.

Cardiovascular

System

THE HEART

Heart

Heart is a central pumping organ. It receives and pumps out blood to the

whole body Shape : Conical or Roughly heart shaped

(like heart of playing card) Size : 12 cm from base to apex.

6 cm antero- posteriorly.

Heart

Situation : situated in the middle mediastinum in between the two lungs, obliquely placed behind the body of sternum and the adjoining portions of ribs and cartilages : about one third of it is on the right side and two third of it on the left side of the middle.

ANATOMY OF HEART

The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little larger than the size of your fist.

By the end of a long life, a person's heart may have beat (expanded and contracted) more than 3.5 billion times.

ANATOMY OF HEART

In fact, each day, the average heart beats 100,000 times, pumping about 2,000 gallons (7,571 liters) of blood.

By the end of a long life, a person's heart may have beat (expanded and contracted) more than 3.5 billion times.

ANATOMY OF HEART

In fact, each day, the average heart beats 100,000 times, pumping about 2,000 gallons (7,571 liters) of blood.

Heart is located between our lungs in the middle of our chest, behind and slightly to the left of our breastbone (sternum).

A double-layered membrane called the pericardium surrounds our heart like a sac.

ANATOMY OF HEART

The outer layer of the pericardium surrounds the roots of our heart's major blood vessels and is attached by ligaments to our spinal column, diaphragm, and other parts of our body.

ANATOMY OF HEART

The inner layer of the pericardium is attached to the heart muscle.

A coating of fluid separates the two layers of membrane, letting the heart move as it beats, yet still be attached to our body

ANATOMY OF HEART

Size, Shape, Location of the Heart

Size of a closed fist Shape

Apex: Blunt rounded point of cone

Base: Flat part at opposite of end of cone

Located in thoracic cavity in mediastinum

Functions of the Heart Generating blood pressure Routing blood

Heart separates pulmonary and systemic circulations

Ensuring one-way blood flow Heart valves ensure one-way flow

Regulating blood supply Changes in contraction rate and force

match blood delivery to changing metabolic needs

Parts of Heart

Heart has got four chambers, with some openings.

The chambers are : Receiving Chambers - a. Right Atrium b. Left Atrium Distributing Chambers - c. Right Ventricle d. Left Ventricle

Parts of Heart

The upper chambers are called the left and right atria, and

The lower chambers are called the left and right ventricles.

A wall of muscle called the septum separates the left and right atria and the left and right ventricles.

Parts of Heart

The left ventricle is the largest and strongest chamber in your heart. The left ventricle's chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into our body.

Base

Apex

Opening of Heart

Heart has got four openings :

a. Right Atrioventricular Opening

b. Left Atrioventricular Opening

c. Pulmonary Opening

d. Aortic Opening

Valves of Heart

Four types of valves regulate blood flow through our heart:

a. The tricuspid valve  

b. The pulmonary valve c. The mitral valve d. The aortic valve

Valves of Heart

The tricuspid valve  

The tricuspid valve regulates blood flow between the right atrium and right ventricle.  

The pulmonary valve

The pulmonary valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to your lungs to pick up oxygen.

The mitral valve

The mitral valve lets oxygen-rich blood from our lungs pass from the left atrium into the left ventricle.

The aortic valve

The aortic valve opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, our body's largest artery, where it is delivered to the rest of the body.

Functions of Valve

Valves help in the flow of blood in one direction.

Prevent regurgitation of back flow of blood by their direction during opening & closure.

They are concerned with the production of heart sound.

Surface Anatomy of the Heart (anterior view)

Surface Anatomy of the Heart (posterior view)

Internal Anatomy of the Heart

Blood Flow Through Heart ???

HowHeart

Circulate Oxygenated Blood

Throughout The Body ?

Lets Seeeee…………

?

Blood Flow Through Heart : Revision

QUIZ – Blood Circulation

Heart/Cardiac Muscles

The heart is the pump that keeps blood circulating throughout the body and thereby transports nutrients, breakdown products, antibodies, hormones, and gases to and from the tissues.

Junctional Tissues of Heart

Cardiac muscle consist especially of certain specialized structures which are responsible for initiation & transmission of cardiac impulses at a regular & faster rate than rest of the muscle.

These are called Junctional tissues of heart.

Junctional Tissues of Heart

Junctional tissues are :

1. The Sinus node

2. The internodal atrial pathway

3. The AV Node

4. The Bundle of His & its Branches

5. Purkinjee System

Anatomy of the Cardiac Conduction System

The Sinoatrial (SA) Node: The Body's Natural Pacemaker

What is Pace maker ?

PM means regulation of motion.

SA node is called Pacemaker of heart.

Because it can initiate normal physiological impulse at first and the rate of discharge is greater than any other part of the heart.

The Sinoatrial Node: The Body's Natural Pacemaker

The sinoatrial node (abbreviated SA node or SAN, also called the sinus node) is the impulse generating (pacemaker) tissue located in the right atrium of the heart.

The Sinoatrial Node: The Body's Natural Pacemaker

It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are modified cardiac myocytes.

SA node : Role as a pacemaker

Although all of the heart's cells possess the ability to generate the electrical impulses (or action potentials) that trigger cardiac contraction, the sinoatrial node is what normally initiates it, simply because it generates impulses slightly faster than the other areas with pacemaker potential.

SA node : Role as a pacemaker

Because cardiac myocytes, like all muscle cells, have refractory periods following contraction during which additional contractions cannot be triggered, their pacemaker potential is overridden by the sinoatrial node.

SA node : Role as a pacemaker

Cells in the SA node will naturally discharge (create action potentials) at about 70-80 times/minute. Because the sinoatrial node is responsible for the rest of the heart's electrical activity, it is sometimes called the primary pacemaker.

SA node : Role as a pacemaker

If the SA node does not function, or the impulse generated in the SA node is blocked before it travels down the electrical conduction system, a group of cells further down the heart will become the heart's pacemaker.

SA Node : Blood Supply

In the majority of patients, the SA node receives blood from the right coronary artery, meaning that a myocardial infarction occluding it will cause ischemia in the SA node unless there is a sufficiently good anastomosis from the left coronary artery. If not, death of the affected cells will stop the SA node from triggering the heartbeat.

SA Node : Blood Supply

If not, death of the affected cells will stop the SA node from triggering the heartbeat.

SA node : Nerve Supply

The SA node is richly innervated by vagal and sympathetic fibers. This makes the SA node susceptible to autonomic influences.

SA node : Nerve Supply

Stimulation of the vagus nerve causes decrease in the SA node rate (thereby causing decrease in the heart rate).

SA node : Nerve Supply

Stimulation via sympathetic fibers causes increase in the SA node rate (thereby increasing the heart rate).

SA Node : Functions

It can initiate the physiological cardiac impulse before any other part of the heart.

It can discharge impulse at a rate of about 70-80 impulse/min

Internodal Pathway

It is the pathway that conduct the impulse from the SA node to AV node and left atrium.

These internodal tracts contain pukinjee type of fibres.

Internodal Pathway : Functions

Serve as preperential pathways for conduction of impulse from SA node to AV node & Left Atrium.

AV Node

The atrioventricular node (abbreviated AV node) is the tissue between the atria and the ventricles of the heart, which conducts the normal electrical impulse from the atria to the ventricles.

AV Node

An important property that is unique to the AV node is decremental conduction. This is the property of the AV node that prevents rapid conduction to the ventricle in cases of rapid atrial rhythms, such as atrial fibrillation or atrial flutter.

AV Node

AV node is normally the only conducting pathway between the atria and the ventricle.

AV Node : Functions

It receives impulse originating from SA node and transmit it to the ventricle through the Bundle of His at a rate of 0.1 m/Sec.

AV Node : Functions

AV node can produce impulse when SA node can fail to produce impulse.

So it is called ‘ reserve pace-maker ‘

The rate of AV nodal impulse 40-60 impulse/min

Bundle Of His or AV Bundle

Bundle Of His extends from AV node. The bundle of His is a collection of

heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node.

The fibers of the Bundle of His allow electrical conduction to occur more easily and quickly than typical cardiac muscle. They are an important part of the electrical conduction system of the heart as they transmit the impulse from the AV node (the ventricular pacemaker) to the rest of the heart.

Bundle Of His or AV Bundle

If the Bundle of His is blocked, it will result in dissociation between the activity of the atria and that of the ventricles, otherwise called a third degree heart block.

A third degree block is very serious medical condition that will most likely require an artificial pacemaker.

Bundle Of His : Pathology

Conduction : Its main function is to conduct the Atrial impulses into ventricle.

Rhythmicity : When SA node & AV node fails, the Bundle of his can originate cardiac impulse 30-36 impulse/min.

Bundle Of His : Functions

Purkinjee Fiber

Purkinje fibers (or Purkyne tissue) are located in the inner ventricular walls of the heart, just beneath the endocardium.

These fibers are specialized myocardial fibers that conduct an electrical stimulus or impulse that enables the heart to contract in a coordinated fashion.

Purkinje fibers work with the sinoatrial node (SA node) and the atrioventricular node (AV node) to control the heart rate.

Purkinjee Fiber : Functions

During the ventricular contraction portion of the cardiac cycle, the Purkinje fibers carry the contraction impulse from the left and right bundle branches to the myocardium of the ventricles.

Purkinjee Fiber : Functions

This causes the muscle tissue of the ventricles to contract and force blood out of the heart — either to the pulmonary circulation (from the right ventricle) or to the systemic circulation (from the left ventricle).

Purkinjee Fiber : Functions

Sequence of events in the electrical excitation of the heart

Properties Of Heart Muscle

1. Autorhythmicity

2. Conductivity

3. Excitability & Contractility

4. Refractory Period

5. Tonicity

Refractory Period

Absolute: Cardiac muscle cell completely insensitive to further stimulation

Relative: Cell exhibits reduced sensitivity to additional stimulation

Long refractory period prevents tetanic contractions

Cardiac Cycle

Cardiac cycle is the term used to describe the sequence of events that occur as a heart works to pump blood through the body. The frequency of the cardiac cycle is the heart rate.

Cardiac Cycle

Every single 'beat' of the heart involves three major stages:

Atrial systole, Ventricular systole and Complete cardiac diastole.

Cardiac Cycle

The term diastole is synonymous with relaxation of a muscle.

Throughout the cardiac cycle, the blood pressure increases and decreases.

Atrial systole Atrial systole is the contraction of the

heart muscle (myocardia) of the left and right atria.

Both atria contract at the same time. The term systole is synonymous with contraction (movement or stretching) of a muscle.

Atrial systole

Electrical systole is the electrical activity that stimulates the myocardium of the chambers of the heart to make them contract.

This is soon followed by Mechanical systole, which is the mechanical contraction of the heart.

Atrial systole

As the atria contract, the blood pressure in each atrium increases, forcing additional blood into the ventricles.

The additional flow of blood is called atrial kick.

Atrial systole

Atrial kick is absent if there is loss of normal electrical conduction in the heart, such as during atrial fibrillation, atrial flutter, and complete heart block.

Atrial systole

Ventricular systole

Ventricular systole is the contraction of the muscles (myocardia) of the left and right ventricles.

The closing of the mitral and tricuspid valves (known together as the atrioventricular valves) at the beginning of ventricular systole cause the first part of the "lub-dub" sound made by the heart as it beats.

Formally, this sound is known the First Heart Tone, or S1.

Ventricular systole

The second part of the "lub-dub" (the Second Heart Tone, or S2), is caused by the closure of the aortic and pulmonic valves at the end of ventricular systole.

Ventricular systole

Ventricular systole

Complete cardiac diastole

Cardiac Diastole is the period of time when the heart relaxes after contraction in preparation for refilling with circulating blood. Ventricular diastole is when the ventricles are relaxing, while atrial diastole is when the atria are relaxing. Together they are known as complete cardiac diastole.

Complete cardiac diastole

Events in the cardiac cycle:

Cardiac Cycle

Cardiac muscle is myogenic, which means that it is self-exciting. This is in contrast with skeletal muscle, which requires either conscious or reflex nervous stimuli for excitation.

Regulation of the cardiac cycle

Regulation of the cardiac cycle

The heart's rhythmic contractions occur spontaneously, although the frequency or heart rate can be changed by nervous or hormonal influences such as exercise or the perception of danger. For example, the phrenic nerve accelerates heart rate and the vagus nerve decelerates heart rate.

The rhythmic sequence of contractions is coordinated by the sinoatrial (SA) and atrioventricular (AV) nodes. The sinoatrial node, often known as the cardiac pacemaker, is located in the upper wall of the right atrium and is responsible for the wave of electrical stimulation (See action potential) that initiates atrial contraction.

Regulation of the cardiac cycle

Once the wave reaches the AV node, situated in the lower right atrium, it is delayed there before being conducted through the bundles of His and back up the Purkinje fibers, leading to a contraction of the ventricles.

The delay at the AV node allows enough time for all of the blood in the atria to fill their respective ventricles.

Regulation of the cardiac cycle

In the event of severe pathology, the AV node can also act as a pacemaker; this is usually not the case because their rate of spontaneous firing is considerably lower than that of the pacemaker cells in the SA node and hence is overridden.

Regulation of the cardiac cycle

Heart sounds

The heart sounds are the noises (sound) generated by the beating heart and the resultant flow of blood through it.

This is also called a heartbeat.

In cardiac auscultation, an examiner uses a stethoscope to listen for these sounds, which include heart tones, or sounds, produced by sudden blood deceleration after the heart valves close, heart murmurs, and adventitious sounds, or clicks.

Heart sounds

Heart sounds are usually divided into the normal heart sounds and the pathological sounds which indicate disease.

The two distinct normal heart tones are often described as a lub and a dub (or dup), and occur in sequence with each heart beat.

Heart sounds

Murmurs are generated by turbulent flow of blood within the heart.

Stenosis, or impaired opening of a heart valve, causes turbulence as blood flows through it.

Heart sounds

Valve insufficiency, or regurgitation, allows backflow of blood when the valve is supposed to be closed.

In these situations, murmurs will be heard in the corresponding part of each cardiac cycle.

Heart sounds

First heart tone, or S1, "lub" : The first heart tone, or S1, is caused by

the sudden block of reverse blood flow due to closure of the atrioventricular valves, mitral and tricuspid, at the beginning of ventricular contraction, or systole.

Normal heart sounds

When the pressure in the ventricles rises above the pressure in the atria, incoming venous blood flow suddenly reverses back toward the atria, catching and closing the inlet valves and preventing regurgitation of blood from the ventricles back into the atria.

The S1 sound results from reverberation within the blood associated with the sudden block of flow reversal.

Normal heart sounds

Second heart tone, or S2 , "dub" :

The second heart tone, or S2, is caused by the sudden block of reversing blood flow due to closure of the aortic valve and pulmonic valve at the end of ventricular systole, i.e beginning of ventricular diastole.

Normal Heart sounds

As the left ventricle empties, its pressure falls below the pressure in the aorta, aortic blood flow quickly reverses back toward the left ventricle and is stopped by aortic (outlet) valve closure.

Normal Heart sounds

Similarly, as the pressure in the right ventricle falls below the pressure in the pulmonary artery, the pulmonic (outlet) valve closes.

The S2 sound results from reverberation within the blood associated with the sudden block of flow reversal.

Normal Heart sounds

Heart Sounds

First heart sound or “lubb” Atrioventricular valves and surrounding fluid

vibrations as valves close at beginning of ventricular systole

Second heart sound or “dupp” Results from closure of aortic and pulmonary

semilunar valves at beginning of ventricular diastole, lasts longer

Third heart sound (occasional) Caused by turbulent blood flow into ventricles and

detected near end of first one-third of diastole

Abnormal sounds Heart murmurs are produced as a result of

turbulent flow of blood, turbulence sufficient to produce audible noise.

They usually are heard as a whooshing sound.

The term murmur only refers to a sound believed to originating within blood flow though or near the heart; rapid blood velocity is necessary to produce a murmur.

Abnormal sounds

Clicks: These are short, high-pitched sounds. The atrioventricular valves of patients with

mitral stenosis may open with an opening snap on the beginning of diastole.

Abnormal sounds

Patients with mitral valve prolapse may have a mid-systolic click along with a murmur.

Aortic and pulmonary stenosis may cause an ejection click immediately after S1.

Rubs: Patients with pericarditis, an inflammation

of the sac surrounding the heart (pericardium), may have an audible pericardial friction rub. This is a characteristic scratching, creaking, high-pitched sound emanating from the rubbing of both layers of inflammated pericardium.

Abnormal sounds

It is the loudest in systole, but can often be heard also at the beginning and at the end of diastole.

It is very dependent on body position and breathing, and changes from hour to hour.

Abnormal sounds

Cardiac output

Cardiac output is the volume of blood that ejected by each ventricle per minute.

It is equal to the heart rate multiplied by the stroke volume.

Therefore, if there are 70 beats per minute, and 70 ml blood is ejected with each beat of the heart, the cardiac output is 4900 ml/minute.

This value is typical for an average adult at rest, although cardiac output may reach up to 30 liters/minute during extreme exercise.

Cardiac output

Stroke volume volume of blood ejected by a ventricle during

systole Depends on:

Preload Degree of stretch prior to contraction

Contractility Forcefulness of contraction

Afterload Pressure that must be exceeded

before ejection of blood from ventricles can occur

Did you know? The average adult body contains about 5 Lit. – 7 Lit. of

blood, so this means all of our blood is pumped through our hearts about once every minute.

Cardiac Index

The cardiac output per minute per square

meter of body surface area is called cardiac index.

The average value is =

3.5 lit/min/sq m of body surface area

Minute Volume

It is the volume of blood ejected by each ventricle per minute.

It can be calculated by multiplying the rate of Heart per minute by stroke volume.

Minute Volume : HR/min x SV

Factors Affecting Cardiac OutputPhysiological factors Age Sex Surface Area Posture Exercise Emotion Temperature

Pathological factors Hyperthyroidism Anemia Fever Fibrillation & Flutter Pagets Disease Arterio-Venous

Fistual

Cardiac Output Decrease in : Hypothyroidism Haemorrhage Congestive Cardiac Failure Shock Oligaemia

Regulation Of Cardiac Output :

Effect of various conditions on cardiac output :

No Change Sleep Moderate

Changes in Environmental temperature

Increase Anxiety &

Excitement (50-100%)

Eating (30%) Exercise High

Environmental temperature

Pregnancy Epinephrine

Decrease Sitting or

Standing Position from lying position (20-30%)

Rapid Arrhythmias

Heart Disease

Factors Regulating Cardiac Output

Venous Return Force Of Contraction Frequency Of Heart Beat Ejection Fraction Peripheral Resistance

Venous Return

It is the amount of blood that comes from periphery to right atria of heart in each minute.

It is equal to cardiac output. It is about 5 lit/min

Factors Affecting Venous Return

Muscular Activity Pumping Action of Heart Pressure Gradient in Vessels Respiratory Pump Gravity Vasomotor Tone

Peripheral resistance

It is the resistance in which blood has to overcome while passing through the periphery.

Total peripheral resistance refers to the cumulative resistance of the thousands of arterioles in the body, or the lungs, respectively.

It is approximately equal to the resistance of the arterioles, since the arterioles are the chief resistance vessels in the body.

Total peripheral resistance

Total Peripheral Resistance =

Mean Arterial Pressure / Cardiac Output

Arterioles are referred to as resistance vessels because of their peripheral resistance.

Total peripheral resistance

Factors Affecting peripheral Resistance

Velocity of blood Viscosity of blood Elasticity of Arterial walls State of lumen of blood vessels

Heart rate

Heart rate is a term used to describe the frequency of the cardiac cycle.

It is considered one of the four vital signs. Usually it is calculated as the number of contractions (heart beats) of the heart in one minute and expressed as "beats per minute" (bpm).

Heart rate

So in very simple expression…..

The number of heart beat per minute is called Heart Rate.

Heart rate : Normal ranges

The heart beats up to 120 times per minute in childhood.

When resting, the adult human heart beats at about 70 bpm (males) and 75 bpm (females), but this rate varies among people.

However, the reference range is nominally between 60 bpm (if less termed bradycardia) and 100 bpm (if greater, termed tachycardia).

Resting heart rates can be significantly lower in athletes.

The infant/neonatal rate of heartbeat is around 130-150 bpm.

The toddler's about 100–130 bpmThe older child's about 90–110 bpm, and The adolescent's about 80–100 bpm.

Heart rate : Normal Ranges

Factors Affecting Heart Rate

Higher Centre Respiration Cardio-vascular

reflexes

a. Baro-receptor reflex

b. Bain-bridge reflex Temperature Intra cranial pressure

Muscular Exercise Age Sex Endocrine Factors

Adrenaline - HR

Thyroxin - HR

Posterior pituitary Hormone - HR

Factors Increasing Heart Rate

Activity of BR Activity of arterial

stretch receptor Inspiration Excitement Anger Most Pain Stimuli

Hypoxia Exercise Fever Epinephrine &

Norepinephrine Thyroid Hormone Bainbridge Reflex

Factors Decreasing Heart Rate

Activity of BR Expiration Fear Grife Intra-cranial pressure Stimulation of Pain fibres in trigeminal

nerve. Athletes

Heart rate

Several factors contribute to regulation of heart rate: (1) Autonomic regulation (medullary CV centre)

Receives input from higher brain centres and variety of sensory receptors

Proprioceptors Chemoreceptors Baroreceptors

Sympathetic output increases heart rate and contractility Parasympathetic impulses decrease heart rate

Little effect on contractility does not innervate ventricular myocardioum

Heart rate

Several factors contribute to regulation of heart rate: (2) Chemical regulation

Cardiac activity depressed by Hypoxia Acidosis Alkalosis

Hormones Catecholamines and thyroid hormones

increase HR and contractility Cations

Alterations in balance of K+, Na+ and Ca2+ alter HR and contractility

Heart rate Several factors contribute to regulation of heart rate:

(3) Other factors Age

U shaped curve Gender

Female HR higher Physical fitness

Resting bradycardia Body temperature

Increase causes SA node to discharge more rapidly

Tachycardia

Tachycardia is an abnormally rapid beating of the heart, defined as a resting heart rate of 100 or more beats per minute in an average adult.

It can have harmful effects, in two ways.

Tachycardia

First, when the heart beats too rapidly, it performs inefficiently (since there is not enough time for the ventricles to fill completely), causing cardiac output to diminish.

Second, it increases the work of the heart, causing it to require more oxygen while also reducing the blood flow to the cardiac muscle tissue, increasing the risk of ischemia and resultant infarction.

Causes of Tachycardia

Increased Body Temperature Autonomic and endocrine causes :

An increase in sympathetic nervous system stimulation causes the heart rate to increase, both by the direct action of sympathetic nerve fibers on the heart and by causing the endocrine system to release hormones such as epinephrine (adrenaline), which have a similar effect.

continued….

Increased sympathetic stimulation is usually due to physical or psychological stress (the so-called "fight or flight" response), but can also be induced by stimulants such as amphetamines.

Endocrine disorders such as pheochromocytoma can cause epinephrine release and tachycardia independent of the nervous system.

Hyperthyroidism is also known to cause tachycardia

Causes of Tachycardia

Hemodynamic responses :

The body contains several feedback mechanisms to maintain adequate blood flow and blood pressure. If blood pressure decreases, the heart beats faster in an attempt to raise it. This is called reflex tachycardia.

This can happen in response to a decrease in blood volume (through dehydration or bleeding), or an unexpected change in blood flow.

continued…

Causes of Tachycardia

The most common cause of the latter is orthostatic hypotension (also called postural hypotension), a sudden drop of blood pressure that occurs with a change in body position (e.g., going from lying down to standing up).

When tachycardia occurs for this reason, it is called

postural orthostatic tachycardia syndrome (POTS). continued…

Causes of Tachycardia

Fever and infection leading to sepsis are also common causes of tachycardia, primarily due to increase in metabolic demands and compensatory increase in heart rate.

Causes of Tachycardia

Tachycardic arrhythmias: If the heart's electrical system is functioning

normally, except that the rate is in excess of 100 beats per minute, it is called sinus tachycardia.

This is caused by any of the factors mentioned above, rather than a malfunction of the heart itself.

Continued….

Causes of Tachycardia

Supraventricular tachycardia (SVT) occurs when an abnormal electrical impulse originates above the ventricles, but instead of causing a single beat and a pause, it causes rapid local impulse cycling and initiates many rapid beats.

Ventricular tachycardia is a similar phenomenon occurring within the tissue of the ventricles, causing an extremely rapid rate with poor pumping action

Causes of Tachycardia

Sinus tachycardia

Sinus tachycardia is a rhythm with elevated rate of impulses originating from the SA node, defined as a rate greater than 100 beats/min in an average adult.

The normal heart rate in the average adult ranges from 60-100 beats/min.

Etiology

Sinus tachycardia is usually a response to normal physiological situations, such as exercise and an increased sympathetic tone with increased catecholamine release --- stress, fright, flight, anger.

Pheochromocytoma Sepsis

Pulmonary embolism Acute coronary ischemia

and myocardial infarction Chronic pulmonary

disease Hypoxia

Intake of nicotine, caffeine, or illicit drugs

Fever Anxiety Dehydration Malignant Hyperthermia Hypovolemia with Hypotension and Shock Anemia Heart failure Hyperthyroidism

Other causes include:

Etiology

Symptoms

Sinus tachycardia is often asymptomatic. If the rate is greater than 140/minute, cardiac output may fall due to the markedly reduced ventricular filling time.

Rapid rates increase myocardial oxygen demand and reduces coronary blood flow, thus precipitating an ischemia heart or valvular disease.

Wolff-Parkinson-White syndrome

Wolff-Parkinson-White syndrome (WPW) is a syndrome of pre-excitation of the ventricles of the heart due to an accessory pathway known as the Bundle of Kent.

This accessory pathway is an abnormal electrical communication from the atria to the ventricles.

Wolff-Parkinson-White syndrome Pathophysiology

In normal individuals,

electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart.

The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart.

This function of the AV node is important, because if the signals generated in the atria of the heart were to increase in rate (as they do during atrial fibrillation or atrial flutter), the AV node will limit the electrical activity that conducts to the ventricles.

Wolff-Parkinson-White syndrome Pathophysiology

For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse of 150 beats per minute).

Another important property of the AV node is that it slows down individual electrical impulses.

Wolff-Parkinson-White syndrome Pathophysiology

Individuals with WPW syndrome have an accessory pathway that connects the atria and the ventricles, in addition to the AV node.

This accessory pathway is known as the bundle of Kent.

This accessory pathway does not share the rate-slowing properties of the AV node, and may conduct electrical activity at a significantly higher rate than the AV node.

Wolff-Parkinson-White syndrome Pathophysiology

For instance, if an individual had an atrial rate of 300 beats per minute, the accessory bundle may conduct all the electrical impulses from the atria to the ventricles, causing the ventricles to activate at 300 beats per minute.

Wolff-Parkinson-White syndrome Pathophysiology

The ventricles are not capable of activating in a uniform manner at rates that fast and will fibrillate instead (ventricular fibrillation).

If not corrected rapidly, ventricular fibrillation leads to sudden cardiac death (SCD).

Wolff-Parkinson-White syndrome Pathophysiology

Lown-Ganong-Levine syndrome

Lown-Ganong-Levine syndrome (LGL) is a syndrome of pre-excitation of the ventricles due to an accessory pathway providing an abnormal electrical communication from the atria to the ventricles.

It is grouped with Wolff-Parkinson-White syndrome as an atrioventricular re-entry tachycardia (AVRE).

Pathophysiology : Same as WPW.

Bradycardia

The term bradycardia means a slow heart rate. Decreased heart rate below the lower normal

physiological limit, usually 60 beats/min, is called bradycardia.

Bradycardia : Causes

There are generally two types of problems that result in bradycardias:

a.Disorders of the sinus node, and

b.Disorders of the atrioventricular node (AV node).

a. Disorders of the sinus node

With sinus node dysfunction (sometimes called sick sinus syndrome), there may be disordered automaticity or impaired conduction of the impulse from the sinus node into the surrounding atrial tissue (an "exit block").

b.Disorders of the atrioventricular node

Atrioventricular conduction disturbances may result from impaired conduction in the AV node, or anywhere below it, such as in the His bundle.

Causes of Bradycardia

Athletes Vagal stimulation Shock

Effect of potassium (k++) on Heart

K++ in ECF

Extreme Dilation of Heart

HR

Effect of Ca++ on Heart

Calcium ions

Spastic contraction

HR

Effect of Na+ on Heart

Na+ ion

Depresses cardiac function

Dilate & flaccid the heart

Slows HR

Effect of Na+ on Heart

Na compete with Calcium, i.e

Na in ECF

Effectiveness of calcium

Contraction

HR

Effects of Adrenaline

It increases the rate & force of contraction, as it

a. Stimulates the SA & AV node

b. Conductivity

c. Automaticity

Effects of Acetylcholine

It decreases the rate & force of contraction

Effects of Atropine At low dose it lowers the heart rate by vaga

stimulation But at high dose it increases heart rate by

medullary stimulation.

Shock

It is an abnormal physiological condition resulting from inadequate propultion of blood to the aorta thus causes inadequate blood flow perfusing the capillaries of tissues & organs.

Shock is a serious medical condition where the tissue perfusion is insufficient to meet the required supply of oxygen and nutrients.

Types of shock

Hypovolaemic shock This is the most common type of shock and based on insufficient circulating volume.

Its primary cause is loss of fluid from the circulation from either an internal or external source.

An internal source may be haemorrhage. External causes may include extensive bleeding, high output fistulae or severe burns.

Cardiogenic shock - This type of shock is caused by the failure of the heart to pump effectively.

This can be due to damage to the heart muscle, most often from a large myocardial infarction.

Other causes of cardiogenic shock include arrhythmias, cardiomyopathy, congestive heart failure (CHF), contusio cordis or cardiac valve problems.

Types of shock

Anaphylactic shock - Caused by a severe anaphylactic reaction to an allergen, antigen, drug or foreign protein causing the release of histamine which causes widespread vasodilation, leading to hypotension and increased capillary permeability

Types of shock

Obstructive shock - In this situation the flow of blood is obstructed which impedes circulation and can result in circulatory arrest.

Aortic stenosis hinders circulation by obstructing the ventricular outflow tract

Types of shock

Aortic valve stenosis (AS)

Aortic valve stenosis (AS) is a heart condition caused by the incomplete opening of the aortic valve.

The aortic valve controls the direction of blood flow from the left ventricle to the aorta.

When in good working order, the aortic valve does not impede the flow of blood between these two spaces.

Aortic valve stenosis (AS)

Under some circumstances, the aortic valve becomes narrower than normal, impeding the flow of blood.

This is known as aortic valve stenosis, or aortic stenosis, often abbreviated as AS.

Aortic valve stenosis (AS)

Heart Block

Occasionally transmission of the impulse through the heart is blocked at a critical point in the conductive system is called Heart Block.

Sites of Heart Block

Between the atria & ventricle One of the bundle branches of Purkinjee

system Rarely between the SA node & the atrial

musculature

Types of Heart Block

When conduction of impulse between atria & ventricle is blocked.

There are three types of heart blocks :

1. AV heart block

2. Bundle of His block

3. SA heart block

AV heart block

There are four basic types of AV nodal block:

First degree heart block Second degree heart block Third degree heart block (Complete heart block)

First degree heart block :

First degree heart block may be due to conduction delay in the AV node, in the His-Purkinje system (made up by the bundle of His and the Purkinje fibers), or a combination of the two. The majority of cases are due to a dysfuction of the AV node

AV heart block

Second degree heart block :

The presence of second degree AV block is diagnosed when one or more (but not all) of the atrial impulses fail to conduct to the ventricles due to impaired conduction.

AV heart block

Third degree heart block (Complete heart block) :

Third degree heart block also known as complete heart block, in which the impulse generated in the top half of the heart (typically the SA node in the right atrium) does not propagate to the left or right ventricles.

AV heart block

Bundle of His block

When the conduction of impulse from AV node to bundle of his is impaired.

It may be right or left bundle block.

SA Heart Block

Here SA node fails to generate or fail to transmit the impulse from SA node to the atrial muscle.

Cause : Over Vagal Stimulation Vasovagal Syndrome Overdose of Digitalis

Cardiac Arrest

It is a condition in which the rhythmic contraction of heart occasionally stop due to disturbed cardiac metabolism.

Hypoxia of Heart during anesthesia or when the coronary blood flow to the SA node is blocked.

Severe myocardial disease.

Cardiac Arrest : Causes

Flutter

Flutter means extremely rapid heart beat with reasonably coordinated contraction of cardiac muscle.

The rate of flutter is usually 200-250 times per beat.

The flutter occurs frequently in the atria & rarely in ventricle.

It occurs when atria become greatly dilated due to valvular heart disease.

Fibrilation

Fibrilation means a very high frequency of heart beat with incordinated contraction of cardiac muscle.

Hemorrhage

It means abnormal internal or external discharge of blood.

It may be atrial, venous or capillary.

Effects of Aging on the Heart

Gradual changes in heart function, minor under resting condition, more significant during exercise

Hypertrophy of left ventricle Maximum heart rate decreases Increased tendency for valves to function

abnormally and arrhythmias to occur Increased oxygen consumption required to

pump same amount of blood

Blood Pressure

Blood Pressure is the lateral pressure exerted by the moving column of blood on the vessel wall by its contained blood while flowing through it .

Blood Pressure =

Cardiac output (CO) X Peripheral Resistance(PR)

CO= Heart rate (HR) X Stroke Volume (SV)

Typical values for a resting,healthy adult human are approximately 120 mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg), with large individual variations.

Blood Pressure : Normal range

Regulation of Blood Pressure

BARORECEPTORS

&

THE SYMPATHETIC NERVOUS SYSTEM

Baro reflexes involving the sympathetic nervous system are responsible for the rapid moment to

moment regulation of BP.

Pressure sensitive neurons send impulses to cardiovascular centers through the spinal cord

Reflex response of

Sympathetic out put Parasympathetic output

to heart & vasculature

Activity of

β1adrenoceplors

on heart

activity of 1 adre,

vasocons trictions on smooth muscle