Diagnostic tests

Focus Topic: Cardiovascular disorders

Technological advances have improved the precision of diagnostic tests. Although cardiac marker studies and electrocardiograms (ECGs) are of great value, imaging tests can pinpoint the exact location and extent of cardiac damage within hours of an acute MI, allowing more effective treatment.

Cardiovascular disorders: Cardiac marker studies

Analysis of cardiac markers (enzymes and proteins) helps diagnose acute MI. After infarction, damaged cardiac tissue releases significant amounts of enzymes into the blood. Serial measurement of enzyme levels reveals the extent of damage and helps monitor healing progress. (See Release of cardiac enzymes and proteins.) These cardiac enzymes include creatine kinase (CK), ischemia-modified albumin (IMA), myoglobin, and troponin I and T. These tests may be used alone or in conjunction with each other. Additional tests that help evaluate the patient’s risk of MI include hemoglobin A1C and C-reactive protein.

Cardiovascular disorders: CK

Heart muscle, skeletal muscle, and brain tissue all contain CK. Its isoenzymes are combinations of the subunits M (muscle) and B (brain). CK-BB appears primarily in brain and nerve tissue; CK-MM, in skeletal muscles; and CK-MB, in the heart muscle. Elevated levels of CK-MB reliably indicate acute MI. Generally, CK-MB levels rise 4 to 8 hours after the onset of acute MI, peak in 12 to 24 hours, and may remain elevated for up to 96 hours.

Nursing considerations

  • Explain to the patient that the test will help confirm or rule out MI.
  • Tell him he won’t need to restrict food or fluids before the test.
  • Inform him that blood specimens will be drawn at timed intervals.
  • Remember that muscle trauma caused by I.M. injections can raise CK levels.
  • Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately.
  • If a hematoma develops at the venipuncture site, apply warm soaks.

Release of cardiac enzymes and proteins

Focus Topic: Cardiovascular disorders

Cardiovascular disorders

 

Cardiovascular disorders: IMA

IMA measures the changes in human serum albumin when it comes in contact with ischemic tissue. Within minutes of the onset of ischemia, IMA reaches detectable levels in the blood because levels rise rapidly when the heart doesn’t receive enough oxygen. An increase in IMA occurs significantly sooner than an increase in troponin or CK, but IMA levels don’t rise after tissue necrosis. This rapid increase means that IMA levels can be used to detect an MI sooner than possible using other tests. Levels return to normal within 6 hours of the resolution of ischemia.

Nursing considerations

  • Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately.
  • IMA is most often performed in conjunction with an ECG and measurement of troponin levels.

Cardiovascular disorders: Myoglobin

Myoglobin is found in both the myocardium and skeletal muscle. Normally, small amounts of myoglobin are continually released into the bloodstream as a result of the turnover of muscle cells. It’s then excreted by the kidneys. During acute MI, myoglobin levels rise as a larger quantity of myoglobin enters the bloodstream. Rising myoglobin levels may be the first marker of cardiac injury after acute MI. Levels may rise within 30 minutes to 4 hours, peak within 6 to 10 hours, and return to baseline by 24 hours. However, because skeletal muscle damage may cause myoglobin levels to rise, it isn’t specific to myocardial injury. Myoglobin levels may be available within 30 minutes.

Nursing considerations

  • Keep in mind that I.M. injections, recent angina, cardioversion, acute alcohol intoxication, dermatomyositis, hypothermia, muscular dystrophy, poly myositis, severe burns, trauma, severe renal failure, and systemic lupus erythematosus (SLE) can cause elevated myoglobin levels.
  • Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately.
  • If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Cardiovascular disorders: Troponin I and troponin T

Troponin is a protein found in skeletal and cardiac muscles. Troponin I and troponin T, two isotypes of troponin, are found in the myocardium. Troponin T may also be found in skeletal muscle.

Troponin I, however, exists in the myocardium — in fact, it’s more specific to myocardial damage than CK, CK-MB isoenzymes, and myoglobin. Because troponin T levels can occur in certain muscle disorders or renal failure, it’s less specific for myocardial injury than troponin I.

Cardiovascular disorders: Rise time

Troponin levels rise within 3 to 6 hours after myocardial damage. Troponin I peaks in 12 hours, with a return to baseline in 3 to 10 days, and troponin T peaks in 12 to 48 hours, with a return to baseline in 7 to 10 days. Because troponin levels stay elevated for a prolonged period of time, they can detect an infarction that occurred several days earlier. Rapid troponin T levels can be determined at the bedside in minutes, making them a useful tool for determining treatment in acute MI.

Nursing considerations

  • Tell the patient he won’t need to restrict food or fluids before the test.
  • Tell him that multiple blood samples may be drawn.
  • Keep in mind that sustained vigorous exercise, cardiotoxic drugs such as doxorubicin (Adriamycin), renal disease, and certain surgical procedures can cause elevated troponin T levels.
  • Handle the collection tube gently to prevent hemolysis, and send the sample to the laboratory immediately.
  • If a hematoma develops at the venipuncture site, apply warm soaks to help ease discomfort.

Cardiovascular disorders: Graphic recording studies

Graphic recording studies to diagnose cardiac disorders include ECG, exercise ECG, and Holter monitoring.

Cardiovascular disorders: ECG

A valuable diagnostic test that’s now a routine part of every cardiovascular evaluation, ECG graphically records electrical current generated by the heart. (See What the ECG strip shows.) This test helps identify primary conduction abnormalities, arrhythmias, cardiac hypertrophy, pericarditis, electrolyte imbalance, and MI (site and extent).

Nursing considerations

  • Tell the patient that an ECG only takes about 10 minutes and causes no discomfort.
  • Explain that he must lie still, relax, breathe normally, and remain quiet.
  • Keep in mind that evaluation of the recording will guide further treatment.
  • Treat chest pain if present (as ordered).
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Cardiovascular disorders

 

Cardiovascular disorders: Exercise ECG

Exercise ECG is a noninvasive test that helps the practitioner assess cardiovascular response to an increased workload. Commonly known as a stress test, it provides diagnostic information that can’t be obtained from a resting ECG. This test may also assess response to treatment.

The test is stopped if the patient experiences chest pain, fatigue, or other signs and symptoms that reflect exercise intolerance. These may include severe dyspnea, claudication, weakness or dizziness, hypotension, pallor or vasoconstriction, disorientation, ataxia, ischemic ECG changes (with or without pain), rhythm disturbances or heart block, and ventricular conduction abnormalities.

Cardiovascular disorders: Drugs do it, too

If the patient can’t exercise, a stress test can be performed by I.V. injection of a coronary vasodilator, such as dipyridamole or adenosine (Adenocard). Other methods of stressing the heart include dobutamine administration and pacing (in the patient with a pacemaker). During the stress test, nuclear scanning or echocardiography may also be performed.

Nursing considerations

  • Inform the patient that he must not eat food, drink caffeinated beverages, or smoke cigarettes for 4 hours before the test.
  • Explain that he should wear loose, lightweight clothing and snug-fitting but comfortable shoes, and emphasize that he should immediately report any chest pain, leg discomfort, breathlessness, or fatigue.
  • Check the practitioner’s orders to determine which cardiac drugs should be administered or withheld before the test. Beta-adrenergic blockers, for example, can limit the patient’s ability to raise his heart rate.
  • Inform the patient that he may receive an injection of thallium during the test so that the doctor can evaluate coronary blood flow. Reassure him that the injection involves negligible radiation exposure.
  • Tell the patient that after the test, his blood pressure and ECG will be monitored for 10 to 15 minutes.
  • Explain that he should wait at least 2 hours before showering, and then he should use warm water.

Cardiovascular disorders: Holter monitoring

Also called ambulatory ECG, Holter monitoring allows recording of heart activity as the patient follows his normal routine. Like an exercise ECG, it can provide considerably more diagnostic information than a standard resting ECG. In addition, Holter monitoring can record intermittent arrhythmias.

This test usually lasts about 24 hours (about 100,000 cardiac cycles). The patient wears a small tape recorder connected to bipolar electrodes placed on his chest and keeps a diary of his activities and associated symptoms.

Nursing considerations

  • Urge the patient not to tamper with the monitor or disconnect lead wires or electrodes. Demonstrate how to check the recorder for proper function.
  • Tell the patient that he can’t bathe or shower while wearing the monitor. He also needs to avoid electrical appliances that can interfere with the monitor’s recording.
  • Emphasize to the patient the importance of keeping track of his activities, regardless of symptoms.
  • Keep in mind that evaluation of the recordings will guide further treatment.

Cardiovascular disorders: Imaging studies

Imaging studies used to diagnose cardiovascular disorders include cardiac catheterization and coronary angiography, chest X-ray, echocardiography, magnetic resonance imaging (MRI), multiple-gated acquisition (MUGA) scanning, technetium-99 (99mTc) pyrophosphate scanning, thallium scanning, transesophageal echocardiography, and ultrafast computed tomography (CT) scan. New methods continue to be developed. (See Diagnosing CAD: Avoid the invasion.)

 

Diagnosing CAD: Avoid the invasion

Focus Topic: Cardiovascular disorders

Cardiovascular disorders

 

Cardiovascular disorders: Cardiac catheterization and coronary angiography

Cardiac catheterization and coronary angiography, two common invasive tests, use a catheter threaded through an artery (for a left-sided catheterization) or vein (for a right-sided catheterization) into the heart to determine the size and location of a coronary lesion, evaluate ventricular function, and measure heart pressures and oxygen saturation.

Nursing considerations

  • Make sure the patient understands why he’s scheduled for catheterization.
  • Check with the practitioner before withholding any medication. Explain to the patient that he won’t be able to have anything to eat or drink for 6 to 8 hours before the test.
  • Explain that he may receive a mild I.V. or oral sedative before or during the procedure and that a local anesthetic will be used at the insertion site.
  • Ask the patient if he’s allergic to contrast media or shellfish; document any allergies and report them to the practitioner
  • Check the patient’s lab values — especially the BUN and creatinine levels — and report abnormal values to the practitioner.

Cardiovascular disorders: A case of the spins

  • Warn the patient that he may feel light-headed, warm, or nauseated for a few moments after the dye injection. He may also receive nitroglycerin during the test to dilate coronary vessels and aid visualization.
  • Tell the patient he must cough or breathe deeply as instructed during the test.
  • Tell the patient he must lie on his back for several hours after the procedure. Instruct him to notify you if he has any chest pain or feelings of wetness or warmth at the catheter insertion site.
  • When the femoral approach is used, tell the patient to keep his leg straight for up to 12 hours or as ordered. Elevate the head of the bed no more than 30 degrees. When the brachial artery is used, tell the patient to keep his arm straight for at least 24 hours or as ordered. To immobilize the leg or arm, place a sandbag over it as ordered.
  • Keep in mind that several devices may be used to seal the arterial puncture site, including absorbable collagen protein plugs and a suture tool that’s placed inside the puncture site so that the wound can be sutured from below the skin.
  • For the first hour after catheterization, monitor the patient’s vital signs every 15 minutes and inspect the dressing frequently for signs of bleeding.

Cardiovascular disorders: Vital checks

  • Check the patient’s skin color, temperature, and pulses distal to the insertion site. An absent or weak pulse may signify an embolus or other problem requiring immediate attention. Notify the practitioner of any changes in peripheral pulses.
  • If the patient’s vital signs change or if he has chest pain (possible indications of arrhythmias, angina, or MI), notify the practitioner.
  • After the first hour, assess the patient every 30 minutes for 2 hours, then every hour for 4 hours, then once every 4 hours.
  • Monitor urine output, especially in cases of impaired renal function.

Cardiovascular disorders: Chest X-ray

A chest X-ray may detect cardiac enlargement, pulmonary congestion, pleural effusion, calcium deposits in or on the heart, pacemaker placement, hemodynamic monitoring lines, and tracheal tube position.

Keep in mind that a chest X-ray alone can’t rule out a cardiac problem. Also, clinical signs may reflect the patient’s condition 24 to 48 hours before problems appear on an X-ray.

Nursing considerations

  • Tell the patient that although this test takes only a few minutes, the practitioner will require extra time to evaluate the quality of the films.
  • Inform him that he’ll wear a gown without snaps but may keep his pants, socks, and shoes on. Instruct him to remove all jewelry from his neck and chest.
  •  Tell him that he’ll need to take a deep breath and hold it as the technician takes the X-ray.
  • Permit the patient to resume activities as ordered.

Cardiovascular disorders: Echocardiography

Echocardiography, a noninvasive imaging technique, records the reflection of ultra-high frequency sound waves directed at the patient’s heart.

Cardiovascular disorders: A sound image

It allows the practitioner to visualize heart size and shape, myocardial wall thickness and motion, and cardiac valve structure and function. It also helps evaluate overall left ventricular function and detect some MI complications. Plus, it can evaluate prosthetic valve function and help detect mitral valve prolapse; mitral, tricuspid, or pulmonic valve insufficiency; cardiac tamponade; pericardial diseases; cardiac tumors; subvalvular stenosis; ventricular aneurysms; cardiomyopathies; and congenital abnormalities.

Nursing considerations

  • Reassure the patient that this 15- to 30-minute test doesn’t cause pain or pose any risk.
  • Mention that he may undergo other tests, such as ECG and phonocardiography, simultaneously. Tell him that two recordings will be made, one with him on his back, and one with him on his left side.
  • Tell him he must sit still while recording takes place because movement may distort results.
  • Permit the patient to resume activities as ordered.

Cardiovascular disorders: MRI

Also known as nuclear magnetic resonance, MRI yields high- resolution, tomographic, three-dimensional images of body structures. It takes advantage of certain body nuclei that are magnetically aligned and fall out of alignment after radio frequency transmission. The MRI scanner records the signals the nuclei emit as they realign in a process called precession and then translates the signals into detailed pictures of body structures. The resulting images show tissue characteristics without lung or bone interference.

MRI permits visualization of valve leaflets and structures, pericardial abnormalities and processes, ventricular hypertrophy, cardiac neoplasm, infarcted tissue, anatomic malformations, and structural deformities. Applications include monitoring the progression of ischemic heart disease and treatment effectiveness.

Nursing considerations

  • Instruct the patient that he’ll need to lie still during the test.
  • Warn him that he’ll hear a thumping noise.
  • Have him remove all jewelry, his watch, his wallet, and other metallic objects before testing. A patient with an internal surgical clip, scalp vein needle, pacemaker, implanted defibrillator, gold fillings, heart valve prosthesis, or other metal object in his body can’t undergo an MRI.

Cardiovascular disorders: MUGA scanning

MUGA scanning is cardiac blood pool imaging used to evaluate regional and global ventricular performance. During a MUGA scan, the camera records 14 to 64 points of a single cardiac cycle, yielding sequential images that can be studied like a motion picture film to evaluate regional wall motion and determine the ejection fraction and other indices of cardiac function.

Cardiovascular disorders: Variations on a theme

Many variations of the MUGA scan exist. In the stress MUGA test, the patient undergoes the same test at rest and after exercise to detect changes in ejection fraction and cardiac output. In the nitroglycerin MUGA test, the scintillation camera records points in the cardiac cycle after the sublingual administration of nitroglycerin (Nitrostat) to assess the drug’s effect on ventricular function.

Nursing considerations

  • Keep in mind that an ECG is required to signal the computer and camera to take images for each cardiac cycle.
  • Understand that if arrhythmias interfere with a reliable ECG, the test may need to be postponed.

Cardiovascular disorders: 99mTc pyrophosphate scanning

Also known as hot spot imaging or PYP scanning,99mTc pyrophosphate s canning helps diagnose acute myocardial injury by showing the location and size of newly damaged myocardial tissue. Especially useful for diagnosing transmural infarction, this test works best when performed 12 hours to 6 days after symptom onset. It also helps diagnose right ventricular infarctions; locate true posterior infarctions; assess trauma, ventricular aneurysm, and heart tumors; and detect myocardial damage from a recent electric shock such as defibrillation.

In this test, the patient receives an injection of 99mTc pyrophosphate, a radioactive material absorbed by injured cells. A scintillation camera scans the heart and displays damaged areas as “hot spots,” or bright areas. A spot’s size usually corresponds to the injury size.

Nursing considerations

  • Tell the patient that the doctor will inject 99mTc pyrophosphate into an arm vein about 3 hours before the start of this 45-minute test. Reassure him that the injection causes only transient discomfort and that it involves only negligible radiation exposure.
  • Instruct the patient to remain still during the test.
  • Permit the patient to resume activities as ordered.

Cardiovascular disorders: Thallium scanning

Also known as cold spot imaging, thallium scanning evaluates myocardial blood flow and myocardial cell status. This test helps determine areas of ischemic myocardium and infarcted tissue. It can also help evaluate coronary artery and ventricular function as well as pericardial effusion. (See Understanding thallium scanning.) Thallium scanning can also detect an MI in its first few hours.

The test uses thallium-201, a radioactive isotope that emits gamma rays and closely resembles potassium. When injected I.V., the isotope enters healthy myocardial tissue rapidly but enters areas with poor blood flow and damaged cells slowly.

Understanding thallium scanning

Focus Topic: Cardiovascular disorders

In thallium scanning, areas with poor blood flow and ischemic cells fail to take up the isotope (thallium-201 or Cardiolite) and thus appear as cold spots on a scan. Thallium imaging should show normal distribution of the isotope throughout the left ventricle and no defects (cold spots).

To distinguish normal from infarcted myocardial tissue, the practitioner may order an exercise thallium scan followed by a resting perfusion scan. A resting perfusion scan helps differentiate between an ischemic area and an infarcted or scarred area of the myocardium. Ischemic myocardium appears as a reversible defect (the cold spot disappears). Infarcted myocardium shows up as a nonreversible defect (the cold spot remains).

Cardiovascular disorders: Looking cool

A camera counts the gamma rays and displays an image. Areas with heavy isotope uptake appear light, whereas areas with poor uptake, known as “cold spots,” look dark. Cold spots represent areas of reduced myocardial perfusion.

Nursing considerations

  • Tell the patient to avoid heavy meals, cigarette smoking, and strenuous activity before the test.
  • If the patient is scheduled for an exercise thallium scan, advise him to wear comfortable clothes or pajamas and snug-fitting shoes or slippers.
  • Permit the patient to resume activities as ordered.

Cardiovascular disorders: Transesophageal echocardiography

Transesophageal echocardiography directs high-frequency sound waves at the heart through the esophagus or stomach. This test provides better resolution than echocardiography because the sound waves travel through less tissue. To perform this test, a flexible tube with a transducer at the tip is inserted endoscopically into the esophagus or stomach.

Nursing considerations

  • Tell the patient that he must fast for 4 to 6 hours before the test.
  • Reassure him that the test only lasts about 15 minutes and that short-acting I.V. sedation is commonly given to reduce anxiety and a topical anesthetic is sprayed in the back of the throat to prevent gagging.
  • Inform him that ECG leads will be placed on his chest and his ECG will be continuously monitored.
  • Explain that he’ll be placed on his left side and will be asked to swallow while the lubricated catheter tip is advanced down his esophagus.
  • Warn the patient that he won’t be able to have anything to eat or drink after the procedure until his gag reflex has returned, typically in 2 hours.
  • Observe the patient for signs and symptoms of esophageal perforation, such as GI bleeding and complaints of pain.

Cardiovascular disorders: Ultrafast CT scan

Ultrafast CT scan, also called electron beam CT, uses a scanner that takes images at fast speeds, resulting in high-resolution pictures. This noninvasive test can identify microcalcifications in the coronary arteries, making it useful for detecting early CAD before symptoms occur, screening symptomatic people at risk for CAD, and evaluating chest pain. This test may also be used to diagnose pulmonary embolus, aortic dissection or aneurysm, congenital heart disease, pericardial disease, and diseases of the great vessels (main vessels that supply organs).

Nursing considerations

  • Explain to the patient that he’ll need to lie still during scanning.
  • If a contrast medium will be used during the test, ask him if he is allergic to contrast media or shellfish.
  • If a contrast medium will be used, encourage the patient to increase his fluid intake after the test to promote excretion of the medium. Monitor his blood urea nitrogen (BUN) and creatinine levels before and after the test.
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