Myocardial scintigraphy

The myocardial scintigraphy (MSZ) or Myokardperfusionsszintigrafie (MPS) is a nuclear medicine examination method, depending on the implementation information about the perfusion ratios, vitality and function of the heart muscle provides (myocardium).

Indications

The most common indications for myocardial scintigraphy are:

• the suspicion of coronary artery disease (CHD) with medium clinical probability.
• the question of the hemodynamic relevance of stenoses in known CHD
• the differentiation between scars and reversible ischemia of the heart muscle before and after revascularizing interventions ( PTCA , coronary artery bypass )

Myocardial scintigraphy is rarely used to determine the left ventricular pumping function of the heart.

Contraindications

A pregnancy is considered, with few exceptions as an absolute contraindication for nuclear medicine examinations, breast-feeding as a relative contraindication. After a myocardial scintigraphy with ^99m technetium, the breastfeeding woman should express and discard the milk for 48 hours. After an examination with ²⁰¹ thallium, breastfeeding has to be done because of the long biological half-life .

For the stress examination, the contraindications (for example recent myocardial infarction , decompensated heart failure or high-grade aortic valve stenosis ) and termination criteria (for example reaching the age-dependent target heart rate, certain EKG or blood pressure changes) of the ergometry or the pharmacological stress must be observed. The guidelines require emergency equipment, such as a defibrillator, to be available .

execution

Thallium chloride

²⁰¹ Tl thallium (I) chloride is supplied via a sodium / potassium - ATPase in active cardiac muscle enriched cells.

The examination should be carried out on an empty stomach. In preparation, depending on the issue, drugs that affect the perfusion of the coronary arteries (e.g. calcium antagonists or beta blockers ) may be discontinued a few days beforehand.

The patient is then initially stressed by an ergometry or pharmacologically (e.g. with adenosine , dipyridamole or dobutamine ). The nuclide is injected intravenously shortly before the end of the exposure, usually around 70 MBq ²⁰¹ thallium (corresponds to around 10 ⁻⁴ to 10 ⁻⁷ g ). About 5 to 6% of the activity is accumulated in the myocardium, the rest is mainly distributed among the stressed skeletal muscles , kidneys, liver and gastrointestinal tract. Immediately after the injection, the first recordings ("stress") are made using SPECT technology. After about three to four hours, during which the patient is supposed to stay sober, images are taken again using the SPECT technique (“rest”) without a second injection of a radiopharmaceutical . In the meantime, there has been a redistribution between the various organs.

Technetium compounds

There are ^99m Tc tracer for myocardial imaging using SPECT developed, including the products sestamibi / Cardio Lite ^® and tetrofosmin / Myoview ^® .

Complex of six molecules of 2-methoxyisobutyl-isonitrile (MIBI) and technetium as ligands in the center

In Cardiolite ^® the complex contains six molecules of 2-methoxyisobutyl-isonitrile (MIBI) as ligands around the central Tc atom. The complex is highly lipophilic and is taken up passively by diffusion into the heart muscle cell. The injection of 250 to 500 MBq ^99m technetium - MIBI (Cardiolite ^® ) is carried out as in the examination with thallium under stress. In contrast to the examination with thallium, the stress recordings are not made immediately, but after a break of about an hour. During this time, the patient should take a stimulant meal (rich in fat and protein). This is used to secrete the bile and to stimulate the stomach and results in better image quality. At 250 to 750 MBq, the resting recordings are made after three hours at the earliest, and even better after one to two days, as less activity can then be applied.

^99m technetium tetrofosmin (Myoview ^® ) is available as a further tracer . The examination protocol differs only slightly from that of the examination with MIBI.

PET tracer

The cardiac blood flow is measured by positron emission tomography at rest and under stress with 1100 MBq ¹⁵ O water , 555 MBq ¹³ N ammonia or 1850 MBq ⁸² Rb rubidium chloride , especially in overweight patients (because of the more precise attenuation correction ), younger patients (because of the low radiation exposure caused by the short half-lives) and (because of the absolute quantification) measured in balanced multivascular diseases, and the vitality question answered with 370 MBq of ¹⁸ F-2-deoxy-2-fluoro-D-glucose (FDG) if necessary .

Cardiac phase triggered recordings

Cardiac phase triggered SPECT recordings allow the analysis of cardiac wall thickness increase during the cardiac cycle and regional wall movement disorders, as well as the determination of the ejection fraction . Certain cardiac arrhythmias, such as arrhythmia absoluta , prevent the acquisition of cardiac phase-triggered data.

interpretation

The distribution of the radionuclide is assessed qualitatively (visually) and semi- quantitatively in comparison to the distribution in a normal group. Three-dimensional evaluations are possible, as well as statistical analyzes of wall thickening, wall mobility and pump function, if recordings triggered by the heart phase could be made. In addition, the myocardial contractility can be assessed visually by recording video sequences.

In the normal finding, all sections of the myocardium of the left ventricle accumulate the nuclide uniformly both in comparison with one another and in comparison between stress and rest or redistribution recordings; there are no regional wall movement disorders. The right ventricle usually has minimal activity.

Sections of the heart muscle that accumulate less activity in the stress recordings than in the rest recordings are interpreted as exercise-induced ischemia . Memory defects detectable in both recordings indicate a scar on the myocardium, for example after a myocardial infarction . With certain restrictions, both findings can be assigned to the districts of individual coronary arteries (branches).

Radiation exposure

The examination with 74 MBq ²⁰¹ thallium chloride causes radiation exposure of around 16 mSv (effective equivalent dose ), the examination with 740 MBq ^99m technetium MIBI of around 7 mSv. With ¹³ N ammonia , 2.4 mSv ( effective dose ) are achieved, with ¹⁵ O water 2.5 mSv, with ¹⁸ F fluorodeoxyglucose 7 mSv and with ⁸² Rb rubidium chloride 13.5 mSv.

In 2005 about three quarters of all tests in Germany were carried out with technetium.

Web links

• Med Uni Wien myocardial scintigraphy
• Patient information from the Austrian Society for Nuclear Medicine (accessed November 25, 2013)

swell

• Schicha / Schober, Nuclear Medicine, Stuttgart 1997

Individual evidence

1. ↑ Cardiolite package insert
2. ↑ Package insert Myoview
3. ^ University of Marburg
4. ^ T. Krause. Heart, circulation, blood vessels. In: T. Kuwert, F. Grünwald, U. Haberkorn, T. Krause: Nuclear medicine. Stuttgart, New York 2008, ISBN 978-3-13-118504-4 .
5. ↑ ASNC Information Statement: Recommendations for reducing radiation exposure in myocardial perfusion imaging. Cerqueira MD, Allman KC, Ficaro EP, Hansen CL, Nichols KJ, Thompson RC, et al. 2010, PDF ( Memento of the original from September 20, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
6. ↑ Lindner O, Burchert W, Bengel FM, et al. : Myocardial scintigraphy in Germany - results of the 2005 survey and location determination . In: Nuclear Medicine . 46, No. 2, 2007, pp. 49-55. PMID 17393039 .