Cardiac Output Introduction Notes

Introduction

Cardiac output is the amount of blood pumped from each ventricle. Usually, it refers to the left ventricular output through the aorta. Cardiac output is the most important factor in the cardiovascular system, because, the rate of blood flow through different parts of the body depends upon the cardiac output.

Definitions And Normal Values

Usually, cardiac output is expressed in three ways:

1. Stroke volume
2. Minute volume
3. Cardiac index.

Read And Learn More: Medical Physiology Notes

However, in routine clinical practice, cardiac output refers to minute volume.

1. Stroke Volume

• The stroke volume is defined as the amount of blood pumped out by each ventricle during each beat.
• Normal value: 70 mL (60-80 mL) when the heart rate is normal (72/minute).

2. Minute Volume

Minute volume is the amount of blood pumped out by each ventricle in one minute.

It is the product of stroke volume and heart rate:

• Minute volume = Stroke volume x Heart rate Normal value: 5 liters/ ventricle/ minute.

3. Cardiac Index

• The cardiac index is the minute volume expressed in relation to the square meter of body surface area.
• It is defined as the amount of blood pumped out per ventricle/minute/ square meter of the body’s surface area.
• Normal value: In an adult, with an average body surface area of 1.734 square meters and a normal minute volume of 5 liters/minute.
• Cardiac index = 2.8 ± 0.3 liters/ square meter of body surface area/ minute.

Ejection Fraction

Ejection fraction is the fraction of end-diastolic volume that is ejected out by each ventricle. Normally it is 60-65%.

Cardiac Reserve

• The cardiac reserve is the maximum amount of blood that can be pumped out by the heart above normal value.
• The cardiac reserve plays an important role in increasing cardiac output during the conditions like exercise.
• It is essential to withstand the stress of exercise.
• A cardiac reserve is usually expressed in percentage. In normal young healthy adult, the cardiac reserve is 300400%.
• In old age, it is about 200-250%. It increases to 500-600% in athletes. In cardiac diseases, the cardiac reserve is minimum or nil.

Variations In Cardiac Output

Physiological Variations

• Age: In children, cardiac output is less because of less blood volume. The cardiac index is more than in adults because of less body surface area.
• Sex: In females, cardiac output is less. The cardiac index is more than in males, because of less body surface area.
• Body build: Greater the body build, more is the cardiac output.
• Diurnal variation: Cardiac output is low in the early morning and increases in the day time. It depends upon the basal conditions of the individuals.
• Environmental temperature: Moderate change in temperature does not affect cardiac output. An increase in temperature above 30°C raises cardiac output.
• Emotional conditions: Anxiety, apprehension, and excitement increase cardiac output by about 50-100% through the release of catecholamines which increase the heart rate and force of contraction.
• After meals: During the first one hour after taking meals, cardiac output increases.
• Exercise: Cardiac output increases during exercise because of an increase in heart rate and force of contraction. However, it depends upon the severity of the exercise.
• High altitude: In high altitudes, the cardiac output increases because of an increase in the secretion of adrenaline. Adrenaline secretion is stimulated by hypoxia (lack of oxygen).
• Posture: While changing from a recumbent to an upright position, the cardiac output decreases.
• Pregnancy: During the later months of pregnancy, cardiac output increases by 40%.
• Sleep: Cardiac output is slightly decreased or unaltered during sleep.

Pathological Variations

Increase in Cardiac Output

Cardiac output increases in the following conditions:

1. Fever. Due to increased oxidative processes
2. Anemia: Due to hypoxia
3. Hyperthyroidism: Due to increased basal metabolic rate.

Decrease in Cardiac Output

Cardiac output decreases in the following conditions:

1. Hypothyroidism: Due to decreased basal metabolic rate
2. Atrial fibrillation: Because of incomplete filling
3. Incomplete heart block with coronary sclerosis or myocardial degeneration: Due to defective pumping action of the heart
4. Congestive cardiac failure: Because of weak contractions of the heart
5. Shock: Due to poor pumping and circulation
6. Hemorrhage: Because of decreased blood volume.

Distribution Of Cardiac Output

• The whole amount of blood pumped out by the right ventricle goes to the lungs.
• But, the blood pumped by the left ventricle is distributed to different parts of the body.
• The fraction of cardiac output distributed to a particular region or organ depends upon the metabolic activities of that region or organ. The distribution of blood pumped out of the left ventricle is
• The heart, which pumps blood to all the other organs, receives the least amount of blood.

Liver: 1500 ml=30%
Kidneys: 1300 mL =26%
Skeletal muscles: 900 mL =18%
Brain: 800 mL =16%
Skin, bone, and GI tract: 300 mL= 6%
Heart: 200 mL = 4%
Total: 5000 mL =100%

Factors Maintaining Cardiac Output

Cardiac output is maintained (determined) by four factors:

1. Venous return
2. Force of contraction
3. Heart rate
4. Peripheral resistance.

1. Venous Return

• Venus return is the amount of blood, which is returned to the heart from different parts of the body.
• When increases, the ventricular filling and cardiac output increase.
• Thus, cardiac output is directly proportional to venous return provided the other factors (force of contraction, heart rate and peripheral resistance) remain constant.

Venous return in turn depends upon five factors:

Respiratory pump

1. Muscle pump
2. Gravity
3. Venous pressure
4. Sympathetic tone.

Respiratory Pump

• The respiratory pump is the respiratory activity that helps return the blood back to the heart during inspiration.
• It is also called an abdominothoracic pump. During inspiration, the thoracic cavity expands and makes the intrathoracic pressure more negative.
• It increases the diameter of the inferior vena cava resulting in increased venous return.
• At the same time, the descent of the diaphragm increases the intra-abdominal pressure which compresses abdominal veins and pushes the blood upward toward the heart, and thereby the venous return is increased.
• The respiratory pump is much stronger in forced respiration and in severe muscular exercise.

Muscle Pump

• Muscle pump is the muscular activity that helps return the blood back to the heart. During muscular activities, the veins are compressed or squeezed.
• Due to the presence of valves in veins, during compression the blood) moved towards the heart. When muscular activity increases the venous return is more.
• When the skeletal muscles contract the vein located n between the muscles is compressed.
• The valve of the vein proximal to the contracting muscles is opened and the blood is propelled towards the heart. The valve of the vein distal to the muscles is closed by the backflow of blood.
• During the relaxation of the muscles, the valve proximal to the muscles closes and prevents the backflow of the blood. And the valve distal to the muscles opens and allows the blood to flow upwards.

Gravity

• Gravitational force reduces the venous return. When a person stands for a long period, gravity causes pooling of blood in the legs, which is called venous pooling.
• Because of venous pooling, the amount of blood returning to the heart decreases.

Venous Pressure

• Venous pressure also affects venous return. The pressure in the venules is 12-18 mm Hg.
• In the smaller and larger veins, the pressure gradually decreases. In the great veins, i.e. inferior vena cava and superior vena cava, the pressure falls to about 5.5 mm Hg.
• At the junction of the vena cavae and right atrium, it is about 4.6 mm Hg. The pressure in the right atrium is still low and it alters during cardiac action.
• It falls to zero during atrial diastole. This pressure gradient at every part of the venous tree helps as a driving force for venous return.

Sympathetic Tone

• The venous return is aided by sympathetic or vasomotor tone also. The sympathetic tone causes constriction of venules.
• The vasoconstriction pushes the blood toward the heart.

2. Force Of Contraction

• The cardiac output is directly proportional to the force of contraction provided the other three factors remain constant.
• The force of contraction depends upon the diastolic period and ventricular filling.
• Frank-Starling law of the heart is applicable to this.
• According to Frank-Starling law, the force of contraction of the heart is directly proportional to the initial length of muscle fibers before the onset of contraction.
• The force of contraction also depends upon preload and afterload.

Preload

• Preload is the stretching of the cardiac muscle fibers at the end of diastole just before contraction.
• It indicates the ventricular filling before its contraction. Preload depends upon venous return and ventricular Fine.
• During the diastolic period due to the ventricular filling, ventricular pressure increases.
• This causes the stretching of muscle fibers resulting in an increase in their length. The length of the muscle fibers determines the force of contraction and cardiac output.
• The force of contraction of the heart and cardiac output are directly proportional to preload.

After load

• After the load is the force against which the ventricles must contract and eject the blood.
• The force is determined by the arterial pressure. At the end of the isometric contraction period, the semilunar valves are opened and blood is ejected into the aorta and pulmonary artery.
• So the pressure increases in these two vessels. Now, the ventricles have to work against this pressure for further ejection.
• Thus, the afterload for the left ventricle is determined by aortic pressure, and the afterload for right ventricular pressure is determined by the pressure in the pulmonary artery.
• The force of contraction of the heart and cardiac output is inversely proportional to afterload.

3. Heart Rate

• Cardiac output is directly proportional to heart rate provided the other three factors remain constant.
• A moderate change in heart rate does not alter the cardiac output. If there is a marked increase in heart rate, cardiac output is increased.
• If there is a marked decrease in heart rate, cardiac output is decreased.

4. Peripheral Resistance

• Peripheral resistance is the resistance offered to blood flow at the peripheral blood vessels. Peripheral resistance is the resistance or load against which the heart has to pump blood.
• So, the cardiac output is inversely proportional to peripheral resistance. The resistance is offered at arterioles. So, the arterioles are called resistant vessels.
• In the body, the maximum peripheral resistance is offered at the splanchnic region. Other details of peripheral resistance.

Measurement Of Cardiac Output

• Cardiac output is measured by direct methods and indirect methods. Direct methods are used only in animals.
• Indirect methods are used both in animals and human beings.
• Measurement Of Cardiac Output By Direct Methods
• Direct methods which are used to measure cardiac output mi animals are;
• By using a cardio-meter using a flowmeter

By Using Flowmeter

Mechanical flowmeter

• The mechanical flowmeter is used to measure cardiac output or the amount of blood flow to any organ.
• It is used only in animals. It has an inlet, a measuring device in the middle, and an outlet.
• The aorta or the artery entering any organ is cut. The inlet and outlet of the flowmeter are inserted into the cut ends of the blood vessel.
• When the blood passes through the flowmeter the measuring device determines the amount of blood flow.

Electromagnetic flowmeter

Electromagnetic flowmeter Principle:

• The principle of this flowmeter is to develop an electromagnetic field by means of two coils of wire.
• If the coils are placed on either side of a blood vessel, the electromagnetic field is produced around the vessel.
• When blood flows through the vessel, there is an alteration in the electromagnetic field.
• By using appropriate electrodes, the changes in the magnetic field can be detected.
• By connecting the electrodes to an electronic device, the velocity of the blood flow is determined on the basis of the changes in the magnetic field.
• From the velocity of blood flow, the volume of blood flow is calculated.

Instrument: An electromagnetic probe is devised with electromagnetic coils and electrodes.

• The probe has a cleft. The probe is fixed in such a way that the intact blood vessel passes through the cleft.
• And the probe almost encircles the blood vessel. The probe is connected to the electronic device to measure the volume of blood flow.
• The advantage of this flowmeter is that the blood vessel need not be cut open.

Ultrasonic Doppler Flowmeter

Ultrasonic Doppler Flowmeter Principle:

• The sound with a very high frequency is known as ultrasound. It is very much beyond the audible range of human ears.
• The waves of the ultrasound are transmitted through a blood vessel. These sound waves are called transmitted waves.
• While passing through the blood vessels, the sound waves hit the blood cells, particularly the red blood cells, and are reflected back.
• The frequency of the reflected waves is different from that of the transmitted waves.
• This effect is called the Doppler effect (named after the discoverer Johann Christian Doppler).
• The alteration in the frequency of the reflected waves depends upon the velocity of the blood flowing through the blood vessel.
• By detecting the differences between the frequencies of transmitted and reflected sound waves, the velocity of blood flow and then the volume of blood flow are determined.

Instrument:

• The ultrasonic device has piezoelectric crystals, which produce the ultrasonic waves and act as sensors to receive the reflected waves.
• This device is connected to a piece of electronic equipment, which detects the difference between the frequencies of transmitted and reflected waves and, thereby determines the velocity of blood flow and the volume of blood flow.

Disadvantages of Direct Methods

• The direct methods to measure cardiac output can be used only in animals.
• The blood vessel has to be cut open at the risk of the animal’s life
• While using an audiometer, the size of the cardio- meter must be suitable for the size of the heart
• While using a mechanical flowmeter, the diameter of the inlet and the outlet of the flowmeter must be equivalent to the diameter of the blood vessel.

Measurement Of Cardiac Output By Indirect Methods

• Several methods are available to measure cardiac output. Each method has its own advantages and disadvantages.
• Generally, the safe and accurate method is preferred. In view of safety, always noninvasive methods are preferred. The invasive method is also accepted provided it gives accurate results.
• In addition to providing measurement of cardiac output, nowadays the methods are expected to provide other hemodynamic data and some useful information about the structure and movements of valves and chambers of the heart.

Invasive and Noninvasive Methods

• Invasive method refers to a procedure that involves invasion or penetration of healthy tissues, organs, or part of the body by means of perforation, puncture, incision, injection, or catheterization.
• The noninvasive method is a procedure that does not involve invasion or penetration of tissues, organs, or parts of the body.

Different Indirect Methods

The indirect methods used to measure the cardiac output are:

1. To Ficks’s principle
2. Indicator (dye) dilution technique
3. Thermodilution technique
4. Ultrasonic Doppler transducer technique
5. Doppler echocardiography
6. Ballistocardiography.

1. By Fick’s Principle

Adolph Fick described Fick’s principle in 1870.

According to this principle, the amount of a substance taken up by an organ (or by the whole body) or given out in a unit of time is the product of the amount of blood flowing through the organ and the arteriovenous difference of the substance across the organ.

Amount of Arteriovenous substance = blood x difference taken or given low/minute

For example,

The amount of blood flowing through the lungs is 5000 mL/ minute 02 content in arterial blood = 20 mL/100 mL of blood 02 content in venous blood = 15 mL/100 mL of blood

Amount of Arteriovenous oxygen = blood x difference of 02 moved from flow/minute
lungs to blood

= 50000x 20-15/100
= 5000x 5/100

Amount of oxygen moved from lungs to blood = 250 mL/ minute

Modification of Fick’s principle to measure cardiac output

• Fick’s principle is modified to measure the cardiac output or a part of cardiac output (amount of blood to an organ).
• Thus, cardiac output, or the amount of blood flowing through an organ in a given unit of time is determined by the formula given below.
• Cardiac Output = Amount of substance taken or given by the organ/minute /Arteriovenous difference of the substance across the organ

By modifying Fick’s principle, cardiac output Is measured in two ways:

1. By using oxygen consumption
2. By using carbon dioxide evolved.

Measurement of Cardiac Output by Using Oxygen Consumption

• Fick’s principle is used to measure cardiac output by determining the amount of oxygen consumed in the body in a given period of time and dividing this value by the arteriovenous difference across the lungs.
• Cardiac output = O2 Consumed (in mL/minute)/Arteriovenous O2 Difference consumed, a respirometer or BMR apparatus (Benedict Roth apparatus) is used.

Oxygen content in arterial blood: For determining the oxygen content in arterial blood, blood is collected from an artery. Oxygen content is determined by blood gas analysis.

Oxygen content in venous blood: For determining the oxygen content of venous blood, only mixed venous blood is used, since oxygen content is different in different veins

• The mixed venous blood is collected from the right atrium or pulmonary artery.
• It is done by introducing a catheter through the basilar vein of the forearm. Oxygen is determined from this blood by blood gas analysis.

Calculation

For example, in a subject, the following data are obtained.

O2 consumed (by lungs) = 250 mL/minute
O2 content in arterial blood = 20 mL/100 mL of blood
O2 content in venous blood = 15 mL/100 mL of blood

5 mL of oxygen is taken by 100 mL of blood while passing through the lungs.

Thus, 250 mL of oxygen is taken by 5000 mL of blood. Since cardiac output is equivalent to the amount of blood passing through the pulmonary circulation, the cardiac output = 5 liters/minute.

Measurement of Cardiac Output by Using Carbon Dioxide

The cardiac output is also measured by knowing the arteriovenous difference of carbon dioxide and the amount of carbon dioxide that evolved from the lungs.

Thus,

Cardiac output= CO2 evolved(in mL/minute)/Arteriovenous CO2 difference

Calculation

For example, in a subject

C02 removed by lungs = 200 mL/minute
C02 content in arterial blood = 56 mL/100 ml of blood
C02 content in venous blood = 60 mL/100 ml of blood

Since, cardiac output is equal to the amount of blood passing through the lungs (pulmonary circulation), the cardiac output = 5 liters/minute
Nitrous oxide is also used to measure cardiac output, by applying Fick’s principle.

Advantage of measurement of cardiac output by Fick’s principle

The results are accurate.

Disadvantage

It is an invasive method and involves the insertion of a catheter through the subject’s vein.

Indicator (Dye) Dilution Method

• The indicator dilution technique The marker substance used to measure cardiac out is lithium chloride.
• Advantage of indicator dilution technique The results are accurate.

Indicator (Dye) Dilution Method Disadvantage

It is an invasive method and involves the injection of a marker substance.

Thermodilution Technique

• Cardiac output can also be measured by the thermodilution technique or thermal indicator method.
• This method is the modified indicator dilution method. It is the popular method to measure cardiac output.
• In this method, a known volume of cold sterile solution is injected into the right atrium by using a catheter.
• Cardiac output is measured by determining the resultant change in the blood temperature in the pulmonary artery.
• For this purpose, two thermistors (temperature transducers) are used. One of them is placed in the inferior vena cava and the second one is placed in the pulmonary artery.
• A pulmonary artery catheter is used to place the thermistors in their positions.
• A known quantity of cold saline or cold dextrose solution is injected into the inferior vena cava.
• The thermistors determine the temperature of blood entering the heart via the inferior vena cava and the temperature of blood leaving the heart via the pulmonary artery.
• From the values of temperature, cardiac output is measured by applying the indicator dilution technique.

Advantages of the thermodilution technique

• The results are accurate. Even low cardiac output can be measured. Saline is also harmless.
• The catheter can also be used to determine hemodynamic pressures and to collect mixed venous blood.

Thermodilution Technique Disadvantage

• It is an invasive method and it requires catheterization.
• Continuous cardiac output measurement catheter
• Cardiac output can be measured continuously by using a modified pulmonary artery catheter called a continuous cardiac output measurement catheter (CCO catheter).
• CCO catheter works on the thermodilution principle. Instead of injecting cold saline a heating filament that delivers heat directly to blood is used.
• The heating filament is fitted to the ventricular portion of the catheter.
• Cardiac output is measured as done in the thermodilution technique. This method is commonly used in intensive care units (ICU).

4. Esophageal Doppler Transducer Technique

• This technique involves the insertion of a flexible probe into the midthoracic part of the esophagus.
• A pulse wave ultrasonic Doppler transducer is fixed at the tip of the probe.
• This transducer calculates the velocity of blood flow in the descending aorta (refer ultrasonic Doppler flow meter for details).
• The diameter of the aorta is determined by echocardiography. Cardiac output is calculated
• by using the values of the velocity of blood flow and the diameter of the aorta.
• Advantages of esophageal Doppler transducer technique
• The advantage of this method is that cardiac output can be measured continuously. This can be used during cardiac surgery.

Disadvantages

It is an invasive method and results are less accurate.

Doppler Echocardiography

• Doppler echocardiography is a method for detecting the direction and velocity of moving blood within the heart.
• This is also a popular method to measure cardiac output.
• Echocardiography is a diagnostic procedure that uses ultrasound waves (more than 20,000 Hz) to produce an image of the heart muscle.
• Ultrasound waves that reflect or echo off the heart can determine the size, shape, and movement of the valves and chambers, and the flow of blood through the heart.
• During an echocardiographic examination, the patient was barechested on the examination.
• A special g – spread over the chest to help the transducer make contact and slide smoothly over the skin.
• The transducer is a small hand-operated device that is attached to the machine by a flexible cable.
• The transducer is placed against the chest. The transducer produces and directs ultrasound waves into the chest.
• Some of the waves get reflected (or echoed) back to the transducer. The reflection of sound waves depends upon the type of tissues and blood.
• The reflected sound waves are received by the transducer and translated into an image of the heart and displayed on a monitor or recorded on paper or tape.
• Echocardiography may also show the abnormalities in functioning of heart valves or damage to the myocardium from an earlier heart attack.
• When the Doppler principle is applied in echocardiography it enables the determination of direction, rate, and other characteristics of blood flow.
• Doppler echocardiography is based on the changes in the frequency of the reflected sound waves from red blood cells.
• By Doppler echocardiography, the velocity of blood flow through the aortic valve is determined.
• The diameter of the aorta is determined by simple echocardiography. From these values, cardiac output is calculated.

Advantages of Doppler echocardiography

It is a non-invasive technique. It also provides other useful information about the structures and movements of valves and chambers of the heart.

Doppler Echocardiography Disadvantage

This method provides less accurate results. It requires well-trained operators.

Ballistocardiographic Method

• Ballistocardiography is the technique to record the movements of the body caused by ballistic recoil associated with the contraction of the heart and the ejection of blood.
• It is based on Newton’s third law of motion (for every action there is an equal and opposite reaction).
• When the heart pumps blood into the aorta and pulmonary artery, a recoiling force is exerted against the heart and the body.
• It is similar to of ballistic recoil when a bullet is fired from a riffle.
• Pulsations due to this ballistic recoil can be recorded graphically by making the subject lie on a suspended bed movable in the long axis of the body.
• The cardiac output is determined by analyzing the graph obtained.

Advantage of Ballistocardiography

The only advantage is that it is a non-invasive method commonly used technique because it involves cub. Some procedures for calibrating the equipment and analyzing the graph. It also does not provide accurate results.

Cardiac Catheterization

Cardiac Catheterization Definition

• The catheter is a thin radiopaque tube, made up of elastic web, rubber, plastic, glass, or metal.
• Cardiac catheterization is an invasive procedure in which a catheter is inserted intravascularly into any chamber of the heart or blood vessel.
• Cardiac catheterization is helpful to study the different variables of hemodynamics both in normal and diseased states.
• Cardiac catheterization was discovered by a German medical student Werner Forsmann, who practiced this technique first himself.
• Conditions When Cardiac Catheterization Is Performed

Cardiac catheterization is generally performed:

1. Whenever there is a need to determine the anatomical and physiological status of heart and blood vessels
2. Whenever there is a need to confirm the suspected cardiac disease of a patient.

Most commonly, the need for cardiac catheterization arises when clinical assessments indicate the rapid deterioration of a patient’s health.

Cardiac Catheterization Procedure

Cardiac catheterization is performed by percutaneous insertion of a catheter into the peripheral blood vessel by needle puncture.

Left Heart Catheterization

• It is done by passing the catheter through the femoral artery, brachial artery, or axillary artery.
• The catheter is guided into the left ventricle under fluoroscopic observation via the aorta. From the left ventricle, the catheter is advanced into the left atrium.
• In patients with aortic stenosis or prosthetic (artificial) valves, the direct left ventricular puncture is performed.
• Under local anesthesia, a needle with a catheter is inserted through the thoracic wall at the level of the apex beat.
• When the needle enters the left ventricle, the catheter is advanced through the needle into the left ventricle and later the needle is removed.
• The latest technology includes catheterization through the radial artery which is called transradial catheterization.

Right Heart Catheterization

• Right heart catheterization is usually performed by venous puncture via the femoral vein.
• The catheter can also be introduced via the internal jugular vein, subclavian vein, or medial vein.
• Under fluoroscopic observation, the catheter is advanced into the right atrium.
• From the right atrium, it can be guided into the right ventricle and also into the pulmonary artery.

Uses Of Cardiac Catheterization

• Cardiac catheterization is useful for both diagnostic and therapeutic purposes.
• It gives crucial information about the need for cardiac surgery, coronary angioplasty, and other therapeutic procedures.
• It also gives information about anticipated risks and reversibility in the patient’s condition during cardiac surgery or other therapeutic interventions.

Diagnostic Uses of Cardiac Catheterization

1. Blood samples are collected during cardiac catheterization to measure oxygen saturation and the concentration of ischemic metabolites like lactate
2. Cardiac output is measured by using Fick’s principle, indicator dilution technique, or thermodilution technique during cardiac catheterization
3. Angiography is done with the help of catheterization. Angiography or arteriography is the diagnostic or therapeutic radiography (imaging technique) in which the fluoroscopic picture is used to visualize the blood-filled structures like cardiac chambers, arteries, and veins of the heart and other blood vessels by using a radiopaque contrast medium.
   1. It is used to determine the obstruction or occlusion of coronary blood vessels or other blood vessels.
   2. It is also used to determine the anomalies of coronary blood vessels.
4. Various pressures are determined by attaching a pressure transducer to the cardiac catheter. By the right heart catheterization, the following pressures are measured:
   1. Right atrial pressure
   2. Right ventricular pressure
   3. Pulmonary arterial pressure
   4. Pulmonary capillary wedge pressure.

By left heart catheterization, the following pressures are measured:

1. Aortic pressure
2. Left ventricular pressure
3. Left atrial pressure.

Therapeutic Uses of Cardiac Catheterization – Interventional Cardiology

• Cardiac catheterization is performed for various therapeutic procedures.
• Interventional cardiology is a branch of cardiology that deals with the performance of traditional surgical procedures by cardiac catheterization.

It helps in:

1. Thrombolysis
2. percutaneous transluminal coronary angioplasty.
3. Laser coronary angioplasty
4. Catheter ablation

1. Thrombolysis

• Thrombolysis (reperfusion therapy) is the procedure used to break up and dissolve a thrombus (clot) in the coronary artery of a patient affected by acute myocardial infarction due to coronary thrombus.
• Cardiac catheterization is used for intracoronary administration of thrombolytic agents which cause thrombolysis.

The thrombolytic agents are:

1. Tissue plasminogen activator
2. Streptokinase
3. Urokinase

All these thrombolytic agents convert plasminogen into plasmin which degrades fibrin in clots and restores normal blood flow.

2. Percutaneous transluminal coronary angioplasty

• Coronary angioplasty means the correction of narrowed or totally obstructed lumen of blood vessels by mechanical methods.
• In percutaneous transluminal coronary angioplasty (PTCA), a narrowed coronary artery is dilated by inflating a balloon attached to the tip of the catheter that
• is introduced into the blood vessel. Sometimes, a stent (expandable wire mesh) is introduced into the corrected blood vessel by the catheter to keep the vessel in a dilated state.

3. Laser coronary angioplasty

• The catheter is also used to emit laser (Light Amplification by Stimulated Emission of Radiation) energy.
• The laser energy that is emitted into the occluded coronary artery vaporizes the atherosclerotic plaque in the diseased vessel.
• This technique is called laser coronary angioplasty.

4. Catheter ablation

• It is the procedure to destroy (ablate) an area of cardiac tissue that blocks the electrical pathway or produces abnormal electrical impulses resulting in cardiac arrhythmias such as supraventricular tachycardia (SVT) or Wolff-Parkinson-White syndrome.
• It involves advancing a catheter (with electrodes attached to its tip) toward the heart via either the femoral vein or the subclavian vein.
• When the catheter enters the right atrium, arrhythmia is induced. Then the electrodes at the tip of the catheter record the electrical potentials.
• By using the recordings, the area of the faulty electrical site is pinpointed. This procedure is called electrical mapping.
• Once the damaged site is confirmed, radiofrequency energy is used to destroy the small amount of tissue that disturbs the electrical flow through the heart.
• Thus, a healthy heart rhythm is restored. The tissue is also destroyed by freezing with intense cold (cryoablation).