chapter 27: assessment of the cardiovascular system

Anatomy and Physiological Structure of the Cardiovascular System

  • The heart is situated in the center of the chest, with the base or the left ventricle tilting toward the left.

  • The heart is composed of three distinct layers:

    • Pericardium: The outermost lining surrounding the heart. Complications occurring here include pericarditis or pericardial effusion.

    • Myocardium: The middle muscle layer of the heart responsible for structural contractions.

    • Endocardium: The innermost layer that lines the inside of the heart, including all valves, ventricles, and atria.

  • The heart contains four chambers:

    • Right Atrium and Left Atrium: The upper chambers.

    • Right Ventricle and Left Ventricle: The lower chambers.

  • Major blood vessels and their functions:

    • Pulmonary Arteries: Carry deoxygenated blood away from the heart to the pulmonary system.

    • Pulmonary Veins: Carry oxygenated blood from the pulmonary system back to the heart.

    • Aorta: Transports oxygenated blood from the heart to the rest of the body.

    • Superior and Inferior Vena Cava: Carry deoxygenated blood from the body back to the heart.

  • Heart valves and their locations:

    • Tricuspid Valve: Located between the right atrium and the right ventricle.

    • Mitral Valve: Located between the left atrium and the left ventricle.

    • Pulmonic Valve: Located between the right ventricle and the pulmonary artery.

    • Aortic Valve: Located between the left ventricle and the aorta.

  • Coronary artery anatomy and clinical significance:

    • Left Anterior Descending (LAD): A major coronary artery; a blockage in the LAD carries the highest mortality risk.

    • Left Circumflex: Supplies blood to the lateral wall and posterior wall of the left ventricle, and usually serves the Sinoatrial (SA) and Atrioventricular (AV) nodes.

    • Right Coronary Artery (RCA): Affects the right ventricle, certain portions of the AV and SA nodes, and the inferior walls.

Blood Flow and Circulation Dynamics

  • The heart acts as a pump connecting systemic circulation and pulmonary circulation.

  • Path of Blood Flow:

    • Deoxygenated blood from the upper body enters via the superior vena cava.

    • Deoxygenated blood from the lower body enters via the inferior vena cava.

    • Blood enters the right atrium, moves through the tricuspid valve into the right ventricle.

    • From the right ventricle, blood passes through the pulmonary semilunar valve into the pulmonary arteries and into the lungs.

    • Gas exchange occurs in the pulmonary alveoli.

    • Oxygenated blood returns via the pulmonary veins to the left atrium.

    • Blood moves from the left atrium to the left ventricle and then exits through the aortic valve into the aorta.

  • Systemic circulation begins in the left ventricle, while pulmonary circulation involves the flow through the lungs for oxygenation.

Electrical Properties and Conduction System

  • The heart possesses four key electrical properties:

    • Automaticity: The pacing function; the ability to create electrical impulses spontaneously and repetitively.

    • Excitability: The ability of the heart cells to respond to electrical stimulation.

    • Conductivity: The ability for electrical impulses to travel along designated pathways.

    • Contractility: The mechanical activity and resulting physical contraction of the heart.

  • Components of the conduction system:

    • SA Node: The primary pacemaker located in the right atrium with an intrinsic rate of 60×100 beats per minute60 \times 100\,\text{beats per minute}. It is represented by the P wave on an EKG.

    • AV Node: The secondary pacemaker with an intrinsic rate of 40×60 beats per minute40 \times 60\,\text{beats per minute}. It slows the impulse to allow for atrial contraction and ventricular filling, a process known as "atrial kick."

    • Bundle of His, Bundle Branches, and Purkinje Fibers: These have intrinsic rates of 30×40 beats per minute30 \times 40\,\text{beats per minute} and are responsible for rapid conduction through the ventricles, leading to ventricular depolarization and contraction.

  • Electrophysiological process:

    • Polarization: The resting state where the inside of the cell contains negative ions and the outside contains positive ions.

    • Depolarization: Occurs when permeability increases to allow sodium (Na+Na^+) and calcium (Ca2++Ca^{2+}+) ions to move into the heart cells, triggering contraction.

    • Repolarization: Occurs when potassium (K+K^+) leaves the cardiac cells, returning the heart to a state of rest.

Hemodynamics and Mechanical Properties

  • Cardiac Output (CO): The total volume of blood pumped from the left ventricle per minute.

    • Formula: CO=Stroke Volume (SV)×Heart Rate (HR)CO = \text{Stroke Volume (SV)} \times \text{Heart Rate (HR)}

    • Typical SV in a healthy adult: 50×75 mL/beat50 \times 75\,mL/\text{beat}

    • Typical CO: 4×8 L/min4 \times 8\,L/min

    • Example: 70 mL×75 bpm=5,250 mL/min70\,mL \times 75\,bpm = 5,250\,mL/min

  • Preload: The amount of myocardial stretch at the end of diastole, determined by the volume of blood in the ventricles.

    • Starling's Law: Stroke volume increases in response to an increase in blood volume filling the heart. Increased preload equals increased cardiac output, though overstretching is harmful.

  • Afterload: The resistance against which the ventricles must pump to circulate blood.

    • Causes of increased afterload: Hypertension and aortic stenosis.

    • Effect: Increased afterload decreases cardiac output and increases the workload of the heart.

  • Contractility: The force of contraction (inotropic state).

    • Cardiac cycle timing: Systole (contraction) accounts for 1/31/3 of the cycle; diastole (resting/filling) accounts for 2/32/3.

  • Heart Rate Effects: Slightly increasing heart rate increases CO. However, excessively high heart rates cause CO to decrease because stroke volume drops due to incomplete ventricular filling.

  • Sympathetic Nervous System (SNS): Controls heart components as part of the "fight or flight" response. It releases norepinephrine, which acts as a positive chronotropic (increases HR) and positive inotropic (increases contractility) agent.

Cardiovascular Aging and Patient History

  • Changes with Aging:

    • Decreased vessel elasticity: Can lead to increased blood pressure.

    • Calcification: Increases the risk for Myocardial Infarction (MI).

    • Impaired valves: Can lead to heart failure, stenosis, and regurgitation.

    • Decreased muscle tone: Reduces contractility and impacts cardiac output.

  • Risk Factors:

    • Non-modifiable: Age, gender, race, family history, and genetics.

    • Modifiable: Smoking and obesity.

  • Medical History Focus:

    • Hypertension, CVA (stroke), bleeding disorders, or existing heart disease.

    • History of multiple strep infections or rheumatic fever.

    • Review of current drugs and herbal supplements.

  • Symptom Identification:

    • Pain, discomfort, fatigue, and edema.

    • Paroxysmal Nocturnal Dyspnea (PND): A sudden episode of severe shortness of breath that awakens a person from sleep, usually after lying down for several hours. It is caused by the redistribution of blood from the lower extremities to the venous system. An ineffective heart cannot pump the extra fluid, leading to pulmonary congestion. This is an early sign of heart failure and may be the only symptom in female patients.

Physical Assessment and Auscultation

  • Perfusion Indicators:

    • Poor perfusion: Cyanosis, cool or moist skin, and clubbing of the nails (long-term effect).

    • Edema: A common sign of heart failure.

    • Arterial vs. Venous disease: Arterial disease presents with weak or absent pulses; venous disease presents with pulses and edema.

  • Heart Sounds (Auscultation):

    • S1: Best heard over the left lower sternal border.

    • S2: Created by the closing of the aortic and pulmonic valves.

    • S3 (Ventricular Gallop): An early sign of heart failure; may be normal in individuals under age 35.

    • S4 (Atrial Gallop): Indicates decreased compliance of either ventricle.

  • Gender Differences: Women often do not present with chest pain but rather discomfort or indigestion. 44%44\% of women over age 20 have some degree of cardiovascular disease.

  • Stethoscope Utilization:

    • Diaphragm: Used for high-pitched sounds (S1, S2) and high-velocity blood movement. Press firmly on the skin.

    • Bell: Used for low-pitched sounds (S3, S4), murmurs, and low-velocity movement. Rest lightly on the skin.

Diagnostic Testing and Laboratory Markers

  • Serum Markers:

    • Troponin: Proteins specific to cardiac muscle not found in healthy patients. Any elevation indicates cardiac necrosis or acute MI. Tests are repeated every 3×6 hours3 \times 6\,\text{hours} as levels are slow to appear in bloodwork.

    • Creatine Kinase (CK): Indicates general muscle breakdown (not cardiac-specific).

    • Lipids: Increased levels cause plaque formation, leading to angina or MI.

  • Coagulation Studies:

    • PT and INR: Used to monitor Warfarin therapy.

    • PTT: Used for patients on Heparin.

  • Other Tests:

    • ABGs: Evaluate oxygenation and acid-base balance, which affect contractility.

    • EKG and EPS: EPS is an invasive electrical stimulation used to evaluate severe dysrhythmias.

    • Stress Tests and Echoes.

    • Lexiscan: A prescription medication used in nuclear stress tests for patients unable to exercise. It mimics exercise response by dilating blood vessels to check for blockages or damage.

  • Cardiac Catheterization:

    • The most definitive and most invasive diagnostic test.

    • Confirms CAD, myocardial disease, and valvular dysfunction.

    • Performed on the right side of the heart first, then the left.

    • Complications: Contrast reactions, pulmonary edema, hypovolemia, and MI (left side) or Pulmonary Embolism (right side).

  • The heart is situated in the center of the chest, with the base or the left ventricle tilting toward the left, protected by the rib cage, which assists in its function while also being surrounded by the mediastinum.

  • The heart is composed of three distinct layers:

    • Pericardium: The outermost lining surrounding the heart. This double-walled structure includes a fibrous outer layer and a serous inner layer, which produces pericardial fluid to decrease friction during heart contractions. Complications occurring here include pericarditis or pericardial effusion, which can hinder cardiac function.

    • Myocardium: The middle muscle layer of the heart responsible for structural contractions. This layer is vital for maintaining the pump function of the heart and is composed of cardiac muscle tissue that is unique to the heart, allowing for rhythmic contractions due to its intrinsic ability to generate electrical impulses.

    • Endocardium: The innermost layer that lines the inside of the heart, including all valves, ventricles, and atria. This smooth layer minimizes surface friction as blood is pumped through the heart.

  • The heart contains four chambers:

    • Right Atrium and Left Atrium: The upper chambers that receive blood from the body and lungs, respectively. The walls of the atria are thinner compared to the ventricles, and they play a critical role in filling the ventricles with blood prior to contraction.

    • Right Ventricle and Left Ventricle: The lower chambers known for their muscular and robust structures, responsible for pumping deoxygenated blood to the lungs (right ventricle) and oxygenated blood to the systemic circulation (left ventricle).

  • Major blood vessels and their functions:

    • Pulmonary Arteries: Carry deoxygenated blood away from the heart to the pulmonary system for gas exchange, where carbon dioxide is expelled, and oxygen is absorbed.

    • Pulmonary Veins: Carry oxygenated blood from the pulmonary system back to the heart, specifically into the left atrium, making them unique as they are the only veins in the body that carry oxygen-rich blood.

    • Aorta: The largest artery in the body, it transports oxygenated blood from the left ventricle to various parts of the body through systemic circulation, distributing nutrients and oxygen.

    • Superior and Inferior Vena Cava: Carry deoxygenated blood from the upper body and lower body back to the heart, respectively, entering into the right atrium to maintain circulation.

  • Heart valves and their locations:

    • Tricuspid Valve: Located between the right atrium and the right ventricle; it prevents backflow of blood into the atrium during ventricular contraction.

    • Mitral Valve: Located between the left atrium and the left ventricle; it ensures that blood flows in one direction into the ventricle to prevent regurgitation.

    • Pulmonic Valve: Located between the right ventricle and the pulmonary artery; it opens to allow deoxygenated blood to flow into the pulmonary arteries for oxygenation.

    • Aortic Valve: Located between the left ventricle and the aorta; it prevents backflow of blood into the ventricle after contraction.

  • Coronary artery anatomy and clinical significance:

    • Left Anterior Descending (LAD): A major coronary artery; a blockage in the LAD carries the highest mortality risk due to its supply to a significant portion of the heart muscle.

    • Left Circumflex: Supplies blood to the lateral wall and posterior wall of the left ventricle, and usually serves the Sinoatrial (SA) and Atrioventricular (AV) nodes, impacting cardiac rhythm.

    • Right Coronary Artery (RCA): Supplies blood to the right ventricle, parts of the heart's conduction system (AV and SA nodes), and the inferior walls, crucial for maintaining electrical conduction and contractility of the heart.

  • The heart acts as a pump connecting systemic circulation and pulmonary circulation, ensuring that oxygen-rich and oxygen-poor blood do not mix. This is vital for optimal oxygen delivery to tissues and organs.

  • Proficiency in Understanding: Knowledge of the cardiovascular system’s anatomy and physiology is fundamental for assessing heart health, diagnosing diseases, and determining appropriate treatment strategies, emphasizing the need for continuous education in cardiovascular medicine.