Nuclear cardiology testing
Iowa Heart Center offers a variety of nuclear cardiology procedures. These procedures are used to assess myocardial perfusion, ventricular wall motion, myocardial viability and left ventricular function. Current imaging agents may be used in a number of ways, allowing for the assessment of several factors in one setting. When used in conjunction with stress testing techniques, nuclear cardiology procedures can be tailored to the patient’s needs.
Myocardial perfusion studies are usually done both at rest and during stress to allow the physician to differentiate between myocardial ischemia and myocardial infarction. A perfusion defect present with stress that “fills in” at rest is indicative of ischemia, whereas a persistent defect suggests an infarction.
Gated wall motion studies, which are acquired during perfusion studies, allow for examination of the left ventricle by segments that correspond to the major arteries and branches. These segments may then be assessed as normal, hypokinetic (abnormally decreased heart wall activity) or dyskinetic (irregular heart wall activity). Iowa Heart Center’s nuclear cardiology department also has a special software program that will calculate the ejection fraction (EF) percentage. Patients must be in sinus rhythm to undergo this test.
Myocardial viability studies are usually performed in conjunction with a perfusion study. These studies are designed to assist the physician in determining if an area of the myocardium (heart wall muscle), previously diagnosed as infarcted (tissue is dead), is viable (tissue is alive). If an area of defect on the perfusion study is persistent, but fills in on the viability study, then it is determined to be viable.
Ventricular function (also known as ejection fraction, or EF) is an assessment of the efficiency of the left ventricle in a resting state. A multi-gated acquisition (muga) test is the nuclear equivalent of a left ventriculogram. Patients must be in sinus rhythm to undergo this test.
The stress techniques used in nuclear cardiology are the standard or modified Bruce protocol treadmill tests. A radionucleide is injected at the peak of stress. When the treadmill is completed, the patient moves to the imaging room and is placed under the gamma camera. “No sweat” stress agents are utilized when a patient is unable to perform the Bruce protocols; they include adenosine, dobutamine and persantine.
Adenosine, recently approved by the FDA, is a vasodilator and does not increase the patient’s heart rate. Its side effects are quickly resolved when the medication is stopped. Adenosine is contraindicated for patients with lung disease (i.e. asthma, emphysema, COPD) who are taking medications for these problems.
Dobutamine is a direct-acting inotropic agent, and is not presently approved for cardiac stress testing. Dobutamine features vasodilating properties and increased cardiac output, which increases the patient’s heart rate to mimic exercise during stress testing. Its effects are readily reversed with esmolol. Significant side effects include ventricular arrhythmias.
