[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"detail-sidebar-cat-0-en-105":3,"doc-seo-657677-105":59,"doc-detail-657677-en":130},{"code":4,"msg":5,"data":6},0,"success",[7,13,18,23,28,33,38,43,48,51,55],{"id":8,"doc_module":4,"doc_module_name":9,"category_name":10,"show_sort_weight":11,"slug":12},1,"Document","Story & Novel",90,"story-novel",{"id":14,"doc_module":4,"doc_module_name":9,"category_name":15,"show_sort_weight":16,"slug":17},2,"Literature",80,"literature",{"id":19,"doc_module":4,"doc_module_name":9,"category_name":20,"show_sort_weight":21,"slug":22},4,"Exam",70,"exam",{"id":24,"doc_module":4,"doc_module_name":9,"category_name":25,"show_sort_weight":26,"slug":27},5,"Comic",60,"comic",{"id":29,"doc_module":4,"doc_module_name":9,"category_name":30,"show_sort_weight":31,"slug":32},6,"Technology",50,"technology",{"id":34,"doc_module":4,"doc_module_name":9,"category_name":35,"show_sort_weight":36,"slug":37},7,"Healthcare",40,"healthcare",{"id":39,"doc_module":4,"doc_module_name":9,"category_name":40,"show_sort_weight":41,"slug":42},8,"Research & Report",30,"research-report",{"id":44,"doc_module":4,"doc_module_name":9,"category_name":45,"show_sort_weight":46,"slug":47},9,"Religion & Spirituality",20,"religion-spirituality",{"id":46,"doc_module":4,"doc_module_name":9,"category_name":49,"show_sort_weight":46,"slug":50},"World Cup","world-cup",{"id":52,"doc_module":4,"doc_module_name":9,"category_name":53,"show_sort_weight":52,"slug":54},10,"Lifestyle","lifestyle",{"id":56,"doc_module":4,"doc_module_name":9,"category_name":57,"show_sort_weight":24,"slug":58},19,"General","general",{"code":4,"msg":60,"data":61},"ok",{"site_id":62,"language":63,"slug":64,"title":65,"keywords":66,"description":67,"schema_data":68,"social_meta":123,"head_meta":125,"extra_data":127,"updated_unix":129},105,"en","the-electrocardiogram-chapter-3-ecg-fundamentals-and-interpretation","The electrocardiogram - Chapter 3 - ECG fundamentals and interpretation","","Explains what an electrocardiogram (ECG) is and how it records the heart’s electrical activity using 10 body electrodes and produces 12-lead traces. Describes cardiac electrical conduction from the sinoatrial node through the atrioventricular node and His bundle to ventricular pathways. Covers how ECG deflections correspond to cardiac cycle phases, the meanings of P wave, PR interval, QRS complex, ST segment, QT/QTc interval, T wave, and U wave, and gives normal interval ranges. Provides a methodical approach for ECG analysis including rate calculation and a logical diagnostic checklist.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/the-electrocardiogram-chapter-3-ecg-fundamentals-and-interpretation/657677/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/the-electrocardiogram-chapter-3-ecg-fundamentals-and-interpretation/657677.png","ImageObject",300,407,{"name":92,"@type":93},"Ivy","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-29","2026-10-26",true,{"@type":102,"interactionType":103,"userInteractionCount":81},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What is recorded by an electrocardiogram (ECG)?","Question",{"text":112,"@type":113},"ECG records the heart’s electrical activity using electrodes placed on specific body locations. The activity is displayed as 12 traces (12-lead surface ECG).","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How do ECG leads produce positive or negative deflections?",{"text":117,"@type":113},"When cardiac electrical activity is directed towards an electrode, it produces a positive deflection; when directed away, it produces a negative deflection on the ECG.",{"name":119,"@type":110,"acceptedAnswer":120},"What are the normal ranges for key ECG intervals?",{"text":121,"@type":113},"Normal ranges include PR interval 0.12–0.20 s, QRS duration \u003C0.12 s, QT interval 0.35–0.45 s, and QTc interval 0.38–0.42 s, with QTc slightly longer in females than males.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},657677,1793098891,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":81,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":144,"read_time":145},549758252649,"https://ap-avatar.wpscdn.com/avatar/8000253669c5317157?_k=1778319167496531819","Chapter 3  \nThe electrocardiogram  \nElectrocardiogram (ECG)  \nThis is a graphical representation of the electrical activity of the heart and is recorded using 10 electrodes placed in specific locations on the body (Fig. 3.1). This electrical activity is displayed as 12 traces (12-lead surface ECG; see Fig. 3.2) . Each deflection of the electrogram represents a particular activity in the cardiac cycle. Very minor changes to the structure or function of the heart can produce quite marked changes of the ECG, which can therefore be a powerful diagnostic tool. It is important to understand the principles behind the ECG so as to understand normality and thereafter recognize abnormality.  \nElectrical activity of the normal heart  \nThe start of electrical activity in the heart occurs inan area of the right atrium where specialized pacemaker cells form the sinoatrial node (SA node) . Electrical discharges from these cells produce depolarization that spreads through the atrial muscle from right to left. The only route by which electrical activity can then reach the ventricles is via further specialized pacemaker cells; the atrioventricular node (AVN) . From the AVN, electrical activity then spreads rapidly down the His bundle, which subsequently divides into right and left branches; the left bundle further divides into anterior and posterior fascicles (Fig. 3.3) .  \nRecording the ECG  \nThe ECG is recorded with the patient lying down and relaxed. Cardiac electrical activity that is directed towards an electrode produces a positive deflection, and when directed away produces a negative deflection, on the ECG.  \n● Standard leads I, II and III are bipolar and oriented in the coronal plane.  \n● Leads aVR, aVL and aVF (‘a’ for augmented as instrumental augmentation is necessary because of the low potential at the extremities) are unipolar leads oriented in the coronal plane.  \n● Leads V1–V6 are unipolar leads oriented in the horizontal plane.  \nThe vectorial orientation of these leads is illustrated in Fig. 3.1.  \nComponents of the normal ECG (Fig. 3.4)  \n● P wave. This represents atrial depolarization. The deflection arising as a result of repolarization is so small that it is not seen in the P wave.  \n● PR interval. This represents the time taken to conduct from the atria to the ventricles, and is taken from the onset of the P wave to the first deflection of the QRS.  \n● QRS complex. This represents ventricular depolarization. Q is the first negative deflection, R the first positive deflection and S is the first negative deflection following a positive deflection. Asthe left ventricle contributes most of the mass of  \n26  \nThe electrocardiogram Chapter 3  \n(a) (c)  \nRight shoulder + aVR  \nII  \nLeft shoulder + aVl  \nI  \nIII  \naVF  \n+  \nLeft foot  \n(b)  \nFig. 3.1 Eindhoven’s triangle: there are three ‘standard’ bipolar limb leads (I–III) and three augmented limb leads (aVR, aVFand aVL) .  \nmyocardium, it also contributes most of the electrical activity of the QRS component. Its duration is measured from the first deflection to the end of the QRS.  \n● ST segment. This is defined as the component of the ECG that occurs from the end of the QRS complex to the start oftheT wave. The QT interval is measured from the onset of the QRS to the end of the T wave. The QT interval is affected by heart rate and so the ‘corrected’ QT interval (QTc) is more clinically useful.  \nQTc = QT/√R–R’ interval  \nWhere the QT is the measured QT in seconds, and R–R’ is the interval between the R waves of consecutive QRS complexes, measured in seconds.  \n● T wave. This represents ventricular repolarization.  \n● U wave. This is usually a small deflection or‘hump’ seen in the end portion or after the T wave. It is not always present and the exact cause of it is unknown.  \n27  \nChapter 3 The electrocardiogram  \nFig. 3.2 Normal 12-lead ECG.(a) Limb lead electrode positions and ECG complexes. (b) Chest lead electrode positions and ECG complexes.  \n28  \nThe electrocardiogram Chapter 3  \nFig. 3","cbCaihbVKJhM9txv","https://ap.wps.com/l/cbCaihbVKJhM9txv","pdf",1221460,15,"English","# The electrocardiogram\n## Electrical activity of the normal heart\n## Recording the ECG\n## Components of the normal ECG\n## Normal intervals\n## Analysing the ECG\n## Cardiac rate and rhythm","[{\"question\":\"What is recorded by an electrocardiogram (ECG)?\",\"answer\":\"ECG records the heart’s electrical activity using electrodes placed on specific body locations. The activity is displayed as 12 traces (12-lead surface ECG).\"},{\"question\":\"How do ECG leads produce positive or negative deflections?\",\"answer\":\"When cardiac electrical activity is directed towards an electrode, it produces a positive deflection; when directed away, it produces a negative deflection on the ECG.\"},{\"question\":\"What are the normal ranges for key ECG intervals?\",\"answer\":\"Normal ranges include PR interval 0.12–0.20 s, QRS duration \\u003c0.12 s, QT interval 0.35–0.45 s, and QTc interval 0.38–0.42 s, with QTc slightly longer in females than males.\"}]","The electrocardiogram - Chapter 3 - ECG fundamentals and interpretation | PDF",1792986191,38]