DR RAVI SHANKAR- Electrical Activity of the Heart & Normal ECG.pdf

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

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DR RAVI SHANKAR- Electrical Activity of the Heart & Normal ECG.pdf