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The following describes the various testing procedures used by physicians for evaluating cardiovascular impairments. It is important to be familiar with the tests because a cardiovascular impairment rating is, to a large degree, dependent upon symptoms associated with the applicant performing activities of daily living. As these symptoms may contain a subjective component, the Guides recommend the physician “obtain objective data about the extent of the limitation and integrate the findings with the subjective data to estimate the degree of permanent impairment” (AMA Guides, page 26).
It is important to understand that different cardiovascular testing yields different data. When evaluating a medical report that pertains to the cardiovascular system, it is important to be aware of the various testing options available. Coronary artery disease, arteriosclerosis of the coronary arteries, is the most common cause of CHD and is the leading cause of death worldwide. One key test for CHD is the EKG exercise stress test (treadmill), which measures the functional status in terms of METS.
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Cardiovascular Impairment Tests
B. Exercise Cardiac Stress Test (Treadmill Stress Test/ECST): Exercise cardiac stress testing is the most widely used cardiac stress test. The patient exercises on a treadmill according to a standardized protocol, with progressive increases in the speed and elevation of the treadmill (typically changing at three minute intervals). During the ECST, the patient's ECG, heart rate, heart rhythm and blood pressure are continuously monitored. If a coronary arterial blockage results in decreased blood flow to a part of the heart during exercise, certain changes may be observed in the ECG, as well as in the response of the heart rate and blood pressure. The exercise stress test evaluates arterial blood flow to (and indirectly the amount of oxygen that will reach) the myocardium (heart muscle) during physical exercise, compared to blood flow while at rest. As an exercise test, the results can also reflect overall physical fitness. Stress test abnormalities (I.e. if it is "positive") are an indication of marked imbalances of relative blood flow to different portions of the left ventricular muscle tissue of the heart. This is important because the left ventricle of the heart performs the greatest amount of work involved in pumping blood around the body However, blood flow imbalances within the heart muscle of the other three heart chambers are not detected this way. Usually, only High Grade Stenosis (i.e. severe narrowing) of the larger coronary (surface of the heart) arteries can be detected.
C. Holter Monitor: A portable ECG device that makes a continuous recording of the heart's electrical activity during a patient's daily routine. Usually worn for 24 to 72 hours, the Holter monitor, which is the size of a small deck of cards, can detect intermittent heart rhythm irregularities.
D. Signal-Averaged Electrocardiogram (SAEKG). Similar to an ECG, the SAEKG electrodes are placed on the skin. These electrodes are attached to the SAEKG machine so that the electrical activity of the heart is visualized, and then electronically manipulated by the signal-averaging software for deeper analysis. The SAEKG essentially strengthens some signals while eliminating "background noise" from other signals. These signals are then filtered and averaged, providing an analysis that yields information about patient risk of future Ventricular Tachycardia (rapid heart activity) and/or Ventricular Fibrillation (irregular heart activity). These weak but very important impulses are called "late potentials" and are commonly not evaluated in a standard ECG. Late potentials arise from damaged or scarred areas of heart muscle used to identify: Ventricular arrhythmia following heart surgery or a heart attack; the cause of fainting (called syncope); and scar tissue from a previous heart attack.
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Electrophysiology study: Used to evaluated arrhythmias (abnormal heartbeats), this study involves several tests to help pinpoint the location, the type of arrhythmia, and how the arrhythmia responds to treatment. A small catheter is guided to the heart. The heart's rhythm is recorded as small amounts of electricity are delivered through the catheter This internal recording is often compared with an external recording (from electrodes placed on the patient's chest and back) taken at the same time.
Homocysteine Testing: A blood test to determine the level of Homocysteine, which is an amino acid that is produced by the body, usually as a byproduct of consuming meat. Elevated levels of homocysteine (>10 micromoles/liter) in the blood may be associated with atherosclerosis (hardening and narrowing of the arteries) as well as an increased risk of heart attacks, strokes, or blood clot formation.
Intima-Media Thickness Scan (IMT): The IMT has recently been added as another diagnostic tool to determine coronary heart disease. The IMT is used to detect plaque at earlier stages of progression, before the artery lumen becomes severely stenosed, or compromised . The IMT scan combines high-resolution ultrasound with software algorithms to measure the tiny thickenings (as small as one tenth of one millimeter) in arterial walls that presage the onset of cardiovascular disease. While the stress test evaluates presence of advanced disease, the IMT evaluates the beginning of that disease before the stress test will show as abnormal.
Intracardiac Electrophysiology Study (EPS): allows a doctor to determine the details of arrhythmias. The study involves placing wire electrodes within the heart to measure electrical activity along the heart's conduction system and within heart muscle cells themselves. The electrodes detect the heart's electrical activity and map out any irregular heartbeats. This helps the doctor see the type of arrhythmia present and where the problem started in the heart. Abnormal electrical activity can occur anywhere along the heart's conduction system.
Magnetic Resonance Angiography (MRA): MRA is a type of magnetic resonance image (MRI) scan to provide pictures of blood vessels inside the body In many cases, MRA can provide information that cannot be obtained from an x-ray, ultrasound, or computed tomography (CT) scan. Like conventional angiography and CT angiography, MRA can provide detailed images of blood vessels.
Myocardial Biopsy: is done by using a bioptome (a small catheter with a grasping device on the end) to obtain a small piece of heart muscle tissue to send to a laboratory for analysis. Used to diagnose cardiomyopathy (inflammation of the heart muscle).