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Cardiac Anatomy Blood Supply 1. Thoracic aorta, venae cavae 2. Histology of great vessels 3. Coronary vasculature Innervation 1. Cardiac innervation 2. Conducting system sdevlin41@qub.ac.ukThoracic Aorta • Arises from left ventricle via aortic vestibule • First branches: • Right and left coronary arteries • Large branches: • Brachiocephalic trunk • Right subclavian • Right common carotid • Left common carotid Smaller, hard to see in • Left subclavian cadavers, less relevant • Small branches: • Posterior intercostal arteries • Mediastinal, oesophageal, bronchial, pericardial • Superior phrenic Mostly in the abdomen Plural – there are 2 Inferior vena cava (IVC): Venae Cavae Superior vena cava (SVC): Formation: Internal jugular v + subclavian v = brachiocephalic v ↓ Right + left brachiocephalic vv = SVC ↓ Enters the right atrium • Both drain into the right atrium along with the blood from the coronary sinus • SVC descends through the superior mediastinum then middle mediastinum Anatomy: • SVC drains into the right atrium Venae Cavae • These veins are valveless (normal veins have valves) Clinical relevance • Therefore, the blood will back up into the systemic venous Jugular venous pressure (JPV) system if it cannot get through the right atrium → right ventricle • Remember internal jugular vein and subclavian combine to form the brachiocephalic vein, right and left brachiocephalic veins combining to form the SVC What prevents right atrium from coping with the venous return? • Right-sided heart failure (cor pulmonale) • Pulmonary hypertension • Fluid overload • Tricuspid regurgitation • SVC obstruction What can be used to augment the JVP? Hepatojugular reflexHistology • All vessels have the same 3 layers: • Tunica intima • Tunica media • Tunica adventitia • Arteries: • Elastic artery • Muscular artery • Veins • Classified by size (large, medium) What is the easiest way to tell the difference in an Aorta = elastic artery Vena cava = large vein artery and a vein in histology? Veins are usually collapsed, the lumens of the arteries will be patentComparison of Thoracic Aorta & Vena Cava Vessel Aorta (elastic artery) Vena cava (large vein) Features Thick walls Relatively thin walls No valves Valves Histology Intima: thin endothelium Intima: thin endothelium Media: thickest laye, with sheets of elastin Media: little elastin, collagen fibres Adventitia: CT, own blood and nerve supply Adventitia: thickest laye, loads of collagen Coronary Vasculature Arteries ‘LAD’ • Coronary blood supply is derived from 2 main branches: lr nticu terve A rir i An t Right coronary artery o Left coronary artery Diagonal Ci r rcum f branches lexart t ery a AVN branch SAN branch Left Posterior Right marginal marginal interventricular ’PDA’Coronary Vasculature Arteries • The RCA and LCA arise from aortic sinuses • Due to gravity, some blood ejected into the aorta will fall back down and be caught in the aortic sinuses • This gives rise to the coronary arteries: 1. Right aortic sinus → right coronary artery 2. Left aortic sinus → left coronary artery 3. Posterior aortic sinus (non-coronary sinus) • Nodule & lunuleCoronary Vasculature Arteries RCA Anterior heart Supplies: • Right atrium • Right ventricle • Sino-atrial node • Atrioventricular node • Inter-atrial septum • Portion of left atrium • Posterior portion of left ventricle ECG area: • Inferior (PDA)Coronary Vasculature Arteries LCA Anterior heart Supplies: • Left atrium • Left ventricle • Portion of interventricular septum • AV bundles ECG areas: (LAD) • LCA = anterolateral • LCX = lateral • LAD = anteriorCoronary Vasculature Arteries Dominance Anterior heart • Can be right or left dominant • Right dominant = the posterior interventricular artery (AKA PDA) arises as a branch of the right coronary artery • Left dominant = the posterior interventricular artery (AKA PDA) arises as a branch of the left (circumflex) coronary artery Dominant side Rate Right 70% Left 10% Co-dominant 20%Coronary Vasculature Arteries Clinical relevance • An ECG will allow you to localise an MI, ie, identify the blocked vessel Relevant arteries for ECGs: Lateral Septal Anterior Inferior Lateral Septal Lateral Inferior Inferior Anterior Lateral ECG reading: https://geekymedics.com/how-to-read-an-ecg/Coronary Vasculature Arteries Clinical relevance • An ECG will allow you to localise an MI, ie, identify the blocked vessel Location Leads Vessel Anterior (V1, V2,) V3, V4 Anterior interventricular / LAD Lateral I, aVL, V5, V6 Circumflex a. Anterolateral V3, V4, V5, V6, I, aVL LCA Inferior II, II, aVF RCACoronary Vasculature Veins • All vv drain into the coronary sinus (posteriorly), which itself lies in the coronary sulcus • Coronary sinus drains directly into the right atrium • Main vv: • Great cardiac v • Middle cardiac v • Small cardiac v • Posterior cardiac v • Anterior cardiac v Coronary Vasculature Veins Posterior Anterior heart heart Plexus = network of nerves (or vessels) Innervation of the Heart Visceral = refers to organ Extrinsic innervation Afferent = sensory from • Autonomic innervation is derived from the cardiac plexus organ to brain • Divided into superficial and deep portions • Formed from sympathetic and parasympathetic fibres travelling to the heart (SA node), as well as visceral afferent fibres travelling from the heart (pain feedback to the brain) – ie., fibres travelling in 2 directions Superficial Deep plexus plexus (To the heart) Innervation of the Heart Sympathetic (fight or flight) • Function = 1) ↑ heart rate (chronotropy), 2) ↑ force of contraction (inotropy) Pathway: Cardiorespiratory centres of medulla oblongata ↓ Synapse in spinal cord (T1-T5/6) ↓ Sympathetic chain (ganglia) ↓ Postganglionic cardiac nerves ↓ Heart (To the heart) Innervation of the Heart Parasympathetic (rest & digest) • Function = 1) ↓ heart rate (chronotropy), 2) ↓ force of contraction (inotropy) Pathway: Vagus nerve (CN X) ↓ Synapse in atrial walls ↓ Effect in heart (To the heart) Innervation of the Heart Most important bit Summary: Autonomic Origin / Effector Effect on heart nervous system Sympathetic Cardiac nerves from the 1. Increase HR (fight or flight) sympathetic trunk 2. Increase force of ↓ contraction Branches to cardiac plexus ↓ Cardiac plexus to heart Parasympathetic Right and left vagus nerves 1. Decrease HR (rest & digest) ↓ 2. Decrease force Cardiac plexus of contraction ↓ Cardiac plexus to heart Vagus nerve descends in mediastinum, then gives the anterior and posterior oesophageal plexuses: left vagus → anterior plexus, right vagus → posterior plexus (From the heart) Innervation of the Heart Feedback system to the brain • There are fibres travelling both ways in the cardiac plexus • Efferent fibres (sympathetic & parasympathetic) from the brain → heart (previous slides) • Afferent fibres (visceral afferents) from the heart → brain • Visceral afferent fibres will transmit pain sensation from the heart → brain (via spinal cord, etc.) ‘referred pain’ Why is pain from an MI felt in the left arm / shoulder / jaw? 1. MI = myocardial cells die, stimulating the visceral afferent fibres (fibres from heart → brain) 2. Visceral afferent fibres follow the sympathetic fibres (travelling in the opposite direction) back to the spinal cord where they enter and synapse between the T1 and T4 levels 3. T1-T4 spinal cord somatic afferents (nerves supplying skin) also enter the spinal cord here 4. Both the visceral afferents (from heart) and somatic afferents (from skin of shoulder / arm) synapse with interneurons, which then cross to the other side of the cord, and then ascend to the somatosensory cortex of the brain which represents the T1-T4 level 5. Brain can’t distinguish between the visceral afferents and somatic afferents, hence pain is interpreted as arising from the skin of the shoulder 6. Felt on the left side because the heart is on the left side of the body (From the heart) Innervation of the Heart Feedback system to the brain Why is pain from an MI felt in the left arm / shoulder / jaw? 1. MI = myocardial cells die, stimulates visceral afferent fibres (fibres from heart → brain) 2. Visceral afferents go to spinal cord, enter between T1-T4 3. Somatic afferents (nerves supplying skin) also enter the spinal cord here 4. Visceral afferents and somatic afferents synapse with interneurons, and ascend to brain 5. Brain confuses visceral afferents and somatic afferents – pain is referred to shoulder 6. Felt on the left side because the heart is on the left side of the bodyInnervation of the Heart Intrinsic innervation At junction of • The conduction system of the heart is responsible for making the heart pump right atrium and SVC Sinoatrial (SA) node (pacemaker) ↓ Impulse spreads myogenically through both At opening of atria coronary sinus in ↓ interatrial septum Impulse reaches atrioventricular (AV) node ↓ Impulse distributed through the bundle of His (AV bundle) ↓ At muscular IV septum, split into right and left bundles (to papillary muscles and moderator band) ↓ Purkinje fibres in ventricular wallsMCQ #1 An 85 year old man presents to ED with central crushing chest pain as 2 hours, radiating to his left arm, with associated nausea, vomiting and sweating. An ECG reveals ST elevation in leads V1, V2, V3 and V4. In what vessel will the stent most likely be placed? 1. Right marginal artery 2. Anterior interventricular artery (LAD) 3. Kugel’s artery 4. Anterior interarticular artery 5. Left coronary arteryMCQ #1 An 85 year old man presents to ED with central crushing chest pain as 2 hours, radiating to his left arm, with associated nausea, vomiting and sweating. An ECG reveals ST elevation in leads V1, V2, V3 and V4. In what vessel will the stent most likely be placed? 1. Right marginal artery 2. Anterior interventricular artery (LAD) 3. Kugel’s artery 4. Anterior interarticular artery 5. Left coronary arteryMCQ #2 A 68 year old woman presents to ED after experiencing severe chest pain for the last 6 hours. It is getting progressively worse. It radiates through to her back. She is lightheaded and nauseous. She has smoked 40 a day for 50 years. CT reconstruction and transoesophageal echocardiography reveal an aortic dissection. In what layer of the aorta has the dissection occurred in? 1. Tunica intima 2. Internal elastic lamina 3. Tunica media 4. External elastic lamina 5. Tunica adventitiaMCQ #2 A 68 year old woman presents to ED after experiencing severe chest pain for the last 6 hours. It is getting progressively worse. It radiates through to her back. She is lightheaded and nauseous. She has smoked 40 a day for 50 years. CT reconstruction and transoesophageal echocardiography reveal an aortic dissection. In what layer of the aorta has the dissection occurred in? 1. Tunica intima 2. Internal elastic lamina 3. Tunica media 4. External elastic lamina 5. Tunica adventitia In an aortic aneurysm, the tunica media is most often weakest / damagedMCQ #3 A 21 year old medical student is relaxing on a Friday night after completing some MCQs. Their smart watch tells them their heart rate is 56BPM. They can’t remember which bit of the autonomic nervous system is responsible for their physiological bradycardia. Which of these nervous structures is responsible? 1. Pons 2. Occipital lobe of brain 3. Nucleus of the solitary tract 4. Sympathetic chain 5. Vagus nerveMCQ #3 A 21 year old medical student is relaxing on a Friday night after completing some MCQs. Their smart watch tells them their heart rate is 56BPM. They can’t remember which bit of the autonomic nervous system is responsible for their physiological bradycardia. Which of these nervous structures is responsible? 1. Pons 2. Occipital lobe of brain 3. Nucleus of the solitary tract 4. Sympathetic chain 5. Vagus nerve Parasympathetic = rest / digest = vagus nerve Sympathetic = fight / flight = sympathetic chainQuestions? Blood Supply 1. Thoracic aorta, venae cavae 2. Histology of great vessels 3. Coronary vasculature Innervation 1. Cardiac innervation 2. Conducting system sdevlin41@qub.ac.uk