Cardiovascular Anatomy and Physiology PDF

1.1 Dr. Ward Cardiovascular Anatomy and Physiology Overview of NRAN 80413: A&P III !"Cardiac Anatomy !"Cardiac Physiology !"Cardiac Pathophysiology !"Anesthetic Considerations and Management Course Schedule Week 1 (01-17-24) !"Overview of Class / Syllabus !"Reading: Nagelhous 7th ed., Ward !"Overvi...

1.1 Dr. Ward Cardiovascular Anatomy and Physiology Overview of NRAN 80413: A&P III !"Cardiac Anatomy !"Cardiac Physiology !"Cardiac Pathophysiology !"Anesthetic Considerations and Management Course Schedule Week 1 (01-17-24) !"Overview of Class / Syllabus !"Reading: Nagelhous 7th ed., Ward !"Overview of Circulatory System !"Reading: Chap. 25 Pressure, Flow, and Resistance !"Cardiac Anatomy / Coronary Perfusion / Myocardial Oxygen Balance !"Reading: widmaier (any edition): Chap. 12 !"Cardiac Conduction (Sections A-D) !"Conduction System Properties of Cardiac Muscle !"Excitation-Contraction Coupling !"Electrophysiology Week 2 (01-24-24) !"Cardiac Physiology !"Reading: Nagelhout 7th ed., Ward !"Cardiac Performance !"Reading: Chap. 25 Cardiac cycle Cardiac Output Pressure Volume Loops Valve Disorders / Anesthetic Management Week 3 (01-31-24) !"EKG Interpretation !"Reading: Guyton Chap. 11, 12, 13 !"Identification of Rhythm Strips (C. Crow) !"The normal EKG and Axis Determination !"12-Lead EKG Interpretation and EKG Manifestations of CAD Week 4 (02-07-24) !"EXAM 1: Weeks 1, 2, 3 !"Ward Week 5 (02-14-24) !"Physiology of Hemostasis !"Reading: widmaier (any edition) Chap. 12 (Section F) !"Reading: Nagelbout Chap. 38 !"Disorders of Hemostasis !"Reading: Same as Week 5 Crow !"Anesthetic Considerations Week 6 (02-21-24) !"EXAM 2: Weeks 5, 6 !"Crow Week 8 (03-06-24) !"SHORT-TERM REGULATION OF ARTERIAL PRESSURE !"Reading: GUYTON CH. 18 ANDERSON !"LONG-TERM REGULATION OF ARTERIAL PRESSURE !"Reading: GUYTON CH. 19 HINES CHS. 9 & 11 !"SYSTEMIC AND PULMONARY HTN/ PERICARDIAL DZ Week 10 (03-20-24) !"SYSTEMIC AND PULMONARY HTN/ PERICARDIAL DZ !"Reading: HINES CHS. 9 & 11 ANDERSON !"ISCHEMIC HEART DISEASE !"Reading: HINES CH. 5 Week 12 (04-03-24) !"EXAM 3: VASCULAR: Weeks 10, 11 !"ANDERSON Week 13 (04-10-24) !"VALVULAR HEART DISEASE !"Reading: HINES CH. 6 ANDERSON !"VASCULAR DISEASE !"Reading: HINES CH. 12 Week 14 (04-17-24) !"CONGENITAL HEART DISEASE !"Reading: HINES CH. 7 ANDERSON !"HEART FAILURE AND CARDIOMYOPATHIES !"Reading: HINES CH. 10 Week 15 (04-24-24) !"EXAM 4: PATHOPHYSIOLOGY: Weeks 13, 14 !"ANDERSON Exams !"Exam I: 20% (Weeks 1, 2, 3) !"Exam II: 20% (Weeks 5, 6) !"Exam III: 20% (Weeks 10, 11) !"Exam IV: 20% (Weeks 13, 14) !"Final Examination: 20% Exam Format !"SEE / NCE style questions !"Multiple choice !"Multi-select !"Short answer / essay !"Hotspot !"Matching Cardiovascular Anatomy Lab !"Anatomy Lab @ UNTHSC !"First lab: January 31, 2024, 1-3 pm !"Will include 2 stations of cardiac !"Full Cardiac Lab: April 17, 2024, 1-3 pm !"Part of A&P II grade Tips for Success !"Assigned readings, lectures, objectives !"Objectives for all lectures posted on D2L within each module !"Videos on D2L and embedded within lectures to facilitate understanding !"Office hours: email for availability (Zoom or in person) Resources !"Nagelhout, J. & Elisha, S. (2017). Nurse Anesthesia, 7th ed., Elsevier Saunders: Philadelphia, PA. !"Chap. 25: Cardiovascular !"Chap 38: Hemostasis !"Widmaier, E.P., Raff, H., & Strang, K. T. (2015). Vander’s Human Physiology, 14th or 15th ed. McGraw-Hill Education: New York, NY. !"Chap 12 – Sections A – D !"Guyton, A.C., & Hall, J.E. (2016). Textbook of medical physiology, 13th ed., Elsevier Saunders: Philadelphia, PA. !"Chapters 11, 12, 13 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 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 Conduction – Wk 1 !"Conduction System !"Properties of Cardiac Muscle !"Excitation-Contraction Coupling !"Electrophysiology and Action Potentials !"Cardiac Physiology – Wk 2 !"Cardiac Performance / Cardiac Output !"Cardiac Cycle !"Wiggers diagram !"Pressure-Volume Loops !"Cardiac Pathophysiology – Wk 2 !"Valve Disorders !"Anesthetic Management !"EKG Interpretation – Wk 3 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 Overview of the Circulatory System !"Components of the Circulatory System !"Blood vessels !"Arteries !"Arterioles !"Capillaries !"Venules !"Veins !"Blood !"Plasma !"Cells !"Heart !"Atria !"Ventricles !"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 Page 15: Blood Vessels !"Arteries: #"Conduct blood away from the heart #"Low resistance tubes with little loss in pressure #"Act as pressure reservoirs for maintaining blood flow #"Consist of three layers: tunica adventitia, tunica media, tunica intima !"Arterioles: #"Major sites of resistance to flow #"Regulate blood-flow distribution to organs #"Participate in regulation of arterial blood pressure !"Capillaries: #"Major sites of nutrient, gas, and fluid exchange between blood and tissues !"Venules: #"Collect blood from capillaries #"Sites of migration of leukocytes from blood into tissues !"Veins: #"Conduits for blood flow back to the heart #"Adjust capacity for blood flow Page 16: Travel of blood through vessels !"Heart > artery > arteriole > capillary > venule > vein > heart Page 17: Systemic Circulation - Arterial !"Arteries: #"Average size = 4mm #"Branch down to arterioles #"Arterioles are the smallest branches in the arterial system #"Powerful muscular system capable of widening or completely closing #"Resistance accounts for the greatest increase in systemic vascular resistance (SVR) Page 18: Arteries versus arterioles !"Arteries: #"Muscular-walled tubes that carry oxygenated blood #"Lead to arterioles #"Have thick walls and carry blood from the heart to different organs !"Arterioles: #"Small branches of arteries that lead to capillaries #"Have thinner walls and regulate blood pressure and blood flow Page 19: Systemic Circulation - Capillaries !"10 billion capillaries in the human body !"Surface area of 500 m2 !"Responsible for the exchange of fluid, nutrients, hormones, and oxygen !"Very thin walls to promote diffusion !"Contraction decreases flow, relaxation increases flow Page 20: Systemic Circulation - Veins !"Veins: #"Remove waste from tissues #"Carry blood toward the heart #"Contain valves to prevent backflow #"Account for 60% of blood volume #"Function as a reservoir #"Sympathetic nervous system (SNS) tone is important for maintaining venous return #"Loss of SNS tone with anesthesia can lead to hypotension Page 21: Blood !"Plasma: #"Liquid portion of blood #"Contains dissolved proteins, nutrients, ions, wastes, gases, and other substances #"90% water #"Plasma proteins: albumins, globulins, and fibrinogen !"Cells: #"Erythrocytes: transport oxygen, produced in bone marrow #"Leukocytes: immune defense #"Platelets: involved in blood clotting Page 22: How does blood move in the CV system? !"Based on Ohm's law !"Correlates flow, pressure, and resistance !"Hemodynamic Ohm's Law: Poiseuille's law !"Incorporates vessel diameter, viscosity, and tube length Page 23: Poiseuille's Law !"Describes the pressure of a fluid as it travels through a cylindrical pipe !"Applicable to blood flow, airway resistance, and IV administration Page 24: 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 a tube !"Transitional flow: laminar flow along vessel walls with turbulent flow in the center !"Turbulent flow: molecules travel in a non-linear path, creating eddies Page 25: Points about flow (Q or F) !"Reynold's number (Re) predicts laminar or turbulent flow !"Re < 2000 predicts laminar flow !"Re > 4000 predicts turbulent flow !"Re = 2000 - 4000 suggests transitional flow !"Turbulent flow results in energy loss, larger pressure gradient, and may produce murmur or bruit Page 26: Pressure, Flow, and Resistance !"Hemodynamics: relationship among blood pressure, blood flow, and resistance !"Flow is always from a region of higher to lower pressure !"Pressure is the force generated by contraction of the heart !"Resistance is the measure of friction that impedes flow !"Flow rate is directly proportional to pressure difference and inversely proportional to resistance Page 27: Pressure, Flow, and Resistance !"Resistance is directly proportional to fluid viscosity and tube length !"Resistance is inversely proportional to the fourth power of the tube's radius Page 28: Blood viscosity !"Viscosity is determined by hematocrit (Hct) and body temperature !"Blood viscosity is inversely proportional to temperature !"Hypothermia increases viscosity and resistance !"Reducing Hct counteracts increased resistance during rewarming phase of CPB Page 29: Poiseuille's Law: relates volume of flow through a tube to diameter, pressure differential, length, and viscosity !"Flow rate is directly proportional to the fourth power of the tube's radius !"Resistance is directly proportional to length and viscosity !"Resistance is inversely proportional to the tube's radius !"Changes in radius have a significant effect on pressure and flow Page 30: Poiseuille's Law: Clinical Application !"Changes in vessel radius have a great effect on pressure and flow !"Vascular constriction leads to high blood pressure !"Changes in heart valve orifice size affect flow and pressure gradients !"Clinical applications include IV catheter size, ETT size, and determination of vascular dilation and constriction Page 31: Relationship of blood flow and resistance !"Resistance can be calculated from the equation: R = ΔP / F !"Vessel diameter is the most important variable that changes rapidly in the body !"Small changes in vessel diameter lead to large changes in resistance Page 32: Resistance and Flow !"Resistance (R) is determined by length (L), viscosity (n), and tube radius (r) !"Flow (F) is inversely proportional to resistance (R) Page 33: Ohm's Law and Hemodynamics !"Ohm's law forms the basis for understanding hemodynamics. !"Current = Voltage Difference or Flow = Pressure Gradient or Q = AP Resistance !"We can translate Ohm's law into some more familiar hemodynamic terms. !"CO = MAP - CVP / SVR !"Hemodynamic Term Symbol: #"Flow: Cardiac Output Q #"Pressure Gradient: MAP - CVP P1-P2 or AP #"Resistance: Systemic Vascular Resistance R Page 34: Applied to Hemodynamics Ohm's Law & Poiseuille's Law !"Ohm's law and Poiseuille's law are applied to hemodynamics. !"Ohm's law forms the basis for understanding hemodynamics. !"Poiseuille's law describes the relationship between flow, pressure, and resistance in a cylindrical tube. !"Ohm's law and Poiseuille's law help in understanding the flow of blood through the cardiovascular system. Page 35: Anatomy of the Heart !"The anatomy of the heart includes: #"Pericardium #"Chambers of the heart #"Valves #"Coronary blood supply #"EKG manifestations Page 36: Pericardium !"The pericardium is divided into two layers: visceral and parietal. !"The pericardial cavity is a thin potential space that contains serous fluid for lubrication. !"Pericardial fluid is located between the visceral and parietal pericardium. Page 37: Structure of the Heart Wall !"The heart wall consists of three layers: epicardium, myocardium, and endocardium. !"The epicardium lines the outer surface of the heart. !"The myocardium is composed of multiple interlocking layers of cardiac muscle tissue. !"The endocardium is the inner lining of the heart. Page 38: Surface Anatomy and Orientation !"The heart lies slightly to the left of the midline. !"The base is the broad superior portion that includes the origin of major blood vessels. !"The apex is the inferior rounded tip that points obliquely to the left. !"The heart is rotated slightly toward the left. Page 39: Surfaces of the Heart: 5 !"The surfaces of the heart include: #"Sternocostal (anterior) #"Diaphragmatic (inferior) #"Base (posterior) #"Left pulmonary surface #"Right pulmonary surface Page 40: Sternocostal Surface !"The sternocostal surface is mainly formed by the right ventricle (RV) and partly by the right atrium (RA) on the right, and the left ventricle (LV) on the left. !"Most of the surface is covered by the lungs, but a part behind the cardiac notch of the left lung is uncovered. Page 41: Diaphragmatic Surface !"The diaphragmatic surface is directed downward and slightly backward. !"It rests on the central tendon of the diaphragm. !"It is mainly formed by the left ventricle (LV) and partly by the right ventricle (RV). Page 42: Base !"The base of the heart is better termed the "posterior surface." !"It is the top of the heart and is formed mainly by the left atrium (LA). !"It resembles the base of a pyramid or cone, extending obliquely to the left. Page 43: Chambers of the Heart !"The heart has two atria and two ventricles. !"Atria are chambers through which blood flows from veins to ventricles. !"Ventricles are chambers whose contractions produce the pressures that drive blood through the pulmonary and systemic vascular systems and back to the heart. !"The left ventricle must generate 6-7 times as much force as the right ventricle to push blood through the systemic circuit. Page 44: Right Atrium !"The right atrium receives deoxygenated blood from the superior vena cava (SVC), inferior vena cava (IVC), and coronary sinus. !"The Eustachian valve is located at the junction of the IVC and RA and directs incoming oxygenated blood from the IVC to the foramen ovale (in the fetus). !"The Thebesian valve is a semicircular fold of the lining membrane of the right atrium at the orifice of the coronary sinus. Page 45: Right Ventricle !"The right ventricle receives deoxygenated blood from the right atrium (RA) through the tricuspid valve. !"The free edges of the tricuspid valve cusps are attached to strings of connective tissue called chordae tendinae. !"The right ventricle tapers into a funnel-shaped passage called the conus arteriosus, where blood is ejected into the pulmonary trunk. !"The pulmonary valve prevents backflow of blood into the right ventricle. Page 46: Left Atrium !"The left atrium receives oxygenated blood from the lungs through the left and right pulmonary veins. !"Oxygenated blood enters the left ventricle (LV) through the mitral valve. !"The left atrium serves as a pump during atrial systole and provides an "atrial kick" to increase left ventricular end-diastolic volume (LVEDV). Page 47: Left Ventricle !"Oxygenated blood is ejected from the left ventricle (LV) through the aortic valve and enters the ascending aorta. !"The left ventricle has a thicker wall than the right ventricle (RV) to overcome systemic vascular resistance (SVR) for cardiac output (CO). !"The left ventricle has two papillary muscles and chordae tendinae to prevent eversion of the mitral valve during ventricular systole. Page 48: Path of blood flow through the heart !"The path of blood flow through the heart includes various chambers, valves, and blood vessels. !"The blood flows from the superior and inferior vena cava to the right atrium, through the tricuspid valve to the right ventricle, and then to the pulmonary artery. !"From the pulmonary artery, the blood flows to the lungs for oxygenation and returns to the left atrium through the pulmonary veins. !"The blood then passes through the mitral valve to the left ventricle and is pumped out to the body through the aorta. Page 49: Two Circuits !"The heart has two circuits: pulmonary circulation and systemic circulation. !"The right heart pumps blood to the lungs, receiving deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus. !"The left heart pumps oxygenated blood to the body, receiving blood from the four pulmonary veins. Page 50: The Right Heart !"The primary function of the right heart is to pump blood to the lungs. !"Blood passes through the right atrium via the tricuspid valve and enters the right ventricle. !"The blood leaves the right ventricle via the pulmonic valve and enters the pulmonary artery, which splits into right and left branches to direct deoxygenated blood to each lung. Page 51: The Left Heart !"The primary function of the left heart is to pump blood to the body. !"Blood is received via four pulmonary veins and enters the left atrium. !"The blood passes through the mitral valve into the left ventricle. !"The blood leaves the left ventricle via the aortic valve and enters the aorta for systemic circulation. Page 52: The Heart !"The right heart and left heart have separate functions but must maintain a balance of blood volume. !"If the volume of blood entering the right heart does not match the volume leaving the left heart, it can lead to heart failure and pulmonary edema. Page 53: Heart Valves !"Heart valves provide unidirectional flow of blood through the circuit. !"Atrioventricular (AV) valves are located between the atria and ventricles, while semilunar valves are found in the pulmonary artery or aorta. !"Valvular pathology can be determined by calculating valvular area using echocardiography and cardiac catheterization. Page 54: Valves !"Atrioventricular valves (AV valves) #"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 #"Mitral $"Normal area = 4-6 cm2 $"2 cusps (bicuspid) $"Symptoms when surface decreased by half !"Semilunar valves #"Aortic $"Normal area = 2.5-3.5 cm2 $"3 cusps $"Symptoms when surface area decreased by 1/3 to 1/2 #"Pulmonic $"Normal area = 2.5-4.0 cm2 $"3 cusps Page 55: 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 #"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 Page 56: 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 !"DBP is the major determinant of CPP !"Decreases in aortic (arterial) pressure or increases in LVEDP decrease coronary perfusion pressure !"Increases in heart rate (reduction in diastolic time) decrease coronary perfusion pressure Page 57: Myocardial Oxygen Supply and Demand !"Supply #"Heart rate (diastolic filling time) #"Coronary perfusion pressure #"Aortic diastolic blood pressure #"Ventricular end-diastolic pressure #"Arterial oxygen content #"Arterial oxygen tension #"Hemoglobin concentration #"Coronary vessel diameter !"Demand #"Basal metabolic requirements #"Heart rate #"Wall tension #"Preload (ventricular radius) #"Afterload #"Contractility Page 58: 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) #"1.34 = oxygen combining capacity (or mL O2 per gram Hgb) #"0.0003 = solubility coefficient of oxygen in vol%/mmHg Page 59: Sample Question !"A 44-year-old woman with a longstanding history of anemia arrives for emergency appendectomy !"Vital signs and ABG values: #"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) Page 60: Putting it together !"Decreased Oxygen Delivery #"Decreased Coronary Flow $"Tachycardia $"Hypertension $"Aortic pressure $"SNS stimulation $"Vessel diameter (spasm or hypocapnia) $"Wall tension $"LV end-diastolic pressure $"LV end-diastolic volume $"Afterload #"Decreased CaO2 $"Contractility $"Hypoxemia $"Anemia $"Decreased Oxygen Extraction $"Left shift of Hgb dissociation curve (P50) $"Capillary density Page 61: Three circumstances affect both sides of the supply-demand equation !"Tachycardia: Supply & Demand #"Decreased Supply $"Tachycardia reduces diastolic filling time, resulting in less time to deliver oxygen to the left ventricle #"Increased Demand $"Increasing the number of cardiac cycles per minute increases ATP and oxygen utilization Page 62: Three circumstances affect both sides of the supply-demand equation !"Increased Aortic Diastolic Pressure: Supply & Demand #"Increased Supply $"Increased aortic pressure increases the pressure head that perfuses the coronary arteries #"Increased Demand $"Increased aortic pressure also increases wall tension and afterload, requiring more oxygen from the myocardium Page 63: Three circumstances affect both sides of the supply-demand equation !"Increased Preload: Supply & Demand #"Decreased Supply $"Increased end-diastolic volume decreases coronary perfusion pressure #"Increased Demand $"Increased preload increases wall stress Page 64: 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 !"Increased myocardial oxygen demand and limited supply decrease coronary reserve flow and can lead to myocardial dysfunction !"Most perioperative MIs occur 24-48 hours following surgery and carry a 20% mortality Page 65: Sample Question !"Which condition increases myocardial O2 consumption? #"Decreased aortic diastolic blood pressure #"Decreased diastolic filling time #"Decreased end-diastolic volume (EDV) #"Decreased P50 Page 66: 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, Right marginal artery !"Left Coronary Artery (LCA) #"Supplies left side of heart (LV and LA) #"Caliber of LCA is > RCA #"Primary branches: Left anterior descending (LAD), Left circumflex Page 67: 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 Page 68: 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 Page 69: EKG Manifestations of CAD !"Bipolar Leads: Limb Leads, Precordial Leads !"Limb Leads: I, II, III, aVR, aVL, aVF !"Precordial Leads: V1, V2, V3, V4, V5, V6 Page 70: 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) Page 71: 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 (lateral wall MI or ischemia) Page 72: Cardiac Blood Supply and EKG Manifestations of CAD Right Coronary Artery Changes in II, III, and AVF (inferior wall MI) !"Right Coronary Artery #"Changes in II, III, and AVF (inferior wall MI) Page 73: 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) !"Effects of increased SNS tone: #"Increases heart rate (chronotropic) #"Increases force of myocardial contraction (inotropic) #"Increases rate of AV node discharge (dromotropic) Page 74: Cardiac Conduction Page 75: Cardiac Conduction System !"Automaticity affects the cardiac rhythm !"Interactions between sympathetic and parasympathetic innervations affect the conduction system !"Intracellular vs. extracellular ionic compositions (Ca++, Na+, and K+) affect the conduction system !"Components of the conduction system: #"SA node #"AV node #"Internodal tracts #"AV bundle #"Purkinje system Page 76: Cardiac Conduction !"Inherent rates of conduction: #"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 transmits impulses from AV node to ventricles with a 1/10 sec conduction delay Page 77: Cardiac Conduction !"SA Node: #"Cardiac pacemaker of the cardiac cycle #"Located near entrance of SVC in wall of RA #"Impulse originates from SA node and travels to AV node via internodal fibers #"Stimulates the myocardial cells of atria to contract #"Bachmann’s bundle: branch of anterior internodal tract 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 Page 78: Properties of Cardiac Muscle !"Myocardial cells are composed of sarcomeres like skeletal muscle !"Myocardial cells contain actin and myosin filaments like skeletal muscle !"T-tubules and sarcoplasmic reticulum maintain Ca++ homeostasis for contraction and relaxation !"Cardiac myocytes generate a resting membrane potential and can propagate an action potential like neural tissue !"Cardiac myocytes contain more mitochondria than skeletal muscle and consume a lot of O2 at rest !"Cardiac cells are aerobic and cannot tolerate oxygen deficiency, unlike skeletal muscles !"Gap junctions and intercalated discs serve as low resistance pathways that help spread the cardiac action potential throughout the myocardium Page 79: Excitation-Contraction Coupling Page 80: Myocardial Sarcomere and the Contractile Apparatus !"Components of the sarcomere: #"Gap junctions #"Myocardial cells #"I band #"A band #"H band #"Z line #"Titin !"Zone of overlap !"M line !"Thin filament !"Thick filament !"Sarcomere Page 81: 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 Page 82: Cardiac muscle excitation-contraction coupling !"Excitation-contraction coupling and relaxation in cardiac muscle !"Action potential enters Ca2+ from adjacent cell !"Voltage-gated Ca2+ channels open !"Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR) !"Local release causes Ca2+ spark !"Summed Ca2+ sparks create a Ca2+ signal !"Ca2+ ions bind to troponin to initiate contraction !"Relaxation occurs when Ca2+ unbinds from troponin !"Ca2+ is pumped back into the sarcoplasmic reticulum for storage !"Ca2+ is exchanged with Na+ !"Na+ gradient is maintained by the Na+-K+-ATPase Page 83: 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 Page 84: Cross-Bridge Interaction and Cycling !"Sliding Filament Mechanism !"Myosin binds to actin !"Uses energy to drag actin filaments toward the center of the sarcomere !"Recurs as long as intracellular Ca+2 concentration remains sufficiently high !"Dependent on incoming action potentials !"Cycle continues until ATP is exhausted !"Excitation-contraction coupling: overall process by which depolarization of muscle fiber causes Ca+2 release from sarcoplasmic reticulum into myoplasm Page 85: Thin Filament (Actin) !"Three major proteins: #"Actin $"Two twisted rows of globular G-actin $"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++ Page 86: 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 with actin filaments, forming cross-bridges #"Myosin heads pivot, producing motion !"Muscle contraction: #"Sliding filament theory #"Thin filaments of sarcomere slide toward the M line, alongside thick filaments #"Z lines move closer together Page 87: Image Page 88: Image Page 89: Image Page 90: Image Page 91: Image Page 92: Image Page 93: Cardiac Excitation-Contraction Coupling !"Link to a YouTube video on cardiac excitation-contraction coupling