BASIC ECG By: Ashish Jai Kishan Moderator: Dr Anil Saxena

History :

History 1842- Carlo Matteucci -electricity is a/w hrt beat 1876- Marey - electric pattern of frog’s heart 1895 - William Einthoven - invention of EKG 1906- Einthoven diagnoses some heart problems 1924 - Noble prize - Einthoven for EKG

History :

History 1938 -AHA & Cardiac society of great Britain defined position of chest leads 1942- Goldberger increased Wilson’s Unipolar lead voltage by 50% & made Augmented leads

ECG interpretation - step-by-step :

ECG interpretation - step-by-step Rate Rhythm Cardiac Axis P – wave PR - interval QRS Complex ST Segment QT interval (T & U wave) Other ECG signs

ELEMENTS OF ECG:

ELEMENTS OF ECG

Cardiac Electrophysiology:

Cardiac Electrophysiology Electrical activity is governed by multiple transmembrane ion conductance changes 3 types of cardiac cells 1. Pacemaker cells - SA node, AV node 2. Specialised conducting tissue - Purkinje fibres 3. Cardiac myocytes

Pacemakers of Heart:

Pacemakers of Heart SA Node - Dominant pacemaker -intrinsic rate of 60 - 100 beats/minute . AV Node - 40 - 60 beats/minute. Ventricular cells - 20 - 45 beats/minute .

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S Allen 2003

Electrocardiogram:

Electrocardiogram Is a recording of electrical activity of heart conducted thru ions in body to surface 13-60

Waveforms & Intervals:

Waveforms & Intervals

Segments and Intervals:

Segments and Intervals Segment – Straight line b/w waves Interval – wave + segment ST segment – end of ventricular depolarization to start of vent. repolarization QT interval – ventricular cycle, 40% of each cardiac cycle

ECG Graph Paper :

ECG Graph Paper Runs at a paper speed of 25 mm/sec Each small block of ECG paper is 1 mm 2 At speed of 25 mm/s, 1 small block = 0.04 s 5 small blocks make up 1 large block = 0.20 s Hence, there are 5 large blocks/sec Voltage: 1 mm = 0.1 mV between each individual block vertically

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Depolarization of both atria Relationship b/w P & QRS - distinguish various arrhythmias Shape & duration of P - indicate atrial enlargement P Wave

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Always +ve in lead I & II Always -ve in lead aVR <3 small sqs - duration <2.5 small sqs - amplitude Biphasic in lead V1 Best seen in lead II P Wave

P Pulmonale:

P Pulmonale P MITRALE

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Onset of P wave to onset of QRS Normal = 0.12 - 2.0 sec Represents A to V conduction time (via His bundle) Prolonged PR interval indicate AV block PR INTERVAL

Short PR Interval:

Short PR Interval WPW Sx Accessory pathway (Bundle of Kent) - early activation of the ventricle (delta wave & short PR interval)

Short PR Interval:

Short PR Interval WPW Sx Accessory pathway (Bundle of Kent) - early activation of the ventricle (delta wave & short PR interval)

Long PR Interval:

Long PR Interval 1 st degree Heart Block

Ventricular Depolarization:

Ventricular Depolarization Includes Bundle of His Bundle Branches Right Left Septal Anterior Posterior Terminal Purkinjie fibers

Ventricular Depolarization:

Ventricular Depolarization Ventricular Waves Q wave – 1 st downward deflection after P wave Rwave – 1 st upward deflection after Q wave R` wave – any second upward deflection S wave – 1 st downward deflection after R wave

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Ventricular depolarization Is > P wave d/t > Ventricular mass Normal duration = 0.08 - 0.12 secs Q wave >1/3 the height of R wave, >0.04 sec –abnormal; may represent MI QRS COMPLEX

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Connects QRS complex & T wave Duration = 0.08 - 0.12 sec ST Segment

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“small to moderate” size +ve deflection wave after QRS complex, Ht is 1/3 rd - 2/3 rd that of corresponding R wave Septal repolarization (not always seen on ECG) T Wave U Wave

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Beginning of QRS to end of T wave Normal QT is usually about 0.40 sec QT varies based on HR- faster HR ,shorter QT . Hence QTc . Bazett’s formula: QT C = QT / √ RR Fredericia’s formula: QT C = QT / RR 1/3 Framingham formula: QT C = QT + 0.154 (1 – RR) Hodges formula: QT C = QT + 1.75 (HR– 60) QT Interval

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Bazett’s formula -most commonly used d/t its simplicity. H/E over-corrects at HR> 100 bpm & under-corrects at HR < 60 bpm , but adequate for HR 60 – 100 bpm . HR >100 bpm range- Fredericia / Framingham If ECG is fortuitously captured while patient’s HR= 60 bpm , absolute QT interval should be used QT Interval

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Maximum slope intercept method - end of T wave as the intercept b/w isoelectric line with tangent drawn through maximum down slope of the T wave When notched T waves are present- tangent drawn from maximum down slope of the 2 nd notch, T2

Some causes of prolonged QT :

Some causes of prolonged QT CAD Cardiomyopathy Severe Bradycardia, High-Grade AV Block Anti-Arrhythmics Psychotropic Drugs HypoCa, Autonomic dysfunction Hypothyroid Hypothermia Congenital Long QT Syndrome

ECG interpretation - step-by-step :

ECG interpretation - step-by-step Rate Rhythm Cardiac Axis P – wave PR - interval QRS Complex ST Segment QT interval (T & U wave) Other ECG signs

CALCULATING RATE 300 number of BIG SQUARE b/w R-R Rate = lead II - rhythm strip . Look at # of square b/w one R-R interval. 1500 number of SMALL SQUARE b/w R-R OR Rate =

Rhythm irregular - # of beats in a 6-sec X by 10 CALCULATING RATE 1 2 3 4 5 6 7 8 = (Number of waves in 6-sec strips) x 10 = 8 x 10 = 80 bpm Rate There are 8 waves in this 6-seconds strip.

Rhythm:

Rhythm

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P -QRS relationships- Lead II is commonly used Regular or irregular? Ventricular rhythm –measured by R-R interval & Atrial rhythm - measured P-P interval. RHYTHM

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RHYTHM ECG rhythm -usual rate b/w 60-99 bpm, every P wave must be followed by a QRS & every QRS is preceded by P wave. P wave is upright in leads I and II Normal Sinus Rhythm

Axis :

Axis

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AXIS Axis refers to general direction of heart's depolarization wave front (or mean electrical vector) in the frontal plane. In healthy conducting system - axis is related to where the major muscle bulk of heart lies.

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William Einthoven developed a system capable of recording small signals & recorded 1 st ECG. Leads were based on Einthoven triangle a/w limb leads. Leads put heart in middle of a triangle

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Excitation begins at SA node atrial walls Cannot propagate across the boundary b/w atria & ventricle Resultant vector - in yellow Projections on Leads I, II and III are all +ve ECG Signal c

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ECG Signal AV node located on A-V boundary & provides conducting path Delay - allow ventricles to fill. Excitation begins with septum

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ECG Signal Depolarization Via bundle branches towards apex Overall electric vector points toward apex as both LV & RV depolarize & begin to contract

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ECG Signal Depolarization of RV reaches epicardium . LV wall is thicker & continues to depolarize

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ECG Signal As there is no compensating electric forces on Rt, electric vector reaches maximum size & points Lt Note: atria ‘ve repolarized, but signal is not seen

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ECG Signal Depolarization front continues to propagate to back of LV wall Electric vector < in size as there is less tissue depolarizing

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ECG Signal Depolarization of ventricles is complete & the electric vector has returned to zero

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ECG Signal Ventricular REPOLARIZATION begins from epicardium with left being slightly dominant

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ECG Signal Note that this produces an electric vector that is directed as the depolarization traveling in opposite direction Repolarization is diffuse & generates a smaller and longer signal than depolarization

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ECG Signal Upon complete repolarization, hrt is ready to go again & we record an ECG trace

ECG Information :

ECG Information 12 leads allow tracing of vector in all 3 planes

Axis Determination & Deviation What is Axis? “The general direction of electrical impulses as they travel through heart” “Sum total of all electrical currents generated by ventricular myocardium during depolarization” Normally from upper Rt to lower Lt

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector There are 3 basic "laws" of Electrocardiography. These "laws" ‘ ve to do with the direction of flow of electrical conduction in the heart or what we term as vector.

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector 1. Movement of electrical impulse towards + ve electrode will result in a + ve deflection on ECG. - + =

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector 2. Movement of electrical impulse toward – ve electrode will result in a – ve deflection on the ECG. - + =

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector 3. Movement of electrical impulse perpendicular to a line b/w + ve & - ve electrodes results in a bi- phasic (part upright & part downward) deflection on ECG. - + =

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AXIS

Basics of 12 Lead ECG's Determining AXIS :

Basics of 12 Lead ECG's Determining AXIS Technique #1: Two Lead Method or Quadrant Method Uses just 2 leads of the 6 limb leads Look at Lead I & aVF

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1. Lead I & aVF divide thorax into quadrants, (Lt, N , Rt, No Man's) 2. If Lead I & aVF are both upright- Axis is normal. 3. If lead I is upright & lead aVF is downward - Axis is Left. AXIS

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4. If lead aVF is upright & lead I is downward - Axis is Rt 5. If both leads are downward - Axis is extreme Right Shoulder & most often is Vent. Tachy AXIS

Axis Determination:

Axis Determination Quick Axis Determination Determine net deflection in Leads I & aVF (+ve / -ve ) Lead I aVF N axis LAD RAD ERAD

The Quadrant Approach:

The Quadrant Approach

Quadrant Approach: Example 1:

Quadrant Approach: Example 1 /

Quadrant Approach: Example 2:

Quadrant Approach: Example 2 /

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector Method 2 : Three Lead technique This method uses – 3 limb leads I, II, III to determine axis of the QRS.

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Axis Lead I Lead II Lead III Normal Positive Positive Positive/Negative Right axis deviation Negative Positive Positive Left axis deviation Positive Negative Negative

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector Method # 3: Using Hexaxial Diagram to find degree of Axis Deviation This technique - most accurate( + or – 10 0 to 15 0 )

The Equiphasic Approach:

The Equiphasic Approach See which lead contains - most equiphasic QRS. Net vector is perpendicular this lead. Examine QRS in whichever lead lies 90° away from this lead. If QRS in this 2 nd lead is predominantly +ve, then axis of this lead is approx same as net QRS axis. If QRS is predominantly –ve , than net QRS- axis lies 180° from axis of this lead.

Basics of 12 Lead ECG Vector :

Basics of 12 Lead ECG Vector Axis scale

Hexaxial Array for Axis Determination :

Determination of angle of HEART AXIS in frontal plain Hexaxial Array for Axis Determination

Example 1 :

Example 1 Lead I Lead aVF Lead aVL

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Lead I If lead I is mostly + ve , the axis must lie in Rt ½ of coordinate system

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If lead AVF is mostly + ve , the axis must lie in the bottom ½ of coordinate system Lead AVF

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I AVF Combining the 2 plots, we see that axis must lie in bottom right hand quadrant

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I AVF AVL

Example 2:

Example 2 Lead I Lead aVF Lead II

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Example 2 Lead I Lead I is mostly - ve , the axis must lie in the Lt ½ of the coordinate.

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Lead AVF Lead aVF is mostly + ve , the axis must lie in the bottom ½ of the coordinate

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I AVF Combining the two plots- axis must lie in bottom Lt hand quadrant (RAD)

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I AVF II

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Since Lead III is the most equiphasic lead and it is slightly more positive than negative, this axis could be estimated at about 40 o . Precise calculation of the axis can be done using the coordinate system to plot net voltages of perpendicular leads, drawing a resultant rectangle, then connecting the origin of the coordinate system with the opposite corner of the rectangle. A protractor can then be used to measure the deflection from 0. Net voltage = 12 Net voltage = 7 Precise Axis Calculation

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CARDIAC AXIS

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Positive Positive Positive N Axis CARDIAC AXIS

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CARDIAC AXIS

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Positive Negative Negative LAD CARDIAC AXIS

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CARDIAC AXIS

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Negative Positive Positive RAD CARDIAC AXIS

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Cardiac Axis Causes LAD Preg , obesity; Ascites , abdo distention, tumour ; LAHB, LVH, IWMI RAD N finding in children & tall thin adults, COPD, LPHB, Anterolateral MI. North West E mphysema , Hyperkalaemia , L ead transposition, Artificial cardiac pacing, VT CARDIAC AXIS

References :

References The EKG made easy-John R. Hampton An Introduction to Electrocardiography – Leo Schamroth Marriot’s Practical Electrocardiography. www.ambulancetechnicianstudy.co.uk www.learntheheart.com

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