Cardiac 1.pptx

Cardiovascular System and Anesthesia • Every anesthetic agent has a direct or indirect effect on the cardiovascular system • Volatile agents, intravenous drugs, regional anesthesia • Position changes during surgery affect cardiovascular system • Response to surgical stimulation, physiologic alterations during surgery, variations in anesthetic depth all result in hemodynamic changes 1 Cardiac Module Overview/Objectives • Overview of the Circulatory System – Wk 1 Components of the Circulatory System Pressure, Flow, and Resistance Anatomy of the Heart Coronary Perfusion/Myocardial Oxygen Balance • Cardiac Blood Supply / EKG Manifestations of CAD • • • • • Cardiac Physiology – Wk 2 • Cardiac Performance / Cardiac Output • Cardiac Cycle • Wiggers diagram • Pressure-Volume Loops • Cardiac Pathophysiology – Wk 2 • Valve Disorders • Cardiac Conduction – Wk 1 • • • • Conduction System Properties of Cardiac Muscle Excitation-Contraction Coupling Electrophysiology and Action Potentials • Anesthetic Management • EKG Interpretation – Wk 3 2 Statistics • Leading cause of death for men, women, and people of most racial and ethnic groups in U.S. • One person dies every 33 seconds in the U.S. • Costs the U.S. ~ $240 billion each year • About 1 in 20 adults age 20 and older have CAD (about 5%) • In 2021, 2 in 10 deaths from CAD happened in adults < 65 years old • In the U.S., a heart attack occurs every 40 seconds • About 1 in 5 are silent • Risk factors: • • • • • • • • HTN Hypercholesterolemia Smoking Diabetes Obesity Unhealthy diet Physical inactivity Excessive alcohol use CDC, National Center for Chronic Disease Prevention and Health Promotion, May 2023 3 Overview of the Circulatory System 4 Components of the Circulatory System • Closed loop and two circuits: originate and terminate in the heart • Systemic circulation • From LV through all organs and tissues (except lungs) then to RA • Pulmonary circulation • Blood pumped from RV through lungs to LA • Blood vessels • • • • • Arteries Arterioles Capillaries Venules Veins • Blood • Plasma • Cells • Heart • Atria • Ventricles 5 Blood Vessels • Arteries: away from the heart • Low resistance tubes conducting blood to various organs with little loss in pressure • Oxygenated blood (exception: pulmonary artery) • Act as pressure reservoirs for maintaining blood flow during ventricular relaxation • 3 layers: tunica adventitia (external); tunica media (middle/thickest layer); tunica intima (innermost/thinnest layer) • Arterioles • Major sites of resistance to flow • Responsible for regulating the pattern of blood-flow distribution to the various organs • Participate in regulation of arterial BP • Capillaries • Major sites of nutrient, gas, metabolic end product, and fluid exchange between blood and tissues • Venules • Collect blood from capillaries • Sites of migration of leukocytes from blood into tissues during inflammation • Veins: to the heart • Low-resistance conduits for blood flow back to the heart • Capacity for blood is adjusted to facilitate this flow 6 Travel of blood through vessels • Heart > artery > arteriole > capillary > venule > vein > heart 7 Systemic Circulation – Arterial • Arteries – average size = 4mm • Branch down to arterioles that are a few microns wide • Arterioles are smallest branch in arterial system • Powerful muscular system capable of widening or completely closing • Resistance accounts for greatest increase in SVR 8 Arteries versus arterioles 9 Systemic Circulation – Capillaries • 10 billion in the human body • Surface area of 500 m2 • Designed to reach every point in the body • Responsible for the exchange of fluid, nutrients, hormones, oxygen • Very thin walls to promote diffusion • Contraction decreases flow/relaxation increases flow 10 Systemic Circulation – Veins • Remove waste • Toward the heart • Contain valves • 60% of blood volume • Function as reservoir • SNS tone important • Loss of SNS tone with anesthesia • Hypotension 11 Blood • Cells • Plasma • Liquid portion of blood (straw colored) • Contains dissolved proteins, nutrients, ions, wastes, gases, and other substances • 90% H2O • Plasma proteins: albumins, globulins, and fibrinogen • Synthesized by liver - many functions • Exert osmotic pressure for absorption of interstitial fluid • Participate in clotting reactions • Erythrocytes • Gas transport/transports oxygen - Hct • Produced in bone marrow / destroyed in spleen and liver • 30 trillion in the body • Leukocytes: immune defense • • • • • • Neutrophils Eosinophils Monocytes Macrophages Basophils Lymphocytes • Platelets (thrombocytes) • Blood clotting 12 How does blood move in the CV system? • Based upon Ohm’s law: • Forms the basis for understanding hemodynamics • Correlates flow of electricity (current), the applied electrical pressure (voltage), and the resistance to this flow (resistance) • Hemodynamic Ohm’s Law: • Poiseuille’s law = adaptation of Ohm’s law in medicine • Incorporates vessel diameter, viscosity, and tube length 13 Poiseuille’s Law • Describes the pressure of a fluid as it travels through a cylindrical pipe • Applicable to aspects of medicine: • Blood flow • Airway resistance • IV administration 14 Points about flow (Q or F) • Flow = movement of liquid, electricity, or air per unit time • Flow can be laminar, turbulent, or transitional • Laminar flow – molecules travel in parallel paths through tube • Transitional flow – laminar flow along vessel walls with turbulent flow in center • Turbulent – molecules travel in non-linear path; eddies are created 15 Points about flow (Q or F) • Reynold’s number (Re) can be used to predict laminar or turbulent flow • Re < 2000 predicts mostly laminar flow • Re > 4000 predicts mostly turbulent flow • Re = 2000 – 4000 suggests transitional flow • When flow is turbulent, energy is lost via heat and vibration; pressure gradient is larger than what is predicted by Poiseuille’s law • Turbulent flow may produce murmur or bruit 16 Pressure, Flow, and Resistance • Hemodynamics • The circulatory system consists of the relationship among blood pressure, blood flow, and the resistance to blood flow (pressure, flow, resistance) • Physiological processes are dictated by the laws of chemistry and physics • Flow (F) = blood flow is always from region of higher to lower pressure • Pressure (P) = hydrostatic pressure: the pressure exerted by blood; force is generated by contraction of the heart • Resistance (R): how difficult it is for blood to flow between two points at any given pressure difference = the measure of the friction that impedes flow • Flow rate is directly proportional to the pressure difference between two points and inversely proportional to the resistance (applies not only to circulatory system but to any system in which liquid or air moves by bulk flow i.e. urinary or respiratory systems) F = ∆P/R >>> 17 Pressure, Flow, and Resistance • n = fluid viscosity • L = length of the tube • r = Inside radius of the tube • Resistance is directly proportional to the viscosity of a fluid (n) and to the length of the tube (L) • It is inversely proportional to the fourth power of the tube’s radius, which is the major variable controlling • 8/π = a mathematical constant 18 Blood viscosity • Viscosity is a result of friction from intermolecular forces as fluid passes through a tube • Determined by the hematocrit (Hct) and body temperature: • Blood viscosity is inversely proportionate to temperature – cooler temps increase viscosity and increase resistance • During CPB, hypothermia is instilled, and the rewarming phase requires higher shear stress to stimulate blood flow • Reducing Hct will counteract this 19 Poiseuille’s Law: relates volume of flow through a tube to diameter, pressure differential, length, and viscosity • At a constant driving pressure, the flow rate of liquid through a capillary tube is directly proportional to the fourth power of the radius of the tube and inversely proportional to the length and viscosity of the tube • A vessel having twice the length of another (each having the same radius) will have twice the resistance to flow • Similarly, if viscosity of blood increases two-fold, resistance increases two-fold • In contrast, an increase in radius will reduce resistance • A change in radius alters resistance to the fourth power of the change in radius i.e. a two-fold increase in radius decreases resistance by 16-fold 20 Poiseuille’s Law: Clinical Application • What does this mean in the body? • Flow does not conform exactly to this relationship because this relationship assumes long, straight tubes (blood vessels) • But it shows the dominant influence of vessel radius on resistance and flow • Changes in vascular tone and pathology such as vascular stenosis changes vessel radius therefore has a great affect on pressure and flow • Arterial/vein/capillary constriction = high blood pressure • Also, changes in heart valve orifice size (valvular stenosis) affect flow and pressure gradients across heart valves • Other clinical applications: • IV catheter size, ETT size, determination of vascular dilation and constriction in response to pharmacologic agents 21 Relationship of blood flow and resistance • Resistance can be calculated from the known relationship: F = ∆P / R • Rearranging the equation slightly: R = ∆P / F • Then … • Which variable changes most rapidly in the body? • The most important quantitively and physiologically is vessel diameter. Changes because of contraction and relaxation of vascular smooth muscle in the wall of the blood vessel. • Very small changes in vessel diameter lead to large changes in resistance. 22 Resistance and Flow 23 Applied to Hemodynamics … CO = MAP – CVP / SVR 24 Anatomy of the Heart • Pericardium • Chambers of the heart • Valves • Coronary blood supply • EKG manifestations 25 Pericardium • Pericardium • Visceral: lines outer surface of heart • Also called epicardium • Parietal: adheres to fibrous pericardium • Makes up parietal sac • Pericardial cavity • Thin, potential space • Contains 10-25 mL of serous fluid to provide lubrication for free movement of the heart within the mediastinum • Pericardial fluid between visceral and parietal pericardium 26 Structure of the Heart Wall • Epicardium: lines outer surface • Myocardium • Multiple interlocking layers of cardiac muscle tissue with associated connective tissue, blood vessels, nerves • Endocardium • Inner lining of the heart 27 Surface Anatomy and Orientation • Lies slightly to left of midline • Base: broad superior portion to include origin of major blood vessels • Apex: inferior rounded tip • At an oblique angle to longitudinal axis • This tilt results in apex pointing obliquely to the left • Rotated slightly toward left 28 Surfaces of the Heart: 5 • Sternocostal (anterior) • Diaphragmatic (inferior) • Base (posterior) • Left pulmonary surface • Right pulmonary surface 29 Sternocostal Surface • Mainly formed by RV and partly by RA on the right, LV on left, and left auricle • Most of the surface is covered by the lungs, but a part that lies behind the cardiac notch of left lung is uncovered 30 Diaphragmatic Surface • Directed downward and slightly backward • Rests on central tendon of diaphragm • Formed mainly by LV and partly by RV 31 Diaphragmatic surface Base • Better termed the “posterior surface” • It is the top of the heart (not the bottom, which is the apex) • At the level of the 3rd costal cartilage – formed maily by LA Base • Resembles the base of a pyramid or cone, extending obliquely to the left 32 Chambers of the Heart • Atria • Chambers through which blood flows from veins to ventricles • Atrial contraction adds to ventricular filling but is not essential • Common wall between atria = interatrial septum • Ventricles • Chambers whose contractions produce the pressures that drive blood through the pulmonary and systemic vascular systems and back to the heart • Left ventricle must generate 6-7 times as much force as the right ventricle to push blood through the systemic circuit • Common wall between ventricles = interventricular septum 33 Right Atrium • Receives deoxygenated blood from SVC, IVC and coronary sinus • Eustachian valve – valve of IVC • Located at junction of IVC and RA • Remnant of fetus • Directed incoming oxygenated blood from IVC to foramen ovale and away from right atrium (in fetus) • Thin linear structure, not routinely imaged • Thebesian valve – valve of the coronary sinus • Semicircular fold of the lining membrane of the right atrium • At orifice of coronary sinus • Its role not entirely known – may prevent regurgitation of blood into coronary sinus during contraction of atrium • Sometimes is cause of difficulties in cannulation of the coronary sinus 34 Right Ventricle • Deoxygenated blood from RA enters RV through tricuspid valve • Free edges of cusps are attached to strings of connective tissue >> chordae tendinae • Anchored to ventricular wall by papillary muscles (conical projections from the wall) • Superiorly, RV tapers into funnelshaped passage, the conus arteriosus, where blood is ejected into the pulmonary trunk • Backflow of blood is prevented by three half-moon flaps attached to base of pulmonary trunk that forms the pulmonary valve • Pulmonary trunk branches into right and left pulmonary arteries 35 Left Atrium • Left (2) and right (2) pulmonary veins drain oxygenated blood from lungs into left atrium • Oxygenated blood enters LV through left atrioventricular (AV) valve → mitral valve • Serves as a pump during atrial systole • Provides “atrial kick” • Provides 20-30% increase in LVEDV • Those with compromised CV or respiratory pathology rely on this to achieve adequate CO 36 Left Ventricle • As oxygenated blood is ejected from LV it passes through aortic valve and enters ascending aorta • LV wall 2-3x as thick as RV – required to overcome SVR for CO • 2 papillary muscles • Anterior – attaches to anterior part of LV wall • Posterior – arises from posterior aspect of inferior wall • Chordae tendinae • Attach from each papillary muscle to cusps of mitral valve to prevent eversion of valve during ventricular systole 37 Path of blood flow through heart What valve is this? 38 Two Circuits • Pulmonary circulation • From right ventricle to lungs and then to the left atrium • Systemic circulation • From left ventricle to peripheral organs and tissues and then to right atrium • One heart or two? → TWO • Right heart - lungs • Blood is received via superior vena cava, inferior vena cava, and coronary sinus → • Coronary sinus: collection of veins that feed into right atrium • Blood enters and is collected into the right atrium • Right ventricle pumps blood to the lungs • Left heart - body • Blood is received via 4 pulmonary veins • Blood enters and is collected into the left atrium • Left ventricle pumps blood out to body 39 The Right Heart • Primary function of the right heart is to pump blood to lungs • Blood passes through the right atrium via the tricuspid valve and into the right ventricle where it is collected. • The blood leaves the right ventricle via the pulmonic valve (also a tri-leaflet [semilunar] valve) and enters the pulmonary artery → the pulmonary circulation • Pulmonary artery splits into right and left, which directs deoxygenated blood to each lung 40 The Left Heart • Primary function of the left heart is to pump blood to the body • Blood is received via four pulmonary veins • The blood enters and is collected into the left atrium • Blood then passes thru the mitral valve (atrioventricular valve) into the left ventricle • Blood leaves the left ventricle via the aortic valve (semilunar valve) and enters the aorta → the systemic circulation 41 The Heart • Points of note: • The right heart does not care about the left heart. The left heart does not care about the right heart. • The only issue between them is that the volume of blood entering the right heart must be the volume of blood leaving the left heart. • If this issue does not occur: • → HEART FAILURE • Manifests as pulmonary edema 42 Heart Valves • Provide unidirectional flow of blood though the circuit • Open/close in response to pressure gradients above (atria) or below(ventricles) the valves • Atrioventricular (AV) = between atria and ventricles • Semilunar = pulmonary artery or aorta • Valvular pathology determined by calculating valvular area (via echocardiography and cardiac catheterization) 43 Valves • Atrioventricular valves (AV valves) • Semilunar valves • Aortic • Normal area = 2.5– 3.5 cm2 • 3 cusps • Symptoms when surface area decreased by 1/3 to 1/2 • Tricuspid • Normal area = 7– 9 cm2 • 3 cusps attached to chordae tendinae, which are attached to papillary muscles • Symptoms when area is < 1.5 cm2 • Pulmonic • Normal area = 2.5– 4.0 cm2 • 3 cusps • Mitral • Normal area = 4– 6 cm2 • 2 cusps (bicuspid) • Symptoms when surface decreased by half 44 Coronary Perfusion • Coronary blood flow • Parallels myocardial metabolic demand • Myocardium is autoregulated to maintain a constant flow over a range of perfusion pressures of 60-140 mmHg at any given myocardial oxygen demand (autoregulation of coronary blood flow is the net effect of local metabolism, myogenic response, and ANS) • Outside of this range, coronary blood flow becomes pressure-dependent (dependent on CPP) • Rate of flow is determined by a change in pressure divided by resistance • Poiseuille’s Law • Coronary Blood Flow = Coronary Perfusion Pressure Coronary Vascular Resistance → 45 Determinants of Coronary Perfusion • Coronary perfusion pressure is determined by the difference between aortic pressure and ventricular pressure • LV is perfused almost entirely during diastole • Coronary perfusion pressure = Aortic Diastolic – LV end-diastolic pressure CPP = Aortic DBP – LVEDP * Under normal conditions DBP = 80 mmHg and LVEDP = 10 mmHg, therefore DBP is the major determinant of CPP • What decreases coronary perfusion pressure? • Decreases in aortic (arterial) pressure or increases in LVEDP • Increases in heart rate (reduction in diastolic time) 46 Myocardial Oxygen Supply and Demand this must be balanced in anesthesia (increase supply while decreasing demand) • Supply • Heart rate (diastolic filling time) • Coronary perfusion pressure • Aortic diastolic blood pressure • Ventricular end-diastolic pressure • Arterial oxygen content • Demand • Basal metabolic requirements • Heart rate • Wall tension • Preload (ventricular radius) • Afterload • Contractility • Arterial oxygen tension • Hemoglobin concentration • Coronary vessel diameter 47 Myocardial Oxygen Balance • Ratio of O2 supply to O2 demand • O2 supply relies on blood O2 content • Arterial oxygen content equation (CaO2) CaO2 = (SaO2 x Hgb X 1.34) + (0.003 x PaO2) * (Amount of O2 bound to Hgb) + (O2 dissolved in plasma) *1.34 = oxygen combining capacity (or mL O2 per gram Hgb): oxygen is poorly soluble in water, therefore without an adjunctive means of transport, it cannot be transported in blood in quantities sufficient to sustain life. *0.0003 = solubility coefficient of oxygen in vol%/mmHg 48 Sample Question • A 44 year-old woman with a longstanding history of anemia arrives for emergency appendectomy. Previous medical history includes asthma. Her vital signs and ABG values are as follows: • • • • • • BP 140-85 mm Hg P 110 bpm RR 30 breaths/min Hgb – 10 g/dL PaO2 – 55 mm Hg SaO2 = 85% • Calculate this patient’s total oxygen content (in total amount of O2/100ml of blood). Show your work. 49 Three circumstances affect both sides of the supply-demand equation 50 Three circumstances affect both sides of the supply-demand equation 51 Three circumstances affect both sides of the supply-demand equation ** CPP = DBP – LVEDP 52 Bottom line of myocardial supply and demand in anesthesia … • Supply and demand must be balanced in anesthesia • Coronary vascular reserve = the difference between maximal coronary blood flow and autoregulated flow • The closer these two values, the lower the coronary reserve of the patient • Increased myocardial oxygen demand and limited supply decrease coronary reserve flow myocardial dysfunction • Most perioperative MIs occur 24-48 hours following surgery and carry a 20% mortality 53 Sample Question: • Which condition increases myocardial O2 consumption? a. Decreased aortic diastolic blood pressure b. Decreased diastolic filling time c. Decreased end-diastolic volume (EDV) d. Decreased P50 54 Cardiac Blood Supply • Right Coronary Artery • Supplies most of the RV, as well as posterior part of LV (in 80-90% of people); RA, SA and AV nodes • Primary branches: • Right posterior descending artery • Inferior aspect of heart • Right marginal artery • Lateral portion of RV • Left Coronary Artery (LCA) • Supplies left side of heart (LV and LA) • Caliber of LCA is > RCA • Increased metabolic needs of LV • Primary branches: • Left anterior descending (LAD) • Front and left side of heart • Left circumflex • Outer side and back of heart 55 Coronary Artery Dominance • Dominance is determined by which coronary artery crosses the junction between the atria and ventricles to supply the posterior descending coronary branch (posterior wall) • RCA in 50% of population • LCA in 10-15% of population • Mixed in 35-40% of population 56 Cardiac Venous Circulation • Each coronary vein runs alongside a coronary artery • • • • Great cardiac vein (LAD) Middle cardiac vein (PDA) Anterior cardiac vein (RCA) Coronary sinus • Blood returning from LV drains into coronary sinus • Can be cannulated to administer retrograde cardioplegia solution during CPB 57 Cardiac Blood Supply and EKG Manifestations of CAD Left Anterior Descending Coronary Artery *Changes can be seen in V1 – V4 In this EKG: Changes are seen in V2 – V5 (anterolateral wall MI) 58 Cardiac Blood Supply and EKG Manifestations of CAD Left Circumflex Coronary Artery *Changes can be seen in I, AVL, V5, V6 In this EKG: Changes (ST depression) can be seen in I and AVL 59 Cardiac Blood Supply and EKG Manifestations of CAD Right Coronary Artery Changes in II, III, and AVF (inferior wall MI) 60 Cardiac Innervation • Neurologic innervation originates from ANS • PNS tone: Vagus nerve (CN X) – right vagus nerve innervates SA node; left vagus innervates AV node • SNS tone: cardiac accelerator fibers • Cardioaccelerator fibers = T1 – T4 (sympathetic fibers) • Suppression or blockade (regional anesthesia) → bradycardia and hypotension • Blockade of the sympathetic ganglia “sympathectomy” • Increased SNS tone: • Increases heart rate (chronotropic) • Increases force of myocardial contraction(inotropic) • Increases rate of AV node discharge (dromotropic) 61 Cardiac Conduction System • Affected by automaticity (the ability to spontaneously generate an AP) • Automatically initiates and coordinates the cardiac rhythm • Affected by interactions between sympathetic and parasympathetic innervations • Affected by intracellular vs. extracellular ionic compositions: Ca+ +, Na+, and K+ • Consists of: • SA node, AV node, internodal tracts, AV bundle, and Purkinje system 62 Cardiac Conduction • Inherent rates: • • • • SA node 60 – 100 beats per minute AV node 40 – 60 beats per minute Bundle of His 1/10 sec conduction delay Ventricular pacing cells 20 – 40 beats per minute * Bundle of His transmit impulses from AV node to ventricles 1/10 sec conduction delay in this transmission 63 Cardiac Conduction • SA Node = cardiac pacemaker of the cardiac cycle • Located near entrance of SVC in wall of RA • Internodal fibers – impulse originates from SA node, travels to AV node by way of intermodal fibers • Stimulate the myocardial cells of atria to contract • Bachmann’s bundle: branch of anterior intermodal trace residing on inner wall of LA • AV Node – impulse slows through the AV node • Travels through interventricular septum via bundle of His • AV bundle divides into right and left bundles that go to the apex • Branches at apex radiate on inner surfaces of ventricles and Purkinje cells distribute the impulse to the myocardial cells of ventricles 64 Properties of Cardiac Muscle • Like skeletal muscle: • Myocardial cells are composed of sarcomeres • Contain actin and myosin filaments • T-tubules and sarcoplasmic reticulum work to maintain Ca++ homeostasis for contraction and relaxation • Like neural tissue: • Cardiac myocytes generate a resting membrane potential • Can propagate an action potential • Unlike skeletal muscle: • Cardiac myocytes contain more mitochondria than skeletal (and consume a lot of O2 at rest (~ 4-8 mL/O2/min) • Cardiac cells are aerobic and cannot tolerate oxygen deficiency • Skeletal muscles can function both aerobically and anaerobically • Gap junctions and intercalated discs serve as low resistance pathways that help spread the cardiac AP throughout the myocardium 65 Structure of the Contractile Apparatus • Thick filaments: myosin • Central region of sarcomere • A bands • Thin filaments: actin • I bands • Troponin, tropomyosin • M lines • Z lines 66 Cardiac muscle excitation-contraction coupling 67 Excitation-Contraction Coupling • Rest • Excitation/Contraction • Ca++ release from SR • Ca++ binds to troponin-tropomyosin complex resulting in conformational change that causes binding sites on actin filaments to become exposed • Myosin cross bridges bind to active filament by alternately attaching and detaching from active sites • Shortening of Z lines • Sliding Filament Theory • Relaxation • Ca++ reuptake into SR as a result of active transport • With limited supply of oxygen as in CAD, infarction can occur 68 Cross-Bridge Interaction and Cycling • Sliding Filament Mechanism • Myosin binds to actin • Uses energy to drag actin filaments toward center of sarcomere • Recurs as long as intracellular Ca+2 concentration remains sufficiently high • Dependent on incoming action potentials • Cycle continues until ATP exhausted • Excitation-contraction coupling: • Overall process by which depolarization of muscle fiber causes Ca+2 release from sarcoplasmic reticulum into myoplasm 69 Thin Filament (Actin) • Three major proteins: • Actin • Two twisted rows of globular Gactin • Active sites on G-actin bind to myosin • Tropomyosin • Double strand • Prevents actin-myosin interaction • Troponin • A globular protein • Binds tropomyosin to G-actin • Controlled by Ca++ 70 Thick Filament (Myosin) • Myosin • Tail: binds to other myosin molecules • Head: • made of 2 globular protein subunits • reaches the nearest thin filament • Myosin action • During contraction myosin heads: • Interact w/ actin filaments, forming cross- bridges • Pivot, producing motion • Muscle contraction • Sliding filament theory: • Thin filaments of sarcomere slide toward M line, alongside thick 71

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