Chapter 32: Cardiovascular System

• Creatine-Kinase MB
• Cardiospecific isoenzyme that is released in the presence of myocardial tissue injury. MB levels begin to rise about 6 hours after symptom onset, peak in about 18 hours, and return to baseline within 24 to 36 hours after myocardial infarction (MI).

Contractile proteins that are released following an MI. Both Troponin T and Troponin I are highly specific to cardiac tissue. Normally the level in the blood is very low, so a rise in level is diagnostic of myocardial injury. cTnT and cTnI are detectable within 4 to 6 hours of myocardial injury, peak 10 to 24 hours and can be detected for up to 10 to 14 days. Troponin is the biomarker of choice in the diagnosis of MI.

Serial sampling often done in conjunction with CK-MB and ECGs.

Low molecular weight protein that is 99% to 100% sensitive for myocardial injury. Serum concentrations rise 30 to 60 minutes after MI. Cleared from the circulation rapidly and most diagnostic if measured within first 12 hours of onset of chest pain.

Marker of inflammation produced by the liver during periods of acute inflammation. that can predict risk of cardiac disease and cardiac events, even in patients with normal lipid values. Stable levels that can be measured nonfasting and any time during the day. May be more predictive of cardiac disease than LDLs for women.

Amino acid produced during protein catabolism that has been identified as a risk factor for cardiovascular disease. Homocysteine may cause damage to the endothelium or have a role in the formation of thrombi. Elevated levels of Hcy may be hereditary or acquired from dietary deficiencies of vitamin B6, vitamin B12, or folate.

Peptide that causes natriureses. Elevation indicates presence of heart failure and may help distinguish cardiac vs. respiratory causes of dyspnea. Infusion of nesiritide (Natrecor) will elevate levels temporarily.

N-terminal pro brain natriuretic peptide. Secreted (along with BNP) is also secreted in the ventricles and is more sensitive but less specific than BNP for heart failure. During heart failure, BNP and NT-pro-BNP are released and increase natriuresis.

< 200 mg/dL

Cholesterol is a blood lipid. Elevated cholesterol is considered a risk factor for atherosclerotic heart disease. Can be obtained in a nonfasting state. A structural component of cell membranes and plasma lipoproteins; a precursor of corticosteroids, sex hormones, and bile salts. In addition to being absorbed from food in the GI tract, cholesterol can also be synthesized in the liver.

< 150 mg/dL

Triglycerides are mixtures of fatty acids. Elevations are associated with cardiovascular disease and diabetes. Must be obtained in a fasting state (at least 12 hours except for water); alcohol should be withheld for 24 hours before testing.

• Includes HDL and LDL.
• HDL: Male > 40 mg/dL
•            Female > 50 mg/dL
• Low risk for CAD: > or equal to 60 mg/dL
• High Risk for CAD: < 40 mg/dL

• LDL
• Recommended: < 100 mg/dL
• Near Optimal: 100- 129 mg/dL
• Moderate risk for CAD: 130- 159 mg/dL
• High Risk for CAD: > 160 mg/ dL

Electrophoresis is done to separate lipoproteins into HDL and LDL. There are marked day-to-day fluctuations in serum lipid levels. More than one determination is needed for accurate diagnosis and treatment.

LDLs: mostly cholesterol with moderate amounts of phospholipids. An elevation in LDL level has a strong and direct association with CAD.

HDL: about one half protein and one half phospholipids and cholesterol. An increased HDL level has been associated with a decreased risk of CAD.

• apo A-I
• The major HDL protein

• apo B
• the major LDL protein

• A. apolipoprotein A-I
• B. apolipoprotein B

Lp (a)

< 30 mg/dL

Increased levels are associated with an increased risk of premature CAD and stroke. Can be obtained in a nonfasting state.

Lp-PLA₂

Released by macrophages. Promotes vascular inflammation through the hydrolysis of oxidized LDLs within the intima of blood vessels, thus contributing directly to the development of  atherosclerosis. Thus, elevated levels are associated with vascular inflammation and increased risk for CAD. Can be obtained in a nonfasting state.

Patient is placed in two upright positions to examine the lung fields and size of the heart. The two common positions are posteroanterior (PA) and lateral. Normal heart size and contour for the individual's age, sex, and size are noted.

Inquire about frequency of recent x-rays and possibility of pregnancy. Provide lead shielding to areas not being viewed. Remove any jewelry or metal objects that may obstruct the view of the heart and lungs.

Electrodes are placed on the chest and extremities, allowing the ECG machine to record cardiac electrical activity from different views. Can detect rhythm of heart, activity of pacemaker, conduction abnormalities, position of heart size, of atria and ventricles, presence of injury, and history of MI.

Prepare skin and apply electrodes and leads. Inform patient that no discomfort is involved. Instruct to avoid moving to decrease motion artifact.

(SAECG)

Signal-averaged ECG is a high-resolution ECG that can identify electrical activity called late potentials indicating a patient is at risk for developing ventricular dysrhythmias (eg ventricular tachycardia).

Prepare skin and apply electrodes and leads. Inform patient that no discomfort is involved. Instruct to avoid moving to decrease motion artifact.

• A type of ambulatory ECG monitoring.
• Recording of ECG rhythm for 24 to 48 hours and then correlating rhythm changes with symptoms recorded in diary. Normal patient activity is encouraged to stimulate conditions that produce symptoms. Electrodes are placed on chest and a recorder is used to store information until it is recalled, printed, and analyzed for any rhythm disturbance. It can be performed on an inpatient or outpatient basis.

Prepare skin and apply electrodes and leads. Explain importance of keeping an accurate diary of activities and symptoms. Tell patient that no bath or shower can be taking during monitoring. Skin irritation may develop from electrodes.

Records rhythm disturbances that are not frequent enough to be recorded in one 24 hour period. It allows more freedom than a regular Holter monitor. Some units have electrodes that are attached to the chest and have a loop of memory that captures the onset and end of an event. Other types are placed directly on the patient's wrist, chest, or fingers and have no loop of memory but records the patient's ECG in real time. Recordings may be transmitted over the phone to a receiving unit.

Instruct in the use of equipment for recording and transmitting (if appropriate) of transient events. Teach patient about skin preparation for lead placement or steady skin contact for units not requiring electrodes. This will ensure the reception of optimal ECG tracings for analysis. Instruct patient to initiate recording as soon as symptoms begin or as soon thereafter as possible.

Various protocols are used to evaluate the effect of exercise tolerance on cardiovascular function. A common protocol uses 3 minute stages at set speeds and elevation of the treadmill belt. The patient can exercise to either predicted HR (subtract person's age from 220) or to peak exercise tolerance, at which time the test is terminated. The test is also terminated for chest discomfort, significant increase or decrease in vital signs from baseline, or significant ECG changes indicating cardiac ischemia. Vital signs and ECG are monitored. The ECG is monitored after exercise for rhythm disturbances or, if ECG changes occurred with exercise, for return to baseline.

Instruct patient to wear comfortable clothes and shoes that can be used for walking and running. Instruct patient about procedure and importance of reporting any symptoms that may occur. Monitor vital signs and obtain 12-lead ECG before exercise, during each stage of exercise, and after exercise until all vital signs and ECG changes have returned to normal. Monitor patients response throughout procedure. Contraindications include any reasons patient is unable to reach peak exercise.

Beta-Adrenergic blockers may be held 24 hours before the test because they will blunt the heart rate and limit the patient's ability to achieve maximal heart rate. Caffeine-containing food and fluids are held for 24 hours. Patients must refrain from smoking and strenuous exercise for 3 hours before test.

Distance patient is able to walk on a flat surface in 6 minutes. Used to measure response to treatments and determine functional capacity for activities of daily living. Useful in people who are unable to perform treadmill or exercise bike testing.

Instruct patient to wear comfortable shoes. Inform patient to carry or pull oxygen if used routinely. Patient should be encouraged to walk as quickly as possible.

• Contrast: involves addition of an intravenous contrast agent (albumin microbubbles, agitated saline) to assist in delineation the images, especially in technically difficult patient (e.g. obese)
• Motion-mode (M-mode): A single ulstrasoung beam is directed toward the heart, recording the motion of the intracardiac structures, as well as detecting wall thickness and chamber size.
• Two-dimensional: Sweeps the ultrasound beam through an arc, producing a cross-sectional view, and shows correct spatial relationships among the structures.
• Color-Flow imaging (duplex): is the combination of 2-D echocardiography and Doppler technology. It uses color changes to demonstrate the velocity and direction of blood flow. Pathologic conditions, such as valvular leaks and congenital defects, can be diagnosed more effectively.
• Real-time three dimensional:  Used multiple 2-D echo images with computer technology to provide a reconstruction of the heart. This technique generates precise information about the structures of the heart and how these structures change during the cardiac cycle.

Transducer that emits and receives ultrasound waves is placed in four positions on the chest above the heart. Transducer recorder sound waves that are bounced off the heart. Also records direction and flow of blood through the heart and transforms it to audio and graphic data that measure valvular abnormalities, congenital cardiac defects, wall motion, ejection fraction, and cardiac functions. IV contrast agent may be used to enhance images.

Place patient in a supine position on left side facing equipment. Instruct patient about procedure and sensations (pressure and mechanical movement from head of transducer). No contraindications to procedure exist.

Used as a substitute for the exercise stress test in individuals unable to exercise. Dobutamine ( a positive inotropic agent) or dipyridamole is infused IV and dosage is increased in 5 minutes intervals while ecchocardiogram is performed to detect wall motion abnormalities at each stage

Start IV infusion. Administer medication per protocol. Monitor vital signs before, during, and after test until baseline is achieved. Monitor patient for signs and symptoms of distress during procedure. Observe patient for side effects (shortness of breath, dizziness, nausea). Aminophylline may be given to prevent or reverse side effects of dipyridamole. Contraindications include any known allergies to medications.

Combination of exercise test and ecchocardiogram. Resting images of the heart are taken with ultrasound and then the patient exercises. Postexercise images are taken immediately after exercise (within 1 minute of stopping exercise). Differences in ventricular wall motion and thickening before and after exercise are evaluated.

Instruct patient to prepare for treadmill or exercise bicycle. Inform patient of importance of timely return to examination table for imaging after exercise. Contraindications include any reason patient is unable to reach peak exercise.

A probe with an ultrasound transducer at the tip is swallowed while the physician controls angle and depth. As it passes down the esophagus, it sends back clear images of heart size, wall motion, valvular abnormalities, endocarditis vegetation, and possible source of thrombi without interference from lungs or chest ribs. A contrast medium may be injected IV for evaluating direction of blood flow if an atrial or ventricular septal defect is suspected. Doppler ultrasound and color-flow imaging can also be used concurrently.

Instruct patient to be NPO for at least 6 hours before test. Remove dentures. A bite block is placed in the mouth. IV sedation is administered and throat locally anesthetized. A designated driver is needed if done in the outpatient department. Monitor vital signs and oxygen saturation levels and perform suctioning as needed during procedure. Assist patient to relax. Patient may not eat or drink until gag reflex returns. Sore throat is temporary.

Study involves IV injection of radioactive isotopes (99m technetium-sestamibi). Radioactive uptake is counted over the heart by scintillation camera. It supplies information about myocardial contractility, myocardial perfusion, and acute cell injury.

Explain procedure to patient. Establish IV line for injection of isotopes. Explain that radioactive isotope used is a small, diagnostic amount and will lose most of its radioactivity in a few hours. Inform the patient that he or she will be lying still on back with arms extended overhead for 20 minutes. Repeat scans are performed within a few minutes to hours after the injection.