DIAGNOSTIC INSTRUMENTS OF CARDIAC PATHOLOGIES

CARDIAC PATHOLOGIES AND ABNORMALITIES

The use of exciting, new, and increasingly sophisticated techniques for diagnosis of heart disorders has burgeoned in recent years. The United States ranks among the world leaders, with remarkable availability of these procedures for patients (30:273). The tests are used not only to diagnose, but also to pinpoint exact locality, extent, and severity of the abnormality, as well as to check the efficacy of treatment and the progress of the disease.

The danger of this mushrooming technology is the possible overuse of tests. It is emphasized that in most cases one or at most two tests are required to gain enough information (31:116). The cornerstones in cardiology are still the taking of accurate history and thorough physical examination. These alone will yield an accurate diagnosis in many if not the majority of cases. In fact, the overuse of modern techniques which may be inadequately interpreted has been linked with poor clinical judgment and management (9:189). In general, diagnosis follows a stepwise progress starting with the simplest, least invasive, least expensive, and least risky methods. With this knowledge, appropriate decisions can be made regarding the use of more sophisticated and/or invasive procedures.

The stethoscope and sphygmomanometer (blood pressure monitor) are the two basic instruments at the start of this diagnostic progression, and they

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depend on the injection into the blood stream of an isotope which, as it decays with time, emits energy in the form of photons, including the invisible gamma rays. These are detected with a gamma-ray camera (scintillation camera), resulting in images of the areas perfused by the radioactive blood (12:459-462). The gamma-ray camera has a flat lead face (collimator) with numerous pores which exclude scattered rays originating outside the area of interest. Next, the gamma rays are absorbed by either one large sodium iodide crystal or several hundred adjacent crystals, where they are converted into visible rays that strike a phosphor plate, releasing electrons. A photomultiplier tube accelerates these electrons resulting in measurable electrical pulses (12:460-462). MUGA scanning (Multiple-gated blood pool imaging, or equilibrium radionuclide angiography) (12:462-466) involves isotope labeling of serum albumin or, more commonly now, red blood corpuscles, either in vitro followed by injection or in vivo. The isotope, technicium-99m, with a half-life of six hours, is inexpensively and easily produced from Mo-90, which has a longer half-life and is thus transportable. Gating to an ECG recording is achieved by R-wave triggering o
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Approximate Word count = 7919
Approximate Pages = 32 (250 words per page)