When normal ECG, exercise ECG, and and cardiac ultrasound (echocardiography) reveal unclear cardiac findings, but an accurate diagnosis cannot be made, myocardial scintigraphy is the method of choice. It is noninvasive and has a high informative value.
What is myocardial scintigraphy?
The physician wants to see how circulatory disturbances affect the heart muscle. The cause of impaired blood flow is usually due to narrowing of the coronary arteries. Myocardial scintigraphy is a gentle, nuclear medicine diagnostic procedure to examine the blood flow, metabolism and mass of the heart muscle. The heart is examined in two phases: under stress and at rest. The findings are then compared with each other. In the scintigram, the doctor can see how circulatory disorders affect the heart muscle. The cause of disturbed blood flow is usually constriction of the coronary arteries. A lack of blood flow to the heart carries the risk of a life-threatening heart attack. Myocardial scintigraphy can determine whether the extent of circulatory problems necessitates cardiac catheterization, and may even spare some patients from having it.
Function, Effect, and Objectives
Myocardial scintigraphy allows the physician to see the amount of blood reaching the heart at rest and under stress. By comparing the images, he can determine if different areas of the heart have poorer blood flow than others under stress. Reduced blood flow could be a sign of vasoconstriction and an increased risk for a heart attack. If the patient has already had a heart attack, the size of the scar, the extent of tissue damage, and the residual blood flow to the infarcted area can be determined. The results determine whether bypass surgery should be performed or a stent placed. Beyond these issues, myocardial scintigraphy provides insight into the heart’s pumping capacity and the patient’s exercise tolerance, which is worse after a heart attack than in healthy, well-perfused tissue. For myocardial scintigraphy, access is made to the arm vein, through which a lightly radioactively labeled carrier substance can be injected during the exercise test on the bicycle ergometer, making the heart vessels visible. For patients with limited physical capacity, e.g. due to orthopedic problems or if blood pressure is already too high at rest, it is possible to administer a drug for the stress test while the patient is lying down. The stress test is controlled by a doctor and monitored by an ECG. In the phase of increased stress, a radioactively enriched carrier substance is injected through the access. The stress is followed by a rest phase of 30 to 60 minutes, during which the patient is supposed to eat a meal that he has brought with him, preferably one that contains fat. After the resting phase, images are taken with the gamma camera for about 20 minutes while the patient is lying down and evaluated. Based on these images, it is decided whether another rest examination is necessary. Sometimes the stress examination is sufficient. If a rest examination is still required for clarification, the radioactivity in the heart must first be reduced for about 2 hours before the second part of the examination follows. This is followed by the same procedure again, only without stress. Myocardial scintigraphy always useful to rule out coronary artery disease (CAD) when the following risk factors are still present:
- Hypertension
- Smoking
- Overweight
- Diabetes mellitus
- Increased cholesterol levels
- Familial disposition to heart disease
- Angina pectoris
- Abnormalities in the ECG
Because myocardial scintigraphy determines the extent of the circulatory disturbance, it can help optimize treatment and avoid unnecessary surgical procedures. After successful treatments, it can be used as a noninvasive method to monitor new vasoconstrictions. It can also determine an individual heart risk. The examination is offered by all statutory and private health insurance companies as a standard benefit.
Risks, side effects, and hazards
Side effects such as allergies rarely occur with radioactive substances, more likely with X-ray examinations as a reaction to contrast media. The radiation exposure is only low and is not higher than with X-rays.Nevertheless, a very small risk of cancer as a late consequence cannot be completely ruled out. Therefore, the benefits and risks should always be weighed individually. The stress phase also rarely leads to complications, even in patients with heart disease. In order to be able to guarantee an optimal informative value of the examination result, the patient must reach the highest possible level for him. In extremely rare cases, this can lead to cardiac arrhythmias and myocardial infarction. Occasionally, mild side effects may occur, such as a tight chest, a feeling of warmth, shortness of breath, a feeling of pressure in the abdomen, headaches, arm and leg discomfort and dizziness. However, these only occur in the case of drug-induced stress. The radioactive substance itself does not cause any side effects. During pregnancy, myocardial scintigraphy is performed only in exceptional cases, and during breastfeeding mothers must pause breastfeeding for two days after the examination. In case of severe organ diseases, the load on the cardiovascular system may be too high. Other contraindications include febrile infections, acute myocardial infarction or severe cardiac insufficiency, unmanageable hypertension, severe cardiac arrhythmias and valve defects, and acute myocarditis. For the examination, patients must be fasting for at least 12 hours, may only drink some low-carbonated water. Medications may be taken, but cardiac medications should be suspended for 24 hours, and beta-blockers for as long as 2 to 3 days. They may be taken before the rest period if needed. Diabetics may eat a small meal, preferably low in fat.
