1 Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc. Chapter 17 Cardiac Function.

1Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc.

Chapter 17Chapter 17

Cardiac FunctionCardiac Function


Cardiovascular AnatomyCardiovascular Anatomy

Primary function of the heart is to reduce Primary function of the heart is to reduce the driving force that propels blood through the driving force that propels blood through the vessels of the circulatory systemthe vessels of the circulatory system

Cardiac dysfunction can lead to abnormal Cardiac dysfunction can lead to abnormal function or death of cells throughout the function or death of cells throughout the bodybody

Cardiovascular disease is the leading Cardiovascular disease is the leading cause of mortality in the United Statescause of mortality in the United States


Cardiovascular Anatomy Cardiovascular Anatomy (Cont.)(Cont.)

HeartHeart Located in the mediastinumLocated in the mediastinum

BaseBase ApexApex

Cardiac valves control the direction of Cardiac valves control the direction of blood flow through the heartblood flow through the heart MitralMitral TricuspidTricuspid PulmonicPulmonic AorticAortic





HeartHeart Papillary muscles prevent the valve Papillary muscles prevent the valve

leaflets from bending backward into the leaflets from bending backward into the atria during ventricular contractionatria during ventricular contraction

Heart muscle Heart muscle EndocardiumEndocardium EpicardiumEpicardium PericardiumPericardium





Circulatory SystemCirculatory System Right-sided heart chambers pump Right-sided heart chambers pump

deoxygenated (venous) blood through the deoxygenated (venous) blood through the lungslungs

Left-sided heart chambers pump Left-sided heart chambers pump oxygenated blood through the systemic oxygenated blood through the systemic circulationcirculation




Cardiac CycleCardiac Cycle

Each heartbeat is composed of a period of Each heartbeat is composed of a period of ventricular contraction (systole) followed ventricular contraction (systole) followed by a period of relaxation (diastole)by a period of relaxation (diastole)

Closure of the AV valves causes the first Closure of the AV valves causes the first heart sound, Sheart sound, S1 1

Closure of the semilunar valves causes Closure of the semilunar valves causes the second heart sound, Sthe second heart sound, S22


Cardiac Cycle Cardiac Cycle (Cont.)(Cont.)

Isovolumic ContractionIsovolumic Contraction Following atrial systole the ventricles Following atrial systole the ventricles

contract, causing intraventricular pressure contract, causing intraventricular pressure to rise and the AV valves to close (Sto rise and the AV valves to close (S11))

Volume remains constant during this Volume remains constant during this phasephase

Rate of rise in pressure is an indication of Rate of rise in pressure is an indication of contractilitycontractility



Ventricular EjectionVentricular Ejection Contraction results in a rapid rise in Contraction results in a rapid rise in

ventricular pressure > aortic pressure, ventricular pressure > aortic pressure, forcing the aortic valve to open with rapid forcing the aortic valve to open with rapid ejection of blood from the ventricleejection of blood from the ventricle



Stroke volume (SV) is the amount of blood Stroke volume (SV) is the amount of blood ejected with each contraction of the ejected with each contraction of the ventricle (SV = EDV – ESV)ventricle (SV = EDV – ESV)

End-diastolic volume is the volume of End-diastolic volume is the volume of blood in the ventricle prior to ejectionblood in the ventricle prior to ejection

End-systolic volume is the amount of blood End-systolic volume is the amount of blood that remains in the ventricle after ejectionthat remains in the ventricle after ejection

Ejection fraction = SV/EDVEjection fraction = SV/EDV



Isovolumic RelaxationIsovolumic Relaxation Begins with semilunar valve closure in Begins with semilunar valve closure in

response to falling ventricular pressures response to falling ventricular pressures and ends when the AV valves open to and ends when the AV valves open to allow ventricular fillingallow ventricular filling

Ventricular blood volume remains constant Ventricular blood volume remains constant during this phaseduring this phase







Atrial EventsAtrial Events The atria have 3 characteristic waves:The atria have 3 characteristic waves:

aa wave corresponds to atrial contraction wave corresponds to atrial contraction cc wave represents the AV valve bulging during wave represents the AV valve bulging during

ventricular contractionventricular contraction vv wave corresponds to atrial filling wave corresponds to atrial filling



Aortic and Pulmonary Artery EventsAortic and Pulmonary Artery Events Arterial pressures fall to their lowest value Arterial pressures fall to their lowest value

just prior to semilunar valve opening = just prior to semilunar valve opening = diastolic blood pressurediastolic blood pressure

Arterial pressure reaches its maximum Arterial pressure reaches its maximum during ventricular ejection = systolic during ventricular ejection = systolic pressurepressure

Dicrotic notch reflects closure of the Dicrotic notch reflects closure of the semilunar valvessemilunar valves


Coronary CirculationCoronary Circulation

Coronary arteries supply blood to the heart Coronary arteries supply blood to the heart musclemuscle

Right and left coronary arteries are located Right and left coronary arteries are located in the sinuses of Valsalvain the sinuses of Valsalva


Coronary Circulation Coronary Circulation (Cont.)(Cont.)

Anatomy of the Coronary VesselsAnatomy of the Coronary Vessels Left main coronary artery divides into left Left main coronary artery divides into left

anterior descending and circumflex anterior descending and circumflex branchesbranches Left anterior descending supplies the septal, Left anterior descending supplies the septal,

anterior, and apical areas anterior, and apical areas Circumflex supplies the lateral and posterior Circumflex supplies the lateral and posterior

left ventriclesleft ventricles



Regulation of Coronary Blood FlowRegulation of Coronary Blood Flow Driving pressure and vascular resistance Driving pressure and vascular resistance

to flowto flow Ohm’s law—an increase in driving Ohm’s law—an increase in driving

pressure increases flow, whereas an pressure increases flow, whereas an increase in resistance reduces flowincrease in resistance reduces flow

Coronary driving pressure equals aortic Coronary driving pressure equals aortic blood pressure (ABP) minus right atrial blood pressure (ABP) minus right atrial pressure (RAP)pressure (RAP)(P) = ABP – RAP(P) = ABP – RAP



Coronary Vascular ResistanceCoronary Vascular Resistance Two major determinants:Two major determinants:

Coronary artery diameter adjusted by Coronary artery diameter adjusted by autoregulation, ATP-sensitive potassium autoregulation, ATP-sensitive potassium channels, nitric oxide levels, and autonomic channels, nitric oxide levels, and autonomic nervous systemnervous system

Varying degree of external compression due to Varying degree of external compression due to myocardial contraction/relaxation (most myocardial contraction/relaxation (most coronary blood flow occurs during diastole)coronary blood flow occurs during diastole)


Cardiac MyocytesCardiac Myocytes

Two general typesTwo general types Working cells with mechanical pumping Working cells with mechanical pumping

functionsfunctions Electrical cells that transmit electrical impulsesElectrical cells that transmit electrical impulses

Both produce and transmit action Both produce and transmit action potentialspotentials


Cardiac Myocytes Cardiac Myocytes (Cont.)(Cont.)

Myocyte StructureMyocyte Structure Myocytes behave as a syncytium because Myocytes behave as a syncytium because

they are jointed by gap junctions within the they are jointed by gap junctions within the intercalated disks that permit the flow of intercalated disks that permit the flow of ions from one cell to the nextions from one cell to the next Sarcolemma—T tubulesSarcolemma—T tubules Sarcoplasmic reticulum—calcium ions—Sarcoplasmic reticulum—calcium ions—

ryanodine receptorsryanodine receptors





Structure of the Contractile ApparatusStructure of the Contractile Apparatus Striation due to organized structure of the Striation due to organized structure of the

proteins of the contractile apparatusproteins of the contractile apparatus Actin and myosin proteins form contractile Actin and myosin proteins form contractile

apparatus; are arranged in contractile units apparatus; are arranged in contractile units called sarcomerescalled sarcomeres Z disks (Z line)Z disks (Z line) I bandI band A bandA band M lineM line





Characteristics of Contractile FilamentsCharacteristics of Contractile Filaments Thick filamentsThick filaments

MyosinMyosin• Enzymatic activity and splits ATPEnzymatic activity and splits ATP• TitinTitin

Thin filamentsThin filaments ActinActin

• TropomyosinTropomyosin• TroponinTroponin


Molecular Basis of ContractionMolecular Basis of Contraction

All myocytes of the chamber must shorten All myocytes of the chamber must shorten simultaneously to produce a forceful simultaneously to produce a forceful contractioncontraction

Specialized cells of the conduction system Specialized cells of the conduction system coordinate myocardial contraction coordinate myocardial contraction


Molecular Basis of Contraction Molecular Basis of Contraction (Cont.)(Cont.)

Overview of ContractionOverview of Contraction Excitation-contraction coupling: Excitation-contraction coupling:

Depolarization causes ion channels of the Depolarization causes ion channels of the plasma membrane and T tubules to open plasma membrane and T tubules to open allowing sodium and calcium entry and allowing sodium and calcium entry and release of calcium from the SR. Presence release of calcium from the SR. Presence of free calcium in the sarcoplasm results in of free calcium in the sarcoplasm results in contraction.contraction.



Sliding Filament/Cross-Bridge Theory of Sliding Filament/Cross-Bridge Theory of Muscle ContractionMuscle Contraction Contraction of cardiac muscle by Contraction of cardiac muscle by

shortening of individual sarcomeres due to shortening of individual sarcomeres due to increased overlap of actin and myosin increased overlap of actin and myosin filamentsfilaments

Myosin heads bind to specific sites on Myosin heads bind to specific sites on actin and pull the thin filaments toward the actin and pull the thin filaments toward the center of the sarcomerecenter of the sarcomere





Sliding Filament/Cross-Bridge Theory of Sliding Filament/Cross-Bridge Theory of Muscle ContractionMuscle Contraction ATP hydrolysis provides the energy for cross-ATP hydrolysis provides the energy for cross-

bridging and affects affinity of myosin for actinbridging and affects affinity of myosin for actin Myosin has high affinity for actin when ADP and Myosin has high affinity for actin when ADP and

Pi are bound; low affinity when ATP is boundPi are bound; low affinity when ATP is bound Myosin cycles between high- and low-affinity Myosin cycles between high- and low-affinity

states, making and breaking cross-bridges with states, making and breaking cross-bridges with the actin filamentthe actin filament





Role of Calcium in Muscle ContractionRole of Calcium in Muscle Contraction Contraction is dependent on adequate Contraction is dependent on adequate

calcium ions in the cytoplasmcalcium ions in the cytoplasm Muscle relaxation (lusitropy) is due to Muscle relaxation (lusitropy) is due to

removal of calcium from the cytoplasmremoval of calcium from the cytoplasm This is an energy-requiring processThis is an energy-requiring process





Energy of Muscle RelaxationEnergy of Muscle Relaxation Significant energy required to pump calcium ions Significant energy required to pump calcium ions

out of the cytoplasmout of the cytoplasm Membrane pumps in the sarcolemma and SR Membrane pumps in the sarcolemma and SR

actively move calcium out of the sarcoplasm actively move calcium out of the sarcoplasm against a concentration gradientagainst a concentration gradient

Sarcolemma has 2 different calcium pumpsSarcolemma has 2 different calcium pumps One that requires ATPOne that requires ATP One that uses the potential energy of the sodium One that uses the potential energy of the sodium

gradient to remove calciumgradient to remove calcium SR calcium pumps (SERCAs) require ATPSR calcium pumps (SERCAs) require ATP


Cardiac Energy MetabolismCardiac Energy Metabolism

Uses energy from ATP hydrolysis to drive Uses energy from ATP hydrolysis to drive energy-requiring functionsenergy-requiring functions

Accomplished by glycolytic and oxidative Accomplished by glycolytic and oxidative reactionsreactions


Cardiac Energy Metabolism Cardiac Energy Metabolism (Cont.)(Cont.)

Oxygen UtilizationOxygen Utilization Creatine phosphate (CP)—storage form of Creatine phosphate (CP)—storage form of

ATP ATP CP an immediately available source of CP an immediately available source of

energyenergy Under conditions of low ATP availability, Under conditions of low ATP availability,

CP is converted to ATP by the enzyme CKCP is converted to ATP by the enzyme CK


Cardiac Energy Metabolism Cardiac Energy Metabolism (Cont.)(Cont.)

Substrate UtilizationSubstrate Utilization Primary energy substrates are fatty acids Primary energy substrates are fatty acids

and glucoseand glucose Able to use lactate and ketones when they Able to use lactate and ketones when they

accumulate in the circulationaccumulate in the circulation Able to use a variety of substrates to Able to use a variety of substrates to

produce ATP under varying metabolic produce ATP under varying metabolic conditionsconditions


Cardiac ElectrophysiologyCardiac Electrophysiology

Heart is rhythmically activated by action Heart is rhythmically activated by action potentialspotentials

Action potentials are generated and Action potentials are generated and transmitted by a specialized conduction transmitted by a specialized conduction systemsystem

Many cardiac disorders result from Many cardiac disorders result from disturbances in electrical function that disturbances in electrical function that produce abnormal conduction pathways, produce abnormal conduction pathways, dysrhythmias, and conduction blocksdysrhythmias, and conduction blocks


Cardiac Electrophysiology Cardiac Electrophysiology (Cont.)(Cont.)

Cardiac Resting PotentialCardiac Resting Potential Resting cardiac cells are negatively Resting cardiac cells are negatively

charged on the insidecharged on the inside Difference in potassium ion concentration Difference in potassium ion concentration

across the cell membrane determines across the cell membrane determines resting membrane potentialresting membrane potential

Increase in extracellular potassium Increase in extracellular potassium hypopolarizes the cell while a decrease hypopolarizes the cell while a decrease hyperpolarizes the cellhyperpolarizes the cell



Cardiac Action PotentialCardiac Action Potential Depolarization of cardiac cells to a Depolarization of cardiac cells to a

threshold point results in activation of threshold point results in activation of voltage-sensitive ion channels in the voltage-sensitive ion channels in the membranemembrane

Action potential in atrial and ventricular Action potential in atrial and ventricular cells has 5 characteristic phasescells has 5 characteristic phases

Atrial action potentials are shorter due to Atrial action potentials are shorter due to reduced phase 2reduced phase 2





Rhythmicity of Myocardial CellsRhythmicity of Myocardial Cells Automaticity refers to intermittent, Automaticity refers to intermittent,

spontaneous generation of action spontaneous generation of action potentialspotentials

The rate of rhythmic discharge is The rate of rhythmic discharge is determined by the relative influx of sodium determined by the relative influx of sodium and calcium, versus the efflux of and calcium, versus the efflux of potassiumpotassium





Specialized Conduction System of the Specialized Conduction System of the HeartHeart Normal excitation of the heart Normal excitation of the heart

SA nodeSA node Atrial internodal pathwaysAtrial internodal pathways AV nodeAV node Bundle of HisBundle of His Ventricular bundle branchesVentricular bundle branches Purkinje fibersPurkinje fibers





Autonomic Regulation of RhythmicityAutonomic Regulation of Rhythmicity Sympathetic innervation is widespread to Sympathetic innervation is widespread to

all areas of the heartall areas of the heart Parasympathetic innervation via the vagus Parasympathetic innervation via the vagus

is localized to the SA and AV nodal areasis localized to the SA and AV nodal areas Right vagus nerve supplies SA nodeRight vagus nerve supplies SA node Left vagus nerve supplies AV nodeLeft vagus nerve supplies AV node



Sympathetic activation increases heart Sympathetic activation increases heart rate (chronotropic effect), speed of rate (chronotropic effect), speed of conduction (dromotropic effect), and force conduction (dromotropic effect), and force of contraction (inotropic effect) via binding of contraction (inotropic effect) via binding of NE to of NE to ββ receptors receptors

Parasympathetic stimulation results in Parasympathetic stimulation results in reduction in heart rate, and speed of action reduction in heart rate, and speed of action potential conduction via binding of potential conduction via binding of acetylcholine to muscarinic receptorsacetylcholine to muscarinic receptors


ElectrocardiographyElectrocardiography

As action potentials spread throughout the As action potentials spread throughout the myocardium, electrical current is myocardium, electrical current is transmitted to the body surfacetransmitted to the body surface

A recording of these electrical currents is A recording of these electrical currents is called an electrocardiogram (ECG)called an electrocardiogram (ECG) P wave corresponds to atrial depolarizationP wave corresponds to atrial depolarization QRS complex represents ventricular QRS complex represents ventricular

depolarizationdepolarization T wave reflects ventricular repolarizationT wave reflects ventricular repolarization


Electrocardiography Electrocardiography (Cont.)(Cont.)


Electrocardiography Electrocardiography (Cont.)(Cont.)


Determinants of Cardiac OutputDeterminants of Cardiac Output

Measure of the amount of blood pumped Measure of the amount of blood pumped out of the heart each minuteout of the heart each minute

Normal resting cardiac output is 5-6 Normal resting cardiac output is 5-6 L/minuteL/minute

Cardiac index is a measure of cardiac Cardiac index is a measure of cardiac output relative to body surface areaoutput relative to body surface area

CO = stroke volume x heart rateCO = stroke volume x heart rate


Determinants of Cardiac Output Determinants of Cardiac Output (Cont.)(Cont.)

Determinants of Heart RateDeterminants of Heart Rate Influence by autonomic nervous system—Influence by autonomic nervous system—

release of norepinephrine increases raterelease of norepinephrine increases rate Baroreceptors detect fall in blood pressure Baroreceptors detect fall in blood pressure

and transmit to CNS—parasympathetic and transmit to CNS—parasympathetic system inhibition and cardia sympathetic system inhibition and cardia sympathetic nerve activation increase heart ratenerve activation increase heart rate

Atrial or ventricular overdistention Atrial or ventricular overdistention suppresses parasympathetic influence; suppresses parasympathetic influence; increases heart rateincreases heart rate



Determinants of Stroke VolumeDeterminants of Stroke Volume The volume of blood in the heart (preload)The volume of blood in the heart (preload) The contractile capabilities (contractility)The contractile capabilities (contractility) Impedance opposing ejection of blood Impedance opposing ejection of blood

from the ventricle (afterload)from the ventricle (afterload)



Volume of Blood in the Heart (Preload)Volume of Blood in the Heart (Preload) Frank-Starling law: increased preload Frank-Starling law: increased preload

stretches the sarcomere, resulting in more stretches the sarcomere, resulting in more forceful contractionforceful contraction

There are limits to the improvement in SV There are limits to the improvement in SV with increased diastolic filling with increased diastolic filling





Contractile Capabilities of the Heart Contractile Capabilities of the Heart (Contractility)(Contractility) The amount of contractile proteins in the The amount of contractile proteins in the

muscle cellsmuscle cells Availability of ATPAvailability of ATP Availability of free calcium ions in the Availability of free calcium ions in the

cytoplasmcytoplasm



Impedance to Ejection from the Ventricle Impedance to Ejection from the Ventricle (Afterload)(Afterload) Aortic valve narrowing can significantly Aortic valve narrowing can significantly

increase afterloadincrease afterload Increase in afterload increases pressure Increase in afterload increases pressure

work and requires greater tension work and requires greater tension development within the walls of the development within the walls of the chamber (wall stress)chamber (wall stress)



Cardiac WorkloadCardiac Workload Oxygen requirements of the heart are Oxygen requirements of the heart are

determined by amount of energy (ATP) determined by amount of energy (ATP) exerted to perform its pumping functionexerted to perform its pumping function

Increases in the 4 determinants of CO are Increases in the 4 determinants of CO are the major determinants of energy needsthe major determinants of energy needs

High afterload is most detrimental because High afterload is most detrimental because it increases cardiac workload without it increases cardiac workload without increasing COincreasing CO


Endocrine Function of the HeartEndocrine Function of the Heart

Secretion of Natriuretic PeptidesSecretion of Natriuretic Peptides Atrial natriuretic peptide synthesized by Atrial natriuretic peptide synthesized by

myocytes and released in response to myocytes and released in response to atrial stretchatrial stretch

B-type natriuretic peptide produced and B-type natriuretic peptide produced and released by ventricles in response to released by ventricles in response to chronic overdistentionchronic overdistention

ANP and BNP cause enhanced excretion ANP and BNP cause enhanced excretion of sodium and water by the kidneysof sodium and water by the kidneys


Tests of Cardiac FunctionTests of Cardiac Function

ElectrocardiographyElectrocardiography Provides graphic illustration of the Provides graphic illustration of the

electrical currents generated by cardiac electrical currents generated by cardiac cellscells Standard bipolar limb leads I, II, IIIStandard bipolar limb leads I, II, III Unipolar augmented leads aVR, aVL, aVFUnipolar augmented leads aVR, aVL, aVF 12-lead ECGs12-lead ECGs


Tests of Cardiac Function Tests of Cardiac Function (Cont.)(Cont.)

Magnetic Resonance Imaging and Magnetic Resonance Imaging and Computed TomographyComputed Tomography Useful for imaging cardiac structuresUseful for imaging cardiac structures May identify:May identify:

Myocardial thickeningMyocardial thickening Pericardial sac diseasePericardial sac disease Valvular structuresValvular structures Congenital malformationsCongenital malformations Coronary plaque burdenCoronary plaque burden



EchocardiographyEchocardiography Uses reflected sound waves to provide an Uses reflected sound waves to provide an

image of cardiac structure and motion image of cardiac structure and motion within the chestwithin the chest

Useful in diagnosis of heart enlargement, Useful in diagnosis of heart enlargement, valvular disorders, collections of fluid in the valvular disorders, collections of fluid in the pericardial space, cardiac tumors, and pericardial space, cardiac tumors, and abnormalities in left ventricular motionabnormalities in left ventricular motion



Nuclear CardiographyNuclear Cardiography Radioactive substances injected into the Radioactive substances injected into the

bloodstream are used to trace the patterns bloodstream are used to trace the patterns of blood flow in the heartof blood flow in the heart

Assesses the adequacy of blood flow to Assesses the adequacy of blood flow to cardiac tissuescardiac tissues



Cardiac Catheterization/Coronary Cardiac Catheterization/Coronary AngiographyAngiography A catheter is passed from the femoral or brachial A catheter is passed from the femoral or brachial

artery into the aortaartery into the aorta Used to directly measure pressures within cardiac Used to directly measure pressures within cardiac

chambers; visualize chamber size, shape, and chambers; visualize chamber size, shape, and movement; sample for blood oxygen content in movement; sample for blood oxygen content in various heart regions; measure CO and EF; and various heart regions; measure CO and EF; and visualize and manage coronary artery visualize and manage coronary artery obstructionsobstructions

1 Elsevier items and derived items © 2010, 2005 by Saunders, an imprint of Elsevier Inc. Chapter 17 Cardiac Function.

Documents

elsevier items

imprint of elsevier

derived items

ventricle slide

cardiac function slide

svedv slide

volume of blood

heart sound