |
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* {{nowrap|< 0.05 s}} in V5 or V6<ref name=uppsala/> |
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* {{nowrap|< 0.03 s}} in V1<ref name=uppsala/> |
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| Measured in increased QRS amplitude<ref name=uppsala/> |
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|- |
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| '''Q wave''' |
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* Duration up to 0.04 seconds in leads other than III and aVR<ref name=meddean>[http://www.meddean.luc.edu/lumen/MedEd/MEDICINE/skills/ekg/les1prnt.htm Loyola University Chicago Stritch School of Medicine. > EKG Interpretive skills] Retrieved on April 22, 2010</ref> |
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* Amplitude less than 1/3 QRS amplitude<ref name=meddean/> (R+S) |
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* Amplitude less than 1/4 of R wave<ref name=meddean/> |
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| Abnormality indicates presence of infarction<ref name=meddean/> |
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|} |
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The QRS complex is also included in estimating the [[QT interval]]. |
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=== Q wave {{anchor|Q}} === |
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Normal Q waves, when present, represent depolarization of the [[interventricular septum]]. For this reason, they are referred to as septal Q waves and can be appreciated in the lateral leads I, aVL, V5 and V6. |
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Pathologic Q waves occur when the electrical signal passes through stunned or scarred [[myocardium|heart muscle]]; as such, they are usually markers of previous [[myocardial infarction]]s, with subsequent fibrosis. A pathologic Q wave is defined as having a deflection amplitude of 25% or more of the subsequent R wave, or being {{nowrap|> 0.04 s}} (40 ms) in width and {{nowrap|> 2 mm}} in amplitude. However, diagnosis requires the presence of this pattern in more than one corresponding lead. |
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[[Myocardial infarction]]s with pathological Q waves are referred to as ST elevation MIs.<ref>{{cite book|title=Primary Care: Art and Science of Advanced Practice Nursing|date=2015|publisher=F.A. Davis|isbn=9780803644946|page=464|url=https://books.google.ca/books?id=fsnXBgAAQBAJ&pg=PA464}}</ref> |
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=== R wave progression === |
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Looking at the precordial leads, the R wave usually progresses from showing an rS-type complex in V<sub>1</sub> with an increasing R and a decreasing S wave when moving toward the left side. There is usually an qR-type of complex in V<sub>5</sub> and V<sub>6</sub> with the R-wave amplitude usually taller in V<sub>5</sub> than in V<sub>6</sub>. It is normal to have a narrow QS and rSr' patterns in V<sub>1</sub>, and this is also the case for qRs and R patterns in V<sub>5</sub> and V<sub>6</sub>. The ''transition zone'' is where the QRS complex changes from predominately negative to predominately positive (R/S ratio becoming >1), and this usually occurs at V<sub>3</sub> or V<sub>4</sub>. It is normal to have the transition zone at V<sub>2</sub> (called "early transition") and at V<sub>5</sub> (called "delayed transition").<ref name=mackennzie2005>''Poor R-Wave Progression''. By: Ross MacKenzie, MD. J Insur Med 2005;37:58–62 [http://www.aaimedicine.org/journal-of-insurance-medicine/jim/2005/037-01-0058.pdf]</ref> In biomedical engineering, the maximum amplitude in the R wave is usually called "R peak amplitude", or just "R peak".<ref name="SzczepaniakLisboa2000">{{cite book|author1=Piotr S. Szczepaniak|author2=Paulo J. G. Lisboa|author3=[[Janusz Kacprzyk]]|title=Fuzzy Systems in Medicine|url=https://books.google.com/books?id=Mvb13e8JZy0C&pg=PA256|year=2000|publisher=Springer|isbn=978-3-7908-1263-3|page=256}}</ref><ref name="GacekPedrycz2011">{{cite book|author1=Adam Gacek|author2=Witold Pedrycz|title=ECG Signal Processing, Classification and Interpretation: A Comprehensive Framework of Computational Intelligence|url=https://books.google.com/books?id=lPTiGqPKY94C&pg=PA108|year=2011|publisher=Springer|isbn=978-0-85729-867-6|page=108}}</ref> Accurate R peak detection is essential in signal processing equipment for [[heart rate]] measurement and it is the main feature used for [[Heart arrhythmia|arrhythmia]] detection.<ref name="Pise2011">{{cite book|author=S J Pise|title=ThinkQuest 2010: Proceedings of the First International Conference on Contours of Computing Technology|url=https://books.google.com/books?id=8OG9JGvGTpMC&pg=PA8|year=2011|publisher=Springer|isbn=978-81-8489-988-7|page=8}}</ref><ref name="YooHoof2010">{{cite book|author1=Hoi-Jun Yoo|author2=Chris van Hoof|title=Bio-Medical CMOS ICs|url=https://books.google.com/books?id=_yoRtbPnreYC&pg=PA197|year=2010|publisher=Springer|isbn=978-1-4419-6596-7|page=197}}</ref> |
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The definition of ''poor R wave progression'' (PRWP) varies in the literature, but a common one is when the R wave is less than 2–4 mm in leads V<sub>3</sub> or V<sub>4</sub> and/or there is presence of a reversed R wave progression, which is defined as R in V<sub>4</sub> < R in V<sub>3</sub> or R in V<sub>3</sub> < R in V<sub>2</sub> or R in V<sub>2</sub> < R in V<sub>1</sub>, or any combination of these.<ref name=mackennzie2005/> ''Poor R wave progression'' is commonly attributed to anterior [[myocardial infarction]], but it may also be caused by [[left bundle branch block]], [[Wolff–Parkinson–White syndrome]], right and left [[ventricular hypertrophy]], or a faulty ECG recording technique.<ref name=mackennzie2005/> |
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=== J-point === |
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The point where the QRS complex meets the [[ST segment]] is the J-point. The J-point is easy to identify when the ST segment is horizontal and forms a sharp angle with the last part of the QRS complex. However, when the ST segment is sloped or the QRS complex is wide, the two features do not form a sharp angle and the location of the J-point is less clear. There is no consensus on the precise location of the J-point in these circumstances.<ref name=Brownfield>{{cite journal|last=Brownfield|first=J|author2=Herbert, M |title=EKG Criteria for Fibrinolysis: What's Up with the J Point?|journal=The western journal of emergency medicine|date=January 2008|volume=9|issue=1|pages=40–2|pmid=19561701|pmc=2672223}}</ref> Two possible definitions are: |
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* The "first point of inflection of the upstroke of the S wave"<ref name=Brownfield /> |
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* The point at which the ECG trace becomes more horizontal than vertical<ref>[http://www.monroecc.edu/depts/PSTC/backup/parasec1.htm#JPT PSTF Paramedic Student Electrocardiography]</ref> |
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== Terminology == |
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[[File:QRS nomenclature.svg|thumb|Various QRS complexes with nomenclature.]] |
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Not every QRS complex contains a Q wave, an R wave, and an S wave. By convention, any combination of these waves can be referred to as a QRS complex. However, correct interpretation of difficult ECGs requires exact labeling of the various waves. Some authors use lowercase and capital letters, depending on the relative size of each wave. For example, an Rs complex would be positively deflected, while an rS complex would be negatively deflected. If both complexes were labeled RS, it would be impossible to appreciate this distinction without viewing the actual ECG. |
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=== Monomorphic or polymorphic === |
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Monomorphic refers to all QRS waves in a single lead being similar in shape. Polymorphic means that the QRS change from complex to complex.<ref>{{cite book |author1=Kenneth M Sutin |author2=Marino, Paul L. |title=The ICU book |publisher=Lippincott Williams & Wilkins |location=Hagerstwon, MD |year=2007 |page=356 |isbn=0-7817-4802-X |oclc= |doi= |accessdate=}}</ref> These terms are used in the description of [[ventricular tachycardia]]. |
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== Algorithms == |
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A common algorithm used for QRS complex detection is the [[Pan-Tompkins]]<ref>{{Cite journal | doi = 10.1109/TBME.1985.325532| title = A Real-Time QRS Detection Algorithm| journal = IEEE Transactions on Biomedical Engineering| issue = 3| pages = 230| year = 1985| last1 = Pan | first1 = J. | last2 = Tompkins | first2 = W. J. }}</ref> algorithm (or method); another is based on the [[Hilbert transform]].<ref name="SobhElleithy2010">{{cite book|author1=Tarek Sobh|author2=Khaled Elleithy|title=Innovations in Computing Sciences and Software Engineering|url=https://books.google.com/books?id=IQ8h_d5rR0MC&pg=PA462|year=2010|publisher=Springer|isbn=978-90-481-9111-6|page=462}}</ref><ref name="LimHong2009">{{cite book|author1=Chwee Teck Lim|author2=James Goh Cho Hong|title=13th International Conference on Biomedical Engineering: ICBME 2008, 3-6 December 2008, Singapore|url=https://books.google.com/books?id=bzxZkEcLo1kC&pg=PA469|year=2009|publisher=Springer|isbn=978-3-540-92840-9|page=469}}</ref><ref name="ChaudhuriPawar2009">{{cite book|author1=Subhasis Chaudhuri|author2=Tanmay D. Pawar|author3=Siddhartha Duttagupta|title=Ambulation Analysis in Wearable ECG|url=https://books.google.com/books?id=MxhxdITUNIsC&pg=PA67|year=2009|publisher=Springer|isbn=978-1-4419-0725-7|page=67}}</ref><ref name="Bos2010">{{cite book|author=Lodewijk Bos|title=Medical and Care Compunetics 6|url=https://books.google.com/books?id=Pvf9Q4bCH-YC&pg=PA41|year=2010|publisher=IOS Press|isbn=978-1-60750-564-8|page=41}}</ref> Numerous other algorithms have been proposed and investigated.<ref>{{Cite journal | doi = 10.1109/51.993193| pmid = 11935987| title = The principles of software QRS detection| journal = IEEE Engineering in Medicine and Biology Magazine| volume = 21| issue = 1| pages = 42–57| year = 2002| last1 = Kohler | first1 = B. -U. | last2 = Hennig | first2 = C.| last3 = Orglmeister | first3 = R.}}</ref> |
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== See also == |
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* [[Electrophysiology]] |
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== References == |
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{{reflist|35em}} |
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{{Cardiovascular physiology}} |
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[[Category:Cardiac electrophysiology]] |
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