ECG (electrocardiogram): indications, interpretation and results | Clinique Omicron<\/title>\n<meta name=\"description\" content=\"The ECG is the gold standard for evaluating the heart. Indications, systematic reading, frequent abnormalities (AF, block, hypertrophy, ischemia) and management in Quebec.\">\n<meta name=\"keywords\" content=\"ECG \u00e9lectrocardiogramme indications, ECG interpr\u00e9tation r\u00e9sultats, \u00e9lectrocardiogramme anomalies, ECG fibrillation auriculaire, ECG bloc de branche, ECG isch\u00e9mie infarctus, ECG hypertrophie ventriculaire, ECG Qu\u00e9bec\">\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=Cinzel:wght@600&family=Poppins:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n<style>\n.co-wrap * { font-family: 'Poppins', sans-serif; box-sizing: border-box; }\n.co-wrap { max-width: 1100px; margin: 0 auto; padding: 30px 0 60px; }\n.co-label { font-family: 'Cinzel', serif; font-size: 14px; font-weight: bold; letter-spacing: 1px; text-transform: uppercase; color: #4D6577; margin-bottom: 14px; display: block; }\n.co-wrap h1 { font-size: 32px; font-weight: 500; color: #323C52; margin: 0 0 22px; line-height: 1.2; }\n.co-intro { font-size: 16px; line-height: 1.75; color: #4D6577; margin-bottom: 36px; padding-bottom: 32px; border-bottom: 1px solid rgba(77,101,119,.2); }\n.co-wrap h2 { font-size: 20px; font-weight: 600; color: #323C52; margin: 32px 0 12px; }\n.co-wrap p { font-size: 15px; color: #4D6577; line-height: 1.7; margin-bottom: 14px; }\n.co-list { list-style: none; padding: 0; margin: 12px 0 24px; }\n.co-list li { font-size: 15px; color: #4D6577; padding: 10px 14px 10px 38px; margin-bottom: 8px; border-radius: 6px; position: relative; background: rgba(77,101,119,.06); border-left: 3px solid #4D6577; }\n.co-list li::before { content: \"\u2713\"; position: absolute; left: 12px; font-weight: 700; color: #4D6577; }\n.co-table { width: 100%; border-collapse: collapse; margin: 14px 0 22px; font-size: 14px; border-radius: 8px; overflow: hidden; table-layout: fixed; }\n.co-table thead tr { background: #323C52; color: #fff; }\n.co-table thead th { padding: 11px 16px; text-align: left; font-weight: 600; font-size: 13px; }\n.co-table tbody tr:nth-child(even) { background: rgba(77,101,119,.06); }\n.co-table tbody tr:nth-child(odd) { background: #fff; }\n.co-table td { padding: 10px 16px; color: #4D6577; border-bottom: 1px solid rgba(77,101,119,.12); font-size: 14px; vertical-align: top; }\n.co-table td:first-child { font-weight: 600; color: #323C52; }\n.co-infobox { display: flex; gap: 12px; background: rgba(77,101,119,.06); border-radius: 8px; border-left: 4px solid #4D6577; padding: 14px 18px; margin: 18px 0 28px; font-size: 14px; color: #4D6577; line-height: 1.65; }\n.co-infobox .ico { font-size: 18px; flex-shrink: 0; }\n.co-urgence { background: #fff8f8; border-left: 5px solid #c0392b; border-radius: 6px; padding: 20px 26px; margin: 24px 0 32px; }\n.co-urgence .co-urgence-titre { font-size: 13px; font-weight: 700; color: #c0392b; letter-spacing: 1.5px; text-transform: uppercase; margin-bottom: 10px; }\n.co-urgence p { color: #5a2020; font-size: 14px; margin: 0 0 10px; line-height: 1.7; }\n.co-urgence p:last-child { margin-bottom: 0; }\n.co-disclaimer { font-size: 13px; color: #8a9aaa; font-style: italic; border-top: 1px solid rgba(77,101,119,.15); padding-top: 24px; margin-top: 40px; line-height: 1.6; }\n<\/style>\n<\/head>\n<body>\n<div class=\"co-wrap\">\n <span class=\"co-label\">Cardiology & Internal Medicine & Family Medicine<\/span>\n <h1>ECG (electrocardiogram)<\/h1>\n\n <div class=\"co-intro\">\n The electrocardiogram (ECG) is a non-invasive, painless and rapid test that records the heart's electrical activity using electrodes placed on the surface of the body. It is the most widely prescribed first-line cardiac examination in medicine - available in less than 5 minutes, without risk and at low cost - and provides essential diagnostic information on heart rhythm, atrioventricular and intraventricular conduction, the morphology of the heart chambers and the state of the myocardium (ischemia, necrosis, pericarditis). The physical principle is based on the detection of electrical potential variations generated by the successive depolarization and repolarization of myocardial cells: the P wave reflects atrial depolarization; the QRS complex, ventricular depolarization; the T (and U) wave, ventricular repolarization. A standard 12-lead ECG explores the heart in the frontal plane (limb leads: DI, DII, DIII, aVR, aVL, aVF) and in the horizontal plane (precordial leads: V1 to V6). The ECG is produced at a standard paper speed of 25 mm\/s (1 small square = 0.04 sec; 1 large square = 0.20 sec) and a calibration of 10 mm\/mV (1 mm = 0.1 mV). The systematic and rigorous reading of an ECG follows a standardized sequence: heart rate \u2192 rhythm (sinus or non-sinus) \u2192 electrical axis \u2192 intervals (PR, QRS, QT\/QTc) \u2192 wave morphology (P, QRS, ST, T, U) \u2192 conclusion. A normal ECG does not exclude significant heart disease - up to 50 % of ECGs are normal in stable angina, and an ECG may be normal in the early hours of a myocardial infarction (MI); clinical correlation is therefore always essential.\n <\/div>\n\n <h2>Clinical indications of ECG<\/h2>\n <ul class=\"co-list\">\n <li><strong>Heart symptoms<\/strong> chest pain (suspected acute coronary syndrome - ACS - or pulmonary embolism); palpitations (arrhythmia - tachycardia, atrial fibrillation, flutter, ESV, SVT); syncope or lipothymia (atrioventricular block, Brugada syndrome, long QT, aortic stenosis); unexplained dyspnea (heart failure, pericarditis, tamponade); lower-limb edema (decompensated heart disease).<\/li>\n <li><strong>Preoperative and Pre-anesthetic Evaluation:<\/strong> recommended for patients \u226540-50 years of age or with cardiovascular risk factors (hypertension, diabetes, smoking, dyslipidemia, history of coronary heart disease) before any intermediate- or high-risk surgery; perioperative cardiac risk assessment (Lee score - Revised Cardiac Risk Index)<\/li>\n <li><strong>Monitoring of chronic diseases and medications:<\/strong> hypertension (left ventricular hypertrophy); heart failure (ejection fraction monitoring - indirect correlation); chronic renal failure (hyperkalemia - sharp T waves, QRS widening); QTc-prolonging drugs (class IA\/III antiarrhythmics, antipsychotics, antiemetics - domperidone, azithromycin, hydroxychloroquine, methadone); tricyclic antidepressants (QRS + PR + QTc prolongation)<\/li>\n <li><strong>Preventive health check-up and sports:<\/strong> screening for cardiopathies at risk of sudden death in athletes (Brugada syndrome, hypertrophic cardiomyopathy - HCM, Wolff-Parkinson-White syndrome - WPW, congenital long QT); pre-employment check-up (certain high-risk jobs - drivers, pilots, divers); annual check-up for patients with high cardiovascular risk factors<\/li>\n <\/ul>\n\n <h2>Systematic reading and frequent anomalies<\/h2>\n <table class=\"co-table\">\n <colgroup><col style=\"width:200px;\"><col style=\"width:42%;\"><col><\/colgroup>\n <thead>\n <tr><th>Setting \/ Anomaly<\/th><th>Normal values, mechanism, and ECG presentation<\/th><th>Clinical significance and management<\/th><\/tr>\n <\/thead>\n <tbody>\n <tr>\n <td>Heart rate and sinus rhythm<br><small style=\"font-weight:400;color:#7a8fa0;\">First reading step<\/small><\/td>\n <td>Normal frequency: 60-100 bpm (quick method: 300 \u00f7 number of large squares between 2 QRS complexes); bradycardia: 100 bpm; sinus rhythm: P wave positive in DII, negative in aVR, identical morphology before each QRS, with constant PR interval 120-200 ms; normal electrical axis: between \u221230\u00b0 and +90\u00b0 (qrs complex positive in DI and aVF); left axis deviation (\u221230\u00b0 to \u221290\u00b0): left anterior hemiblock, LVH, inferior MI; right axis deviation (+90\u00b0 to +180\u00b0): RA, pulmonary embolism, RVH, left posterior hemiblock<\/td>\n <td>Sinus bradycardia: often benign (athletes, vagotonia, sleep, medications\u2014beta-blockers, digoxin, amiodarone); symptomatic bradycardia (<40 bpm, syncope) \u2192 cardiological evaluation + ECG Holter; sinus tachycardia: always secondary (fever, pain, anemia, hypovolemia, hyperthyroidism, PE, heart failure, anxiety, medications) \u2192 treat underlying cause; non-sinus rhythm \u2192 analyze P waves and P\/QRS ratio to identify mechanism<\/td>\n <\/tr>\n <tr>\n <td>Atrial fibrillation (AF) and flutter<br><small style=\"font-weight:400;color:#7a8fa0;\">Most frequent sustained arrhythmia<\/small><\/td>\n <td>Atrial fibrillation (AFib): absence of distinct P waves \u2192 irregular isoelectric line (coarse or fine fibrillation) + completely irregular RR intervals + narrow QRS complexes (unless there's an associated bundle branch block or Wolff-Parkinson-White syndrome); variable ventricular rate (often 100\u2013160 bpm if uncontrolled); atrial flutter: sawtooth F waves at 300 bpm (best seen in leads II, III, aVF, and V1) \u2014 regular \u2014 variable ventricular conduction (most often 2:1 \u2192 HR ~150 bpm or 3:1 \u2192 HR ~100 bpm); AFib with slow ventricular response: regularly spaced QRS complexes + AFib \u2192 consider associated complete AV block (especially with digoxin).<\/td>\n <td>FA : arythmie la plus fr\u00e9quente \u2014 pr\u00e9valence 1\u20132 % adultes, 10 % apr\u00e8s 80 ans ; risque embolique majeur (AVC isch\u00e9mique \u00d75 \u2014 score CHA\u2082DS\u2082-VASc pour l'anticoagulation) ; contr\u00f4le de la fr\u00e9quence (cible <110 bpm au repos) : b\u00eatabloquants ou inhibiteurs calciques non DHP (v\u00e9rapamil, diltiazem) \u2014 ou digoxine si FEVG <40 % ; cardioversion (\u00e9lectrique ou pharmacologique \u2014 amiodarone, fl\u00e9ca\u00efnide) si FA 95 %)<\/td>\n <\/tr>\n <tr>\n <td>Atrioventricular block (AVB)<br><small style=\"font-weight:400;color:#7a8fa0;\">Nodal conduction disorders<\/small><\/td>\n <td>First-degree AV block: PR >200 ms \u2014 constant \u2014 each P wave conducts a QRS complex \u2192 benign; Second-degree AV block, Mobitz I (Wenckebach) type: progressive PR prolongation \u2192 blocked P wave (not followed by a QRS complex) \u2192 cycle repeats \u2192 often nodal \u2014 benign (vagotonia, athletes, inferior MI); Second-degree AV block, Mobitz II type: fixed PR + intermittently blocked P wave without prior PR prolongation \u2192 often infranodal (His bundle\/branches) \u2192 risk of progression to complete AV block; Third-degree AV block (complete AV block): complete atrioventricular dissociation \u2014 independent P waves and QRS complexes \u2014 junctional escape rhythm (narrow QRS, 40\u201360 bpm) or ventricular (wide QRS, 20\u201340 bpm)<\/td>\n <td>First-degree AV block and asymptomatic Mobitz I: monitoring, no urgent treatment; Mobitz II and complete AV block: indication for permanent cardiac pacing (pacemaker) \u2014 urgent if complete AV block with syncope or hemodynamic instability (0.5\u20131 mg IV atropine drip + transcutaneous pacing); common causes: inferior MI (transient nodal AV block \u2014 spontaneous recovery), Lenegre-Lev disease (idiopathic conduction tissue degeneration), medications (digoxin, beta-blockers, verapamil, amiodarone), myocarditis, sarcoidosis, Lyme disease<\/td>\n <\/tr>\n <tr>\n <td>Branch blocks (BBD \/ BBG)<br><small style=\"font-weight:400;color:#7a8fa0;\">Intraventricular conduction disorders<\/small><\/td>\n <td>Complete Right Bundle Branch Block (RBBB): QRS \u2265120 ms + rSR' or RSR' in V1 (rabbit ears) + wide S wave in I and V6 + negative T wave in V1\u2013V3 (secondary repolarization); Incomplete RBBB: same criteria but QRS 100\u2013119 ms; Complete Left Bundle Branch Block (LBBB): QRS \u2265120 ms + wide monophasic R wave in I, aVL, V5, V6 (absence of septal q) + QS or rS pattern in V1 + discordant T wave (negative where QRS is positive); New Complete LBBB: equivalent to STEMI until proven otherwise (Sgarbossa criteria); Left Anterior Fascicular Block (LAFB): left axis deviation (\u221230\u00b0 to \u221290\u00b0) + qR in I\/aVL + rS in II\/III\/aVF + QRS <120 ms<\/td>\n <td>Isolated bundle branch block: often benign (idiopathic, elderly) - no treatment if asymptomatic; bundle branch block + hemiblock = bifascicular block \u2192 risk of progression to complete heart block \u2192 monitoring + Holter; new complete bundle branch block in a patient with chest pain \u2192 treat as STEMI (urgent coronary angiography); pre-existing complete bundle branch block + chest pain \u2192 Sgarbossa criteria to detect superimposed ischemia (ST elevation \u22651 mm concordant with the QRS - most specific criterion)<\/td>\n <\/tr>\n <tr>\n <td>Ischemia and myocardial infarction (ACS)<br><small style=\"font-weight:400;color:#7a8fa0;\">Diagnostic and therapeutic emergency<\/small><\/td>\n <td>STEMI (ST-elevation myocardial infarction): ST elevation \u22651 mm in \u22652 contiguous limb leads or \u22652 mm in V1\u2013V4 \u2192 coronary territory: anterior (V1\u2013V4 \u2192 LAD); inferior (II, III, aVF \u2192 RCA or Cx); lateral (I, aVL, V5\u2013V6 \u2192 Cx); posterior (ST depression in V1\u2013V3 + dominant R \u2192 mirror image \u2014 V7\u2013V9 leads); hyperacute T wave (peaked and symmetrical T wave \u2014 very early stage); Q wave of necrosis (Q \u22650.04 sec and\/or \u226525 % of the subsequent R wave); NSTEMI \/ Unstable angina: horizontal or downward sloping ST depression \u22650.5\u20131 mm; symmetrical T wave inversion; normal ECG possible in 50 % of NSTEMI<\/td>\n <td>STEMI: Emergency reperfusion \u2014 Primary PCI (angioplasty) within 90 min (door-to-balloon time) or thrombolysis if PCI time >120 min \u2014 immediate 911 call \u2014 aspirin 325 mg + ticagrelor or clopidogrel upon diagnosis; NSTEMI: IV heparin + dual antiplatelet therapy + coronary angiography within 24\u201372h according to risk score (GRACE, TIMI); continuous ECG monitoring; repeat ECG at 15\u201330 min if initial ECG is non-diagnostic with persistent chest pain; hs troponins at H0 and H1 or H0 and H3 (ESC 2023 algorithm)<\/td>\n <\/tr>\n <tr>\n <td>QT prolongation and ion disorders<br><small style=\"font-weight:400;color:#7a8fa0;\">Risk of torsade de pointes<\/small><\/td>\n <td>QT interval measured from the beginning of QRS to the end of the T wave in lead II or V5; QTc (heart rate corrected) using Bazett's formula: QTc = QT \/ \u221aRR (seconds); normal QTc: male <440 ms, female 450 ms (male) or >470 ms (female) \u2014 risk of torsades de pointes if QTc >500 ms; causes: medications (Class IA\/III antiarrhythmics, antipsychotics, domperidone, azithromycin, methadone, hydroxychloroquine), hypokalemia (flattened T wave + prominent U wave), hypomagnesemia, hypocalcemia (prolonged ST segment), congenital long QT syndrome (Romano-Ward, Jervell-Lange-Nielsen); hyperkalemia: peaked, symmetric T waves (K\u207a 6\u20137 mmol\/L) \u2192 prolonged PR + QRS \u2192 sine wave + arrest (K\u207a >8\u20139 mmol\/L)<\/td>\n <td>QTc >500 ms: stop or substitute the responsible medication + correct electrolytes (target K\u207a >4.0 mmol\/L, Mg\u00b2\u207a >0.8 mmol\/L); torsades de pointes: IV magnesium sulfate 2 g in 5\u201310 min + temporary pacemaker (isoproterenol or pacemaker to increase HR \u2192 shorten QT); concerning hyperkalemia (widened QRS + sine wave): IV calcium gluconate 1 g in 2\u20133 min (membrane stabilization) + bicarbonate + glucose-insulin + Kayexalate or patiromer + dialysis if ARF; monitor QTc before and after introducing any QT-prolonging medication (riskQT.com \u2014 complete list)<\/td>\n <\/tr>\n <\/tbody>\n <\/table>\n\n <div class=\"co-infobox\">\n <span class=\"ico\">\u2139\ufe0f<\/span>\n <span>Visit <strong>Wolff-Parkinson-White (WPW) syndrome<\/strong> is a congenital conduction anomaly characterized by the presence of an atrioventricular accessory pathway (bundle of Kent) that bypasses the AV node \u2192 early ventricular pre-excitation. On ECG: short PR interval (<120 ms) + delta wave (slow and slurred upstroke at the beginning of the QRS) + widened QRS \u2265120 ms + secondary repolarization abnormalities (discordant T wave). WPW predisposes to reentrant tachycardias (AVRT \u2014 80 % \u2014 narrow QRS if orthodromic conduction, wide QRS if antidromic) and, in case of associated AFib, to rapid antegrade conduction through the accessory pathway (pre-excited AFib) \u2192 risk of <strong>ventricular fibrillation and sudden death<\/strong>. Pre-excited AFib on WPW (short irregular R-Rs + polymorphic wide QRSs) is a life-threatening emergency\u2014an absolute contraindication for AV node blocking drugs (adenosine, digoxin, verapamil, diltiazem) \u2192 immediate electrical cardioversion. Definitive treatment: catheter ablation of the accessory pathway (success >95 %).<\/span>\n <\/div>\n\n <div class=\"co-urgence\">\n <div class=\"co-urgence-titre\">Emergency \u2014 ECG abnormalities requiring immediate intervention<\/div>\n <p>Dial <strong>911<\/strong> immediately if an ECG shows any of the following abnormalities in a compatible clinical context: <strong>ST-segment depression in \u22652 contiguous leads<\/strong> (STEMI - reperfusion within 90 min); ; <strong>Complete AV block with severe bradycardia<\/strong> (<30\u201340 bpm) or hemodynamic instability (hypotension, syncope); ; <strong>sustained ventricular tachycardia<\/strong> (QRS wide \u2265120 ms, regular, >100 bpm, >30 sec) or <strong>ventricular fibrillation<\/strong> (chaotic pattern with no identifiable complexes) \u2192 immediate defibrillation ; <strong>Atrial Flutter with pre-excitation on WPW<\/strong> (irregular short RR + polymorphic wide QRS) \u2192 urgent electrical cardioversion ; <strong>sinusoidal wave<\/strong> (severe hyperkalemia - risk of asystole).<\/p>\n <p>A normal ECG in the context of chest pain <strong>does not exclude a SCA<\/strong> - repeat ECG at 15-30 min and measure troponin hs.<\/p>\n <\/div>\n\n <h2>Consult at Clinique Omicron<\/h2>\n <p>Clinique Omicron offers the performance and interpretation of 12-lead ECGs as part of preventive assessments, pre-operative assessments, chronic disease monitoring, and cardiovascular symptom evaluation. Results are interpreted by physicians and transmitted promptly. In case of an abnormality requiring specialized follow-up, a referral to cardiology is organized. Consultations are available at our service points in Quebec and via telemedicine for follow-up. To book an appointment, visit <a href=\"https:\/\/cliniqueomicron.ca\">cliniqueomicron.ca<\/a>.<\/p>\n\n <p class=\"co-disclaimer\">The content of this page is provided for informational purposes only and does not substitute for the advice of a qualified healthcare professional. Any acute cardiac symptoms (chest pain, palpitations, syncope) require immediate medical evaluation.<\/p>\n<\/div>\n<\/body>\n<\/html>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"<p>ECG (\u00e9lectrocardiogramme) : indications, interpr\u00e9tation et r\u00e9sultats | Clinique Omicron Cardiologie & M\u00e9decine interne & M\u00e9decine de famille ECG (\u00e9lectrocardiogramme) L’\u00e9lectrocardiogramme (ECG) est un examen non invasif, indolore et rapide qui enregistre l’activit\u00e9 \u00e9lectrique du c\u0153ur \u00e0 partir d’\u00e9lectrodes plac\u00e9es \u00e0 la surface du corps. Il constitue l’examen cardiaque de premi\u00e8re ligne le plus prescrit… <a href=\"https:\/\/cliniqueomicron.ca\/en\/ecg-electrocardiogramme\/\" rel=\"bookmark\">Read More \"<span class=\"screen-reader-text\">ECG (electrocardiogram): indications, interpretation and results | Clinique Omicron<\/span><\/a><\/p>","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"off","neve_meta_content_width":100,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","_themeisle_gutenberg_block_has_review":false,"_metasync_otto_title":"Cardiogramme normal : valeurs et interpr\u00e9tation | Omicron","_metasync_otto_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en...","_metasync_otto_keywords":"","_metasync_otto_og_title":"ECG (\u00e9lectrocardiogramme) : | Brossard | Clinique Omicron","_metasync_otto_og_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en...","_metasync_otto_twitter_title":"ECG (\u00e9lectrocardiogramme) : | Brossard | Clinique Omicron","_metasync_otto_twitter_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. 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Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en charge au Qu\u00e9bec.","_metasync_seo_title":"","_metasync_seo_desc":"","_metasync_breadcrumb_title":"","_metasync_primary_category":0,"_metasync_primary_product_cat":0,"_metasync_otto_disabled":"","_metasync_hreflang":"","_metasync_plugin_sync_ts":"{\"aioseo\":\"2026-05-04T21:53:18+00:00\"}","_metasync_robots_advanced":"","footnotes":""},"class_list":["post-24527","page","type-page","status-publish","hentry"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t<meta name=\"description\" content=\"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. 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\n\t\t\t\t\t\n\n\n\n\nECG (electrocardiogram): indications, interpretation and results | Clinique Omicron<\/title>\n<meta name=\"description\" content=\"The ECG is the gold standard for evaluating the heart. Indications, systematic reading, frequent abnormalities (AF, block, hypertrophy, ischemia) and management in Quebec.\">\n<meta name=\"keywords\" content=\"ECG \u00e9lectrocardiogramme indications, ECG interpr\u00e9tation r\u00e9sultats, \u00e9lectrocardiogramme anomalies, ECG fibrillation auriculaire, ECG bloc de branche, ECG isch\u00e9mie infarctus, ECG hypertrophie ventriculaire, ECG Qu\u00e9bec\">\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=Cinzel:wght@600&family=Poppins:wght@400;500;600;700&display=swap\" rel=\"stylesheet\">\n<style>\n.co-wrap * { font-family: 'Poppins', sans-serif; box-sizing: border-box; }\n.co-wrap { max-width: 1100px; margin: 0 auto; padding: 30px 0 60px; }\n.co-label { font-family: 'Cinzel', serif; font-size: 14px; font-weight: bold; letter-spacing: 1px; text-transform: uppercase; color: #4D6577; margin-bottom: 14px; display: block; }\n.co-wrap h1 { font-size: 32px; font-weight: 500; color: #323C52; margin: 0 0 22px; line-height: 1.2; }\n.co-intro { font-size: 16px; line-height: 1.75; color: #4D6577; margin-bottom: 36px; padding-bottom: 32px; border-bottom: 1px solid rgba(77,101,119,.2); }\n.co-wrap h2 { font-size: 20px; font-weight: 600; color: #323C52; margin: 32px 0 12px; }\n.co-wrap p { font-size: 15px; color: #4D6577; line-height: 1.7; margin-bottom: 14px; }\n.co-list { list-style: none; padding: 0; margin: 12px 0 24px; }\n.co-list li { font-size: 15px; color: #4D6577; padding: 10px 14px 10px 38px; margin-bottom: 8px; border-radius: 6px; position: relative; background: rgba(77,101,119,.06); border-left: 3px solid #4D6577; }\n.co-list li::before { content: \"\u2713\"; position: absolute; left: 12px; font-weight: 700; color: #4D6577; }\n.co-table { width: 100%; border-collapse: collapse; margin: 14px 0 22px; font-size: 14px; border-radius: 8px; overflow: hidden; table-layout: fixed; }\n.co-table thead tr { background: #323C52; color: #fff; }\n.co-table thead th { padding: 11px 16px; text-align: left; font-weight: 600; font-size: 13px; }\n.co-table tbody tr:nth-child(even) { background: rgba(77,101,119,.06); }\n.co-table tbody tr:nth-child(odd) { background: #fff; }\n.co-table td { padding: 10px 16px; color: #4D6577; border-bottom: 1px solid rgba(77,101,119,.12); font-size: 14px; vertical-align: top; }\n.co-table td:first-child { font-weight: 600; color: #323C52; }\n.co-infobox { display: flex; gap: 12px; background: rgba(77,101,119,.06); border-radius: 8px; border-left: 4px solid #4D6577; padding: 14px 18px; margin: 18px 0 28px; font-size: 14px; color: #4D6577; line-height: 1.65; }\n.co-infobox .ico { font-size: 18px; flex-shrink: 0; }\n.co-urgence { background: #fff8f8; border-left: 5px solid #c0392b; border-radius: 6px; padding: 20px 26px; margin: 24px 0 32px; }\n.co-urgence .co-urgence-titre { font-size: 13px; font-weight: 700; color: #c0392b; letter-spacing: 1.5px; text-transform: uppercase; margin-bottom: 10px; }\n.co-urgence p { color: #5a2020; font-size: 14px; margin: 0 0 10px; line-height: 1.7; }\n.co-urgence p:last-child { margin-bottom: 0; }\n.co-disclaimer { font-size: 13px; color: #8a9aaa; font-style: italic; border-top: 1px solid rgba(77,101,119,.15); padding-top: 24px; margin-top: 40px; line-height: 1.6; }\n<\/style>\n<\/head>\n<body>\n<div class=\"co-wrap\">\n <span class=\"co-label\">Cardiology & Internal Medicine & Family Medicine<\/span>\n <h1>ECG (electrocardiogram)<\/h1>\n\n <div class=\"co-intro\">\n The electrocardiogram (ECG) is a non-invasive, painless and rapid test that records the heart's electrical activity using electrodes placed on the surface of the body. It is the most widely prescribed first-line cardiac examination in medicine - available in less than 5 minutes, without risk and at low cost - and provides essential diagnostic information on heart rhythm, atrioventricular and intraventricular conduction, the morphology of the heart chambers and the state of the myocardium (ischemia, necrosis, pericarditis). The physical principle is based on the detection of electrical potential variations generated by the successive depolarization and repolarization of myocardial cells: the P wave reflects atrial depolarization; the QRS complex, ventricular depolarization; the T (and U) wave, ventricular repolarization. A standard 12-lead ECG explores the heart in the frontal plane (limb leads: DI, DII, DIII, aVR, aVL, aVF) and in the horizontal plane (precordial leads: V1 to V6). The ECG is produced at a standard paper speed of 25 mm\/s (1 small square = 0.04 sec; 1 large square = 0.20 sec) and a calibration of 10 mm\/mV (1 mm = 0.1 mV). The systematic and rigorous reading of an ECG follows a standardized sequence: heart rate \u2192 rhythm (sinus or non-sinus) \u2192 electrical axis \u2192 intervals (PR, QRS, QT\/QTc) \u2192 wave morphology (P, QRS, ST, T, U) \u2192 conclusion. A normal ECG does not exclude significant heart disease - up to 50 % of ECGs are normal in stable angina, and an ECG may be normal in the early hours of a myocardial infarction (MI); clinical correlation is therefore always essential.\n <\/div>\n\n <h2>Clinical indications of ECG<\/h2>\n <ul class=\"co-list\">\n <li><strong>Heart symptoms<\/strong> chest pain (suspected acute coronary syndrome - ACS - or pulmonary embolism); palpitations (arrhythmia - tachycardia, atrial fibrillation, flutter, ESV, SVT); syncope or lipothymia (atrioventricular block, Brugada syndrome, long QT, aortic stenosis); unexplained dyspnea (heart failure, pericarditis, tamponade); lower-limb edema (decompensated heart disease).<\/li>\n <li><strong>Preoperative and Pre-anesthetic Evaluation:<\/strong> recommended for patients \u226540-50 years of age or with cardiovascular risk factors (hypertension, diabetes, smoking, dyslipidemia, history of coronary heart disease) before any intermediate- or high-risk surgery; perioperative cardiac risk assessment (Lee score - Revised Cardiac Risk Index)<\/li>\n <li><strong>Monitoring of chronic diseases and medications:<\/strong> hypertension (left ventricular hypertrophy); heart failure (ejection fraction monitoring - indirect correlation); chronic renal failure (hyperkalemia - sharp T waves, QRS widening); QTc-prolonging drugs (class IA\/III antiarrhythmics, antipsychotics, antiemetics - domperidone, azithromycin, hydroxychloroquine, methadone); tricyclic antidepressants (QRS + PR + QTc prolongation)<\/li>\n <li><strong>Preventive health check-up and sports:<\/strong> screening for cardiopathies at risk of sudden death in athletes (Brugada syndrome, hypertrophic cardiomyopathy - HCM, Wolff-Parkinson-White syndrome - WPW, congenital long QT); pre-employment check-up (certain high-risk jobs - drivers, pilots, divers); annual check-up for patients with high cardiovascular risk factors<\/li>\n <\/ul>\n\n <h2>Systematic reading and frequent anomalies<\/h2>\n <table class=\"co-table\">\n <colgroup><col style=\"width:200px;\"><col style=\"width:42%;\"><col><\/colgroup>\n <thead>\n <tr><th>Setting \/ Anomaly<\/th><th>Normal values, mechanism, and ECG presentation<\/th><th>Clinical significance and management<\/th><\/tr>\n <\/thead>\n <tbody>\n <tr>\n <td>Heart rate and sinus rhythm<br><small style=\"font-weight:400;color:#7a8fa0;\">First reading step<\/small><\/td>\n <td>Normal frequency: 60-100 bpm (quick method: 300 \u00f7 number of large squares between 2 QRS complexes); bradycardia: 100 bpm; sinus rhythm: P wave positive in DII, negative in aVR, identical morphology before each QRS, with constant PR interval 120-200 ms; normal electrical axis: between \u221230\u00b0 and +90\u00b0 (qrs complex positive in DI and aVF); left axis deviation (\u221230\u00b0 to \u221290\u00b0): left anterior hemiblock, LVH, inferior MI; right axis deviation (+90\u00b0 to +180\u00b0): RA, pulmonary embolism, RVH, left posterior hemiblock<\/td>\n <td>Sinus bradycardia: often benign (athletes, vagotonia, sleep, medications\u2014beta-blockers, digoxin, amiodarone); symptomatic bradycardia (<40 bpm, syncope) \u2192 cardiological evaluation + ECG Holter; sinus tachycardia: always secondary (fever, pain, anemia, hypovolemia, hyperthyroidism, PE, heart failure, anxiety, medications) \u2192 treat underlying cause; non-sinus rhythm \u2192 analyze P waves and P\/QRS ratio to identify mechanism<\/td>\n <\/tr>\n <tr>\n <td>Atrial fibrillation (AF) and flutter<br><small style=\"font-weight:400;color:#7a8fa0;\">Most frequent sustained arrhythmia<\/small><\/td>\n <td>Atrial fibrillation (AFib): absence of distinct P waves \u2192 irregular isoelectric line (coarse or fine fibrillation) + completely irregular RR intervals + narrow QRS complexes (unless there's an associated bundle branch block or Wolff-Parkinson-White syndrome); variable ventricular rate (often 100\u2013160 bpm if uncontrolled); atrial flutter: sawtooth F waves at 300 bpm (best seen in leads II, III, aVF, and V1) \u2014 regular \u2014 variable ventricular conduction (most often 2:1 \u2192 HR ~150 bpm or 3:1 \u2192 HR ~100 bpm); AFib with slow ventricular response: regularly spaced QRS complexes + AFib \u2192 consider associated complete AV block (especially with digoxin).<\/td>\n <td>FA : arythmie la plus fr\u00e9quente \u2014 pr\u00e9valence 1\u20132 % adultes, 10 % apr\u00e8s 80 ans ; risque embolique majeur (AVC isch\u00e9mique \u00d75 \u2014 score CHA\u2082DS\u2082-VASc pour l'anticoagulation) ; contr\u00f4le de la fr\u00e9quence (cible <110 bpm au repos) : b\u00eatabloquants ou inhibiteurs calciques non DHP (v\u00e9rapamil, diltiazem) \u2014 ou digoxine si FEVG <40 % ; cardioversion (\u00e9lectrique ou pharmacologique \u2014 amiodarone, fl\u00e9ca\u00efnide) si FA 95 %)<\/td>\n <\/tr>\n <tr>\n <td>Atrioventricular block (AVB)<br><small style=\"font-weight:400;color:#7a8fa0;\">Nodal conduction disorders<\/small><\/td>\n <td>First-degree AV block: PR >200 ms \u2014 constant \u2014 each P wave conducts a QRS complex \u2192 benign; Second-degree AV block, Mobitz I (Wenckebach) type: progressive PR prolongation \u2192 blocked P wave (not followed by a QRS complex) \u2192 cycle repeats \u2192 often nodal \u2014 benign (vagotonia, athletes, inferior MI); Second-degree AV block, Mobitz II type: fixed PR + intermittently blocked P wave without prior PR prolongation \u2192 often infranodal (His bundle\/branches) \u2192 risk of progression to complete AV block; Third-degree AV block (complete AV block): complete atrioventricular dissociation \u2014 independent P waves and QRS complexes \u2014 junctional escape rhythm (narrow QRS, 40\u201360 bpm) or ventricular (wide QRS, 20\u201340 bpm)<\/td>\n <td>First-degree AV block and asymptomatic Mobitz I: monitoring, no urgent treatment; Mobitz II and complete AV block: indication for permanent cardiac pacing (pacemaker) \u2014 urgent if complete AV block with syncope or hemodynamic instability (0.5\u20131 mg IV atropine drip + transcutaneous pacing); common causes: inferior MI (transient nodal AV block \u2014 spontaneous recovery), Lenegre-Lev disease (idiopathic conduction tissue degeneration), medications (digoxin, beta-blockers, verapamil, amiodarone), myocarditis, sarcoidosis, Lyme disease<\/td>\n <\/tr>\n <tr>\n <td>Branch blocks (BBD \/ BBG)<br><small style=\"font-weight:400;color:#7a8fa0;\">Intraventricular conduction disorders<\/small><\/td>\n <td>Complete Right Bundle Branch Block (RBBB): QRS \u2265120 ms + rSR' or RSR' in V1 (rabbit ears) + wide S wave in I and V6 + negative T wave in V1\u2013V3 (secondary repolarization); Incomplete RBBB: same criteria but QRS 100\u2013119 ms; Complete Left Bundle Branch Block (LBBB): QRS \u2265120 ms + wide monophasic R wave in I, aVL, V5, V6 (absence of septal q) + QS or rS pattern in V1 + discordant T wave (negative where QRS is positive); New Complete LBBB: equivalent to STEMI until proven otherwise (Sgarbossa criteria); Left Anterior Fascicular Block (LAFB): left axis deviation (\u221230\u00b0 to \u221290\u00b0) + qR in I\/aVL + rS in II\/III\/aVF + QRS <120 ms<\/td>\n <td>Isolated bundle branch block: often benign (idiopathic, elderly) - no treatment if asymptomatic; bundle branch block + hemiblock = bifascicular block \u2192 risk of progression to complete heart block \u2192 monitoring + Holter; new complete bundle branch block in a patient with chest pain \u2192 treat as STEMI (urgent coronary angiography); pre-existing complete bundle branch block + chest pain \u2192 Sgarbossa criteria to detect superimposed ischemia (ST elevation \u22651 mm concordant with the QRS - most specific criterion)<\/td>\n <\/tr>\n <tr>\n <td>Ischemia and myocardial infarction (ACS)<br><small style=\"font-weight:400;color:#7a8fa0;\">Diagnostic and therapeutic emergency<\/small><\/td>\n <td>STEMI (ST-elevation myocardial infarction): ST elevation \u22651 mm in \u22652 contiguous limb leads or \u22652 mm in V1\u2013V4 \u2192 coronary territory: anterior (V1\u2013V4 \u2192 LAD); inferior (II, III, aVF \u2192 RCA or Cx); lateral (I, aVL, V5\u2013V6 \u2192 Cx); posterior (ST depression in V1\u2013V3 + dominant R \u2192 mirror image \u2014 V7\u2013V9 leads); hyperacute T wave (peaked and symmetrical T wave \u2014 very early stage); Q wave of necrosis (Q \u22650.04 sec and\/or \u226525 % of the subsequent R wave); NSTEMI \/ Unstable angina: horizontal or downward sloping ST depression \u22650.5\u20131 mm; symmetrical T wave inversion; normal ECG possible in 50 % of NSTEMI<\/td>\n <td>STEMI: Emergency reperfusion \u2014 Primary PCI (angioplasty) within 90 min (door-to-balloon time) or thrombolysis if PCI time >120 min \u2014 immediate 911 call \u2014 aspirin 325 mg + ticagrelor or clopidogrel upon diagnosis; NSTEMI: IV heparin + dual antiplatelet therapy + coronary angiography within 24\u201372h according to risk score (GRACE, TIMI); continuous ECG monitoring; repeat ECG at 15\u201330 min if initial ECG is non-diagnostic with persistent chest pain; hs troponins at H0 and H1 or H0 and H3 (ESC 2023 algorithm)<\/td>\n <\/tr>\n <tr>\n <td>QT prolongation and ion disorders<br><small style=\"font-weight:400;color:#7a8fa0;\">Risk of torsade de pointes<\/small><\/td>\n <td>QT interval measured from the beginning of QRS to the end of the T wave in lead II or V5; QTc (heart rate corrected) using Bazett's formula: QTc = QT \/ \u221aRR (seconds); normal QTc: male <440 ms, female 450 ms (male) or >470 ms (female) \u2014 risk of torsades de pointes if QTc >500 ms; causes: medications (Class IA\/III antiarrhythmics, antipsychotics, domperidone, azithromycin, methadone, hydroxychloroquine), hypokalemia (flattened T wave + prominent U wave), hypomagnesemia, hypocalcemia (prolonged ST segment), congenital long QT syndrome (Romano-Ward, Jervell-Lange-Nielsen); hyperkalemia: peaked, symmetric T waves (K\u207a 6\u20137 mmol\/L) \u2192 prolonged PR + QRS \u2192 sine wave + arrest (K\u207a >8\u20139 mmol\/L)<\/td>\n <td>QTc >500 ms: stop or substitute the responsible medication + correct electrolytes (target K\u207a >4.0 mmol\/L, Mg\u00b2\u207a >0.8 mmol\/L); torsades de pointes: IV magnesium sulfate 2 g in 5\u201310 min + temporary pacemaker (isoproterenol or pacemaker to increase HR \u2192 shorten QT); concerning hyperkalemia (widened QRS + sine wave): IV calcium gluconate 1 g in 2\u20133 min (membrane stabilization) + bicarbonate + glucose-insulin + Kayexalate or patiromer + dialysis if ARF; monitor QTc before and after introducing any QT-prolonging medication (riskQT.com \u2014 complete list)<\/td>\n <\/tr>\n <\/tbody>\n <\/table>\n\n <div class=\"co-infobox\">\n <span class=\"ico\">\u2139\ufe0f<\/span>\n <span>Visit <strong>Wolff-Parkinson-White (WPW) syndrome<\/strong> is a congenital conduction anomaly characterized by the presence of an atrioventricular accessory pathway (bundle of Kent) that bypasses the AV node \u2192 early ventricular pre-excitation. On ECG: short PR interval (<120 ms) + delta wave (slow and slurred upstroke at the beginning of the QRS) + widened QRS \u2265120 ms + secondary repolarization abnormalities (discordant T wave). WPW predisposes to reentrant tachycardias (AVRT \u2014 80 % \u2014 narrow QRS if orthodromic conduction, wide QRS if antidromic) and, in case of associated AFib, to rapid antegrade conduction through the accessory pathway (pre-excited AFib) \u2192 risk of <strong>ventricular fibrillation and sudden death<\/strong>. Pre-excited AFib on WPW (short irregular R-Rs + polymorphic wide QRSs) is a life-threatening emergency\u2014an absolute contraindication for AV node blocking drugs (adenosine, digoxin, verapamil, diltiazem) \u2192 immediate electrical cardioversion. Definitive treatment: catheter ablation of the accessory pathway (success >95 %).<\/span>\n <\/div>\n\n <div class=\"co-urgence\">\n <div class=\"co-urgence-titre\">Emergency \u2014 ECG abnormalities requiring immediate intervention<\/div>\n <p>Dial <strong>911<\/strong> immediately if an ECG shows any of the following abnormalities in a compatible clinical context: <strong>ST-segment depression in \u22652 contiguous leads<\/strong> (STEMI - reperfusion within 90 min); ; <strong>Complete AV block with severe bradycardia<\/strong> (<30\u201340 bpm) or hemodynamic instability (hypotension, syncope); ; <strong>sustained ventricular tachycardia<\/strong> (QRS wide \u2265120 ms, regular, >100 bpm, >30 sec) or <strong>ventricular fibrillation<\/strong> (chaotic pattern with no identifiable complexes) \u2192 immediate defibrillation ; <strong>Atrial Flutter with pre-excitation on WPW<\/strong> (irregular short RR + polymorphic wide QRS) \u2192 urgent electrical cardioversion ; <strong>sinusoidal wave<\/strong> (severe hyperkalemia - risk of asystole).<\/p>\n <p>A normal ECG in the context of chest pain <strong>does not exclude a SCA<\/strong> - repeat ECG at 15-30 min and measure troponin hs.<\/p>\n <\/div>\n\n <h2>Consult at Clinique Omicron<\/h2>\n <p>Clinique Omicron offers the performance and interpretation of 12-lead ECGs as part of preventive assessments, pre-operative assessments, chronic disease monitoring, and cardiovascular symptom evaluation. Results are interpreted by physicians and transmitted promptly. In case of an abnormality requiring specialized follow-up, a referral to cardiology is organized. Consultations are available at our service points in Quebec and via telemedicine for follow-up. To book an appointment, visit <a href=\"https:\/\/cliniqueomicron.ca\">cliniqueomicron.ca<\/a>.<\/p>\n\n <p class=\"co-disclaimer\">The content of this page is provided for informational purposes only and does not substitute for the advice of a qualified healthcare professional. Any acute cardiac symptoms (chest pain, palpitations, syncope) require immediate medical evaluation.<\/p>\n<\/div>\n<\/body>\n<\/html>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"<p>ECG (\u00e9lectrocardiogramme) : indications, interpr\u00e9tation et r\u00e9sultats | Clinique Omicron Cardiologie & M\u00e9decine interne & M\u00e9decine de famille ECG (\u00e9lectrocardiogramme) L’\u00e9lectrocardiogramme (ECG) est un examen non invasif, indolore et rapide qui enregistre l’activit\u00e9 \u00e9lectrique du c\u0153ur \u00e0 partir d’\u00e9lectrodes plac\u00e9es \u00e0 la surface du corps. Il constitue l’examen cardiaque de premi\u00e8re ligne le plus prescrit… <a href=\"https:\/\/cliniqueomicron.ca\/en\/ecg-electrocardiogramme\/\" rel=\"bookmark\">Read More \"<span class=\"screen-reader-text\">ECG (electrocardiogram): indications, interpretation and results | Clinique Omicron<\/span><\/a><\/p>","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"off","neve_meta_content_width":100,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","_themeisle_gutenberg_block_has_review":false,"_metasync_otto_title":"Cardiogramme normal : valeurs et interpr\u00e9tation | Omicron","_metasync_otto_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en...","_metasync_otto_keywords":"","_metasync_otto_og_title":"ECG (\u00e9lectrocardiogramme) : | Brossard | Clinique Omicron","_metasync_otto_og_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en...","_metasync_otto_twitter_title":"ECG (\u00e9lectrocardiogramme) : | Brossard | Clinique Omicron","_metasync_otto_twitter_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. Indications, lecture syst\u00e9matique, anomalies fr\u00e9quentes (FA, bloc, hypertrophie, isch\u00e9mie) et prise en...","rank_math_title":"","rank_math_description":"","_yoast_wpseo_title":"","_yoast_wpseo_metadesc":"","_aioseo_title":"ECG (\u00e9lectrocardiogramme) : indications, interpr\u00e9tation et r\u00e9sultats | Clinique Omicron","_aioseo_description":"L'ECG est l'examen de r\u00e9f\u00e9rence pour \u00e9valuer le c\u0153ur. 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