What is myocardial scintigraphy?
Myocardial scintigraphy can be used to visualize the blood flow in the heart muscle. A radioactively labeled substance (radiopharmaceutical) is administered to the fasting patient via a vein. distributes itself according to the blood flow (perfusion) in the heart tissue and is absorbed by the heart muscle cells. The radiation emitted is measured and displayed as an image.
Techneticum-99m (99mTc) is usually used for radioactive labeling of the substance used.
Myocardial scintigraphy can be performed at rest or under stress. In the second case, the patient sits during the examination, for example, on a bicycle ergometer.
If actual stress is not possible in this way, medication can be used to simulate a careful strain on the heart. Vasodilators such as adenosine are usually used. If such agents cannot be given for medical reasons (for example, in asthma or low blood pressure), the catecholamine dobutamine is used as an alternative. The agent is administered as an infusion.
Less radiation with poor blood circulation
If the reduced accumulation occurs only under stress but not under rest, a reversible perfusion defect is present. If, on the other hand, it is also detectable at rest, the perfusion defect is non-reversible. The affected heart tissue is irreversibly destroyed (“scarred”).
However, the actual constrictions (stenoses) in the coronary vessels cannot be localized with myocardial scintigraphy. For this purpose, coronary angiography, i.e. a radiological examination of the vessels (angiography) of the heart muscle, must be performed. This is done as part of a cardiac catheterization.
When is myocardial scintigraphy performed?
Myocardial scintigraphy is performed primarily when coronary artery disease (CAD) is suspected or when CAD is known, in order to clarify its extent.
The examination is also often used to decide whether a narrowed coronary vessel should be treated with medication or surgery (bypass or stenting). Surgery has a chance of success, for example, if an area of the heart is only reversibly damaged: the operation can then possibly improve its blood flow again.
Even after a heart attack, the physician can use myocardial scintigraphy to assess blood flow and thus the condition of the heart muscle (i.e., its vitality).
Myocardial scintigraphy: preparation
This includes, for example, that you must appear for the examination on an empty stomach. This helps to ensure that the radioactively labeled substance is absorbed into the heart tissue in the best possible way and accumulates only minimally in other tissue (such as the gastrointestinal tract). Fasting means that you must not eat anything in the four hours before the examination. An exception is made for diabetics – they are allowed a light breakfast.
If a drug load with a vasodilator is planned, you must not consume any food or drink containing caffeine (chocolate, coffee, cola, black tea, etc.) for at least 12 hours beforehand. You must stop taking certain medications (preparations containing caffeine, theophylline or dipyridamole) at least 24 hours before the myocardial scintigraphy. The physician will give you more detailed instructions on this.
Myocardial scintigraphy: risks and side effects
Physical exertion on a bicycle ergometer can lead to cardiac arrhythmia and heart attack in patients with heart disease (like any physical exertion).
The medicinal stress during myocardial scintigraphy can trigger side effects such as chest pain, shortness of breath, flush (sudden reddening of the skin, for example on the face), drop in blood pressure, cardiac arrhythmia and, in extreme cases, even a heart attack.
Thus, the natural annual radiation exposure per person in Germany is on average 2.1 mSv (with a fluctuation range of 1 to 10 mSv – depending on place of residence, dietary habits, etc.). In Austria, one is exposed to an average of 3.8 mSv of natural radiation per year (range of variation: 2 to 6 mSv). For Switzerland, the natural annual radiation exposure per person is given as 5.8 mSv, although here too there is a range of variation depending on the place of residence and other factors.
For comparison, the radiation exposure during a myocardial scintigraphy is 6.5 millisieverts (mSv) on average for substances labeled with technetium.
