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evaluations can help determine the need for supplemental oxygen therapy and mechanical
    ventilatory support in these patients. Oxygen is the first drug provided during a suspected MI. Refer to Chapter 2 and Appendix Ill-A for further description of arterial blood gas interpretation and supplemental oxygen, respectively.
    Chest Radiography
    Chest x-ray can be ordered for patients to assist in the diagnosis of
    CHF or cardiomegaly (enlarged heart). Patients in CHF have an

    32 AClJfE CARE HANDBOOK FOR I)HYSICAL TI-IERJWISTS
    increased density in pulmonary vasculature markings, giVing the
    appearance of congestion in rhe vessels.'·7 Refer to Chapter 2 for further description of chest x-rays.
    Echocardiography
    Transthoracic echocardiography or "cardiac echo" is a noninvasive
    procedure that uses ultrasound to evaluate the function of the heart.
    Evaluation includes the size of the ventricular cavity, the thickness
    and integtiry of the seprum, valve integrity, and the motion of individual segments of the ventricular wall. Volumes of the ventricles are quantified, and EF can be estimated '
    Transesophageal echocardiography is a newer technique that provides a better view of the mediastinum in cases of pulmonary disease, chest wall abnormality, and obesity, which make standard echocardiography difficulr.'2.32 For this test, the oropharynx is anesthesized and the patient is given enough sedation to be relaxed but still awake since he or she needs to cooperate by swallowing the
    catheter. The catheter, a piezoelectric crystal mounted on an endoscope, is passed into the esophagus. Specific indications for transthoracic echocardiography include bacterial endocarditis, aortic dissection, regurgitation through or around a prosthetic mitral or
    tricuspid valve, left atrial thrombus, intracardiac source of an embolus, and interarterial septal defect. Patients usually fast for at least 4
    hours prior to the procedure.32
    Principal indications for echocardiography are to assist in the diagnosis of pericardial effusion, cardiac tamponade, idiopathic or hypertrophic cardiomyopathy, a variety of valvular diseases, intracardiac masses, ischemic cardiac muscle, left ventricular aneurysm, ventricular thrombi, and a variery of congenital heart diseases.'2
    Transthoracic echocardiography can also be performed during or
    immediately following bicycle or treadmill exercise to identify
    ischemia-induced wall motion abnormalities or during a pharmacologically induced exercise stress teSt (e.g., a dobutamine stress echocardiograph [DSEj). This stress echo cardiograph adds to the
    information obtained from standard stress tests (ECGs) and may be
    used as an alternative to nuclear scanning procedures. Transient
    depression of wall motion during or after stress sugges(s ischemia.33
    Contrast Echocardiograph
    The ability of the echocardiograph to diagnose perfusion abnormalities and myocardial chambers is improved by using an intra-

    CARDIAC SYSTEM
    33
    venously injected contrast agent. The contrast allows greater
    visualization of wall motion and wall thickness, and calculation
    of EF."
    Dobulamille Stress Echocardiograph
    Dobutamine is a potent alpha-l (al) agonist and a beta-receptor
    agonist with prominent inotropic and less-prominent chronotropic
    effects on the myocardium. Dobutamine (which-unlike persantine-increases contractility, HR, and BP in a manner similar to exercise) is injected in high doses into subjects as an alternative to
    exercise.JJ Dobutamine infusion is increased in a stepwise fashion
    similar to an exercise protocol. The initial infusion is 0.01 mglkg
    and is increased 0.01 mglkg every 3 minutes until a maximum infusion of 0.04 mglkg is reached. This infusion is maintained for 5 minutes for a total dose of approximately 0.38 mglkg. Typically, the echocardiograph image of wall motion is obtained during the final
    minute(s) of infusion. This image can then be compared to baseline
    recordings.33 If needed, atropine is occasionally