cardiovascular assessment

• Structure and Function


  The cardiovascular system is highly complex, consisting of the heart and a closed system of blood vessels. To collect accurate data and correctly interpret it, the examiner must have an understanding of the structure and function of the heart, the great vessels, the electrical conduction system of the heart, the cardiac cycle, the production of heart sounds, cardiac output (CO), and the neck vessels. This information helps the examiner to differentiate between normal and abnormal findings as they relate to the cardiovascular system.

  
• Heart and Great Vessels

  The heart is a hollow, muscular, four-chambered (left and right atria, and left and right ventricles) organ located in the middle of the thoracic cavity between the lungs in the space called the mediastinum. It is about the size of a clenched fist and weighs approximately 255 g (9 oz) in women and 310 g (10.9 oz) in men. The heart extends vertically from the left second to the left fifth intercostal space (ICS) and horizontally from the right edge of the sternum to the left midclavicular line (MCL). The heart can be described as an inverted cone. The upper portion, near the left second ICS, is the base; the lower portion, near the left fifth ICS and the left MCL, is the apex. The anterior chest area that overlies the heart and great vessels is called the precordium (Fig. 21-1). The right side of the heart pumps blood to the lungs for gas exchange (pulmonary circulation) by removing CO2 from blood and replenishing oxygen supply. It occurs between alveoli and the blood of lungs; the left side of the heart pumps blood to all other parts of the body (systemic circulation). Perfusion occurs when blood flows to tissues and organs promoting the diffusion of oxygen and carbon dioxide.

  
• Great Vessels


  The large veins and arteries leading directly to and away from the heart are referred to as the great vessels. The superior and inferior vena cava return blood to the right atrium from the upper and lower torsos, respectively. The pulmonary artery exits the right ventricle, bifurcates, and carries blood to the lungs. The pulmonary veins (two from each lung) return oxygenated blood to the left atrium. The aorta transports oxygenated blood from the left ventricle to the body (Fig. 21-2).
• Heart Chambers and Valves

  The heart consists of four chambers, or cavities: two upper chambers, the right and left atria, and two lower chambers, the right and left ventricles. The right and left sides of the heart are separated by a partition called the septum. The thin-walled atria receive blood returning to the heart and pump blood into the ventricles. The thicker-walled ventricles pump blood out of the heart. The left ventricle is thicker than the right ventricle because the left side of the heart has a greater workload.

  The entrance and exit of each ventricle are protected by one-way valves that direct the flow of blood through the heart. The atrioventricular (AV) valves are located at the entrance to the ventricles. There are two AV valves: the tricuspid valve and the bicuspid (mitral) valve. The tricuspid valve is composed of three cusps, or flaps, and is located between the right atrium and the right ventricle; the bicuspid (mitral) valve is composed of two cusps and is located between the left atrium and the left ventricle. Collagen fibers, called chordae tendineae, anchor the AV valve flaps to papillary muscles within the ventricles.

  Open AV valves allow blood to flow from the atria into the ventricles. However, as the ventricles begin to contract, the AV valves snap shut, preventing the regurgitation of blood into the atria. The valves are prevented from blowing open in the reverse direction (i.e., toward the atria) by their secure anchors to the papillary muscles of the ventricular wall. The semilunar valves are located at the exit of each ventricle at the beginning of the great vessels. Each valve has three cusps that look like half-moons, hence the name "semilunar." There are two semilunar valves: the pulmonic valve is located at the entrance of the pulmonary artery as it exits the right ventricle and the aortic valve is located at the beginning of the ascending aorta as it exits the left ventricle. These valves are open during ventricular contraction and close from the pressure of blood when the ventricles relax. Blood is thus prevented from flowing backward into the relaxed ventricles (Fig. 21-2).

  
• Heart Covering and Walls


  The pericardium is a tough, inextensible, loose-fitting, fibroserous sac that attaches to the great vessels and surrounds the heart. A serous membrane lining, the parietal pericardium, secretes a small amount of pericardial fluid that allows for smooth, friction-free movement of the heart. This same type of serous membrane covers the outer surface of the heart and is known as the epicardium. The myocardium is the thickest layer of the heart, made up of contractile cardiac muscle cells. The endocardium is a thin layer of endothelial tissue that forms the innermost layer of the heart and is continuous with the endothelial lining of blood vessels (Fig. 21-2).

  
• Electrical Conduction of the Heart

  Cardiac muscle cells have a unique inherent ability. They can spontaneously generate an electrical impulse and conduct it through the heart. The generation and conduction of electrical impulses by specialized sections of the myocardium regulate the events associated with the filling and emptying of the cardiac chambers. The process is called the cardiac cycle (see description in next section).

  The sinoatrial (SA) node (or sinus node) is located on the posterior wall of the right atrium near the junction of the superior and inferior vena cava. The SA node, with inherent rhythmicity, generates impulses (at a rate of 60–100/min) that are conducted over both atria, causing them to contract simultaneously and send blood into the ventricles. The current, initiated by the SA node, is conducted across the atria to the AV node located in the lower interatrial septum (Fig. 21-3). The AV node slightly delays incoming electrical impulses from the atria and then relays the impulse to the AV bundle (bundle of His) in the upper interventricular septum. The electrical impulse then travels down the right and left bundle branches and the Purkinje fibers in the myocardium of both ventricles, causing them to contract almost simultaneously. Although the SA node functions as the "pacemaker of the heart," this activity shifts to other areas of the conduction system, such as the Bundle of His (with an inherent discharge of 40–60/min), if the SA node cannot function.

  
• Electrical Activity


  Electrical impulses, which are generated by the SA node and travel throughout the cardiac conduction circuit, can be detected on the surface of the skin. This electrical activity can be measured and recorded by electrocardiography (ECG, also abbreviated as EKG), which records the depolarization and repolarization of the cardiac muscle. The phases of the ECG are known as P, Q, R, S, and T.

  
• Phases of the Electrocardiogram

  • P wave: Atrial depolarization; conduction of the impulse throughout the atria
  • PR interval: Time from the beginning of the atrial depolarization to the beginning of ventricular depolarization, that is, from the beginning of the P wave to the beginning of the QRS complex
  • QRS complex: Ventricular depolarization (also atrial repolarization); conduction of the impulse throughout the ventricles, which then triggers contraction of the ventricles; measured from the beginning of the Q wave to the end of the S wave
  • ST segment: Period between ventricular depolarization and the beginning of ventricular repolarization
  • T wave: Ventricular repolarization; the ventricles return to a resting state
  • QT interval: Total time for ventricular depolarization and repolarization, that is, from the beginning of the Q wave to the end of the T wave; the QT interval varies with heart rate (HR)
  • U wave: May or may not be present; if present, it follows the T wave and represents the final phase of ventricular repolarization

  
• The Cardiac Cycle


  The cardiac cycle refers to the filling and emptying of the heart's chambers. The cardiac cycle has two phases: diastole (relaxation of the ventricles, known as filling) and systole (contraction of the ventricles, known as emptying). Diastole endures for approximately two thirds of the cardiac cycle and systole is the remaining one third (Fig. 21-4).

  
• Diastole


  During ventricular diastole, the AV valves are open and the ventricles are relaxed. This causes higher pressure in the atria than in the ventricles. Therefore, blood rushes through the atria into the ventricles. This early, rapid, passive filling is called early or protodiastolic filling. This is followed by a period of slow passive filling. Finally, near the end of ventricular diastole, the atria contract and complete the emptying of blood out of the upper chambers by propelling it into the ventricles. This final active filling phase is called presystole, atrial systole, or sometimes the atrial kick. This action raises left ventricular pressure.
• Systole


  The filling phases during diastole result in a large amount of blood in the ventricles, causing the pressure in the ventricles to be higher than in the atria. This causes the AV valves (mitral and tricuspid) to shut. Closure of the AV valves produces the first heart sound (S1), which is the beginning of systole. This valve closure also prevents blood from flowing backward (a process known as regurgitation) into the atria during ventricular contraction.

  At this point in systole, all four valves are closed and the ventricles contract (isometric contraction). There is now high pressure inside the ventricles, causing the aortic valve to open on the left side of the heart and the pulmonic valve to open on the right side of the heart. Blood is ejected rapidly through these valves. With ventricular emptying, the ventricular pressure falls and the semilunar valves close. This closure produces the second heart sound (S2), which signals the end of systole.

  After closure of the semilunar valves, the ventricles relax. Atrial pressure is now higher than the ventricular pressure, causing the AV valves to open and diastolic filling to begin again.
• Heart Sounds


  Heart sounds are produced by valve closure, as just described. The opening of valves is silent. Normal heart sounds, characterized as "lub-dub" (S1 and S2), and occasionally extra heart sounds and murmurs can be auscultated with a stethoscope over the precordium, the area of the anterior chest overlying the heart and great vessels.

  
• Normal Heart Sounds


  The first heart sound (S1) is the result of closure of the AV valves: the mitral and tricuspid valves. As mentioned previously, S1 correlates with the beginning of systole (see Box 21-2 for more information about S1 and variations of S1). S1 ("lub") is usually heard as one sound but may be heard as two sounds (Fig. 21-4). If heard as two sounds, the first component represents mitral valve closure (M1) and the second component represents tricuspid closure (T1). M1 occurs first because of increased pressure on the left side of the heart and because of the route of myocardial depolarization. S1 may be heard over the entire precordium but is heard best at the apex (left MCL, fifth ICS).

  
• Understanding Normal S1 Sounds and Variations


  • S1, which is the first heart sound, is produced by the AV valves

  
• Heart sounds


  • S1 (lub) - Closure of AV valves (mitral and tricuspid)
  • S2 (dub) - Closure of semilunar valves (aortic and pulmonic)
  • S3 and S4 - Diastolic filling sounds, ventricular vibration
• S1


  Correlates with the beginning of systole
• S2


  Correlates with the beginning of diastole
• S1 production


  1. Mitral valve closure (M1)

  2. Tricuspid valve closure (T1)
• Variations in S1


  • Softer at the base, louder at the apex
  • May be split along the lower left sternal border
• S2 production


  1. Aortic valve closure (A2)

  2. Pulmonic valve closure (P2)
• Variations in S2


  • Split S2 - A2 and P2
  • A2 heard best over 2nd right ICS, P2 normally softer than A2
• S3


  Early diastolic filling sound, ventricular vibration
• S4

  Late diastolic filling sound, ventricular vibration due to noncompliance
• Extra heart sounds (S3 and S4) are described further in the Physical Assessment section

  
• Murmurs are caused by turbulent blood flow due to increased velocity, structural valve defects, valve malfunction, or abnormal chamber openings
• Cardiac output (CO)


  Amount of blood pumped by the ventricles per minute, determined by stroke volume (SV) x heart rate (HR)

  
• Factors influencing stroke volume (SV)


  • Preload (degree of heart muscle stretch)
  • Afterload (pressure against which heart ejects blood)
  • Contractility of myocardium
  • Compliance of ventricles
  • Synchrony of myocardial contraction
• Autonomic nervous system influence on cardiac activity


  • Sympathetic impulses increase HR and CO
  • Parasympathetic impulses decrease HR and CO
• Carotid artery pulse


  • Smooth, rapid upstroke in early systole, gradual downstroke
  • Reflects amplitude and contour of pulse wave

  
• Jugular venous pulse


  • a wave - atrial contraction
  • x descent - atrial relaxation and descent
  • v wave - atrial filling, increased volume and pressure
  • y descent - atrial emptying into ventricle
• Jugular venous pressure reflects right atrial (central venous) pressure and right ventricular diastolic filling pressure
• Decreased jugular venous pressure occurs with reduced left ventricular output or reduced blood volume
• Carotid artery stiffness and diameter are related to developing atherosclerosis and cardiac/stroke risk
• Hispanics in the US have increasing carotid artery stiffness with age, but also increased carotid diameter which may account for their reduced ischemic stroke mortality compared to non-Hispanic Whites
• Collecting Subjective Data: The Nursing Health History
• Subjective data


  Data collected about the heart and neck vessels to identify abnormal conditions that may affect the client's ability to perform activities of daily living (ADLs) and to fulfill their role and responsibilities

  
• Subjective data


  Provides information on the client's risk for cardiovascular disease and helps to identify areas for which health education is needed
• The client may not be aware of the significant role that health promotion activities can play in preventing cardiovascular disease
• When compiling the nursing history


  Explore signs and symptoms that the client brings to your attention either intentionally or inadvertently
• Chest pain


  Can be cardiac, pulmonary, muscular, or gastrointestinal in origin