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8/16/2019 DR RAVI SHANKAR- Electrical Activity of the Heart & Normal ECG.pdf
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Electrical Activity of HearNormal ECG & Its Interpreta
Dr S RAVI SHANKMBBS, MD, Dip Cardio
Associate Profe
Faculty of Med
UniKL R
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Lecture Outlines• Conduction system of the heart
• Origin & Spread of Cardiac Impulse
• Basis of ECG
• Leads : types & placement
• Different types of Waves Intervals & segments
• Uses of ECG
• Calculate : Heart rate
• Identify : Rhythm
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Subsystemsof the Heart
• Myocardium : Sync
Atrial & Ventric
• Conduction System
•
Coronary Circulatio• Valves
• Autonomic Innerva
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Pacemaker / Junctional Tissue / Conduction Syste
Internodal Pathw
• Anterior : Bachmann
• Middle : Wenkebach
• Posterior : Thorel
Interatrial Pathw
Left Bundle Branch (
Left Anterior Fascicle ( LAF )
Left Posterior Fascicle ( LPF
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Conduction SystemConduction Velocity
• SAN & AVN : 0.5 m /s• Atrial pathways
Bundle of HIS
Ventricular Muscle
= 1 m /s• Purkinje system
= 4 m /s
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Origin & Spread of Cardiac Impulse
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Introduction to ECG• Willem Einthoven (1903) - 1st to record ECG
• Electrocardiogram ( ECG / EKG ) : graphic tracing of variation
electrical potentials (algebraic sum of APs )
caused by excitation of cardiac muscles &
detected at body surface
- measures potential difference b / w 2 points on body
• Electrocardiograph : instrument ( galvanometer )
• Electrocardiography : process
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Basis of ECG• Heart : generator - acts as a moving dipole
• Body : good volume conductordue to electrolytes
• Cardiac Dipole : Vector Arrow
Length : magnitude Head : direction
• Surface Potential : magnitude of voltage at body surface
Function of : electrode position &
orientation & magnitude of dipole
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Einthoven’s Triangle
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ECG Conventions• Depolarisation
- towards electrode : + ve deflection- away from electrode : - ve deflection
- perpendicular to electrode : no deflection ( Isoelectric )
• Total charge ∞ mass of tissue &
magnitude of mem potentials
• More muscle mass = more deflection
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ECG Paper
• Sensitivity : 10 mm = 1 mV
• Paper speed : 25 mm / sec
• Distance moved in 1 minute
60 x 25 = 1500 mm
• HR = 1500 / R - R interval (
300 ÷ number of large squa
between 2 consecutive be
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ECG Leads• Measure the potential difference ( pd ) between 2 electrod
• Standard bipolar limb leads : - I - II - III• Unipolar chest leads : V1 - V6
• Augmented unipolar limb leads : - aVR - aVL - aVF
- recording / active / exploring electrode
- Wilson central terminal : reference electrode• Normally 12 leads only
• 15 / 18 lead ECG : additional V7 - V9 & / or additional V4R -
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Standard Bipolar Limb Leads
•
Lead I : p d b / w left arm & right arm= LA - RA
• Lead II : p d b / w left leg & right arm
= LL - RA
• Lead III : p d b / w left leg & left arm
= LL - LA
• Einthoven’s law / Einthoven’s Equation : I + III = II
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Augmented Unipolar Limb Leads
• A single positive electrode is referenced against a combinatio
of the other limb electrodes
• aVR : p d b / w RA - ( LA + LL )
• aVL : p d b / w LA - ( RA + LL )
• aVF : p d b / w LL - ( RA + LA )
• Potential recorded is one and a half times that recorded by
unipolar limb lead i.e. augmented
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Unipolar Chest Leads• V1 : 4
th ICS at right sternal border
• V2 : 4th ICS at left sternal border
• V3 : equidistant between V2 & V4
• V4 : 5th ICS on left midclavicular line
V5 - V9 are taken in the same horizontal place as V4
• V5 : Anterior axillary line
• V6 : Mid axillary line
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Spread of Cardiac Impulse
• Depolarisation :
- Endocardium to epicardi
- Apex to base
• Repolarisation
vice versa
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Septal Depolarisation
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Ventricular Depolarisation
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Spread of Cardiac Impulse
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Normal ECGVAT = R - 0.02 s L - 0.
•Inconsistent U waveSlow repolarization o
papillary muscles
• Rapid ascent & slow d
Opposite of T wave• Hypokalemia : T flatt
U taller with ↓ [ K ]
J Point
Ventricular
Activation Time
Intrinsicoid Deflection
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Normal ECG
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Ventricular Depolarisation
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Recordings from Chest / Precordial Lead
R wave progression from V 1 to V 6 , Transition V3 - 4
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ECG From DiffeLeads InFrontal Plane
Note : all waves in aVR
inverted ?
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Uses of ECG
Imp diagnostic & prognostic tool to assess CV function
• Anatomical orientation / abnormalities of heart
• Relative size of atria & ventricles
• Defects in origin & conduction of cardiac impulse
• Different types of arrhythmias
• Extent location & progress of ischaemic damage
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Uses of ECG
•
Effects of altered electrolyte concentrations• Influence of certain drugs eg digitalis & its derivatives
• Cardiac effects of other systemic diseases
• Pericarditis
EKG gives no direct information
concerning the mechanical performance
of the heart as a pump
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Heart Rate : Regular
Big Box : 1 2 3 4 5 6
HR = 300 150 100 75 60 50
Normal Sinus Rhythm : 60 - 100 bpm
HR = 1500
RR (mm)= 300
no. of big squ
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Mean Electrical Axis
• Infancy : + 90 - 140o
• Childhood : 90 - 120o
• I & aVF + ve : Normal
• I & aVF - ve : EAD
• I : - ve & aVF + ve : RAD
• I : + ve & aVF - ve :II : + ve : Normal
II : - ve : LAD
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1st Degree Heart Block
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THANK YOUTERIMA
KASIH