Heart and Conduction System PDF

The Heart and Conduction System Sheila Nunn Professor of Anatomy Email: [email protected] Please email me any questions or to set up a 1:1 TEAMS meeting The Heart Is The Only Organ That Takes No Rest.” Germ...

The Heart and Conduction System Sheila Nunn Professor of Anatomy Email: [email protected] Please email me any questions or to set up a 1:1 TEAMS meeting The Heart Is The Only Organ That Takes No Rest.” German-American physician and writer Martin Fischer  Objectives Describe the physical layout of the heart within the middle mediastinum (heart borders and surface anatomy) and relate this to its overlying bony features Describe the pericardium: composition, sinuses, blood and nervous supply, and clinical implications regarding this structure. Describe the 4 chambers of the heart: what structures are found within each chamber (e.g., similarities and differences between right and left ventricles) and any associated embryological origins/remnants. Explain the flow of blood through the heart Compare heart valve location and auscultation site Describe the coronary arteries: their branches and anastomoses between the different arteries, regions of distribution, dominance of the heart, disease processes associated with the coronary arteries i Describe the venous drainage of the heart Indicate the location of the structures that are involved with the conduction system of the heart. Explain the innervation of heart Discuss the heart pathologies and possible treatments covered V Mediastinum S A septum or space in the thoracic cavity Contains the thoracic viscera except the lungs inferior Subdivided into : S = superior P = posterior M = middle thymus A = anterior Please note there is no tissue planes separating mediastinal compartments  Characteristics of the Mediastinum Mobile  loose connective tissue: (accommodate changes in volume & pressure) Clinical Relevance: Displacement of Structures & their Relationships Mediastinal narrowing Mediastinal widening (silhouetting)  Tumors  Lung masses  Aneurysm  Pleural effusion  Pericardial effusion Normal Surface landmarks: Sternal Angle (Angle of Louis) Transverse thoracic plane The sternal angle is an important anatomical landmark 1. Separation between superior and inferior mediastinum 2. Beginning and end of the aortic arch 3. Bifurcation of the trachea into 2 right and left primary bronchi 4. Azygos vein arches over the roof of the Rt. Lung and opens into SVC 5. The upper limit of the base of the heart (upper border of the atria of the heart) (When body lying in supine position) Note in some textbooks azygos is called azygous i Location of the Heart is the Middle Mediastinum S Content of Middle Mediastinum: 1. Heart 2. Major vessels i. Superior vena cava Pericardium ii. Inferior vena cava iii. Pulmonary trunk iv. Pulmonary veins v. Ascending aorta  Heart & Surface Anatomy V R Auricle L Aur LV RV Note particularly the hearts relationship to the ribs and sternum: important in evaluating what structures may have been damaged with penetrating wounds e.g., stabbing, shotgun. Relate also to medical imaging of the heart session v Some Examples of “Danger Areas” Left of 1st intercostal space : pulmonary artery TIE Left 2nd intercostal space (parasternal border): left atrium Left 3rd-5th ribs (parasternal border): right ventricle Right 3rd-6th ribs: right atrium It  v Heart Borders & Surface Anatomy GLAVIN 1. Superior border: right and left atria and auricle 2. Inferior/diaphragmatic border: Left ventricle & Right ventricle (mainly) 3. Right border: (right 3rd rib and 6th rib at right parasternal border) Right atrium, SVC and IVC 4. Left border: (left 2nd rib and 5th intercostal space midclavicular line) left ventricle (mainly) and left auricle v Apex of the Heart Formed by the inferolateral part of the left ventricle Where the sound of closure of mitral valve is maximal Lies along the mid-clavicular line deep to LEFT 5th intercostal space The point of maximal impulse ((PMI) apical pulse) is where the cardiac impulse can be best palpated on the chest wall. Frequently, this is at the LEFT 5th intercostal space at the mid-clavicular line.  The Base of the Heart Posterior aspect opposite of the apex Posterior view LA Formed mainly by the left atrium and partly by the right atrium (LA) Corresponds to the T5-T8 vertebrae Receives pulmonary veins (R & L) on its left atrial Heart removed; part; SVC & IVC of its right atrial part anterior thoracic view Overlays esophagus and thoracic aorta Pericardium Clinical Relevance: Mitral valve insufficiency  Mitral valve leaflets disorder  Blood regurgitates into the left atrium Esophagus  Dilated left atrium likely to compress esophagus = dysphagia Thoracic aorta  Also, tumors in left atrium can compress esophagus Posterior view  Pericardium Fibrous membrane covering the heart and the origin of great vessels Three Layers: 1. Fibrous Pericardium (F): Attached to the central tendon of the diaphragm and sternum. Serous pericardium: 2. Parietal layer of serous pericardium. 3. Visceral layer (V) of serous pericardium (epicardium). The phrenic nerve provides somatic innervation to the fibrous and parietal layers Anterior view  Pericardial cavity:  Space between parietal and visceral layers of serous aorta pericardium Pericardial fluid: Left lung  Contained within the pericardial cavity. FP  Secreted by serous mesothelium  Link to cardiac tamponade later in VLSP lecture Anterior view thoracic cage removed  Pericardial sinuses SVG Transverse pericardial sinus (TS): A passage behind the ascending aorta and pulmonary trunk. TS OS A Anterior view with heart removed Formed via degeneration of dorsal mesocardium A ligature is passed through the Transverse sinus to clamp the Ascending aorta and Pulmonary trunk during cardiac surgery Oblique sinus (OS): AA PT Located posterior to the heart. Reflection of pericardium surrounding the pulmonary veins, IVC and pericardium overlying the esophagus.  Clinical Relevance i. Pericarditis: Inflammation of the pericardium  Causes chest pain  “Pericardial friction rub” (sounds like rustle of silk)  i ii. Pericardial Effusion:  The pericardial space normally contains 15-50 mL of fluid, which serves as lubrication for the visceral and parietal layers of the pericardium.  An effusion is excess fluid in the pericardial cavity ("fluid around the heart”)  At first, pericardial effusion can be asymptomatic. Over time, however, it can cause chest pain, shortness of breath, and compression of near structures. Ultimately, if the pressure inside the pericardial cavity increases enough to compress the heart muscle, it may lead to pericardial tamponade  In some cases, pericarditis, leads to the effusion. As it becomes inflamed, more fluid is produced Pericardial effusion can also occur when the flow of pericardial fluid is blocked or when blood collects within the pericardium, such as from a chest trauma v Clinical complications of Pericardial Effusion Cardiac Tamponade (Heart compression):  Due to extensive pericardial effusion  Compressed volume does not allow for full expansion of the heart  limits amount of blood heart receives  reduces cardiac output Symptoms- “Beck’s Triad” 1. Hypotension (↓ stroke volume, ↓ cardiac output) 2. Jugular-venous distention 3. Muffled heart sounds Treatment: Pericardiocentesis: withdrawal of fluid from pericardial sac. Sites: Left 5th or 6th intercostal space near the sternum or infrasternal angle  Heart Chambers: Right atrium Auricle Receives venous blood (poorly oxygenated) from 4 sources Crista terminalis 1. Superior vena cava 2. Inferior vena cava SVC 3. Coronary sinus 4. Anterior cardiac veins Sinus venarum Internal aspect IVC  Sinus venarum (smooth portion)  Pectinate muscle (rough portion)  Crista terminalis Fossa ovalis Pectinate muscle Opening of  Fossa ovalis coronary sinus  Auricle Link to their embryological origins  Trabeculae carneae (rough portion) Right Ventricle Conus arteriosus/ infundibulum (smooth portion) Pulmonary valve  Leads to pulmonary trunk through the Conus pulmonary valve arterios us Tricuspid valve Papillar S Is y  Chordae tendineae muscle  Papillary muscles (3): Anterior, Posterior, Septal P A Tricuspid valve Septomarginal trabeculae (Moderator band) Chordae tendineae  Contains right branch of the AV bundle Trabeculae carneae Septomargin al trabecula  Pulmonary trunk Takes poorly oxygenated blood from i the right ventricle to the lungs. Right superior Left pulmonary pulmonary artery Divides into right and left pulmonary artery arteries. Right pulmonary Left pulmonary artery artery Right inferior pulmonary artery Pulmonary Posteroinferior view Trunk  Left Atrium Auricle Receives venous blood (rich in oxygen) from the 4 pulmonary veins (2 superior and 2 inferior) Internal aspect  Larger smooth wall portion and smaller muscular portion than right atrium  Auricle (contains pectinate muscle)  Semilunar depression (floor of fossa ovalis). Note that the valve of the Floor of oval fossa is the surrounding ridge Fossa ovalis Pulmonary veins  Aortic vestibule Left Ventricle Papillary Similar to right ventricle structures muscles A Trabeculae carneae (rough pt) Aortic vestibule (smooth pt) P Bicuspid (Mitral) valve Bicuspid valve  Chordae tendineae Trabeculae carneae Chordae tendineae  Papillary muscles (2): anterior and posterior NOseptal R L Thicker wall than right ventricle Aortic valve opened  Valves Tricuspid valve  RA to RV Pulmonary or pulmonic valve  RV to pulmonary trunk Mitral valve (bicuspid)  LA to LV Aortic valve  LV to aorta Blood Flow Through the Heart Least oxygenated blood Most highly oxygenated blood  Heart Valves: anatomical location vs auscultation sites soundest Anatomical Location (white circles) Auscultation site (red circles) hear Aortic- medial Aortic- 2nd intercostal aspect of left 3rd space, right intercostal space, parasternal behind sternum Pulmonic- 2nd Pulmonic- medial intercostal space, left aspect of left 3rd parasternal costal cartilage Tricuspid- 5th Tricuspid- medial intercostal space, left aspect of right 5th parasternal costal cartilage, Mitral- 5th intercostal behind sternum space, left Mitral- medial midclavicular line aspect of left 3rd intercostal space  Auscultation Sites Physicians All L 2nd intercostal space, 2nd intercostal space, right parasternal left parasternal Pulmonary valve Aortic valve Tricuspid valve Mitral valve Take Money 5th intercostal space, 5th intercostal space, left parasternal left midclavicular line Auscultation performed at the sites where the sound waves reverberate - NOT at the anatomical location of the valves.  Vasculature of Heart Coronary arteries  Right and Left coronary arteries. Aortic sinus i  The first branches of the aorta and arise from the Right & Left aortic sinuses. Cardiac veins  Great  Middle  Small cardiac veins  Coronary Sinus  Thebesian cardiac veins (Not visible at gross level)  Right Coronary Artery: Contains 4 branches you need to know 1. SA nodal 2. AV nodal 1 3. Posterior interventricular 4. Right marginal Left Coronary Artery (LCA): Contains 2 branches you need to know 1. Circumflex which gives off the  Left marginal 2. LAD/left anterior descending)/ Anterior interventricular which gives off the  Diagonal branch i  l Which Branches Supply Where? Posterior third of IVS* In addition, Right Coronary Artery supplies: anterior  SA Nodal: SA node and pulmonary trunk RCA supply= Dark pink  AV Nodal: AV node RV LV LCA supply= Light pink In addition, left coronary artery supplies:  Septal: anterior 2/3 IVS* and bundle of His Coronary Arteries Variation Dominance depends on the origin of the posterior interventricular artery Normal - RCA dominant LCA dominant Other variations 15% LC A RCA PIV 1 J N RV LV ~70% population ~15% population  Left Coronary Collateral Circulation coronary Right coronary Circumflex In NORMAL circulation: Anastomoses between the termination of coronary arteries Anastomoses at the apex i  LAD & Posterior interventricular artery Posterior At the coronary sulcus interventricular Anterior interventricular  LCA (Circumflex) & RCA (LAD)  Blockage and Collateral Flow X Y i Unblocked flow Blocked flow X marks site of blockage: low pressure inferior to blockage e.g., point Y Anomalous Left Coronary Artery When left coronary artery arises from the pulmonary artery instead of left aortic sinus Congenital heart defect, usually, an isolated defect Result. Left ventricular myocardium perfused by relatively desaturated blood under low pressure, leading to myocardial ischemia Collateral circulation between the right and left coronary systems ensues. Left coronary artery flow reverses and enters the pulmonic trunk due to the low pulmonary vascular resistance (coronary steal phenomena). Result, left ventricular myocardium remains underperfused. Ultimately congestive heart failure (CHF) symptoms (tachypnea, poor feeding, irritability, diaphoresis) in the young infant).  Venous Drainage of the Heart TWO pathways: 1. Coronary Sinus and its tributaries Great cardiac vein, Small cardiac and Middle cardiac veins 2. Anterior cardiac veins – drain directly into the right atrium  Which Vein Runs With Which Artery i in the Coronary Circulation?  Myocardial Infarction (MI): Sudden occlusion of a major artery (by an embolus)  Region of heart supplied by occluded vessels become infarcted (rendered bloodless) and becomes necrotic (tissue death) Most common cause of MI = 3 most common sites of occlusion coronary artery insufficiency from atherosclerosis 1. LAD = 40-50% 2. RCA = 30-40% 3. Circumflex = 15-20%  Conduction System of Heart The conducting system of the heart is regulated by the ANS:  Vagus provides parasympathetic innervation: SA and AV nodes and coronary arteries. Slows heart rate  Thoracic cord segments T1-T5 sympathetic to the above. Increases heart rate Note Visceral afferent fibers travel with (hitchhike) sympathetic fibers and carry the visceral pain relating to angina pectoris  Conduction system Location within the heart structure v Sinuatrial (SA) node Located in the Rt. atrium between Crista terminalis and opening of SVC Bachmann’s Bundle Right to Left atrium Atrioventricular (AV) Located in the Rt. atrium at interatrial septum close to the opening of coronary node sinus. Bundle of His Membranous pt. of interventricular (IV) septum Right bundle branches Muscular IV septum, moderator band, wall of R. ventricle Left bundle branches Muscular IV septum, wall of L. ventricle Purkinje fibers Right side- IVS, wall of R. ventricle, Ant. papillary muscle (subendocardial brs.) Left side- IVS, wall of L. ventricle, Ant. and Post. papillary muscle