Chapter 9 Cardiovascular System - Heart: Comprehensive Study Guide

Cardiovascular System Objectives and Word Parts

• Core Learning Objectives:

  • Apply the rules of medical language to build, analyze, spell, pronounce, abbreviate, and define terms as they relate to the cardiovascular system.

  • Identify meanings of key word components of the cardiovascular system.

  • Categorize diagnostic, therapeutic, procedural, or anatomic terms related to the cardiovascular system.

  • Use terms related to the cardiovascular system.

  • Use terms related to the diseases and disorders of the cardiovascular system.

Quantitative Overview of Heart Function

• Vital Organ Characteristics:

  • The heart is a fist-sized vital organ whose sole functional task is to pump blood through the circulatory system.

• Contraction Frequency Metrics:

  • Average resting heart rate: $75\,\text{bpm}$.

  • Daily heartbeats: Approximately $108,000\,\text{times}$ per day.

  • Annual heartbeats: Over $39,000,000\,\text{times}$ ($39\text{ million}$) per year.

  • Lifetime heartbeats: Nearly $3,000,000,000\,\text{times}$ ($3\text{ billion}$) over a $75\text{-year}$ lifespan.

• Volumetric Displacement Metrics:

  • Resting stroke volume: Approximately $70\,mL$ of blood ejected per contraction per major pumping chamber in an adult.

  • Minute cardiac volume: Equivalent to $5.25\,L/\text{min}$ of blood pumped per minute.

  • Daily cardiac volume: Approximately $14,000\,L/\text{day}$ of blood pumped per day.

  • Annual cardiac volume: Approximately $10,000,000\,L/\text{yr}$ ($10\text{ million liters}$) sent through roughly $100,000\,km$ of blood vessels.

Anatomy and Location of the Heart

• Thoracic Cavity Positioning:

  • Mediastinum: The heart is located medially within the thoracic cavity between the lungs in the anatomical region called the mediastinum.

  • Pericardial Cavity: Situated within its own dedicated space inside the mediastinum called the pericardial cavity, separated from other mediastinal structures by the pericardium (pericardial sac).

• Gross Anatomical Landmarks:

  • Base: The broad superior surface of the heart where the great vessels (which carry blood to and from the heart) attach. The base is located at the anatomical level of the third costal cartilage.

  • Apex: The inferior pointed tip of the heart, which lies just to the left of the sternum between the junction of the fourth and fifth ribs.

Membranes and Layers of the Heart Wall

• Pericardium (Pericardial Sac):

  • Fibrous Pericardium: The sturdy outer layer composed of tough, dense connective tissue that physically protects the heart and holds it securely in position within the thorax.

  • Serous Pericardium: The inner double-layered membrane separated by the fluid-filled pericardial cavity containing lubricating pericardial fluid. It consists of:

  • Parietal Pericardium: Outer layer of the serous pericardium, fused directly to the fibrous pericardium.

  • Visceral Pericardium (Epicardium): Inner layer of the serous pericardium, fused directly to the heart muscle to form the outermost layer of the heart wall.

• Layers of the Heart Wall:

  • Epicardium: Outer structural layer of the heart wall (synonymous with the visceral pericardium).

  • Myocardium: Thick middle layer composed primarily of cardiac muscle tissue, providing the contractile force required to pump blood.

  • Endocardium: Thin inner lining composed of endothelial tissue covering the heart chambers and forming the primary component of the heart valves.

Internal Structures and Valves of the Heart

• Heart Chambers:

  • Atria: The two upper receiving chambers of the heart (right atrium and left atrium; singular: atrium).

  • Ventricles: The two lower primary pumping chambers of the heart (right ventricle and left ventricle).

• Internal Septa:

  • Interatrial Septum: Membrane wall separating the right atrium from the left atrium.

  • Interventricular Septum: Thick muscular wall separating the right ventricle from the left ventricle.

• Atrioventricular (AV) Valves:

  • Tricuspid Valve (Right AV Valve): Valve separating the right atrium and right ventricle.

  • Bicuspid Valve / Mitral Valve (Left AV Valve): Valve separating the left atrium and left ventricle.

• Semilunar (SL) Valves:

  • Pulmonary Valve: Semilunar valve separating the right ventricle from the pulmonary trunk.

  • Aortic Valve: Semilunar valve separating the left ventricle from the aorta.

• Valve Acoustics:

  • Heart sounds detected through a stethoscope during auscultation are produced by the synchronized closing of the four heart valves at specific points during the cardiac cycle.

Physiology of Heart Function and Dual Circulation

• Functional Integration:

  • Heart function depends on three interdependent mechanisms:

  1. Circulation through the heart to deliver oxygen and nutrients to every systemic cell.

  2. Coronary circulation supplying blood directly to the cellular tissues of the heart organ itself.

  3. The intrinsic cardiac conduction system generating and propagating electrical impulses to stimulate myocardial contraction.

• Dual Circulatory Circuits:

  • Pulmonary Circuit: Transports blood to and from the lungs where blood drops off carbon dioxide ($CO_2$) and absorbs oxygen ($O_2$).

  • Systemic Circuit: Transports freshly oxygenated blood from the heart to all tissues of the body and returns deoxygenated blood and carbon dioxide back to the heart.

• Complete Pathway of Blood Circulation:

  1. Deoxygenated blood carrying carbon dioxide and tissue metabolic waste returns to the right atrium via the superior vena cava and inferior vena cava.

  2. Blood flows from the right atrium through the tricuspid valve into the right ventricle.

  3. The right ventricle contracts, pumping deoxygenated blood through the pulmonary valve into the pulmonary trunk.

  4. The pulmonary trunk bifurcates into the right and left pulmonary arteries, which carry deoxygenated blood to the lungs (pulmonary arteries are the only post-natal arteries carrying deoxygenated blood, depicted in blue on anatomical diagrams).

  5. Blood enters the pulmonary capillaries surrounding lung alveoli, where gas exchange occurs ($CO_2$ leaves blood, $O_2$ enters blood).

  6. Freshly oxygenated blood leaves the lungs and returns to the left atrium via the pulmonary veins (pulmonary veins are the only veins in the body carrying oxygenated blood, depicted in red on anatomical diagrams).

  7. Blood passes from the left atrium through the mitral valve into the left ventricle.

  8. The left ventricle contracts, pumping oxygenated blood through the aortic valve into the aorta, distributing blood through systemic arteries to body tissues.

Cardiac Cycle

• Dynamic Rhythmic Phases:

  • Diastole: The relaxation phase of the cardiac cycle during which the heart muscle relaxes, atria and ventricles fill with blood, and AV valves remain open to allow ventricular filling.

  • Systole: The contraction phase of the cardiac cycle during which the myocardium contracts, AV valves slam shut (preventing backflow), ventricles eject blood through open semilunar valves into the pulmonary trunk and aorta, and semilunar valves subsequently close as relaxation begins.

Diseases and Disorders of the Heart

• Cardiomyopathy:

  • Definition: Pathological condition affecting the myocardium that impairs the heart's contracting and pumping capacity, frequently leading to heart failure.

  • Athletic Hypertrophy vs. Pathological Enlargement: Exercise training increases muscle cell size (hypertrophy), allowing athletes to pump blood efficiently at lower heart rates. Abnormally enlarged hearts unrelated to exercise are pathological.

  • Hypertrophic Cardiomyopathy: Idiopathic abnormal enlargement of heart muscle; often undiagnosed and can cause sudden death in otherwise healthy young individuals.

  • Dilated Cardiomyopathy: Idiopathic condition affecting individuals of any age, characterized by abnormal enlargement of one of the heart ventricles.

  • Arrhythmogenic Cardiomyopathy: Inherited genetic disease resulting in irregular heart rhythms due to myocardial degeneration.

  • Restrictive Cardiomyopathy: Secondary complication of conditions that cause myocardial scarring or stiffening, restricting ventricular filling.

  • Associated Causes: Myocardial infarction, myocardial infections, pregnancy, chronic alcohol abuse, cocaine abuse, autoimmune diseases, and endocrine disorders.

• Heart Failure (Congestive Heart Failure - CHF):

  • Inability of the heart to pump sufficient blood volume to satisfy metabolic requirements of body tissues.

  • Manifestations: Shortness of breath (dyspnea) and lower extremity swelling due to pulmonary fluid accumulation.

  • Causes: Secondary to cardiomyopathy, hypertension, and chronic heart valve disorders.

• Valvular Heart Disease:

  • Pathophysiology: Impaired opening or closing of heart valves, preventing unidirectional blood flow.

  • Etiologies: Rheumatic disease, bacterial endocarditis (producing scar tissue), congenital valve malformations, autoimmune conditions, aortic aneurysms, and atherosclerosis.

  • Detection & Symptoms: Detected by a heart murmur during stethoscope auscultation; symptoms include dyspnea, arrhythmias, and fatigue.

  • Mitral Valve Prolapse (MVP): Disease or malformation of the mitral (bicuspid) valve preventing complete closure during systole, allowing blood regurgitation back into the left atrium and reducing systemic ejection volume.

  • Aortic Stenosis: Narrowing and hardening of the aortic valve preventing full opening and restricting blood outflow to systemic circulation (can affect any valve, but most frequently involves the aortic valve).

Congenital Heart Defects

• Fetal Circulatory Structures:

  • Foramen Ovale: Opening in the fetal interatrial septum allowing blood to bypass non-functional fetal lungs.

  • Ductus Arteriosus: Vessel connecting the fetal pulmonary trunk directly to the aorta.

  • Fetal Reoxygenation: Oxygenation occurs via placental exchange with maternal circulation; fetal openings normally close near birth.

• Congenital Anomalies:

  • Patent Ductus Arteriosus (PDA): Failure of the ductus arteriosus to close after birth; if untreated, leads to congestive heart failure.

  • Patent Foramen Ovale (PFO): Failure of the interatrial septal hole to close at birth (a form of atrial septal defect, ASD). Affects $20\text{ to }25\%$ of the general population; mostly benign and asymptomatic, but extreme cases require surgical closure.

  • Tetralogy of Fallot (TOF): Complex congenital heart defect caused by an opening in the interventricular septum alongside pulmonary trunk obstruction (typically at the pulmonary semilunar valve). Allows low-oxygen blood from the right ventricle to mix with high-oxygen blood in the left ventricle.

  • Anatomic components: Interventricular septal defect, stenosed pulmonary semilunar valve, overriding aorta (emerging from both ventricles), and right ventricular hypertrophy.

  • Clinical signs: Distinct heart murmur, low blood oxygen saturation, dyspnea, polycythemia, finger and toe clubbing, feeding difficulty, and failure to thrive in children.

  • Clinical significance: Primary cause of cyanosis following birth; confirmed via echocardiography imaging.

  • Blue Baby Condition: Severe septal defects (including Tetralogy of Fallot and patent foramen ovale) impairing proper blood oxygenation, resulting in systemic cyanosis, particularly during physical activity.

Diseases of Coronary Circulation and Surgical Interventions

• Coronary Artery Disease (CAD):

  • Pathophysiology: Progressive accumulation of lipid plaque within coronary arteries (atherosclerosis), obstructing blood flow and reducing vessel compliance.

  • Clinical Consequences: Myocardial ischemia leading to chest pain (angina pectoris); can progress to myocardial infarction if unmanaged.

  • Risk Factors: Smoking, family history, hypertension, hyperlipidemia, obesity, diabetes mellitus, excessive alcohol consumption, physical inactivity, and stress.

• Diagnostic Angiography:

  • Angiogram: X-ray imaging using radiopaque dye to visualize coronary artery blockages, such as occlusions in the common trunk of the left coronary artery or circumflex artery.

• Interventional Procedures and Surgeries:

  • Angioplasty: Mechanical widening of an occluded blood vessel using a specialized balloon-tipped catheter inserted through arm or leg vessels to the site of blockage. Balloon inflation compresses plaque against vessel walls; a specialized mesh stent is typically placed to maintain vessel patency and prevent re-occlusion.

• Coronary Artery Bypass Graft (CABG): Open surgical procedure in which a healthy replacement blood vessel harvested from another body area is grafted to bypass blocked coronary arteries. Procedures are classified as single, double, triple, or quadruple bypass based on the number of bypassed vessels.

Myocardial Infarction

• Definition and Pathophysiology:

  • Myocardial Infarction (MI): Clinical term for a heart attack, defined as death of cardiac muscle cells resulting from prolonged ischemia (lack of blood flow).

  • Causes: Occlusion of coronary arteries by atherosclerotic plaque or thromboembolism from ruptured plaque lodging in distal coronary vessels.

  • Triggers: Excessive physical exertion (exceeding blood supply capacity of narrowed vessels) or severe emotional stress (inducing coronary smooth muscle spasm).

• Clinical Presentation:

  • Acute Myocardial Infarction (AMI): Sudden retrosternal pain beneath the sternum (angina pectoris), typically radiating down the left arm in males (radiation pattern often absent or atypical in females).

  • Systemic Symptoms: Dyspnea, palpitations, nausea, vomiting, diaphoresis (sweating), anxiety, and syncope.

  • Silent MIs: An estimated $22\text{ to }64\%$ of myocardial infarctions are clinically silent (asymptomatic).

• Diagnostic Tools and Biomarkers:

  • Electrocardiogram (ECG): Detects electrical changes indicative of cardiac tissue necrosis or ischemia.

  • Imaging Modalities: Echocardiography, cardiac CT, and cardiac MRI.

  • Blood Serum Biomarkers: Elevated blood levels of cardiac troponin and creatine kinase MB ($\text{CK-MB}$) released by dying myocardial cells.

• Comprehensive Risk Factors:

  • CAD, advanced age, smoking, elevated LDL cholesterol, reduced HDL cholesterol, hypertension, diabetes mellitus, obesity, sedentary lifestyle, chronic kidney disease, excessive alcohol consumption, and illicit drug use.

Diseases of the Electrical Conduction System

• Pacemaker Function and Arrhythmias:

  • Sinoatrial (SA) Node: Heart's natural electrical pacemaker, firing spontaneous action potentials at $60\text{ to }90\,\text{bpm}$ in resting adults.

  • Electrocardiograph: Instrument used to detect and record heart electrical activity through skin electrodes.

  • Arrhythmia: Definition is the absence of a regular rhythm (heart rate too fast, too slow, or irregular). It does not mean absence of a heartbeat (absence of heartbeat is asystole or flat line).

• Fibrillation and Defibrillation:

  • Fibrillation: Uncontrolled, rapid cardiac twitches preventing organized pumping action.

  • Atrial Fibrillation: Serious arrhythmia; non-immediately life-threatening as long as ventricular pumping is maintained.

  • Ventricular Fibrillation: Immediate medical emergency; ventricles fail to pump blood, leading to brain death if untreated.

  • Defibrillation: Delivery of electrical shock via paddles or pads to depolarize heart tissue, stopping chaotic activity so the SA node can re-establish normal sinus rhythm.

  • Automated External Defibrillators (AEDs): Publicly accessible devices (in schools, airports, restaurants) providing spoken instructions to enable non-medical personnel to administer defibrillation.

Abnormal Heart Rates and Conduction Blocks

• Bradycardia:

  • Definition: Resting adult heart rate below $60\,\text{bpm}$.

  • Clinical Significance: Asymptomatic bradycardia is non-pathological. Symptomatic bradycardia (weakness, fatigue, dizziness, syncope, chest discomfort, palpitations, respiratory distress) indicates inadequate tissue oxygenation. Most patients remain asymptomatic as long as heart rate exceeds $50\,\text{bpm}$.

  • Relative Bradycardia: Patient possesses a heart rate within normal range ($60\text{--}100\,\text{bpm}$) that is nevertheless functionally insufficient for their physiological state, causing clinical symptoms.

• Tachycardia:

  • Definition: Resting adult heart rate exceeding $100\,\text{bpm}$.

  • Features: Abnormal in resting adults (excluding pregnant women or extreme emotional stress).

  • Symptoms: Dizziness, shortness of breath, rapid pulse, palpitations, chest pain, and syncope.

  • Management: Pharmacotherapy, implantable cardioverter defibrillators (ICDs), catheter ablation, or surgery.

• Heart Block:

  • Definition: Interruption or impairment along the normal electrical conduction pathway.

  • Nomenclature: Named after the involved conduction site (e.g., bundle branch blocks occurring within the right or left atrioventricular bundle branches).

Medical Specialties and Clinical Roles

• Cardiologists: Medical doctors specializing in non-invasive diagnosis and medical management of cardiovascular disorders.

• Cardiovascular/Thoracic Surgeons: Medical specialists providing surgical treatment for diseases affecting the heart, great vessels, and thoracic organs.

• Cardiology Technologists: Trained professionals executing diagnostic tests including electrocardiography (ECG), exercise stress testing, Holter monitoring, ambulatory blood pressure monitoring, and pacemaker programming.

• Cardiovascular Perfusionists: Specialized healthcare professionals operating heart-lung bypass machinery during open-heart surgery, managing patient vitals, administering intravenous fluids, and controlling pharmacological interventions.