Chapter 35 Assessment: Cardiovascular System KEY POINTS Structures and Functions of CARDIOVASCULAR SYSTEM Heart • Four chambers: the right and left atrium and right and left ventricles. • Composed of three layers: endocardium, myocardium, and epicardium. • Surrounded by a fibroserous sac called the pericardium. • Four valves: mitral, aortic, tricuspid, and pulmonary. These maintain the one-way flow of blood. • The right side of the heart receives venous blood from the body (via the vena cava) and pumps it to the lungs where it is oxygenated. Blood returns to the left side of the heart (via the pulmonary veins) and is pumped to the body via the aorta. • The coronary circulation provides blood to the myocardium (heart muscle). The right and left coronary arteries are the first two branches off the aorta. • The conduction system consists of specialized cells that create and transport the electrical impulse, or action potential. These electrical impulses start depolarization of the myocardium. This triggers a cardiac contraction. Each electrical impulse starts at the SA node (in the right atrium), travels to the AV node (at the atrioventricular junction), through the bundle of His, down the right and left bundle branches (in the ventricular septum), and ends in the Purkinje fibers. • An electrocardiogram (ECG) records the electrical activity of the heart. Copyright © 2023 by Elsevier, Inc. All rights reserved. • Contraction of the myocardium, or systole, results in ejecting blood from the ventricles. Relaxation of the myocardium, or diastole, allows for filling the ventricles. • Cardiac output (CO) is the amount of blood pumped by each ventricle in 1 minute. It is calculated by multiplying the amount of blood ejected from the ventricle with each heartbeat (stroke volume [SV]) by the heart rate (HR) per minute: CO = SV HR. • Cardiac index (CI) reflects the relative CO for the body size. • Factors affecting SV are preload, contractility, and afterload. Preload is the volume of blood in the ventricles at the end of diastole. Afterload represents the systemic resistance against which the left ventricle must pump. Regulation of Cardiovascular System • Stimulation of the sympathetic nervous system increases HR, speed of conduction through the AV node, and force of atrial and ventricular contractions, while stimulation of the parasympathetic nervous system decreases HR. • Stimulation of baroreceptors and chemoreceptors, found in the aortic arch and carotid sinus, can initiate changes in HR and arterial pressure. Cardiac reserve is the ability to maintain or increase CO in response to the body’s needs. • The arterial blood pressure is a measure of the force exerted by blood against the walls of the arterial system. Normal BP is systolic BP <120 mm Hg and diastolic BP <80 mm Hg. • Pulse pressure is the difference between the SBP and DBP. It is normally about one third of the SBP. • Mean arterial pressure (MAP) is the average pressure in the arteries. A MAP >60 mm Hg is needed to sustain the vital organs of an average person under most conditions. Copyright © 2023 by Elsevier, Inc. All rights reserved. • The two main factors influencing BP are cardiac output (CO) and systemic vascular resistance (SVR), which is the force opposing the movement of blood. • We can measure BP by invasive techniques (catheter inserted in an artery) and noninvasive techniques (using a sphygmomanometer and a stethoscope, or an automated noninvasive device). Auscultating a BP requires identifying sounds of turbulent blood flow, Korotkoff sounds, through a compressed artery. Assessment OF CARDIOVASCULAR SYSTEM Health History • A health history for the cardiac system consists of assessment of past health history, medications, surgery or other treatments, family health history, psychosocial history, risk factor identification, and a review of systems using functional health patterns. • Obtain a thorough history of the present illness. Explore and document common signs of heart problems (e.g., pain, dyspnea). Describe the course of the patient’s illness, including when it began, the type of symptoms, and factors that alleviate or worsen these symptoms. Physical Examination • Obtain vital signs including bilateral BPs and orthostatic (postural) BPs and HRs prior to the physical examination. During physical examination, assess the skin, neck veins, capillary refill, thorax, epigastric area, and lungs. Check for heaves, sustained lifts of the chest wall that you can see or palpate. Palpate for the point of maximal impulse (PMI), or apical pulse. Auscultate the carotid arteries, abdominal aorta, and femoral arteries. • When listening to the heart sounds, note S1, S2, and any murmurs, clicks, pericardial friction rubs, or extra heart sounds (S3 or S4). Copyright © 2023 by Elsevier, Inc. All rights reserved. HEMODYNAMIC MONITORING • Hemodynamic monitoring refers to the measurement of pressure, flow, and oxygenation within the cardiovascular system. The purpose of hemodynamic monitoring is to assess heart function, fluid balance, and the effects of fluids and drugs on CO. • Invasive and noninvasive hemodynamic measurements are made in the ICU, ED, and OR. • Values commonly measured include systemic and pulmonary arterial pressures, central venous pressure (CVP), cardiac output (CO), cardiac index (CI), stroke volume (SV), pulmonary artery wedge pressure (PAWP), SV/SV index (SVI), O2 saturation of the hemoglobin of arterial blood (SaO2), and mixed venous O2 saturation (SvO2). • PAWP, a measurement of pulmonary capillary pressure, reflects left ventricular end diastolic pressure under normal conditions. • CVP, measured in the right atrium or in the vena cava close to the heart, is the right ventricular preload or right ventricular end-diastolic pressure under normal conditions. • Systemic vascular resistance (SVR) is the resistance of the systemic vascular bed. Pulmonary vascular resistance (PVR) is the resistance of the pulmonary vascular bed. SVR and PVR are adjusted for body size. PRINCIPLES OF INVASIVE PRESSURE MONITORING Copyright © 2023 by Elsevier, Inc. All rights reserved. • To accurately measure pressure, equipment must be referenced and zero balanced to the environment and dynamic response characteristics optimized. • Referencing means positioning the transducer so that the zero-reference point is at the level of the atria of the heart or the phlebostatic axis. • Zeroing confirms that when pressure within the system is 0, the monitor reads 0. TYPES OF INVASIVE PRESSURE MONITORING • Continuous arterial pressure monitoring is used to obtain systolic, diastolic, and mean BPs in patients with acute hypertension and hypotension, respiratory failure, shock, neurologic injury, coronary interventional procedures, continuous infusion of vasoactive drugs, and frequent arterial blood gas (ABG) sampling. • Arterial pressure-based cardiac output (APCO) monitoring is a minimally invasive technique to determine continuous CO (CCO)/continuous CI (CCI). It is used to assess a patient’s ability to respond to fluids. • Pulmonary artery (PA) pressure monitoring helps guide acute-phase management of patients with complicated cardiac, pulmonary, and intravascular volume problems by providing information about SV, fluid volume, PA diastolic and wedge pressures, CVP, core temperature, and oxygen saturation. • Both CVP and PA catheters can include sensors to measure oxygen saturation of Copyright © 2023 by Elsevier, Inc. All rights reserved. hemoglobin in venous blood termed central venous oxygen saturation (ScvO2) and SvO2. • SvO2 and ScvO2 reflect the balance among oxygenation of the arterial blood, tissue perfusion, and tissue O2 consumption. Sustained decreases may indicate decreased arterial oxygenation, low CO, low hemoglobin level, or increased O2 consumption or extraction. NONINVASIVE ARTERIAL OXYGENATION MONITORING • Pulse oximetry is a noninvasive and continuous method of determining arterial oxygenation (SpO2). Monitoring SpO2 may reduce the frequency of ABG sampling. • Accurate SpO2 measurements may be hard to obtain on patients who are hypothermic, receiving IV vasopressor therapy, or have hypoperfusion and vasoconstriction. NONINVASIVE HEMODYNAMIC MONITORING • Continuous or intermittent noninvasive method of obtaining cardiac output (CO) and assessing thoracic fluid status. • Major indications (1) early signs and symptoms of pulmonary or cardiac dysfunction, (2) determining cardiac or pulmonary cause of shortness of breath, (3) evaluating the cause and management of hypotension, (4) monitoring after removing a PA catheter or justifying insertion of a PA catheter, (5) evaluating drug therapy, and (6) diagnosing rejection Copyright © 2023 by Elsevier, Inc. All rights reserved. after heart transplantation. NURSING AND INTERPROFESSIONAL MANAGEMENT: HEMODYNAMIC MONITORING • Obtain baseline data about the patient’s general appearance, vital signs, level of consciousness, skin color and temperature, peripheral pulses, capillary refill, and urine output to correlate with the data from biotechnology. • Single hemodynamic values are rarely significant. Monitor trends in these values and evaluate the whole clinical picture to recognizing early clues and intervene before problems escalate Diagnostic Studies OF CARDIOVASCULAR SYSTEM Blood Studies • Cardiac-specific troponin, copeptin, and creatine kinase (CK)-MB are sensitive indicators of early myocardial injury and infarction. • Changes in the lipid profile, cholesterol, triglycerides, and high-density and low-density lipoproteins are linked to heart disease. • High sensitivity C-reactive protein is an independent risk factor for CAD and may be a predictor of heart events. • B-type natriuretic peptide (BNP) is the marker of choice for differentiating a cardiac or respiratory cause of dyspnea. Diagnostic Studies • 12-lead electrocardiogram (ECG) Copyright © 2023 by Elsevier, Inc. All rights reserved. • Deviations from the normal sinus rhythm can indicate abnormalities in heart function. • ECGs can be obtained as a one-time recording or for longer periods of time using ambulatory ECG or event monitors. • Exercise or stress testing is used to evaluate the cardiovascular response to physical stress. Perfusion imaging with exercise testing can distinguish viable myocardial tissue from scar tissue and assess the effectiveness of therapies. • An echocardiogram provides information about valvular structure and motion, heart chamber size and contents, ventricular muscle and septal motion and thickness and pericardial sac. The echocardiogram can also measure ejection fraction (EF), the percentage of end-diastolic blood volume ejected during systole. • Nuclear medicine studies provide information on the structure and function of the heart in determining the presence and extent of heart disease. These include multigated acquisition or cardiac blood pool scans (MUGA), single-photon emission computed tomography (SPECT), positron emission tomography (PET), cardiovascular magnetic resonance imaging (CMRI), magnetic resonance angiography (MRA), and variations of computed tomography angiography (CT scan). In cardiac catheterization and coronary angiography, contrast media and fluoroscopy are used to obtain information about the coronary arteries, heart chambers and valves, ventricular function, intracardiac pressures, O2 levels in various parts of the heart, CO, and EF. • Electrophysiology study (EPS) obtains information on the heart’s conduction system and is useful in identifying the source and guiding treatment in dysrhythmias. Copyright © 2023 by Elsevier, Inc. All rights reserved.
