Cardio Vascular System Circulation ECG Heart Block YouTube Lecture Handouts
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Types of Vessels
- Windkessel (distensible vessels)
- Distributing vessels (arteries)
- Resistance vessels (arterioles)
- Exchange vessels (capillaries)
- Venules & Veins
Type of vessel | Diameter | Functions |
---|---|---|
Elastic art. (Large art.) | Greater than 1 cm. | Conduction of blood |
Muscular art. (Medium art.) | 0.1 to 10 mm. | Distribute blood to arterioles |
Arteriole | 10 to 100 µm. | Main site of peripheral resistance |
Capillary | 4 to 10 µm. | Exchange of material at tissue level |
Venules | 10 to 100 µm. | Collect blood |
Veins | 0.1 mm or greater | Return 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
- 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
Fenestrated Capillaries
Discontinuous/Sinusoids
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
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
Haemodynamics
- 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
Reynolds Number
- Turbulence increases with the increase in Reynolds no.
- It starts appearing at Re. no. 2000
- Above Re. 3000 always present
Electrocardiogram
- 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
ECG
- 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
ECG: Leads
Recording is by Leads
- Lead is a pair of electrodes
Leads are of two types
- Bipolar &
- Unipolar
Limb & Chest Leads
Bipolar
- Limb leads- are used
- Chest leads- not in use … X
Unipolar
- 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
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
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
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
Basic Rule
- Flow of current towards recording electrode gives + ve deflection
- Flow away gives – ve deflection
- Magnitute of voltage depends on muscle mass
ECG – Waves, Intervals & Segments
Normal ECG has
Waves
- P
- QRS
- T
Intervals
- PR
- QT
Seg
- Segments
- PR &
- QT
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
Intervals
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
Segments
- 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
Calculation of the Mean Electrical Axis
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.
Normal Axis Deviations
- Normal Lt. Axis deviation-horizontal position of heart:
- Normal Rt. Axis deviation-Vertical position of heart:
- Oblique position of heart:
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
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
Sick Sinus Syndrome -Diseases affecting sinus node lead to marked bradycardia associated with dizziness & syncope
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
ECG
Second Degree Heart Block
- Mobitz type I Wenckebach phenomenon Gradual increase in PR interval, till one beat drops
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
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
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
Arrhythmias
Two types:
- Physiological
- pathological
Physiological Arrhy
Rhythm is generated at SA node
- Normocardia normal resting heart rate of 60 to 100 beats/min.