Echocardiography

• Echocardiography is used to visualize and assess cardiac function, structure, and hemodynamic abnormalities. It is the most commonly used noninvasive cardiac imaging tool.
• A record of high-frequency sound vibrations that have been sent into the heart through the chest wall. The cardiac structures return the echoes derived from the ultrasound. The motions of the echoes are traced on an oscilloscope and recorded on film.
• Clinical usefulness includes demonstration of valvular and other structural deformities, detection of pericardial effusion, evaluation of prosthetic valve function, diagnosis of cardiac tumors of asymmetric thickening of interventricular septum, diagnosis of cardiomegaly (heart enlargement).
• Types include two-dimensional (2-D) and M-mode. The methods are complementary and are commonly used in conjunction.
  • 2-D echocardiography provides a wider view of the heart and its structures because it involves a planar ultrasound beam.
  • M-mode utilizes a single ultrasound beam and provides a narrow segmental view.

CLASS I INDICATIONS

(Clear indications for stress testing)

• Suspected or proven coronary artery disease (CAD)
• Male patients who present with atypical chest pain
• Evaluate functional capacity and assess prognosis of patients with CAD
• Patients with exercise-related palpitations, dizziness, or syncope
• Evaluation of recurrent exercise-induced arrhythmias

CLASS II INDICATIONS

(Stress testing may be indicated)

• Evaluation of typical or atypical symptoms in women
• Evaluation of variant angina
• Evaluation of patients who are on digoxin preparations or who have a right bundle-branch block

CLASS III INDICATIONS

(Stress testing is probably not necessary)

• Young or middle-age asymptomatic patients who have no risk factors for CAD
• Young or middle-age asymptomatic patients who present with noncardiac chest pain
• Evaluation of patients for CAD who have complete left bundle-branch block
• Evaluation of patients for CAD who have pre-excitation syndrome

Nursing and Patient Care Considerations

• Advise patient that traditional echocardiography is noninvasive and that no preparation is necessary.
• Position patient on his left side, if tolerated, to bring the heart closer to the chest wall. Assist patient to clean chest of transducer gel after the test.

Tread Mill Stress Testing

• In treadmill stress testing, the patient walks a treadmill or rides a stationary bicycle until reaching a target heart rate; typically 70% to 80% of the maximum predicted heart rate. Treadmill stress testing has 70% sensitivity and specificity among the general population.
• Indications for stress testing have been adapted from the American Heart Association (AHA) and the American College of Cardiology (ACC) 
• Reasons for terminating a stress test include:
  • ST-segment elevations of 2 mm or more.
  • 20 mm Hg drop in systolic blood pressure.
  • Drop in heart rate or the development of heart block.
  • Progressively increasing angina.
  • ST-segment depression of 2 mm or greater.
  • Three or more premature ventricular contractions (PVCs).
  • Supraventricular arrhythmias.
  • Severe hypertension.
  • ST-segment depression at baseline that progresses during the test.
  • Claudication.
  • Fatigue, dyspnea, or feelings of light-headedness.
  • Equipment malfunction.
• Complications of stress testing include supraventricular tachyarrhythmias, bradycardias, heart failure, hypotension, ventricular ectopy (due to ventricular tachycardia), ventricular fibrillation, stroke, MI, and death.
• Contraindications for performing a stress test include:
  • AMI.
  • Unstable coronary syndrome.
  • Wolff-Parkinson-White syndrome.
  • Uncontrolled arrhythmias.
  • High-degree atrioventricular (AV) blocks.
  • Acute myocarditis.
  • Acute pericarditis.
  • Severe aortic stenosis.
  • Uncontrolled hypertension.

Nursing and Patient Care Considerations

• Explain to patient how the procedure will be done and screen for contraindications.
• Advise patient to abstain from eating, smoking, and consuming caffeine for 2 hours before the test.
• Inform patient that monitoring will occur throughout the test for signs of complications.
• Advise patient to inform you of how he is feeling during the test.
• Monitor patient throughout testing for color, respirations, ECG changes, and blood pressure.

Myocardial Imaging

With the use of radionuclides and scintillation cameras, radionuclide angiograms can be used to assess left ventricular performance.

• Thallium 201 is a radionuclide (an unstable atom that produces a small amount of energy in the form of g-rays) that behaves like potassium in the body and is distributed throughout the myocardium in proportion to blood flow.
• Technetium-99m- labeled sestamibi is a myocardial perfusion marker used to assess cell membrane and mitochondrial integrity and to reveal myocardial perfusion.
  • Sestamibi is not taken up by acute or chronic infarct tissue, and the amount of uptake of the radionuclide by other tissue correlates with the size of the infarction, the amount of CK released in the blood, and the postinfarction left ventricular ejection fraction (LVEF).
• Hot spot or positive imaging with technetium 99m stannous pyrophosphate is used when diagnosis of MI is unclear.
• Negative result of cold spot imaging with thallium 201 rules out MI. A positive result, on the other hand, is inconclusive because it cannot differentiate between old and new infarction or areas of ischemia versus infarction.
• Radionuclide ventriculogram with technetium 99m is used to evaluate valve structure and ventricular function. In this test, a contrast medium is injected through a catheter, opacifying the ventricular cavity to enable measuring of right and LVEF. The test also distinguishes regional from global ventricular wall motion and allows subjective analysis of cardiac anatomy to detect intracardiac shunts as well as valvular or congenital abnormalities.
  • Complications of ventriculography include arrhythmias, intramyocardial or pericardial injection of contrast medium and, possibly, development of emboli due to injection of air or a thrombosis through the catheter.

Nursing and Patient Care Considerations

• Advise patient that a radionuclide will be injected through a central venous, Swan-Ganz, or I.V. catheter, or into an antecubital vein.
• Reassure patient that the radionuclide will not cause radiation injury or affect heart function.
• Explain to patient that he may experience hot flashes and nausea or vomiting. A test dose will be administered before the dose required for contrast to assess patient's tolerance of radionuclide.
• The results of the study will be discussed with patient by the physician or primary care provider.