Myocardial scintigraphy

What is it?

Myocardial scintigraphy is the nuclear imaging of the heart. The purpose of scintigraphy is to assess the viability of the myocardium, thus differentiating live areas from infarcted or ischemic areas.

When is this exam indicated?

The major area of application relates to ischemic heart disease (myocardial infarction, angina pectoris) where it is often used to provide indications for the execution of a coronarography, and if necessary coronary angioplasty.

How is it performed?

Scintigraphy can be performed with stress or with dipyridamole or adenosine. The one with stress test is performed by having the patient perform a physical activity (by exercise bike or treadmill) that is gradually increased. The effort increases the cardiac oxygen demand and this causes an increase in coronary flow. If possible, the test should be performed in such a way as to adequately explore this parameter (in which case the effort is considered maximal). To define this limit, there are age-specific heart rate values for the patient; in the maximal test, at least 85% of the value sought (220 - patient's age [years]) is reached without the appearance of symptoms or signs of ischemia, without a drop in systolic blood pressure <20 mmHg from baseline, or changes in the electrocardiogram. If the test does not reach this threshold, its sensitivity decreases. Once the maximum effort is reached, it is maintained for at least 90 seconds after administration of the radiopharmaceutical [see later]. This time frame allows the creation of the flow difference between the ischemic and healthy areas. The test can be done in therapy (maintaining all the cardiological drugs already taken) or suspending some of them depending on the case. The scintigraphy with dipyridamole and adenosine explores the coronary reserve without increasing the oxygen demand, in practice these drugs cause a global increase in flow in all districts except those of stenotic afferent vessels. The images then will show the stenotic areas are relatively less perfused than the others.

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Contraindications

The contraindications are only related to scintigraphy performed pharmacologically (dipyridamole and adenosine): asthma and COPD ( as these drugs affect the beta agonists used for the treatment of these diseases), a recent cerebral ischemic case (the vasodilation induced by the drug also occurs in the brain), atrio-ventricular block ( since it is accentuated by these drugs), severe hypotension (<100 mmHg). In case these drugs are applied it is also advisable that the patient does not take theophylline (contained in tea) or similar substances such as caffeine contained in coffee as well as in chocolate (even the few traces present in the "decaffeinated" product can disrupt the results of the examination).

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