Cardio Vascular System Circulation ECG Heart Block Youtube Lecture Handouts

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Cardio Vascular System
Types of Distensible Vessels

Types of Vessels

  • Windkessel (distensible vessels)
  • Distributing vessels (arteries)
  • Resistance vessels (arterioles)
  • Exchange vessels (capillaries)
  • Venules & Veins
Details of the Capillary Network
Table of Type of Vessel
Type of vesselDiameterFunctions
Elastic art. (Large art.)Greater than 1 cm.Conduction of blood
Muscular art. (Medium art.)0.1 to 10 mm.Distribute blood to arterioles
Arteriole10 to 100 µm.Main site of peripheral resistance
Capillary4 to 10 µm.Exchange of material at tissue level
Venules10 to 100 µm.Collect blood
Veins0.1 mm or greaterReturn blood to heart

Windkessel Vessels

  • Rich in elastic tissue show elastic recoil
  • Resists too much ↑ in BP during systole & too much ↓ in BP during diastole
  • Aging causes loss of elasticity & there is
    • ↑ in systolic BP
    • ↓ in diastolic BP
    • ↑ pulse Pressure
  • Example, aorta, pulmonary artery & their large branches

Resistance Vessels

Resistance Vessels
  • Rich sym. Inner. Nerves normally discharge@1 impulse/sec. which can Increase upto 10 to 16 impulses/sec. Maximum vasoconstriction
  • It can decrease to 0.0 impulses/sec. Max. Vasodilatation
  • Example, Arterioles

Metarterioles & Pre-Capillary Sphincters

They control size of capillary bed

Their radius is controlled by

1. Neurogenic factor i.e.. Symp. Fib.

2. Local metabolites

  • Local dila. as ↑ , lactic acid concern & adenosine
  • Local cons. as serotonin, ↓in temp.

Exchange Vessels

  • Are capillaries

Only 25 % are open at rest

  • Dia. controlled by precapillary sph.

Types of Capillaries

1. Non-fenestrated or continuous present in most tissues, have 4 nm wide intercellular cleft. Glucose can pass but plasma proteins cannot. Example muscles, skin, connective tissues.

2. Fenestrated (pores of 20 to 100 nm dia.) eg. Present in kidney, exo. & endocrinal glands, intestinal villi, choroid plexuses of brain

3. Discontinuous or sinusoidal they have large spaces between two cells, are present in bone marrow, liver & spleen

Non Fenestrated/Continuous

Non Fenestrated for Capillaries

Fenestrated Capillaries

Fenestrated for Capillaries


Basement Membrane for Sinusoids
Sinusoids Image-2

Capacitance Vessels

  • About 60 % of blood is present in veins
  • Veins can store large amount of blood by enlarging themselves
    • Blood Reservoirs
  • Liver
  • Spleen
  • Skin
Capacitance Vessels

Injury to Juglar Vein

Is life threatening because it can cause air embolism

Shunt Vessels

  • Also called preferential channels or thoroughfare channels
  • Provide direct connection between metarterioles and Venules
Shunt Vessels


  • Blood flow depends on pressure and resistance
  • Hagen-Poiseuille՚s Law:

Types of Blood Flow

  • Normally Laminar or Streamlined velocity is greatest in the centre
  • Sometimes turbulent above critical level flow becomes turbulent
  • Turbulence depends on
  • Diameter of vessel &
  • Viscosity of blood

Streamline & Turbulent Flow

Streamline & Turbulent Flow

Reynolds Number

  • Turbulence increases with the increase in Reynolds no.
  • It starts appearing at Re. no. 2000
  • Above Re. 3000 always present
Reynolds Number


  • It is surface recording of electrical changes taking place in heart from beat to beat
  • Electrocardiograph is instrument used
  • Electrocardiography is branch of physiology related to recording and analysis of electrical activity of heart
  • Electrogram is the record


  • Recording Ecg
  • Record is taken on Ecg paper with the help of Ecg machine

Body is a Volume Conductor

  • Heart is suspended in a conductive media
  • Body fluids surrounding the heart conduct the electricity very easily &
  • Potentials can be picked easily with electrodes
Body is a Volume Conductor
Right Arm aVR and Left Arm aVL and Normal

ECG: Leads

Recording is by Leads

  • Lead is a pair of electrodes

Leads are of two types

  • Bipolar &
  • Unipolar
Recording Device
Bipolar Lead and Unipolar Lead

Limb & Chest Leads


  • Limb leads- are used
  • Chest leads- not in use … X


  • Limb leads replaced by Augmented limb leads
  • Chest leads- are in use

Bipolar leads

Both electrodes are recording electrodes & the recorded potential is

Difference of Potential between Two Points

Unipolar Leads

  • Unipolar leads-one electrode is called exploring/recording electrode
  • Another is indifferent electrode & is prepared by connecting three limb leads to a common terminal through electrical resistance. It records zero potential
  • Exploring electrode records absolute voltage

Routine 12 Lead ECG

A routine ECG has

  • Standard bipolar leads … 3
  • Augmented limb leads … 3
  • Unipolar chest leads … 6

Total 12 Leads

Other leads – Oesophageal leads, intracardiac leads & Rt. sided chest leads & posterior leads

Standard Leads

Bipolar leads (standard leads) – both electrodes are active

Lead I … Rt. Arm – ve

Lt. Arm + ve

Lead I … Rt. Arm -ve

Lt. Leg + ve

Lead III … Lt. Arm -ve

Lt. Leg + ve

Standard Leads

Einthoven՚S Triangle

  • It is the equilateral triangle with the Rt. & Lt. shoulders & Lt. leg as the three apices. The Rt. leg serves as a ground conductor.
  • If an arm is amputed, the electrode can be placed on the stump that is left

Einthoven՚S Law

  • It states that if electric potentials of any two of the bipolar leads are known the potential of third one can be determined mathematically
  • According to it voltage in
    • I + III = II
    • I + (-II) + III = 0

Unipolar Leads

  • They are of two types
    • Unipolar Limb Leads are replaced by Augmented limb leads
    • Unipolar Chest Leads are in use

Augmented Limb Leads

Unipolar limb leads are replaced by augmented limb leads. Potential in augmented lead is 50 % more than that of limb lead.

Three augmented limb leads are

  • aVR
  • aVL
  • aVF
Connected Augmented Limb Leads
Non-Connected Augmented Limb Leads
Unipolar Chest Leads

Unipolar Chest Leads

Unipolar chest leads: total six in no.

  • V1 — IV ICS. just to the Rt. of sternum
  • V2 — IV ICS. just to the Lt. of sternum
  • V3 — halfway between V2 & V4
  • V4 — V ICS. midclavicular line
  • V5 — same level as V4in ant. axillary line
  • V6 — same level as V4, midaxillary line
Clavicula, Mid Clavicular Line and Mid Axillary Line
Scapula for Chest Leads
Heart Orientation in Chest
The Cardiac Position and Axis Orientation of Chest
Big Square and Small Square

ECG: Reading

Basic Rules

  • During most of depolarization base is – ve & apex + ve only during last part of depolarization it reverses it՚s very brief period. Average current flow is from base to apex.
  • It is also mean electrical axis of heart.
  • During repolarization also current flow is from base to apex
ECG Paper
Mean Electrical Axis

Basic Rule

  • Flow of current towards recording electrode gives + ve deflection
  • Flow away gives – ve deflection
  • Magnitute of voltage depends on muscle mass
Positive and Negative Deflection
Positive and Negative Deflection Circle

ECG – Waves, Intervals & Segments

Normal ECG has


  • P
  • QRS
  • T


  • PR
  • QT


  • Segments
  • PR &
  • QT
ECG – Waves, Intervals & Segments Image

P Wave

Wave of Atrial Depolarization + ve in Standard limb leads & - ve in a VR

  • Duration … 0.1 sec.
  • Voltage … 0.25 mv or Amplitude
  • Abnormalities P Wave
  • Absent or replaced by very high speed fibrillatory waves – in Atrial fibrillation
  • P pulmonale - Large high voltage , in Rt Atrial hypertrophy
  • P mitrale – Broad & notched in Lt. Atrial hypertrophy
  • Inverted in nodal rhythm

QRS Complex

Is caused by ventricular depolarization it measures intraventricular conduction time

  • Duration … 0.08 - 0.12 sec.
  • Voltage 0.5 – 1.5 mv

Prominent Q wave indicates old infarction

Abnormalities of QRS Complex

Prolonged QRS complex seen in

  • Bundle branch block
  • Hypertrophy of ventricles

Prolonged & bizarre QRS

  • Cardiac muscle destroyed in various areas & replaced by fibrous tissue
  • Block in conduction of impulses by Purkinje system

T Wave

  • Produced by ventricular depolarization.
  • It is normally positive because apex of heart repolarizes earlier than the base
  • Duration … 0.27 sec
  • Voltage … 0.5 mv

Abnormalities of T Wave

  • Flattened in old age
  • High amplitude in exercise
  • Inverted in ischemia of heart
  • Abn. of T wave in lead I & II are of diagnostic importance in myocardial damage

Atrial Repolarization

  • Atrial repolarization wave not visible, merged with QRS complex, Sometimes U wave may be present. Caused by slow repolarization of papillary muscles
  • PR Interval — from beginning of P wave to beginning of Q/R wave. Time from atrial activation to the beginning of ven. depol.

Normal … 0.12 to 0.2 Sec

> 0.2 sec …

I degree heart block

< 0.12 sec … >

Nodal rhythm

WPW syndrome


QT interval … from the beginning of Q wave to the end of T wave. It represents ventricular depolarization & repolarization time

  • Duration — 0.40 to 0.43 sec
  • Prolonged in ventricular conduction defects

P-P interval … interval between two successive beats, normally equal


  • PR segment is Isoelectric period from the end of P wave to the beginning of Q wave
    • Duration … 0.04 sec
  • ST segment is isoelectric period from the end of S wave to the beginning of T wave
    • Duration … 0.04 to 0.08 sec

ECG … st Seg. Shift

  • Whenever current of injury is present ST Seg. & TP seg. are not at same level
  • Actually TP seg. Shifts but
  • We record it as shift of ST Seg.
  • It records presence of current of injury

J Point

  • Point of no electrical activity potential is zero
  • Point between S wave & beginning of ST Seg.

Calculating HEART RATE from ECG

Important points

  • ECG paper moves at a speed of 25 mm/sec
  • So in 1 minute paper will move (1500 small squares or 300 big squares)
  • Count no. of small squares between two R, R waves say it is n
  • Heart rate is = 1500/n or
  • Count no. of big squares, say N

Now heart rate is = 300/N

Cardiac Vector

Vector is an arrow, depicting two things

Direction of current flow, arrow points always towards positive side

ve + ve

Length of arrow is proportionate to magnitude of voltage

Cardiac Vector

Calculation of the Mean Electrical Axis

Calculation of the Mean Electrical Axis Image

Mean Electrical Axis of Heart

During most of the ventricular depolarization vector is from base to apex. This is called Mean Electrical Axis of heart

Normally it is

Range is Lt.

Mean Electrical Axis of Heart
ECG Hexaxial System

Normal Axis Deviations

  • Normal Lt. Axis deviation-horizontal position of heart:
  • Normal Rt. Axis deviation-Vertical position of heart:
  • Oblique position of heart:
Normal Axis Deviations
Vertricular Hypertrophy

Abnormal Axis Deviations

  • Lt. Axis deviation
  • Lt Ven. Hypertrophy
  • Lt. Bundle branch block

ECG Findings

  • Lead I … prominent R wave
  • Lead III- prominent S wave
  • (R1 S3 pattern)
  • Rt. Axis deviation -Axis Rt. To
  • Rt. Ven. Hypertrophy.
  • Rt. Bundle branch block

ECG Findings

  • Lead I … prominent S wave
  • Lead III … prominent R wave
  • (S1 R3 pattern)

Abnormal ECG

ECG in

  • Heart Block
  • Ectopic cardiac rhythm
  • Myocardial Infarction
  • Change in ionic composition

Heart Block

Conduction of impulse from Pace maker is interrupted Can be

  • SA (Sino atrial) block
  • AV (Atrio ventricular) block
  • Bundle Branch Block
Heart Block

SA Block/Arrest

  • Initially heart stops beating
  • After some time a new Pacemaker starts functioning.
  • Heart resumes its function
  • It starts beating at a new rhythm


Sick Sinus Syndrome -Diseases affecting sinus node lead to marked bradycardia associated with dizziness & syncope

Cross-Section of the Chest with a Pacemaker
Sick Sinus Syndrome
Sinus Pause

S-A Block with A-V Nodal Rhythm

S-A Block with A-V Nodal Rhythm

First Degree Heart Block

  • All impulses reach to the ventricles
  • Prolonged P-R interval > 0.2 sec.
  • Rate of atrial & ventricular contractions are same


First Degree Heart Block

Second Degree Heart Block

  • Mobitz type I Wenckebach phenomenon Gradual increase in PR interval, till one beat drops
Second Degree Heart Block Type-I

Mobitz Type II - all impulses are not conducted

  • 2: 1 Block alternate impulses conducted
  • Atrial: ventricles rate … 2: 1
  • 3: 1 Block ratio is … 3: 1
Second Degree Heart Block Type - II

III Degree Heart Block

Impulses not conducted from Atria to Ventricles

  • Caused by organic diseases of heart
  • Atrioventricular dissociation
  • Remaining nodal tissue becomes pacemaker. The rhythm generated is Idioventricular Rhythm
  • Rate of Idioven. Rhy. is about 45 beats

Strokes-Adams Syndrome

  • If ventricular pacemaker is located more peripherally in the conducting system ventricular rate is lower
  • Rate can be as low as 15 beats/min.
  • Delayed pickup of heart is there, delay can be of 5 to 30 seconds
  • Delay caused by overdrive supression

Resultant Cerebral Ischemia Causes Dizziness & Fainting

Cerebral Ischemia Causes Dizziness and Fainting
Complete AV Block Hrart Block

Atrio-Ventricular Dissociation

Atrio-Ventricular Dissociation

Bundle Branch Block

  • Block in one or more branches of bundle of His
  • QRS complexes prolonged & deformed
  • Axis deviation present

His Bundle Electrogram

His Bundle Electrogram


Two types:

  • Physiological
  • pathological

Physiological Arrhy

Rhythm is generated at SA node

  • Normocardia normal resting heart rate of 60 to 100 beats/min.

Sinus Bradycardia

Sinus Bradycardia

Sinus Tachycardia

Sinus Tachycardia

Sinus Arrhythmia

Sinus Arrhythmia

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