Ch 10 HO

Learning Outcomes: Cardiovascular System

• 10.1: Use medical terminology related to the cardiovascular system.

• 10.2: Identify the chambers, valves, and features of the heart.

• 10.3: Relate the structure of cardiac muscle to its function.

• 10.4: Explain why the heart does not fatigue.

• 10.5: Trace blood flow through the heart.

• 10.6: Describe the heart’s electrical conduction system.

• 10.7: Describe the events that produce the heart’s cycle of contraction and relaxation.

• 10.8: Interpret a normal EKG, explaining what is happening electrically in the heart.

• 10.9: Calculate cardiac output given heart rate and stroke volume.

  • Cardiac Output (CO) is calculated as: $CO = HR Imes SV$ (Heart Rate times Stroke Volume).

• 10.10: Explain the factors that govern cardiac output.

• 10.11: Summarize nervous and chemical factors that alter heart rate, stroke volume, and cardiac output.

• 10.12: Locate and identify the major arteries and veins of the body.

• 10.13: Compare the anatomy of the three types of blood vessels.

• 10.14: Describe coronary and systemic circulatory routes.

• 10.15: Explain how blood in veins is returned to the heart.

• 10.16: Explain the relationship between blood pressure, resistance, and flow.

• 10.17: Describe how blood pressure is expressed and how mean arterial pressure and pulse pressure are calculated.

  • Pulse Pressure (PP) is calculated as: $PP = SP - DP$ (Systolic Pressure minus Diastolic Pressure).

  • Mean Arterial Pressure (MAP) is calculated as: $MAP = DP + frac{1}{3}PP$

• 10.18: Explain how blood pressure and flow are regulated.

• 10.19: Explain the effect of exercise on cardiac output.

• 10.20: Summarize the effects of aging on the cardiovascular system.

• 10.21: Describe common diagnostic tests used to diagnose heart and vessel disorders.

• 10.22: Describe heart and vessel disorders and relate abnormal function to pathology.

Overview: Word Roots and Combining Forms

• arter/o: artery

• arteri/o: artery

• ather/o: fatty substance

• atri/o: atrium

• brady/: slow

• cardi/o: heart

• coron/o: heart

• pericardi/o: pericardium

• rhythm/o: rhythm

• sphygm/o: pulse

• steth/o: chest

• tachy/: rapid

• vas/o: vessel

• vascul/o: vessel

• ven/i: vein

• ven/o: vein

• ventricul/o: ventricle

• The heart serves as a pump to circulate blood through a system of vessels.

Heart Anatomy

• Heart Location:

  • Located in the mediastinum.

  • Behind the sternum and just above the diaphragm.

  • Tilted, with two-thirds resting left of the midsagittal plane.

  • Size of an adult fist.

  • Weighs about 300 g, or 10 oz (about 0.45% of a man’s body weight and about 0.40% of a woman’s).

• Base and Apex:

  • Base lies beneath the 2nd rib.

  • Apex lies at the left 5th intercostal space at the midclavicular line.

• Surfaces of the Heart:

  • Anterior (Front) surface: Mostly formed by the right atrium and the right ventricle, with the left ventricle contributing a small portion. The right ventricle is the heart area that lies most directly behind the sternum.

  • Inferior (Diaphragmatic) surface: Is formed by the left and right ventricles and a small portion of the right atrium. The left ventricle makes up most of the inferior surface.

  • The heart’s base (upper portion): is formed by the left atrium, a small portion of the right atrium, and portions of the superior and inferior venae cavae and the pulmonary veins.

  • The heart’s apex (lower portion): is formed by the left ventricle’s tip.

Pericardium

• The heart is surrounded by the pericardium.

  • Outer fibrous layer

    • Attached to diaphragm, sternum, vertebral column, connective tissues

  • Inner parietal pericardium

    • Lines fibrous pericardium

    • Folds back to form visceral pericardium, which is the outer heart wall

• Clinical Application:

  • The right and left phrenic nerves, which innervate the diaphragm, pass through the fibrous pericardium as they descend to the diaphragm.

  • Because these nerves supply sensory fibers to the fibrous pericardium, the parietal serous pericardium, and the mediastinal pleura, discomfort related to conditions affecting the pericardium may be felt in the areas above the shoulders or lateral neck.

Heart Wall

• Epicardium (visceral pericardium)

  • Outermost layer

  • Contains blood vessels that nourish the heart

• Myocardium

  • Layer of cardiac muscle

  • Provides force for contraction

• Endocardium

  • Inner layer of simple squamous epithelium

  • Also lines inside of blood vessels attached to heart

Heart Wall Anatomy: Myocardium

• Consisting of cardiac muscle fibers (cells) responsible for the heart’s pumping action.

• The innermost half of the myocardium is called the subendocardial area.

• The outermost half is called the subepicardial area.

• The myocardium’s muscle fibers are separated by connective tissues that have a rich supply of capillaries and nerve fibers.

Myocardium: Syncytium

• The arrangement of the cardiac muscle fibers and intercalated disks allows cardiac muscle to function as a syncytium, which means that all fibers will become stimulated when one cardiac muscle fiber is stimulated.

• The heart consists of two syncytia, atrial and ventricular, which are separated by fibrous tissue.

• The presence of two syncytia allows the atria to contract a short time before ventricular contraction.

Wall of the Heart

• Epicardium (Visceral Pericardium)

  • Composition:

    • Serous membrane of connective tissue covered with epithelium and including blood capillaries, lymph capillaries, and nerve fibers

  • Function:

    • Forms a protective outer covering; secretes serous fluid

• Myocardium

  • Composition:

    • Cardiac muscle tissue separated by connective tissue and including blood capillaries, lymph capillaries, and nerve fibers

  • Function:

    • Contracts to pump blood from the heart chambers

• Endocardium

  • Composition:

    • Membrane of epithelium and underlying connective tissue, including blood vessels

  • Function:

    • Forms a protective inner lining of the chambers and valves

Clinical Application: Ischemia

• The main coronary arteries lie on the epicardial surface of the heart.

  • They feed the subepicardial area first before entering the myocardium and supplying the heart’s inner layers with oxygenated blood

• The heart’s subendocardial area is at the greatest risk of ischemia because it has a high oxygen demand and is fed by the coronary arteries’ most distal branches.

Heart Anatomy: Chambers and Valves

• Chambers

  • 2 atria

    • Receive blood from veins

  • 2 ventricles

    • Pump blood to arteries

  • Atrial septum

  • Interventricular septum

Heart Chambers and Valves Function

• Right atrium:

  • Receives blood returning from systemic circuit (from the superior and inferior venae cavae and coronary sinus); pumps blood to RV

• Right ventricle:

  • Receives blood from the RA; pumps blood to lungs

• Left atrium:

  • Receives blood from the pulmonary veins; pumps blood to LV ventricle

• Left ventricle:

  • Receives blood from the LA; pumps blood to systemic circuit

Heart Valves

• Blood flows in one direction through the heart due to valves.

  • Atrioventricular valves:

    • Separate the atria from the ventricles.

    • Allow flow from atria to ventricles.

    • Prevent backflow.

  • Semilunar valves:

    • Located at the base of blood vessels attached to ventricles.

    • Allow flow from ventricles to Pulmonary trunk and Aorta.

    • Prevent backflow.

• Atrioventricular valves (AV):

  • Tricuspid valve:

    • lies between the right atrium and the right ventricle. It consists of three separate cusps or flaps.

  • Bicuspid (Mitral) valve:

    • lies between the left atrium and the left ventricle. It consists of two separate cusps or flaps.

    • The mitral valve is so named because of its resemblance to a miter, which is a double-cusp bishop’s hat, when open.

More on Heart Valves

• Chordae Tendineae (Tendinous Cords):

  • are thin strands of connective tissue attached between the underside of the AV valves and the papillary muscles.

  • Papillary muscles project inward from the ventricular walls. When the ventricles contract and relax, so do the papillary muscles. The papillary muscles adjust their tension on the chordae tendineae, preventing them from bulging too far into the atria. Thus, the chordae tendineae and papillary muscles serve as anchors.

  • Because the chordae tendineae are thin and string-like, they are sometimes called “heart strings.”

• Semilunar valves (SL):

  • They have three cusps shaped like half-moons. The SL valves prevent the backflow of blood from the aorta and pulmonary arteries into the ventricles.

    • Pulmonary (Pulmonic) valve:

      • lies between the right ventricle and the pulmonary trunk.

    • Aortic valve:

      • lies between the left ventricle and the Aorta.

Heart Valve Location and Function

• Tricuspid valve:

  • Right AV orifice

  • Prevents blood from moving from the right ventricle into the right atrium during ventricular contraction

• Pulmonary valve:

  • Entrance to pulmonary trunk

  • Prevents blood from moving from the pulmonary trunk into the right ventricle during ventricular relaxation

• Mitral valve:

  • Left AV orifice

  • Prevents blood from moving from the left ventricle into the left atrium during ventricular contraction

• Aortic valve:

  • Entrance to aorta

  • Prevents blood from moving from the aorta into the left ventricle during ventricular relaxation

Side and Cusps

• Right Side

  • Tricuspid / 3 cusps

  • Pulmonary

• Left Side

  • Mitral / 2 cusps

  • Aortic

• Entry: Atrioventricular (AV valves)

• Exit: Semilunar

Clinical Application: Improper Valve Function

• Improper valve function (Valvular heart disease):

  • Valvular prolapse: a valve flap inverts. Prolapse can occur if one valve flap is larger than the other or if the chordae tendineae stretch markedly or rupture.

  • Valvular regurgitation (incompetence or insufficiency): blood can flow backward, or regurgitate, if one or more of the heart’s valves does not close properly.

  • Valvular stenosis: a valve narrows, stiffens, or thickens. The heart must work harder to pump blood through a stenosed valve.

Cardiac Muscle Tissue

• Cardiac muscle is striated, is branching, has one nucleus per cell, and has intercalated disks.

• Cardiac muscle tissue is specially adapted to stay aerobic.

  • Cardiac muscle cells have many very large mitochondria to perform aerobic respiration.

  • Cardiac muscle cells are rich in myoglobin.

  • Cardiac muscle cells are rich in glycogen.

  • Cardiac muscle cells can use a variety of fuels as energy sources (glucose, fatty acids, amino acids, and ketones).

Skeleton of the Heart

• Rings of dense connective tissue surround origins of pulmonary trunk and aorta, and orifices between atria and ventricles.

  • Provide attachments for heart valves and muscle fibers

  • Prevent excess dilation of heart chambers during contraction

• These rings, along with other fibrous masses in the interventricular septum, make up the skeleton of the heart.

Blood Supply to the Heart

• The left and right coronary arteries supply blood to tissues of the heart. The coronary arteries are first 2 branches of the aorta.

• The myocardium receives its fresh supply of oxygenated blood from the coronary arteries during ventricular diastole

Coronary Arteries

• The coronary arteries encircle the myocardium like a crown or corona.

• The main coronary arteries lie on the outer (i.e., epicardial) surface of the heart. Thus, the epicardium has a rich blood supply to draw from.

• Branches of the main coronary arteries penetrate the heart’s muscle mass and supply the subendocardium with blood.

• The diameter of these “feeder branches” (i.e., collateral circulation) is much narrower.

• The tissues supplied by these branches get enough blood and oxygen to survive, but they do not have much extra blood flow.

• The three major epicardial coronary arteries include:

  • Left anterior descending (LAD) artery [= anterior interventricular artery]: branch from the left coronary artery.

  • Circumflex (Cx) artery: branch from the left coronary artery.

  • Right coronary artery (RCA).

• A person is said to have coronary artery disease (CAD) if there is more than 50% diameter narrowing (i.e., stenosis) in one or more of these vessels.

Right Coronary Artery

• It travels along the groove between the right atrium and the right ventricle.

• The major branches of the right coronary artery are:

  • The marginal artery.

  • The posterior interventricular artery.

• It supplies the following structures:

  • Right atrium

  • Right ventricle

  • Inferior surface of the left ventricle (in about 85% of individuals)

  • Posterior surface of the left ventricle in 85%

  • Sinoatrial (SA) node in about 60%

  • AV bundle in 85% to 90%

Left Coronary Artery

• It has two primary branches:

  • Left anterior descending artery (LAD, which is also called the anterior interventricular artery):

  • Circumflex (Cx) artery.

• Left anterior descending artery (LAD):

  • It travels along the groove that lies between the right and left ventricles (i.e., the anterior interventricular sulcus) toward the heart’s apex.

  • In most patients, the LAD travels around the left ventricle’s apex and ends along the left ventricle’s inferior surface.

  • In the remaining patients, the LAD does not reach the inferior surface. Instead, it stops at or before the heart’s apex.

  • Occlusion of the proximal LAD coronary artery has been referred to as the “widow maker” because of its association with sudden cardiac arrest when it is blocked.

• The major branches of the LAD are the septal and diagonal arteries. The LAD supplies blood to the following:

  • The anterior surface of the left ventricle

  • Part of the lateral surface of the left ventricle

  • The anterior two-thirds of the interventricular septum

• It circles around the left side of the heart in a groove on the back of the heart that separates the left atrium from the left ventricle called the coronary sulcus. It supplies blood to the following:

  • The left atrium

  • Part of the lateral surface of the left ventricle

  • The inferior surface of the left ventricle in about 15% of individuals

  • The posterior surface of the left ventricle in 15%

  • The SA node in about 40%

  • The AV bundle in 10% to 15%

Coronary Artery Dominance

• The coronary artery that forms the posterior descending artery is considered the dominant coronary artery.

• In most people, a branch of the RCA becomes the posterior descending artery, which is described as a right-dominant system.

• If the Cx branches and ends at the posterior descending artery, the coronary artery arrangement is described as a left-dominant system.

• In some people, neither coronary artery is dominant. If damage to the left ventricle’s posterior wall is suspected, a cardiac catheterization usually is necessary to determine which coronary artery is involved.

Coronary Arteries and the Areas they feed

• Right coronary artery

  • Portion of Conduction System Supplied

    • Sinoatrial (SA) node (about 60%)

    • Atrioventricular (AV) bundle (85% to 90%)

  • Portion of Myocardium Supplied

    • Right atrium

    • Right ventricle

    • Inferior surface of left ventricle (about 85%)

    • Posterior surface of left ventricle (85%)

• Left anterior descending artery

  • Portion of Conduction System Supplied

    • Most of right bundle branch

    • Part of left bundle branch

  • Portion of Myocardium Supplied

    • Anterior surface of left ventricle

    • Part of lateral surface of left ventricle

    • Anterior two-thirds of interventricular septum

• Circumflex artery

  • Portion of Conduction System Supplied

    • SA node (about 40%)

    • AV bundle (10% to 15%)

  • Portion of Myocardium Supplied

    • Left atrium

    • Part of lateral surface of left ventricle

    • Inferior surface of left ventricle (about 15%)

    • Posterior surface of left ventricle (15%)

Acute Coronary Syndromes

• Acute coronary syndrome (ACS) is a term that refers to distinct conditions caused by pathologic events involving abruptly reduced coronary artery blood flow.

• This results in conditions that range from myocardial ischemia or injury to death (i.e., necrosis) of the heart muscle.

• The usual cause of an ACS is the rupture of an atherosclerotic plaque.

Angina Pectoris

• Angina pectoris is chest discomfort or other related symptoms that occur suddenly when the heart’s increased oxygen demand temporarily exceeds the blood supply.

• Angina is a symptom of myocardial ischemia, and it most often occurs in patients with CAD that involves at least one coronary artery. However, it can be present in patients with normal coronary arteries.

• Angina also occurs in people with uncontrolled high blood pressure or valvular heart disease.

Acute Coronary Syndromes - Blocked Coronary Artery

• The area supplied by a blocked coronary artery goes through a sequence of events that have been identified as zones of ischemia, injury, and infarction.

• Each zone is associated with characteristic ECG changes.

• When myocardial ischemia or infarction is suspected, an understanding of coronary artery anatomy and the heart areas that each vessel supplies helps you predict which coronary artery is blocked and anticipate problems associated with blockage of that vessel.

• If the blocked coronary vessel is quickly opened to restore blood flow and oxygen to the injured area, no tissue death occurs. Methods of restoring blood flow may include giving clot-busting drugs (i.e., fibrinolytics) or performing endovascular therapies.

Inflammatory Markers

• When myocardial cells die, such as during myocardial infarction, substances in intracardiac cells pass through broken cell membranes and leak into the bloodstream.

• These substances are called inflammatory markers, cardiac biomarkers, or serum cardiac markers, and include creatine kinase myocardial band (CK-MB), myoglobin, troponin I, and troponin T.

• Blood tests are used to measure their levels in the blood and determine if an infarction has occurred.

Coronary Veins

• The coronary (cardiac) veins travel alongside the arteries.

• The coronary sinus (lies in the sulcus that separates the atria from the ventricles) receives blood from the great, middle, and small cardiac veins; a vein of the left atrium; and the left ventricle’s posterior vein. The coronary sinus drains into the right atrium.

• The anterior cardiac veins do not join the coronary sinus but empty directly into the right atrium.

Heart Physiology: Blood Flow

• Blood flows from the venae cavae to the right atrium

• Through the tricuspid valve to the right ventricle

• Through the pulmonary valve to the pulmonary trunk

• To the pulmonary arteries, and to the lungs

• Blood then returns from the lungs through the pulmonary veins

• To the left atrium

• Through the bicuspid valve, to the left ventricle

• Through the aortic valve, to the rest of the body

Pulmonary and Systemic Circuits

• Pulmonary circuit

  • Right side of the heart

  • Pumps blood to the lungs and back

• Systemic circuit

  • Left side of the heart

  • Pumps blood to the body, from the heart

Cardiac Conduction System

• Cardiac muscle is autorhythmic.

• Electrical impulses start at the sinoatrial (SA) node.

  • Pacemaker

  • Right atria and to the atrioventricular (AV) node

• AV bundle and bundle branches to the Purkinje fibers

More about Cardiac Conduction System

• Electrical energy stimulates heart muscle:

  • Nodes

    • Sinoatrial (SA) node (pacemaker): upper RA wall

    • Atrioventricular (AV) node: bottom of interatrial septum

  • Specialized fibers

    • Atrioventricular bundle (bundle of His): top of IV septum

    • Purkinje fibers (conduction myofibers)

  • Intercalated disks

Major Components of the Cardiac Conduction System

• SA (Sinoatrial) Node:

  • Pacemaker; initiates rhythmic contractions of the heart

• Internodal Atrial Muscle:

  • Conducts impulses from SA node to atria

• Junctional Fibers:

  • Conduct impulses from SA node to AV node

• AV (Atrioventricular) Node:

  • Conducts impulses to AV Bundle; delays impulse, so that atria finish contracting before ventricles contract

• AV (Atrioventricular) Bundle (of His):

  • Conducts impulses rapidly between AV node and bundle branches

• Left and Right Bundle Branches:

  • Split off from AV bundle, conduct impulses to Purkinje fibers on both sides of heart

• Purkinje Fibers:

  • Large fibers that conduct impulses to ventricular myocardium

Cardiac Cycle

• A cardiac cycle is one complete contraction and relaxation of the heart.

• Systole is contraction, and diastole is relaxation.

• Systole increases pressure and decreases volume.

• Diastole decreases pressure and increases volume.

• Atria contract while ventricles relax. Ventricles contract while atria relax.

• Series of event occurring in the heart during one heartbeat

  • Systole (active phase, contraction)

  • Diastole (resting phase)

Phases of the Cardiac Cycle

• Atrial systole

  • SA node fires = atria depolarize

  • Atrial contract together

  • Atrial volume decreases

  • Ventricular volume and pressure increases

• Atrial diastole

  • Atrial repolarize together

  • Atria relax

  • Atria fill

• Ventricular systole

  • Impulse passes through AV node to the Purkinje fibers

  • Ventricles depolarized

  • Ventricles contract together

  • Papillary muscles contract ensuring the AV valves stay closed

  • Ventricular pressure increases - semilunar valve pushes open

  • Ventricles empty

  • Ventricular volume decreases

• Ventricular diastole

  • Ventricles repolarize

  • Ventricles relax

  • Ventricular pressure decreases

  • Ventricular volume increases

  • Ventricles fill

Atrial Kick

• As the atria fill with blood, the pressure within the atrial chamber rises. This pressure forces the tricuspid and mitral valves open, and the ventricles begin to fill, gradually increasing the pressure within the ventricles.

• About 80% of this blood flows directly through the atria and into the ventricles before the atria contract (passive filling).

• When the atria contract, an additional 20% of the returning blood is added to the ventricles. This additional contribution of blood resulting from atrial contraction is called atrial kick.

Isovolumetric Contraction

• The term isovolumetric contraction describes the brief period between the start of ventricular systole and the semilunar valves’ opening.

• During this period, the ventricular volume remains constant as the pressure within the chamber rises sharply.

• The term Preload, which is also called the end-diastolic volume, is the force exerted on the ventricles’ walls at the end of diastole.

Apical Impulse

• When the left ventricle contracts, it normally produces an impulse that can be felt at the heart’s apex (apical impulse).

• This palpable impulse occurs because the left ventricle rotates forward as it contracts. In a normal heart, this causes the apex of the left ventricle to hit the chest wall. You may be able to see the apical impulse in thin individuals.

Valves Open and Close During Ventricular Contraction

• When the ventricles contract, what valves close?

  • Atrioventricular valves

• What valves open?

  • Semilunar Valves

Heart Sounds

• Heart Sounds during the Cardiac Cycle

  • Listened to with a stethoscope

  • Lubb-dupp (pause) lubb-dupp

    • 1st heart sound (S1) Lubb:

      • closing of AV valves during ventricular systole

      • is heard loudest at the apex of the heart

    • 2ND heart sound (S2) Dupp:

      • closing of semilunar valves during ventricular diastole

      • is heard loudest at the base of the heart

• Heart Sounds during the Cardiac Cycle

  • A third heart sound (S3) is a low-frequency sound produced by ventricular filling.

  • It is a normal variant in children and healthy young adults, but when heard in people older than 40 years of age, it is generally considered abnormal and is often associated with heart failure.

  • An S1–S2–S3 sequence is called a ventricular gallop or gallop rhythm. It sounds like “Kentucky”—Ken (S1) -tuck (S2) -y (S3).

Heart Sound Characteristics

• Lubb (S1)

  • Long, low pitched

  • Ventricular systole

  • Closure of AV valves

• Dupp (S2)

  • Shorter and sharper

  • Ventricular diastole

  • Closure of semilunar valves

Heart Sound Auscultation Points

• Tricuspid

  • Just to the left of the lower part of the sternum near the fifth intercostal space

• Mitral (bicuspid)

  • Heart apex in the left fifth intercostal space at the midclavicular line

• Pulmonic (pulmonary)

  • Left second intercostal space close to the sternum

• Aortic

  • Right second intercostal space close to the sternum

Abnormal Heart Sounds

• Murmers: Abnormal heart sounds, usually due to faulty valve action

  • Stenosis: Narrowing of a valve opening.

  • Regurgitation: Blood leaking back, incomplete closure.

  • Causes:

    • Congenital defects

    • Heart disease

    • Psychological variations

      • Organic: Structural changes in the heart or great vessels

      • Functional: Normal sounds of rapid ventricular filling

Cardiac Rhythm

• A normal pace (sinus rhythm) is usually 70 to 80 beats per minute.

• Vagal tone is braking provided by the parasympathetic nervous system

• An ectopic focus occurs when any part of the conduction system other than the SA node is setting the pace.

• A nodal rhythm occurs if the AV node is the ectopic focus.

• Hypoxemia, caffeine, nicotine, electrolyte imbalance, & some drugs may cause an ectopic focus.

Normal Sinus Rhythms and Related Terms

• Normal Sinus Rhythm is higher in infants and lower in athletes

• Bradycardia: <60

• Tachycardia: >100

• Sinus arrhythmia: regular variation of HR (normal)

Arrhythmia and Other Conduction Issues

• Arrhythmia is an abnormal heart rhythm.

• Heart block, in which one part of the heart’s conduction system fails to send its signals

• Backup Pacemakers: Damage to SA node may lead to AV node taking over, and act as secondary pacemaker; 40-60 BPM.

• The ventricles may only be 20 to 40 times per minute

Ectopic Focuses and Premature Beats

• An ectopic focus occurs when any part of the conduction system other than the SA node is setting the pace.

• Premature beat (extra systole):

  • Beat that occurs before the next expected beat, due to

    • Caffeine

    • Nicotine

    • Psychological

    • Heart disease

More Arrythmia Definitions

• Fibrillation:

  • Uncoordinated, chaotic contraction of small areas of myocardium

  • Atrial fibrillation not life-threatening

  • Ventricular fibrillation is often fatal

• Flutter:

  • Rapid, regular contraction of a heart chamber, 250-350 beats/min

Replacing the Heart Techniques

• Heart Transplant

  • Replacement of most of a failing heart with a donor heart

• Left Ventricular Assist Device (LVAD)

  • Mechanical half-heart, used in some cases temporarily, until donor heart is available

• Implantable Replacement Heart

  • Titanium and plastic artificial heart, used in people that cannot have heart transplant, and do not have long to live

• Stem Cell Technology

  • Cardiac muscle tissue can now be cultured from altered somatic cells or from stem cells. This may allow “stem cell heart patches” in the future.

Electrocardiogram

• An electrocardiogram (ECG or EKG) shows the electrical activity of the heart during a cardiac cycle.

• It includes P, Q, R, S, and T waves.

  • P wave: atrial depolarization

  • QRS wave: ventricular depolarization

  • T wave: ventricular repolarization

Cardiac Output

• Cardiac output is the amount of blood ejected by each ventricle of the heart each minute.

• Cardiac output is dependent on heart rate and stroke volume. $CO = HR Imes SV$.

• Cardiac reserve

  • Difference between resting cardiac output and maximum cardiac output

Stroke Volume Dependent Factors

• Heart rate

  • Measured by feeling the pulse

  • Normal heart rate: 64 to 80 bpm

• Stroke volume: amount of blood ejected per beat

  • Depends on:

    • Preload – amount of stretch of the myocardium

      • Frank-Starling law of the heart

    • Contractility – responsiveness of cardiac muscle to contract

    • Afterload – BP pushing back off the semilunar valves

Heart Regulation

• The heart can be regulated by the ANS through the cardiac accelerator and inhibitory centers in the medulla oblongata, which get information from:

  • Proprioceptors

  • Baroreceptors

  • Chemoreceptors

Heart Regulation: Effects

• Chronotropic Effect: Refers to a change in heart rate.

  • A +ve chronotropic effect refers to an ↑ in heart rate.

  • A -ve chronotropic effect refers to an ↓ in heart rate.

• Inotropic effect: Refers to a change in myocardial contractility.

  • A +ve inotropic effect  ↑ in myocardial contractility.

  • A -ve inotropic effect  ↓ in myocardial contractility.

• Dromotropic effect: Refers to the speed of impulse transmission through the conduction system.

  • A +ve dromotropic effect  ↑ in conduction velocity.

  • A -ve dromotropic effect  ↓ in conduction velocity.

Chronotropic Effects of Chemicals

• Epinephrine

  • Positive chronotropic effect

• Other positive chronotropic chemicals

  • Caffeine

  • Norepinephrine

  • Nicotine

  • Thyroid hormone

• Potassium ions have a negative chronotropic effect

Chronotropic Factors of the ANS

• Medulla oblongata

  • Cardiac accelerator center

    • Sympathetic neurons to stimulate the SA and AV nodes to speed up the heart rate

  • Cardiac inhibitory center

    • Parasympathetic neurons of the vagus nerve to keep the SA node at 70 to 80 beats/min (vagal tone)

  • Proprioceptors

    • The information they send alerts the cardiac centers to any change in the body’s activity level.

  • Baroreceptors

    • Located in the aorta and carotid arteries

    • Alert the cardiac centers to any changes in BP:

      • If BP falls, the cardiac accelerator center stimulates the SA and AV nodes to ↑ HR in an effort to restore BP to homeostasis

  • Chemoreceptors

    • Sensors monitor pH, $CO<em>2$, and $O</em>2$ in the blood.

    • Located in:

      • aortic arch