ekg lecture 1
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An Approach to EKGs
By: Siraj Mithoowani & Richa Parashar 2012Medical Education Interest Group
The EKG Lecture Series
• What these lectures are:– An introduction to EKG interpretation– Focused on clinically relevant material– A safe forum to participate, practice and make
mistakes
• What these lectures aren’t:– A comprehensive course in electrophysiology
Schedule
• Week One: Introduction, Cardiac Physiology and Electrophysiology
• Week Two: Approach to EKG Intepretation, Rate, Rhythm• Week Three: Axis and Hypertrophy• Week Three: Tachyarrhythmias• Week Four: Bradyarrhythmias, Conduction Abnormalities• Week Five: Ischemic Changes & Electrolyte Abnormalities• Week Six: Review and Q&A
• Check the medportal calendar/forums/facebook for updates!
Recommended resources
• Dubin’s Rapid Interpretation of EKGs• Lilly, EKG Chapter• ECG Wave Maven (Harvard)
(http://ecg.bidmc.harvard.edu)• ECG Made Simple (UofT)
(http://www.ecgmadesimple.com/)• BMJ ABCs of EKGs (on Medportal IM Clerkship page)• Our Medportal forum posts• Your tutors, preceptors, residents...
Agenda
• Why study EKG interpretation?• What does the EKG tell you?• Basic cardiac anatomy/physiology• Introduction to EKGs• Lead placement• Physiology of the waveform (P, QRS, T)
Why study EKG interpretation?
• They’re everywhere!• Relevant to all specialties– (Yes, even Psychiatry)
• The earlier you learn, the earlier you start practicing in real life
• Look like a superstar (superclerk?) on the wards
What does the EKG tell you?
• Ischemia/infarction• Conduction
– Heart block, bundle branch block...• Rhythm
– Atrial fibrillation, ventricular tachycardia...• Anatomy
– Left ventricular hypertrophy...• Electrolytes
– Hyperkalemia, hypocalcemia...
• Remember, the EKG is a non-invasive diagnostic test that can be performed in minutes
Anatomy and blood flowSVC/IVC
Right Atrium
Right Ventricle
Pulmonary Artery
LUNGS
Pulmonary Vein
Left Atrium
Left Ventricle
Aorta
Illustration: NIAAA/Chung, M.K., and Rich, M.W. Introduction to the cardiovascular system. Alcohol Health and Research World 14(4):269–276, 1990.
The cardiac cycle
Illustration: Guyton's: Textbook of Medical Physiology, 10th Edition. 2000. Chapter 9 . Page 99.
Blood Supply
The conduction system
Illustration: University of the West of England, Bristol. http://hsc.uwe.ac.uk/rcp/cs-heart-inside.aspx
SA node (60 – 100 bpm)
AV node (40 – 60 bpm)
Bundle of His
Left Bundle Branch (2) and Right Bundle Branch
Purkinje Fibers
Myocardial cells (20 – 40 bpm)(endocardium outwards)
Ye olde action potential
Illustration: Wikipedia (Cardiac action potential). http://en.wikipedia.org/wiki/Cardiac_action_potential.
At last... the EKG
EKG: University of Nebraska, Department of Internal Medicine. http://www.unmc.edu/intmed/geriatrics/ekgs.htm.
EKG paper
Amplitude: 1 small box = 1 mm = 0.1 mVTime: 1 small box = 40 ms = 0.04 seconds
1 large box = 200 ms = 0.2 secondsLength of EKG paper = 10 seconds
Illustration: Wikipedia (ECG). http://upload.wikimedia.org/wikipedia/commons/9/96/ECG_Paper_v2.svg.
EKG Leads
• Electrodes placed on the skin that pick up the current
• “View” the heart from different directions• Current towards the electrodes, or
repolarization going away = positive deflection on the EKG
• Current going away the electrodes = negative deflection
Lead Axes
• 12 leads in a standard EKG• Imagine the body sectioned two ways:– Frontal – represents the zones of the limb leads– Transverse – represents the zones of the
precordial leads• Limb leads: I, II, II, avR, avL, avF• Precordial leads: V1 to V6
Precordial leads: V1 to V6
Limb leads: I, II, II, avR, avL, avF
Inferior: II, III, AVF
Anterior: V1, V2, V3, V4
Lateral: I, AVL, V5, V6
The Typical Wave Form
P wave
• Represents atrial depolarization– Starting at the sinus node
• The first and second halves represent right and left atrial depolarization respectively
• Atrial repolarization is usually buried in the QRS complex
• <0.12 seconds (3 small squares)
P-R Interval
• From the beginning of the P wave to the first deflection after
• Represents conduction through the AV node (delay) and the His-Purkinje system.
• Anatomically, this delay allows for ___ ?
• Normal length: 0.12 to 0.20 s (3 to 5 small squares)
QRS Complex
• Represents ventricular depolarization– Septal depolarization from left to right– Ventricular depolarization (dominated by the left
ventricle)– Endo- to epicardium
• Q waves: marker for infarcts• Width of the QRS complex• Normal width: </= 0.12 s (3 small boxes)
QRS Complex
ST Segment
• Represents the isoelectric period between depolarization and repolarization
• Elevation/depression can be a marker for ischemia
T wave
• Represents ventricular repolarization• Normally upright (inverted in avR and III)
QT Interval
• Represents the whole of ventricular depolarization and repolarization
• Long QT predisposes patient to lethal arrhythmias
• Changes with heart rate • QTc
U wave
• ???• May represent repolarization of the His-
Purkinje system• Present in hypokalemia• Can be confused for T waves
TP segment
BASELINE
Putting it all together…whew!
Next week…
• Begin reading EKGs!• Rate, rhythm, axis, intervals• Email: richa.parashar@medportal.ca,
siraj.mithoowani@medportal.ca• FB page and medportal
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