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Making sense of the ECG
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Aims
• Clinical role/Purpose • Anatomic Correla3on -‐ normal -‐ abnormal • Systema3c approach to an ECG • In Context
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Purpose of ECG
• Screen • Diagnose • Monitor -‐ An instantaneous screenshot of the heart: hence need for serial ECGs or long strip ECGs
-‐ An examina3on of the wiring of the heart
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Different modali3es of heart imaging
• CXR – visualise heart size, aor3c knuckle, heart posi3on, lung pathology
• 2DECHO – valve patency, func3on and heart func3on/volumes
• Angiography – heart vasculature, vessel occlusion • CT/MRI – Visualise heart, vessels, pericardium, collec3ons like pericardial effusion
• PET scan – muscle metabolic func3on, very rare
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What about the ECG?
• Only modality that can give you a picture of the wiring and precise rhythm of the heart
• Arrhythmias are an important category of heart disease
• Implicated in mul3ple pathologies
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Impulse
• Describe the electrical anatomy of the impulse.
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Impulse
• SA node – Innerva3on? • AV node – func3on? • Bundle of His • LeV (ant. & pos.) and right bundle • (Myocardium) – impulse spreads via gap junc3ons
• most efficient pathway -‐ like a highway
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Placing the 12-‐lead ECG
• If I am now a medical student, and I’m learning how to place an ECG, walk me through the process.
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Placing the 12-‐lead ECG
• 3(4) Limbs, 6 pre-‐cordial -‐ 4th and 5th IC space • I, II, III are calculated from aVL, aVR and aVF • Diff groups of lead look at diff parts of the heart
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From: lifeinthefastlane
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The ECG paper
• usually calibrated @ 25mm/s • therefore 1 small square is 0.04s or 40 ms • 1 big square is 0.2s or 200ms • dura3on of squares change with calibra3on change
• you “slow down” the ecg as your paper speed increases
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First Principles
• Wave of depolarisa3on registers posi3ve when it moves toward a lead; registers nega3ve when it move away from a lead
• true of repol waves too, but in reverse
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The Cardiac Cycle
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Parts of the ECG
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P wave
• Atrial contrac3on • SA node > R atrium (via Bachmann Bundle) L atrium
• you do not see the SA node depolarisa3on • P wave the result of synchronised atrial contrac3on with origin from SA node
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What can go wrong?
• No P • Weird P • Many weird Ps • “Taller” P • P with 2 peaks
• Sinus rhythm -‐ what does this mean?
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QRS complex
• what is q, r & s? • corresponds to ventricular depol • usually less than 0.12s (how many ms is that? how many small squares is that?)
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What can go wrong?
• Length • Morphology -‐ shape & voltage • Both • what goes on behind this?
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R wave progression
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ST-‐segment
• s3ll corresponds to ventricular depolarisa3on • normally isoelectric or slightly raised • J-‐point to end of T-‐wave
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What can go wrong?
• elevated -‐ regional or global • w/ reciprocal changes • depression -‐ may or may not be due to ischemic changes
• length -‐ prolonged in hypocal, shortened in hypercal
• morphology
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T-‐waves
• corresponds to ventricular repolarisa3on • typically nega3ve in aVR & V1 • usually broader and asymmetrical
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What can go wrong?
• too tall • peaked • too short • inverted • biphasic • camel hump
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Intervals & dura3ons
• PR -‐ 0.12-‐0.2 -‐ what can go wrong? • QRS -‐ <0.12 • RR -‐ how is it related to heart rate? • QT -‐ QT vs QTc
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lead aVR
• an important marker to check before reading any ECG
• what is aVR normally? • VT • Pacemaker • extreme RAD • wrong leads • dextrocardia
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Therefore, an approach
• aVR • Sinus or non-‐sinus -‐ look for P waves • regular or irregular • tachy or brady • Axis • QRS T wave > P wave • ST segment • Intervals • R-‐wave progression • any other observa3ons 34
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Now It’s your turn to try (:
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Some 3ps
• Go big to small • do not skip steps • even if you manage to eyeball pathologies, s3ll be thorough
• break ECGs down into sec3ons if complicated • come up with possible differen3als based on scenarios/context
• some things you won’t see unless you look for it • don’t overread (:
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Context
• syncope • chest pain • breathlessness • palpita3ons • LoC • weakness • shock
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Chest Pain • 65/Chi/Male • Sudden onset chest pain. Central. Radiates to both arms. Associated with vomi3ng.
• what is your approach? • what if he had 2 weeks history of fever and produc3ve cough? • what if he is a known chronic smoker? • what if you find absent breath sounds on one side? • what if he were very tall and had long finger and limbs? • what if this pa3ent just underwent an OGD? • what if this pa3ent is a known Colon CA pa3ent? • what if the pain was pinpoint and reproducible with movement and pressure?
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Chest Pain
Non-life threatening Life-threatening
AMI
PE
Aortic dsxn MSK
Lung
Cardiac
Oesoph Rupture
Uns Angina
Superficial GI
Psychogenic
Pleuritic
Parenchymal
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Breathlessness
• 70/Indian/Female • acute onset breathlessness of 1 day. Sore throat, mild fever, cough. No travel Hx. Chronic smoker.
• what is your approach? causes? • what if she has a family hx of AMI? • what if she has some leg swelling? • what if she just returned from US? • what if she was a known HCC pa3ent? • what if she had severe diarrhoea 2 weeks ago? • what if she was a known T1DM pt? • in which of these would an ECG be helpful? 41
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SoB
Pulmonary Cardiac Others
ACS
CCF
Tamponade
Airway
Parenchymal
Pleura
PE
Metab
Neuro
Sepsis
MSK Anemia
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Syncope • 30/Malay/Male • sudden onset of syncope, brought to Emergency department. men3on he could feel his heart bea3ng very fast before he fainted. No significant PMHx or Rxhx
• define syncope • causes? • what if he had a PMHx of a previous AMI? • what if he had recurrent atacks • what if he has a long standing hx of uncontrolled T2DM • what if he has a pacemaker implanted? • what if he has long standing HTN and recently changed medica3on? • in which of these scenarios is the ECG helpful? 43
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Syncope
Orthostatic Reflex Cardiac
Vasovagal
Situational
Carotid Sinus
Primary
Secondary
Volume
Drugs
structure
rhythms
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For M3
• Normal ECG • Sinus Tachy/Brady • Heart Blocks • STEMI/NSTEMI • VT • VF • AF • AFlut
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Resources
• ECG made easy, Hampton • The only EKG Book You’ll Ever Need, Malcolm S. Thaler
• learntheheart.com • lifeinthefastlane.com • various ECG quizzes e.g. 6-‐second ECG quiz
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