Nuclear medical heart examinations
The goal of nuclear medical heart examinations is to,
- Detect CAD,
- Determine it´s severity,
- Make a prognosis
- And document therapy success.
The myocardic-perfusion-scintigraphy registers the functional consequences of coronary heart diseases. In this case, there is a disproportion between, firstly, the needed blood circulation of the heart muscle and, secondly, the reserve vessel area.
The ideal substance must:
- Show a high blood intake into the heart muscle, proportional to the regional blood flow, under a relatively slow outflow;
- Thus there is a broad time-frame for data acquisition.
These requirements are fulfilled by the low radioactively-radiating TI-201 as well as many Tc99m-marked agents.
The better illustration abilities of the former so called “radiopharmaceuticles”, limited through higher radiation energy, allow tomographic imaging compled on the ECG phases. Thus additional functional analysis of the heart’s work and movement can be accomplished.
This information shall give you an overview about
- Coronary heart diseases
- The Myocardic scintigraphy and
- Preparations and procedure of nuclear cardiologic examinations
Potential questions have now been answered to some extent. If you have additional queries, you should maybe contact your doctor, especially before a pending examination, who surely be willing to give you more information.
Coronary Heart Disease
The coronary heart disease (Disease of the coronary arteries) is a widespread disease of the industrial nations and describes the most common cause of death within the population. During the last years the mortality rate steadily decreased. This pleasant trend primarily is a result of consequent preventative measures through a reduction of risk factors, such as the decline of blood fats and abdication of smoking. Advances in cardiologic treatment – baloon dilatation and stent implantation – and cardiac surgical treatment – Bypass-operation, heart transplantation and artificial substite heartdevice – additionally contribute.
The stress echocardiography and the nuclear cardiologic examinations methods allow the investigation of information needed about the blood circulation situation of the heart. The nuclear medical methods can non-invasively (this means without intervention into vessels) illustrate the function, blood circulation and the metabolism of the heart muscle.
Patients with a coronary heart disease often suffer from the circumstance that the heart muscle, particularly under stress (physical and psychological), is insufficiently supplied with blood. Thus there is a disproportion between oxygen demand and oxygen supply. If this is the case, some patients complain about chest pain (Angina pectoris) and feel a certain shortage of breath. Within others, particularly long-time diabetes-patients, this very important alarm signal is missing for many reasons and makes an early diagnosis of the disease more difficult. Bearing this in mind, non-invasive (this means without intervention into vessels) methods of the diagnostic of blood circulation malfunctions are very special importance.
Why is a myocardial scintigraphy performed?
If coronary heart disease is suspected
The step-diagnostic is implemented beginning with the assessment of the climical symptoms under implication of the clinical image and the exercise ECGand if necessary the echocardiography. (Heart ultrasound).
A myocardial perfusion scintigraphy is indicated of there is continuing diagnostic uncertainty. This facilitates the cardiologists decision, whether a or not coronary angiography is needed.
In case of a stable post-infarction patient and a medium-rated risk, a nuclear medical examination may also contribute to the decision about the necessity of a intracardiac catheter.
1. About prefield diagnostics (Exclusion or confirmation of a suspected diagnosis of a coronary heart disease):
The resting ECG is inapplicable for the detection of any individual heart infarction risk. A normal resting ECG does not exclude a high-grade coronary heart disease. The exercise ECG is limited through the fact that an age and gender specific workload is only possible within 36% of all patients and a coronary heart disease can be prognosed in only 60% of all cases.
Echo-cardiography and stress-echo-cardiography do not always supply sufficient information for a sure diagnosis or to exclude a coronary heart disease with the highest possible probability. A myocardial scintigraphy can meanfully angment the lineup of non-invasive diagnostic, mearsures.
2. After a coronary angiography (Determination of the functional significance and the extent of the coronary heart disease):
If a coronary angiography is performed and a narrowing of the heart arteries is diagnosed, the question arises, whether
the determined abstinent narrowing is actually significant for the function and whether it should be treated
or whether in the supply area of a closed coronary artery still there is a sufficient amount of vital heart muscle tissue that can recover after treatment (Balloon dilatation or bypass operation) and can resume its former function.
That information is important for the disease’s trend and prognosis
3. After a balloon dilatation or bypass operation (therapie evaluation, queries about a potential re-stenosis):
After a successful balloon dilatation or bypass operation it sometimes happens that chest pain with same or other intensity/character continue or arise again. To differentiate, whether pain has arisen through insufficient blood circulation of the heart muscle (myocardial ischemia) or through another cause, the myocardial scintigraphy is used in most cases to assess the regional perfusion ratio in order not to perform another coronary angiography again.
How is a myocardial scintigraphy examination performed?
The examination’s target is to assess the heart muscle perfusion under neutral and stress conditions. Thus the coronary arteries’ perfusion capacity for the heart muscle s assessed. The examination consists of two parts:
- Myocardial scintigraphy under stress conditions
- Myocardial scintigraphy under resting conditions
Myocardial scintigraphy – What does actually happen?
For this examination which is performed at both stress and resting conditions, the treating doctor or his assistant puts a small hypodermic needle (Butterfly or in-dwelling catheter) in a basilica vein through which a weak radioactive test substance is injected into the vein.
The time of injection depends on reaching the expeeded heartrate and the patient’s symptoms respectively. This test substance transported through coronary vessels towards the heart muscle. It then accumulates in the myocytes according blood perfusion.
This allows the doctor using a so called Gamma-camera to record the heart perfusion. The imaging takes about 20 to 30 minutes and is painless. The analysis of the images is complex and needs a considerable amount of calculation time. Thus the results are not available directly after such an examination.
The examination part under stress conditions serves as method to assess the heart muscle blood circulation under age-adjusted maximum heart capacity. There are various possibilities to achieve maximum heart straining:
Usually, this happens through a bicycle ergometer (in setting or half-lying position) or a treadmill. Thus the patient is exercised in continuously increasing steps. During which both heart and circulation parameters (ECG, blood pressure and pulse) are registered and supervised by the doctor.
Pharmacological excercise testing:
If corporal excercise is not possible or cannot be performed, the desired maximum heart performance can be reached through an infusion of medicamtion. The choice of the medication depends on the problem of the conducted myocardial scintigraphy. During this excercise both heart and circulation parameters (ECG, blood pressure, pulse) are continuously registered and supervised by the doctor. Corporal exercise can simulated through a dobutamine infusion. However, to achieve the maximum dilatation of the capillaries of the coronary vessels both adenosine and dipyridamole infusions can be applied. However, no stimulants, such as coffee, tea or Coca-Cola, may be consumed, as they would have a disadvantageous influence on the medicaments’ effects. Asthma-patients are not suited for this kind of excercise and, thus, such a treatment is not applied to them.
Psychological stress procedure, „Cold-Pressure-Test”, etc:
These stress procedures are only used under a special circumsances. To perform the “Cold-Pressure-Test” both arms are bathed in cold water to stimulate a narrowing of the vessels. Such a reflectory narrowing of the coronary vessels can unmask a coronary stenosis. However, this is performed quite rarely.
If the designated maximum heart performance or the maximum stress is achieved, the test substance is injected through the formerig installed hypodermic needle. As soon as the test substance has accumulated in the heart muscle, a myocardial scintigraphy is performed under stress conditions.
The examination under resting conditions serves to assess the heart muscle perfusion in a resting state as basis perfusion and further to detect a potential heart tissue scarring, e.g. through a cardiac infarction, heart muscle inflammation or an organ rejection reaction after a heart transplantation. Thereby the test substance is injected under maintenance of resting conditions in the arm vein. As soon as the test substance is accumulated in the heart muscle, a myocardial scintigraphy is performed under resting conditions.
Depending on the test substance dose, both examination parts (Stress and rest) can be performed at one or at two different days. Usually, a test substance [99m TC-Sestamibi] is used with better radiation qualities and radiation hygiene (short half-life and small radiation dose).
To achieve a better selectivity and to obtain an overlapping-free exposure of both examination conditions, but also to reduce the radioactivity dose, the examinations under stress and resting conditions are performed on two different days. Under certain circumstances a test substance with not as optional radiation qualities and radiation hygiene [201 TICI] is used; the examinations are then performed on one day, as result of physiologic behaviour of the test substance.
Are there any preparations necessary for myocardial examinations?
Breakfast and medication:
To achieve a better image quality (ratio Heart / Gastrointestinal area), examinations should not be performed after a big meal.
A small breakfast, which means low-calory food, can be consumed. Thereby coffee, tea and high calory-drinks, such as Coca-Cola, should be avoided
Insulin-dependent patients should not abstain from their small meal, as their insulin should be injected as usual.
Beta blockers should be discontinued three days before the examinations. Other medication against hypertension and cardiac dysrhythmia (ACE-Hemmer, Verpamil) can be taken in as usual, thenouse exercise may not be performed due to high blood pressure.
All other medicaments can be taken in as usual. Exceptions are heart muscle perfusion promoting medication (Nitrates); these should be brought with the patient to the examination. This particularly counts for patients undergoing-diagnostics, to rule out or confirm a coronary heart disease of a heart catheter examination.
Besides this, it counts for patients after a balloon dilatation or bypass operation, who have to be examined, whether the treated coronary artery or others, or bypasses are limted in their function.
Patients with known coronary heart disease, who (for any reasons) cannot be treated with a balloon dilatation or bypass operation, and who can only be treated conservatively using medication, should take their heart medication prior to examination, as in this case it has to be assessed, whether the medication have achieved it´s desired effects.
Radioactivity, radiation exposure and risks of straining examinations
The test substances used for myocardial scintigraphy are weakly radioactive. The radiation exposure is minute and adds up to:
Effective equivalent dose
- = 3 mSv at 740 MBq 99mTc-Sestamibi (Half-life = 6 hrs)
- = 17 mSv at 74 MBq 201TICI (Half-life = 73 hrs)
The examination performance must not be performed during pregnancy due to protection of the unborn.
Every year there are millions of nuclear medical examinations. Experience shows that these examination methods are very safe. Nonetheless, these strain examinations involve a small risk, similar to a normal exercise ECG. The frequency of complications (Morbidity) during stress examinations was described in literature with 0,02 – 0,18%, the occurrence of ventricular fibrillation with 0 – 0,08% and the mortality with 0 – 0,009%.
To cope with such complications nuclear medical departments are equipped with corresponding pieces of equipment and medication and all assistants are well-trained. In case of emergency a hospitalisation observance may be necessary.