Unit 2 biomedical

Cardiovascular Measurements
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UNIT 2
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Objective
At the end of this Unit
You will learn
Different Biomedical measurements such
as ECG, Blood pressure measurement,
Cardiac Measurements

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Cardiac Function Measurements

Measuring Cardiac Function
1. Blood Pressure
2. Electrocardiogram
3. Stress Test
4. Angiography
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Measuring Cardiac Function
1. Blood Pressure
 Measure of fluid pressure within system
a. Systolic Pressure: Pressure generated by contraction
b. Diastolic Pressure: Pressure achieved between contractions.
 SBP reflects the amount of work the heart is performing
 DBP indicates the amount of peripheral resistance
encountered
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Blood Pressure Measurement

Blood Pressure Measurements
Adequate blood pressure is essential to maintain the blood
supply and function of vital organs.
A history of blood pressure measurements has saved
many person from death by providing warnings of
dangerously high blood pressure (hypertension) in time to
provide treatment.
The maximum pressure reached during cardiac ejection is
called Systole.
Minimum pressure occurring at the end of ventricular
relaxation is called diastole.
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In routine clinical tests, blood pressure is usually measured by
means of an indirect method using a sphygmomanometer
(from the Greek word, sphygmos, meaning pulse).
This method is easy to use and can be automated.
The automated indirect method of B.P measurement is called
Electro sphygmomanometer
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It has, however, certain disadvantages in that it does not
provide a continuous recording of pressure variations and
its practical repetition rate is limited.
Blood pressure is measured in millimeters of mercury (mm Hg)
and recorded with the systolic number first, followed by the
diastolic number.
A normal blood pressure would be recorded as 120/80 mm
Hg.
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
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 The systolic pressure is the maximum pressure in an artery at
the moment when the heart is beating and pumping blood
through the body.
The diastolic pressure is the lowest pressure in an artery in the
moments between beats when the heart is resting.
Both the systolic and diastolic pressure measurements are
important
If either one is raised, it means you have high blood pressure
(hypertension).
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The nominal values in the basic circulatory system
Arterial system-------30-300mmHg
Venous system--------5-15mmHg
Pulmonary system----6-25mmHg
Blood pressure measurement can be classified in to
1. Indirect
2. Direct
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Indirect
Simple equipment ,Very little discomfort, Less informative
and Intermittent
The indirect method is also somewhat subjective, and often fails
when the blood pressure is very low (as would be the case when
a patient is in shock).
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Indirect Blood Pressure Measurement

Blood pressure measurements
1. Auscultatory
 Auscultatory method uses aneroid sphygmomanometer with
a stethoscope.
 The auscultatory method comes from the Latin word
"listening.
2. Oscillometric
 The oscillometric method was first demonstrated in 1876 and
involves the observation of oscillations in the
sphygmomanometer cuff pressure which are caused by the
oscillations of blood flow, i.e., the pulse.
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Blood pressure measurements
3. Palpatory
 Physician identifies the flow o blood in the arteries by
feeling the pulse
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1. B.P measurements using sphygmomanometer
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Blood pressure measurements using sphygmomanometer
First, a cuff is placed around your arm and inflated with a
pump until the circulation is cut off.
A small valve slowly deflates the cuff, and the doctor
measuring blood pressure uses a stethoscope, placed over your
arm, to listen for the sound of blood pulsing through the
arteries.
That first sound of rushing blood refers to the systolic blood
pressure; once the sound fades, the second number indicates
the diastolic pressure.
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Direct Blood Pressure Measurement

2. Direct Blood Pressure Measurements
Provide continuous measurement
Reliable information
Transducers are directly inserted in to the blood stream
Methods for direct blood pressure measurement, on the other
hand, do provide a continuous readout or recording of the blood
pressure waveform and are considerably more accurate than the
indirect method
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Direct B.P Measurement
Methods of direct blood pressure were classified in to two
1. The clinical method by which the measuring device was
coupled to the patient
2.Second, by the electrical principle involved.
First category is expanded, with the electrical principles
involved being used as four subcategories.
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B.P measurements using direct method
 ln l972, Hales inserted a glass tube into the artery of a horse
and vulgarly measured arterial pressure.
Regardless of the electrical or physical principles involved, direct
measurement of blood pressure is usually obtained by one of
three methods
1.Catheterization (vessel cut down).
2.Percutaneous insertion.
3.Implantation of a transducer in a vessel or in the heart.
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1. A catheterization method involving the sensing of blood
pressure through a liquid column.
 In this method the transducer is external to the body, and the
blood pressure is transmitted through a saline solution
column in a catheter to this transducer
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2. The catheterization method involving the placement of
the transducer through a catheter at the actual site of
measurement in the blood stream or by mounting the
transducer on the tip of the catheter.
3. Percutaneous methods in which the blood pressure is
sensed in the vessel just under the skin by the use of a
needle or catheter.
4. Implantation techniques in which the transducer is more
Permanently placed in the blood vessel or the heart by
surgical methods.
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1. Percutaneous insertion ( direct method)
Typically, for Percutaneous insertion , a local anesthetic is
injected near the site of invasion.
The vessel is occluded and a hollow needle is inserted at a
slight angle towards the vessel.
When the needle is in place, a catheter is fed through the
hollow needle , usually with some sort of a guide.

When the catheter is securely place in the vessel, the needle
and guide are withdrawn.
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Percutaneous insertion ( direct method)
For some measurements, a type of needle attached to an airtight
tube is used, so that the needle can be left in the vessel and the
blood pressure sensed directly by attaching a transducer to
the tube.
Other types have the transducer built in-the tip of the catheter.
This latter type is used in both percutaneous and
catheterization models.
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2. Catheterization( direct method)
It was first developed in the late 1940s and has become a major
technique for analyzing the heart and other components.
Catheter is a long tube that is inserted in to the heart or major
vessels.
Sterilized catheters are used
Apart from obtaining blood pressures in the heart chamber
and great vessels, this technique is also used to obtain blood
samples from the heart for oxygen-content analysis and to
detect the location of abnormal blood flow pathways.
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Catheterization( direct method)
Measurement of blood pressure with a catheter can be achieved
in two ways.
In the first method is to introduce a sterile saline solution into
the catheter so that the fluid pressure is transmitted to a
transducer out side the body.
In the second method, pressure measurements are obtained at
the source.
Here,the transducer is introduced into the catheter and pushed
to the point at which the pressure is to be measured. or the
transducer is mounted at the tip of the catheter.
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This device is called a catheter-tip blood pressure transducer.
For mounting at the end of a catheter, one manufacturer uses an
un bonded resistance strain gage in the transducer, whereas
another uses a variable inductance transducer .
Implantation techniques involve major surgery.
Transducers can be categorized by the type of circuit element
used to sense the pressure variations, such as capacitive,
inductive, and resistive.
Since the resistive types are most frequently used.
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B.P measurements using direct method
 ln l972, Hales inserted a glass tube into the artery of a horse and
crudely measured arterial pressure.
Regardless of the electrical or physical principles involved, direct
measurement of blood pressure is usually obtained by one of three
methods
Percutaneous insertion.
Catheterization (vessel cut down).
lmplantation of a transducer in a vessel or in the heart.
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Heart
The cardiovascular system is made of the heart, blood and
blood vessels
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Anatomy of the Heart
The human heart is a four-chambered muscular organ
The heart is enclosed in a pericardial bag.
The purpose of it is to protect and lubricate the heart.
The peircardium is the outermost covering of your heart.
It protects against friction rubs and protects against
shocks(traumatic) as it contains 40-50 ml of pericardial fluid.
It acts as a shock absorber
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Heart normally pumps 5 liters of blood per minute
Two side of the wall is separated by the septum or dividing
wall of tissue.
This septum include AV node
Right auricle is lies between inferior(lower) and
superior(upper) vena cava
At the junction of Superior vena cava and right atrium SA
node is situated.
.
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The communication between atria and ventricle is
accomplished only through AV node and delay line.
The activated AV node, after a delay, initiates an impulse in to
the ventricle, through the bundle of his, and bundle branches
that connect to the purkinje fibers.
1. Ventricle wall is thicker than auricular wall
2. Left atrium is smaller than Right atrium
3. Left ventricle is considered as most important.
4. It wall thickness is 3 times than right ventricle.
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Heart anatomy
Left heart is considered as pressure pump
Right heart is similar to a volume pump
Muscle contraction of left heart is larger and stronger than
that of right heart.
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Heart circulation
The work of the heart is to pump blood to the lungs through
pulmonary circulation and to the rest of the body through
systemic circulation.
In pulmonary circulation, the pressure difference between
arteries and veins is small.
In systemic circulation, the pressure difference between
arteries and veins is very high.
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Heart Valves
The pumping action is accomplished by systematic contraction
and relaxation of the cardiac muscle in the myocardium.
Cardiac muscles gets the blood supply from coronary
circulation.
Heart contains 4 valves
Tricuspid---Between RA and RV----- Three cups
Pulmonary/Semi lunar-- Between RV and Right lungs
Mitral/Bicuspid--- Between LA and LV---- Two cups
Aortic--- Between LV and aorta
The sounds associated with the heartbeat are due to vibrations
in the tissues and blood caused by closure of the valves.
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Heart Sound
Listening of sound produced by heart is called auscultation
Heart sound is heard by the physician through his stethoscope.
This sound is called Korotkoff sound
The sounds associated with the heartbeat are due to
vibrations in the tissues and blood caused by closure of the
valves.
Normal heart produces two sounds called lub-dub
Lub is called the first heart sound
It occurs at the time of QRS complex of the ECG
Lub is related to the closure of atrioventricular valve
Which permits blood flow from auricle to ventricles.
It prevents blood flow in reverse direction
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Heart Sound
Dub is called the second heart sound
Dub is related to the closure of semilunar valve
This valve releases blood into the pulmonary and systemic
circulation system.
It occurs at the end of the T wave of of the ECG
Abnormal heart sounds is called murmurs.
It is due to the improper opening of the valve.
Graphic recording of heart sound is also possible
It is called phonocardiogram
Recording of the vibrations of the heart against thoracic
cavity is called vibrocariogram
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Cardiac Output and Rate

Cardiac Output
Cardiac output is the volume of blood pumped by the heart
per minute (mL blood/min).
Cardiac output is a function of heart rate and stroke volume.
Cardiac Output in mL/min = heart rate (beats/min) X stroke
volume (mL/beat)
Cardiac Output = 70 (beats/min) X 70 (mL/beat) = 4900
mL/minute.
The total volume of blood in the circulatory system of an
average person is about 5 liters (5000 mL).
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Cardiac Output
The heart rate is simply the number of heart beats per
minute.
This can be easily measured through the use of heart rate
monitors or taking ones pulse (counting the ‘pulses’ at the
radial artery for example over a one minute period).
Children (ages 6 - 15) 70 – 100 beats per minute
Adults (age 18 and over) 60 – 100 beats per minute
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Cardiac Output
The stroke volume is the volume of blood, in milliliters (mL),
pumped out of the heart with each beat.
Stroke volume (SV) refers to the quantity of blood pumped
out of the left ventricle with every heart beat.
If the volume of blood increased (waste products not being
removed to the kidneys due to kidney failure for example)
then there would be a greater quantity of blood within the
system increasing the pressure within.
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Cardiac Output
Increasing either heart rate or stroke volume increases cardiac
output.
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Cardiac Output
The SA node of the heart is enervated by both sympathetic and
parasympathetic nerve fibers.
Under conditions of rest the parasympathetic fibers release
acetylcholine, which acts to slow the pacemaker potential of the
SA node and thus reduce heart rate.
Under conditions of physical or emotional activity sympathetic
nerve fibers release norepinephrine, which acts to speed up the
pacemaker potential of the SA node thus increasing heart rate.
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Cardiac Output
Stroke volume is increased by 2 mechanisms:
1. Increase in end-diastolic volume
2. Increase in sympathetic system activity
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Cardiac Output
An increase in venous return of blood to the heart will result in
greater filling of the ventricles during diastole.
Consequently the volume of blood in the ventricles at the end of
diastole, called end-diastolic volume, will be increased.
A larger end-diastolic volume will stretch the heart.
Stretching the muscles of the heart optimizes the length-
strength relationship of the cardiac muscle fibers, resulting in
stronger contractility and greater stroke volume.
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Electro Cardio Gram(ECG)
Bio electric potentials generated by heart muscles are called
Electro Cardio Gram.
It is sometimes called EKG(Electro Kardio Gram)
Electrocardiography (ECG) is an interpretation of the
electrical activity of the heart over a period of time.
The recording produced by this noninvasive procedure is
termed as electrocardiogram (also ECG or EKG).
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Early ECG measurement system
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Heart is divided in to 4 chamber
Upper chamber------ Atria( left and right)
Lower chamber------Ventricles(left and right)
Right auricles receives blood from the veins and pump in to
right ventricles.
The right ventricle pump the blood to lungs, where it is
oxygenated
The oxygenated blood enters in to left auricle.
Left auricle pumps blood in to left ventricle.
To work the cardiovascular system properly , the atria and
ventricles must operate in a proper time relationship.
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Action potential in the heart originates near the top of the
right atrium at a point called pacemaker or sinoatrial node (S.A
node).
This action potential is then propagated in all directions along
the surface of both atria.
The waves terminate at a point near the centre of the heart is
called A.V node(Atrioventricular node)
At this point some special fiber act as a delay line to provide
proper timing between the action of auricles and ventricles.
Once electrical pulses has passed through the delay line , it is
spread to all parts of both ventricles by the bundle of His
It is called purkinje fibers.
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This bundle is divided in to two branches to initiate action
potential simultaneously in the two ventricles.
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ECG waveform/ PQRST wave form

The “P” wave is called base line or isopotential line.
P wave ----- De polarization of Auricles.
Combined QRS wave---- Re-polarization of atria and
depolarization of ventricles
T wave ----- Ventricular re polarization
U wave --- after potentials in the ventricles
P-Q interval – Time during which excitation wave is delayed
in the fiber near AV node.
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Simple ECG measurement system
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ECG measurement system
The ECG system comprises four stages, each stage is as follows:
(1)The first stage is a transducer—AgCl electrode, which
convert ECG into electrical voltage. The voltage is in the range of
1 mV ~ 5 mV.
(2) The second stage is an instrumentation amplifier (Analog
Device, AD624), which has a very high CMRR (90dB) and high
gain (1000), with power supply +9V and -9V.
(3) We use an opto-coupler (NEC PS2506) to isolate the In-
Amp and output.
(4) After the opto-coupler is a bandpass filter of 0.04 Hz to 150
Hz filter. It’s implemented by cascading a low-pass filter and a
high pass filter.

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Simple Block diagram of ECG
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EKG Leads
Leads are electrodes which measure the difference in
electrical potential between either:
1. Two different points on the body (bipolar leads)
2. One point on the body and a virtual reference point with
zero electrical potential, located in the center of the
heart (unipolar leads)

EKG Leads
The standard EKG has 12 leads:
3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint from
which it looks at the heart.

Placement of ECG electrode

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Eintovan’s triangle
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Eintovan’s triangle
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ECG Leads
Two types of Leads
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Standard Limb Leads
1. Lead I = (VLA - VRL) - (VRA - VRL) = VLA – VRA
2. Lead II = (VLL - VRL) - (VRA - VRL) = VLL – VRA
3. Lead III = (VLL - VRL) - (VLA - VRL) = VLL - VLA
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Augmented Limb Leads

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Chest Leads
Unipolar (+) chest leads (horizontal plane):

Leads V1, V2, V3: (Posterior Anterior)
Leads V4, V5, V6:(Right Left, or lateral)
 The 6 leads are labelled as "V" leads and numbered V1 to V6.
They are positioned in specific positions on the rib cage.
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ECG Amplifier
We measure the ECG by connecting two electrodes on the
right and left chest respectively, as shown.
The body should be connected to ground of the circuits, so that
we connect the leg to the ground.
To boost the raw ECG signal level without boosting the noise
amplifiers are used.
An electronic circuit should amplify the potential difference
across a lead
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ECG Amplifier

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Instrumentation Amplifier
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Practical Instrumentation Amplifier
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Low signal noise
Very high open-loop gain
Very high common-mode rejection ratio
Very high input impedance
Instrumentation amplifier can reduce common-mode noise, but
not completely
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Heart Sound
Listening to sound produced by human organ is called
auscultation.
Heat sound is related with the closing of valves.
Hippocrates (460-377 BC) provided the foundation for
auscultation when he put his ear against the chest of a patient
and described the sounds he could hear from the heart.
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Heart Sound
The biggest breakthrough in auscultation came in 1816 when
René Laennec (1781-1826) invented the stethoscope
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Heart Sound
There are two types of sounds
1. High frequency sounds associated with closing and opening of
the valves and
2. Low frequency sounds related to early and late ventricular
filling events.
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Heart Sound
1. Mitral area:
2. Tricuspid area:
3. Aortic area:
4. Pulmonic area:
 Microphones and accelerometers are the natural choice of
sensor when recording sound.
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Heart Sound
1. The first heart sound (S1) – systolic sound:
Appears at 0.02 – 0.04s after the QRS complex
the “lub”
frequency of 30-40Hz
2. The second heart sound (S2) – diastolic sound
Appears in the terminal period of the T wave
the “dub”
frequency of 50-70 Hz
3. The third heart sound (S3) - protodiastolic sound
Low frequency
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Heart Sound
4. The fourth heart sound (S4) – presistolic sound
Appears at 0.04s after the P wave (late diastolic-just before
S1)
Low frequency
 S1 – onset of the ventricular contraction
 S2 – closure of the semilunar valves
 S3 – ventricular run
 S4 – atrial gallop
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Phonocardiography
Graphic recording of heart sound is called phonocardiogram
( PCG)
Phonocardiography, diagnostic technique that creates a graphic
record, or phonocardiogram, of the sounds and murmurs
produced by the contracting heart,
The phonocardiogram is obtained either with a chest
microphone or with a miniature sensor in the tip of a small
tubular instrument that is introduced via the blood vessels into
one of the heart chambers.
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Phonocardiography
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Phonocardiography
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Ballistocardiograph

Ballistocardiograph(BCG)
Ballistocardiography (BCG) is based upon Newton's Third
Law, which states that for every action there is an equal and
opposite reaction.
Ballistocardiography, graphic recording of the stroke
volume of the heart for the purpose of calculating cardiac
output.
BCG measures cardiac output by means of recoil forces. With
each systole, blood is ejected through the aorta.
There are two basic types of ballistocardiographic methods.
In the older method, high-frequency BCG, the subject is
restrained and force is measured by displacement of a
supporting spring.
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Ballistocardiograph
In ultra-low-frequency BCG, the subject is free to move and
force is calculated from his/her mass and the measured
acceleration.
Typically, in obtaining a BCG the subject lies on a light,
frictionless table which is either suspended from the ceiling or
supported from below on an air cushion.
The movements of this ballistotable, resulting from body
movements produced by cardiac activity, are transduced into
electrical energy by means of either mechanoelectronic tubes
(Geddes & Baker, 1968) or a compound transducer in which
movement of the table is converted into a varying light
intensity
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Ballistocardiograph Methods
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Ballistocardiograph
Dock and Taubman (1949) recorded body movements without
the use of a ballistotable by devising a photoelectric
transducer which was attached to the shins of the subject.
Cardiac-induced body movements alter the transmission of
light to these photoelectric detectors, thus producing a
variable electrical output proportional to movement.
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Ballistocardiograph
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Defibrillator
Defibrillation is a process in which an electronic device gives
an electric shock to the heart.
This depolarizes a critical mass of the heart muscle,
terminates the arrhythmia and allows normal sinus rhythm
to be reestablished.
This helps reestablish normal contraction rhythms in a heart
having dangerous arrhythmia or in cardiac arrest.
Defibrillation is a common treatment for life-threatening
ventricular fibrillation and pulse less ventricular
tachycardia.
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Defibrillator
Defibrillators were first demonstrated in 1899 by Jean-
Louis Prévost and Frédéric Batelli, two physiologists from
University of Geneva, Switzerland.
These early defibrillators used the alternating current from
a power socket, transformed from the 110–240 volts
available in the line, up to between 300 and 1000 volts, to the
exposed heart by way of "paddle" type electrodes.
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Defibrillator
Early successful experiments of successful defibrillation by the
discharge of a capacitor performed on animals were reported
by N. L. Gurvich and G. S. Yunyev in 1939.
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Defibrillator
In recent years small portable defibrillators have become
available.
These are called automated external defibrillators or AEDs.
Nowadays implantable defibrillator are available in the
market
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Defibrillator Principles
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There are many types of defibrillators
1. Monophasic,
2. Biphasic and
3. Internal.
The first two types are known as external defibrillators, and
these are used on the exterior of the patient’s chest.
Pads are placed on the chest and a button is pushed to send
an electrical current to the heart.
The type of external defibrillator determines the type of
current sent to the heart.
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A monophasic defibrillator sends out a single electrical pulse.
This shot of electricity goes from one pad to the other with
the heart in between.
A monophasic defibrillator needs high electricity levels to
function correctly.
The charge is typically started at 200 joules and increased to
300 joules; if necessary, the highest level is 360 joules.
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The second type of external device is biphasic, and it sends out
two electrical currents.
A current first travels from one pad to the other.
The electricity then reverses direction and returns a current
to the first pad.
This enables the biphasic device to use less electricity than the
monophasic variety.
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The biphasic defibrillator also is able to adjust to the patient's
body type.
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The third type of defibrillator is the internal or implantable
variety, which is surgically placed in the chest of a patient.
The electrode wires are inserted through the veins into the
right chamber of the heart.
An internal defibrillator monitors the heartbeat for any
irregularities.
Internal defibrillators run on battery power instead of
electricity.
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Block Diagram of Defibrillator
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Defibrillator Electrodes
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Pad Electrode
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Pacemaker
A pacemaker (or artificial pacemaker, so as not to be
confused with the heart's natural pacemaker) is a medical
device that uses electrical impulses, delivered by electrodes
contracting the heart muscles.
The primary purpose of a pacemaker is to maintain an
adequate heart rate,
Modern pacemakers are externally programmable and allow
the cardiologist to select the optimum pacing modes for
individual patients.
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Pacemaker
Doctors recommend pacemakers for many reasons.
The most common reasons are bradycardia and heart block.
Bradycardia is a heartbeat that is slower than normal.
Heart block is a disorder that occurs if an electrical signal is
slowed or disrupted as it moves through the heart.
Heart block can happen as a result of aging, damage to the
heart from a heart attack, or other conditions that disrupt the
heart's electrical activity.
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Pacemaker
A pacemaker consists of a battery, a computerized generator,
and wires with sensors at their tips. (The sensors are called
electrodes.)
The battery powers the generator, and both are surrounded by
a thin metal box.
The wires connect the generator to the heart.
A pacemaker helps monitor and control your heartbeat.
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Pacemaker
The electrodes detect your heart's electrical activity and send
data through the wires to the computer in the generator.
The two main types of programming for pacemakers are
demand pacing and rate-responsive pacing.
A demand pacemaker monitors your heart rhythm.
It only sends electrical pulses to your heart if your heart is
beating too slow or if it misses a beat.
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Pacemaker
A rate-responsive pacemaker will speed up or slow down
your heart rate depending on how active you are.
To do this, the device monitors your sinus node rate,
breathing, blood temperature, and other factors to determine
your activity level.
People may need a pacemaker for a variety of reasons —
mostly due to one of a group of conditions called arrhythmias,
in which the heart's rhythm is abnormal.
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Pacemaker
During an arrhythmia, the heart may not be able to pump
enough blood to the body.
This can cause symptoms such as fatigue (tiredness),
shortness of breath, or weakness.
Severe arrhythmias can damage the body's vital organs and
may even cause loss of consciousness or death.
A pacemaker can often be implanted in your chest with a
minor surgery.
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Pacemaker Types
There are three types of artificial pacemakers
Single chamber pacemakers set the pace of only one of your
Heart s chamber s , usually the left ventricle , and need just
one lead
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Pacemaker Types
Dual chamber pacemakers set the pace of two of your hearts
chambers and need two leads
Dual chamber pacemakers are ideal if you have heart block
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Pacemaker Types
Biventricular pacemakers use three leads, one in the right
atrium (one of the top pumping chambers in your heart) and
one in each of the ventricles (left and right)
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Pacemaker Types
1. Pacing function
2. Sensing function
3. Capture function
Atrial pacing:
stimulation of RT atrium produce spic on ECG preceding P
wave
Ventricle pacing :
stimulation of RT or LT ventricle produce a spic on ECG
preceding QRS complex
AVpacing:
direct stimulation of RT atrium and either ventricles
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Pacemaker Types
Sensing :
Ability of the cardiac pace maker to see intrinsic cardiac
activity when it occurs
Demand:
pacing stimulation delivered only if the heart rate falls
below the preset limit.
Fixed:
 no ability to sense. constantly delivers the preset stimulus at
preset rate.
Triggered:
delivers stimuli in response to (sensing )cardiac event.
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Pacemaker Types
Capture:
Ability of the pacemaker to generate a response from the
heart (contraction) after electrical stimulation
According to pacing
1. Permanent
2. Temporary
3. biventricular
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Unit 2 biomedical

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