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Chapter 20 The Heart Lecture Presentation by Lee Ann Frederick University of Texas at Arlington © 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System • The Pulmonary Circuit • Carries blood to and from gas exchange surfaces of lungs • The Systemic Circuit • Carries blood to and from the body • Blood alternates between pulmonary circuit and systemic circuit © 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System • Three Types of Blood Vessels 1. Arteries • Carry blood away from heart 2. Veins • Carry blood to heart 3. Capillaries • Networks between arteries and veins © 2015 Pearson Education, Inc. An Introduction to the Cardiovascular System • Capillaries • Also called exchange vessels • Exchange materials between blood and tissues • Materials include dissolved gases, nutrients, waste products © 2015 Pearson Education, Inc. Figure 20-1 An Overview of the Cardiovascular System. PULMONARY CIRCUIT Pulmonary arteries Pulmonary veins Capillaries in lungs Right atrium Right ventricle Capillaries in trunk and lower limbs © 2015 Pearson Education, Inc. SYSTEMIC CIRCUIT Systemic arteries Systemic veins Capillaries in head, neck, upper limbs Left atrium Left ventricle An Introduction to the Cardiovascular System • Four Chambers of the Heart 1. Right atrium • Collects blood from systemic circuit 2. Right ventricle • Pumps blood to pulmonary circuit 3. Left atrium • Collects blood from pulmonary circuit 4. Left ventricle • Pumps blood to systemic circuit © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Heart • • • • Great veins and arteries at the base Pointed tip is apex Surrounded by pericardial sac Sits between two pleural cavities in the mediastinum © 2015 Pearson Education, Inc. Figure 20-2a The Location of the Heart in the Thoracic Cavity. Trachea First rib (cut) Thyroid gland Base of heart Right lung Left lung Parietal pericardium (cut) Apex of heart Diaphragm a An anterior view of the chest, showing the position of the heart and major blood vessels relative to the ribs, lungs, and diaphragm. © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Pericardium • Double lining of the pericardial cavity • Visceral pericardium • Inner layer of pericardium • Parietal pericardium • Outer layer • Forms inner layer of pericardial sac © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Pericardium • Pericardial cavity • Is between parietal and visceral layers • Contains pericardial fluid • Pericardial sac • Fibrous tissue • Surrounds and stabilizes heart © 2015 Pearson Education, Inc. Figure 20-2b The Location of the Heart in the Thoracic Cavity. Posterior mediastinum Aorta (arch segment removed) Esophagus Left pulmonary artery Right pleural cavity Right lung Left pleural cavity Left lung Bronchus of lung Left pulmonary vein Right pulmonary artery Pulmonary trunk Aortic arch Right pulmonary vein Left atrium Left ventricle Superior vena cava Pericardial cavity Right atrium Epicardium Right ventricle Anterior mediastinum Pericardial sac Sternum b A superior view of the organs in the mediastinum; portions of the lungs have been removed to reveal blood vessels and airways. The heart is located in the anterior part of the mediastinum, immediately posterior to the sternum. © 2015 Pearson Education, Inc. Figure 20-2c The Location of the Heart in the Thoracic Cavity. Base of heart Cut edge of parietal pericardium Fibrous tissue of pericardial sac Wrist (corresponds to base of heart) Inner wall (corresponds to epicardium) Parietal pericardium Areolar tissue Mesothelium Fibrous attachment to diaphragm Air space (corresponds to pericardial cavity) Cut edge of epicardium Outer wall (corresponds to parietal pericardium) Apex of heart Balloon c The relationship between the heart and the pericardial cavity; compare with the fist-and-balloon example. © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Superficial Anatomy of the Heart • Atria • Thin-walled • Expandable outer auricle (atrial appendage) © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Superficial Anatomy of the Heart • Sulci • Coronary sulcus divides atria and ventricles • Anterior interventricular sulcus and posterior interventricular sulcus • Separate left and right ventricles • Contain blood vessels of cardiac muscle © 2015 Pearson Education, Inc. Figure 20-3a The Position and Superficial Anatomy of the Heart. Base of heart 1 2 3 4 5 6 7 8 9 10 1 Ribs 2 3 4 5 6 7 8 9 10 a Heart position relative to the rib cage. © 2015 Pearson Education, Inc. Apex of heart Figure 20-3b The Position and Superficial Anatomy of the Heart. Left subclavian artery Left common carotid artery Arch of aorta Ligamentum arteriosum Brachiocephalic trunk Descending aorta Ascending aorta Left pulmonary artery Superior vena cava Auricle of right atrium Pulmonary trunk Right atrium Auricle of left atrium Right ventricle Fat and vessels in coronary sulcus Fat and vessels in anterior interventricular sulcus Left ventricle b Major anatomical features on the anterior surface. © 2015 Pearson Education, Inc. Figure 20-3c The Position and Superficial Anatomy of the Heart. Left subclavian artery Left common carotid artery Ligamentum arteriosum Brachiocephalic trunk Left pulmonary artery Ascending aorta Pulmonary trunk Superior vena cava Auricle of left atrium Auricle of right atrium Left coronary artery (LCA) Right atrium Anterior interventricular sulcus Right coronary artery Coronary sulcus Marginal branch of right coronary artery Right ventricle Left ventricle Anterior interventricular branch of LCA c Anterior surface of the heart, cadaver dissection. © 2015 Pearson Education, Inc. Figure 20-3d The Position and Superficial Anatomy of the Heart. Arch of aorta Left pulmonary artery Right pulmonary artery Left pulmonary veins Fat and vessels in coronary sulcus Superior vena cava Left atrium Coronary sinus Right atrium Left ventricle Right ventricle Right pulmonary veins (superior and inferior) Inferior vena cava Fat and vessels in posterior interventricular sulcus d Major landmarks on the posterior surface. Coronary arteries (which supply the heart itself) are shown in red; coronary veins are shown in blue. © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Heart Wall 1. Epicardium 2. Myocardium 3. Endocardium © 2015 Pearson Education, Inc. Figure 20-5c Cardiac Muscle Cells. Intercalated discs Cardiac muscle tissue c Cardiac muscle tissue © 2015 Pearson Education, Inc. LM x 575 20-1 Anatomy of the Heart • Internal Anatomy and Organization • Interatrial septum separates atria • Interventricular septum separates ventricles © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Internal Anatomy and Organization • Atrioventricular (AV) valves • Connect right atrium to right ventricle and left atrium to left ventricle • Are folds of fibrous tissue that extend into openings between atria and ventricles • Permit blood flow in one direction • From atria to ventricles © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Right Atrium • Superior vena cava • Receives blood from head, neck, upper limbs, and chest • Inferior vena cava • Receives blood from trunk, viscera, and lower limbs • Coronary sinus • Cardiac veins return blood to coronary sinus • Coronary sinus opens into right atrium © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Right Atrium • Foramen ovale • Before birth, is an opening through interatrial septum • Connects the two atria • Seals off at birth, forming fossa ovalis © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Right Atrium • Pectinate muscles • Contain prominent muscular ridges • On anterior atrial wall and inner surfaces of right auricle © 2015 Pearson Education, Inc. Figure 20-6a The Sectional Anatomy of the Heart. Left common carotid artery Left subclavian artery Brachiocephalic trunk Superior vena cava Ligamentum arteriosum Pulmonary trunk Aortic arch Pulmonary valve Right pulmonary arteries Left pulmonary arteries Ascending aorta Fossa ovalis Opening of coronary sinus Right atrium Pectinate muscles Left atrium Left pulmonary veins Interatrial septum Aortic valve Cusp of left AV (mitral) valve Conus arteriosus Left ventricle Cusp of right AV (tricuspid) valve Chordae tendineae Papillary muscles Right ventricle Interventricular septum Trabeculae carneae Inferior vena cava Moderator band Descending aorta a A diagrammatic frontal section through the heart, showing major landmarks and the path of blood flow (marked by arrows) through the atria, ventricles, and associated vessels. © 2015 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart. Left subclavian artery Left common carotid artery Brachiocephalic trunk Superior vena cava Ascending aorta Pulmonary trunk Cusp of pulmonary valve Auricle of left atrium Right atrium Cusp of left AV (bicuspid) valve Chordae tendineae Cusps of right AV (tricuspid) valve Papillary muscles Left ventricle Trabeculae carneae Right ventricle c Anterior view of a frontally sectioned heart showing internal features and valves. © 2015 Pearson Education, Inc. Interventricular septum 20-1 Anatomy of the Heart • The Right Ventricle • Free edges attach to chordae tendineae from papillary muscles of ventricle • Prevent valve from opening backward • Right atrioventricular (AV) valve • • • • Also called tricuspid valve Opening from right atrium to right ventricle Has three cusps Prevents backflow © 2015 Pearson Education, Inc. Figure 20-6b The Sectional Anatomy of the Heart. Chordae tendineae Papillary muscles b The papillary muscles and chordae tendineae support the right AV (tricuspid) valve. The photograph was taken from inside the right ventricle, looking toward a light shining from the right atrium. © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Pulmonary Circuit • Pulmonary trunk divides into left and right pulmonary arteries • Blood flows from right ventricle to pulmonary trunk through pulmonary valve • Pulmonary valve has three semilunar cusps © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Left Atrium • Blood gathers into left and right pulmonary veins • Pulmonary veins deliver to left atrium • Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve • A two-cusped bicuspid valve or mitral valve © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Left Ventricle • Systemic circulation • Blood leaves left ventricle through aortic valve into ascending aorta • Ascending aorta turns (aortic arch) and becomes descending aorta © 2015 Pearson Education, Inc. Figure 20-6c The Sectional Anatomy of the Heart. Left subclavian artery Left common carotid artery Brachiocephalic trunk Superior vena cava Ascending aorta Pulmonary trunk Cusp of pulmonary valve Auricle of left atrium Right atrium Cusp of left AV (bicuspid) valve Chordae tendineae Cusps of right AV (tricuspid) valve Papillary muscles Left ventricle Trabeculae carneae Right ventricle c Anterior view of a frontally sectioned heart showing internal features and valves. © 2015 Pearson Education, Inc. Interventricular septum Figure 20-7a Structural Differences between the Left and Right Ventricles. Posterior interventricular sulcus Left ventricle Right ventricle Fat in anterior interventricular sulcus a © 2015 Pearson Education, Inc. A diagrammatic sectional view through the heart, showing the relative thicknesses of the two ventricles. Notice the pouchlike shape of the right ventricle and the greater thickness of the left ventricle. Figure 20-8a Valves of the Heart (Part 1 of 2). Transverse Sections, Superior View, Atria and Vessels Removed POSTERIOR Cardiac skeleton Relaxed ventricles RIGHT VENTRICLE Left AV (bicuspid) valve (open) LEFT VENTRICLE Right AV (tricuspid) valve (open) Aortic valve (closed) ANTERIOR a Aortic valve closed © 2015 Pearson Education, Inc. Pulmonary valve (closed) When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. Figure 20-8a Valves of the Heart (Part 2 of 2). Frontal Sections through Left Atrium and Ventricle Pulmonary veins Relaxed ventricles LEFT ATRIUM Left AV (bicuspid) valve (open) Aortic valve (closed) Chordae tendineae (loose) Papillary muscles (relaxed) LEFT VENTRICLE (relaxed and filling with blood) a © 2015 Pearson Education, Inc. When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. Figure 20-8b Valves of the Heart (Part 1 of 2). Contracting ventricles Right AV (tricuspid) valve (closed) RIGHT VENTRICLE Cardiac skeleton Left AV (bicuspid) valve (closed) LEFT VENTRICLE Aortic valve (open) Pulmonary valve (open) b When the ventricles are contracting, Aortic valve open © 2015 Pearson Education, Inc. the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles. Contracting ventricles Figure 20-8b Valves of the Heart (Part 2 of 2). Aorta Aortic sinus Aortic valve (open) LEFT ATRIUM Left AV (bicuspid) valve (closed) Chordae tendineae (tense) Papillary muscles (contracted) Left ventricle (contracted) b When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles. © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Blood Supply to the Heart • = Coronary circulation • Supplies blood to muscle tissue of heart • Coronary arteries and cardiac veins © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Coronary Arteries • Left and right • Originate at aortic sinuses • High blood pressure, elastic rebound forces blood through coronary arteries between contractions © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Right Coronary Artery • Supplies blood to: • • • • • Right atrium Portions of both ventricles Cells of sinoatrial (SA) and atrioventricular nodes Marginal arteries (surface of right ventricle) Posterior interventricular artery © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Left Coronary Artery • Supplies blood to: • Left ventricle • Left atrium • Interventricular septum © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Two Main Branches of Left Coronary Artery 1. Circumflex artery 2. Anterior interventricular artery • Arterial Anastomoses • Interconnect anterior and posterior interventricular arteries • Stabilize blood supply to cardiac muscle © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • The Cardiac Veins • Great cardiac vein • Drains blood from area of anterior interventricular artery into coronary sinus • Anterior cardiac veins • Empty into right atrium • Posterior cardiac vein, middle cardiac vein, and small cardiac vein • Empty into great cardiac vein or coronary sinus © 2015 Pearson Education, Inc. Figure 20-9a The Coronary Circulation. Aortic arch Ascending aorta Right coronary artery Left coronary artery Pulmonary trunk Circumflex artery Anterior interventricular artery Atrial arteries Great cardiac vein Anterior cardiac veins Small cardiac vein Marginal artery © 2015 Pearson Education, Inc. a Coronary vessels supplying and draining the anterior surface of the heart. Figure 20-9b The Coronary Circulation. Coronary sinus Circumflex artery Great cardiac vein Marginal artery Posterior interventricular artery Posterior cardiac vein Small cardiac vein Left ventricle Right coronary artery Middle cardiac vein Marginal artery b Coronary vessels supplying and draining the posterior surface of the heart. © 2015 Pearson Education, Inc. Figure 20-9c The Coronary Circulation. Auricle of left atrium Left pulmonary veins Left pulmonary artery Right pulmonary artery Circumflex artery Superior vena cava Great cardiac vein Marginal artery Right pulmonary veins Posterior cardiac vein Left atrium Right atrium Inferior vena cava Coronary sinus Middle cardiac vein Right ventricle Posterior interventricular artery c A posterior view of the heart; the vessels have been injected with colored latex (liquid rubber). © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Coronary artery disease (CAD) • Areas of partial or complete blockage of coronary circulation • Cardiac muscle cells need a constant supply of oxygen and nutrients • Usual cause is formation of a fatty deposit, or atherosclerotic plaque, in the wall of a coronary vessel © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Myocardial infarction (MI), or heart attack • Part of the coronary circulation becomes blocked, and cardiac muscle cells die from lack of oxygen • The death of affected tissue creates a nonfunctional area known as an infarct • Heart attacks most commonly result from severe coronary artery disease (CAD) © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Treatment of CAD and myocardial infarction • Risk factor modification • Stop smoking • High blood pressure treatment • Dietary modification to lower cholesterol and promote weight loss • Stress reduction • Increased physical activity (where appropriate) © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Treatment of CAD and myocardial infarction • Drug treatment • Drugs that reduce coagulation and therefore the risk of thrombosis, such as aspirin and coumadin • Drugs that block sympathetic stimulation (propranolol or metoprolol) • Drugs that cause vasodilation, such as nitroglycerin • Drugs that block calcium movement into the cardiac and vascular smooth muscle cells (calcium channel blockers) • In a myocardial infarction, drugs to relieve pain, fibrinolytic agents to help dissolve clots, and oxygen © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Treatment of CAD and myocardial infarction • Noninvasive surgery • Atherectomy • Blockage by a single, soft plaque may be reduced with the aid of a long, slender catheter inserted into a coronary artery to the plaque © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Treatment of CAD and myocardial infarction • Noninvasive surgery • Balloon angioplasty • The tip of the catheter contains an inflatable balloon • Once in position, the balloon is inflated, pressing the plaque against the vessel walls • Because plaques commonly redevelop after angioplasty, a fine tubular wire mesh called a stent may be inserted into the vessel, holding it open © 2015 Pearson Education, Inc. 20-1 Anatomy of the Heart • Heart Disease – Coronary Artery Disease • Treatment of CAD and myocardial infarction • Coronary artery bypass graft (CABG) • In a coronary artery bypass graft, a small section is removed from either a small artery or a peripheral vein and is used to create a detour around the obstructed portion of a coronary artery • As many as four coronary arteries can be rerouted this way during a single operation • The procedures are named according to the number of vessels repaired, so we speak of single, double, triple, or quadruple coronary bypasses © 2015 Pearson Education, Inc. Figure 20-10 Heart Disease and Heart Attacks (Part 1 of 4). Normal Heart A color-enhanced digital subtraction angiography (DSA) scan of a normal heart. © 2015 Pearson Education, Inc. 20-2 The Conducting System • Heartbeat • A single contraction of the heart • The entire heart contracts in series • First the atria • Then the ventricles © 2015 Pearson Education, Inc. 20-2 The Conducting System • The Cardiac Cycle • Begins with action potential at SA node • Transmitted through conducting system • Produces action potentials in cardiac muscle cells (contractile cells) • Electrocardiogram (ECG or EKG) • Electrical events in the cardiac cycle can be recorded on an electrocardiogram © 2015 Pearson Education, Inc. 20-2 The Conducting System • Structures of the Conducting System • Sinoatrial (SA) node – wall of right atrium • Atrioventricular (AV) node – junction between atria and ventricles • Conducting cells – throughout myocardium © 2015 Pearson Education, Inc. Figure 20-11a The Conducting System of the Heart. Sinoatrial (SA) node Internodal pathways Atrioventricular (AV) node AV bundle Bundle branches Purkinje fibers a Components of the conducting system. © 2015 Pearson Education, Inc. 20-2 The Conducting System • The Sinoatrial (SA) Node • • • • In posterior wall of right atrium Contains pacemaker cells Connected to AV node by internodal pathways Begins atrial activation (Step 1) © 2015 Pearson Education, Inc. 20-2 The Conducting System • The Atrioventricular (AV) Node • • • • In floor of right atrium Receives impulse from SA node (Step 2) Delays impulse (Step 3) Atrial contraction begins © 2015 Pearson Education, Inc. 20-2 The Conducting System • The AV Bundle • In the septum • Carries impulse to left and right bundle branches • Which conduct to Purkinje fibers (Step 4) • And to the moderator band • Which conducts to papillary muscles © 2015 Pearson Education, Inc. 20-2 The Conducting System • Purkinje Fibers • Distribute impulse through ventricles (Step 5) • Atrial contraction is completed • Ventricular contraction begins © 2015 Pearson Education, Inc. 20-2 The Conducting System • Abnormal Pacemaker Function • Bradycardia – abnormally slow heart rate • Tachycardia – abnormally fast heart rate • Ectopic pacemaker • • • • Abnormal cells Generate high rate of action potentials Bypass conducting system Disrupt ventricular contractions © 2015 Pearson Education, Inc. 20-2 The Conducting System • The Electrocardiogram (ECG or EKG) • A recording of electrical events in the heart • Obtained by electrodes at specific body locations • Abnormal patterns diagnose damage © 2015 Pearson Education, Inc. 20-2 The Conducting System • Features of an ECG • P wave • Atria depolarize • QRS complex • Ventricles depolarize • T wave • Ventricles repolarize © 2015 Pearson Education, Inc. 20-2 The Conducting System • Time Intervals between ECG Waves • P–R interval • From start of atrial depolarization • To start of QRS complex • Q–T interval • From ventricular depolarization • To ventricular repolarization © 2015 Pearson Education, Inc. Figure 20-13a An Electrocardiogram. a Electrode placement for recording a standard ECG. © 2015 Pearson Education, Inc. Figure 20-13b An Electrocardiogram. 800 msec +1 R P wave (atria depolarize) R T wave (ventricles repolarize) P–R segment S–T segment +0.5 0 Q S P–R interval S–T interval Q–T interval b Millivolts QRS interval (ventricles depolarize) −0.5 An ECG printout is a strip of graph paper containing a record of the electrical events monitored by the electrodes. The placement of electrodes on the body surface affects the size and shape of the waves recorded. The example is a normal ECG; the enlarged section indicates the major components of the ECG and the measurements most often taken during clinical analysis. © 2015 Pearson Education, Inc. Figure 20-14 Cardiac Arrhythmias (Part 1 of 2). Premature Atrial Contractions (PACs) P P P Paroxysmal Atrial Tachycardia (PAR) P P P Atrial Fibrillation (AF) © 2015 Pearson Education, Inc. P P P Premature atrial contractions (PACs) often occur in healthy individuals. In a PAC, the normal atrial rhythm is momentarily interrupted by a “surprise” atrial contraction. Stress, caffeine, and various drugs may increase the incidence of PACs, presumably by increasing the permeabilities of the SA pacemakers. The impulse spreads along the conduction pathway, and a normal ventricular contraction follows the atrial beat. In paroxysmal (par-ok-SIZ-mal) atrial tachycardia, or PAT, a premature atrial contraction triggers a flurry of atrial activity. The ventricles are still able to keep pace, and the heart rate jumps to about 180 beats per minute. During atrial fibrillation (fib-ri-LĀ-shun), the impulses move over the atrial surface at rates of perhaps 500 beats per minute. The atrial wall quivers instead of producing an organized contraction. The ventricular rate cannot follow the atrial rate and may remain within normal limits. Even though the atria are now nonfunctional, their contribution to ventricular end-diastolic volume (the maximum amount of blood the ventricles can hold at the end of atrial contraction) is so small that the condition may go unnoticed in older individuals. Figure 20-14 Cardiac Arrhythmias (Part 2 of 2). Premature Ventricular Contractions (PVCs) P T P T P Ventricular Tachycardia (VT) P Ventricular Fibrillation (VF) © 2015 Pearson Education, Inc. T Premature ventricular contractions (PVCs) occur when a Purkinje cell or ventricular myocardial cell depolarizes to threshold and triggers a premature contraction. Single PVCs are common and not dangerous. The cell Ventricular tachycardia is defined as four or more PVCs without intervening normal beats. It is also known as VT or V-tach. Multiple PVCs and VT may indicate that serious cardiac problems exist. Ventricular fibrillation (VF) is responsible for the condition known as cardiac arrest. VF is rapidly fatal, because the ventricles quiver and stop pumping blood. responsible is called an ectopic pacemaker. The frequency of PVCs can be increased by exposure to epinephrine, to other stimulatory drugs, or to ionic changes that depolarize cardiac muscle plasma membranes. 20-3 The Cardiac Cycle • The Cardiac Cycle • Is the period between the start of one heartbeat and the beginning of the next • Includes both contraction and relaxation © 2015 Pearson Education, Inc. 20-3 The Cardiac Cycle • Two Phases of the Cardiac Cycle • Within any one chamber 1. Systole (contraction) 2. Diastole (relaxation) © 2015 Pearson Education, Inc. 20-3 The Cardiac Cycle • Blood Pressure • In any chamber • Rises during systole • Falls during diastole • Blood flows from high to low pressure • Controlled by timing of contractions • Directed by one-way valves © 2015 Pearson Education, Inc. 20-3 The Cardiac Cycle • Cardiac Cycle and Heart Rate • At 75 beats per minute (bpm) • Cardiac cycle lasts about 800 msec • When heart rate increases • All phases of cardiac cycle shorten, particularly diastole © 2015 Pearson Education, Inc. 20-3 The Cardiac Cycle • Heart Sounds • S1 • Loud sounds • Produced by AV valves • S2 • Loud sounds • Produced by semilunar valves © 2015 Pearson Education, Inc. 20-3 The Cardiac Cycle • S3, S4 • Soft sounds • Blood flow into ventricles and atrial contraction • Heart Murmur • Sounds produced by regurgitation through valves © 2015 Pearson Education, Inc. Figure 20-18a Heart Sounds. Sounds heard Valve location Aortic valve Valve location Pulmonary Sounds heard valve Sounds heard Valve location Left AV valve Valve location Sounds heard Right AV valve a Placements of a stethoscope for listening to the different sounds produced by individual valves © 2015 Pearson Education, Inc. 20-4 Cardiodynamics • Cardiodynamics • The movement and force generated by cardiac contractions • End-diastolic volume (EDV) • End-systolic volume (ESV) • Stroke volume (SV) • SV = EDV – ESV • Ejection fraction • The percentage of EDV represented by SV © 2015 Pearson Education, Inc. 20-4 Cardiodynamics • Cardiac Output (CO) • The volume pumped by left ventricle in one minute • CO = HR SV • CO = cardiac output (mL/min) • HR = heart rate (beats/min) • SV = stroke volume (mL/beat) © 2015 Pearson Education, Inc.