Scans- Help Evaluate Heart Muscle Perfusion-Hypertension
- By:Robert Baird Baird
A thallium scan-a radionuclide study-can help evaluate heart muscle perfusion. The examiner injects thallium I.V. and then performs the scan. Ischemic and infarcted areas of heart muscle don't take up the thallium, and they appear as cold spots on the scan. A physician may order an exercise stress test with a thallium scan to assess a patient for ischemia during exercise. Scans are performed at levels of peak exercise and 2 to 4 hours after exercise.
A physician may use dipyridamole thallium scanning for patients who are physically unable to exercise. Dipyridamole simulates exercise conditions by dilating the coronary arteries. Scans are performed when the arteries are dilated and 2 to 4 hours later.
In a multiple gated acquisition scan, another radionuclide scan, technetium is injected, and the heart is scanned during several cardiac cycles. This test analyzes ventricular wall motion and determines the ejection fraction-the amount of blood ejected from the ventricle during contraction. In a patient with CAD, this test shows abnormal movement and reduced performance of the left ventricular wall and a below-normal ejection fraction.
Using Cardiac Troponin Levels to Determine Myocardial Damage
Cardiac troponins, proteins that regulate calcium-dependent interactions between myosin and actin, facilitate cardiac contraction and relaxation. These proteins have three forms: troponin C, troponin I, and troponin T. Troponin C is found in cardiac and skeletal muscle cells. Troponin I and troponin T are specific to cardiac muscle.
Studies of patients with chest pain show that measurements of troponin I and troponin T levels may be more sensitive indicators of myocardial damage than measurements of creatine kinase levels. And measuring cardiac troponin blood levels may more specifically identify patients who are at increased risk for cardiac complications.
In one study of 1,404 patients with unstable angina and non-Q-wave myocardial infarctions (Mis), those with troponin I levels of 0.4 ng/ml or more had a significantly higher short-term risk of death.
In another study, patients with lower troponin T levels had improved long-term outcomes. During the first 4 months of follow-up, the risk of an Ml or death increased with higher troponin T levels.About the author:
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