X-ray examination of heart function

In a healthy person, about 1 time per second, a wave of excitation spreads through the myocardium - there is a contraction and then a relaxation of the heart. The simplest and most accessible method for their registration is fluoroscopy. It allows you to visually assess the contraction and relaxation of the heart, pulsation of the aorta and pulmonary artery. In this case, changing the position of the patient behind the screen, you can bring to the circuit, i.e. Make the marginal, all parts of the heart and blood vessels. However, in recent years, due to the development of ultrasound diagnostics and its wide introduction into clinical practice, the role of fluoroscopy in the study of the functional activity of the heart has decreased significantly because of the high enough radiation load.

The main method of studying the contractile function of the heart muscle is ultrasound (ultrasound).

In cardiology, several ultrasound techniques are used: one-dimensional echocardiography - the M-method; two-dimensional echocardiography (sonography) - B-method; one-dimensional Doppler echocardiography; two-dimensional color Doppler mapping. An effective method of studying the heart is also a duplex study - a combination of sonography and dopplerography.

One-dimensional echocardiogram has the form of a group of curves, each of which corresponds to a certain structure of the heart: ventricular and atrial walls, interatrial and interventricular septum, valves, pericardium, etc. The amplitude of the curve on the echocardiogram indicates the range of systolic movements of the recorded anatomical structure.

Sonography makes it possible to observe the movement of the walls of the heart and valves in real time on the display screen. To study a number of parameters characterizing the function of the heart, the heart contour is monitored on the screen of the monitor on the freeze frames fixed on the top of the R wave of the electrocardiogram and the descending knee of the T wave. A special computer program available in an ultrasound unit allows us to compare and analyze these two images and obtain parameters of the end systolic and terminal diastolic volumes of the left ventricle and atrium, the size of the surface of the right ventricle, the ventricular ejection fraction, the fraction of orozhneniya atrial systolic and minute volumes, wall thickness of the myocardium. It is very valuable that at the same time, indices of regional contractility of the left ventricular wall can be obtained, which is extremely important in the diagnosis of coronary heart disease and other cardiac muscle lesions.

Dopplerography of the heart is carried out mainly in the pulsed mode. With its help it is possible not only to study the movement of the valves and walls of the heart in any phase of the cardiac cycle, but also in the chosen control volume to measure the velocity of the blood movement, the direction and nature of its course. Particular importance in the study of the functional parameters of the heart acquired new methods of Doppler ultrasound: color mapping, energy and tissue Doppler. Currently, these options for ultrasound are the leading instrumental techniques for examining cardiac patients, especially in out-patient practice.

Along with ultrasonic diagnostics, recently radionuclide methods for the study of the heart and blood vessels have been developing rapidly. Among these methods, it is necessary to distinguish three: equilibrium ventriculography (dynamic radiocardiography), radionuclide angiocardiography and perfusion synthography. They allow you to obtain important, sometimes unique information about the function of the heart, do not require the catheterization of blood vessels, they can be performed both at rest and after functional loads. The latter circumstance is most important when assessing the reserve abilities of the heart muscle.

Equilibrium ventriculography is one of the most common methods of examining the heart. With its help determine the pumping function of the heart and the nature of the movement of its walls. The object of research is, as a rule, the left ventricle, but special methods have been developed for studying the right ventricle of the heart. The principle of the method consists in registering a series of images in the computer memory of a gamma camera. These images are obtained from the gamma radiation of RFP, introduced into the blood and long-term in the bloodstream, i.e. Not diffusing through the vessel wall. Concentration of such RFP in the bloodstream for a long time remains constant, therefore it is accepted to say that the blood pool (from the English pool - pool, pool) is being investigated.

The easiest way to create a blood pool is to inject albumin into the bloodstream. However, the protein is still broken down in the body, and the released radionuclide leaves the bloodstream, and the radioactivity of the blood gradually falls, and the accuracy of the test decreases. A more accurate way to create a stable radioactive pool was the label of the patient's erythrocytes. To this end, a small amount of pyrophosphate is injected into the vein, about 0.5 mg. It is actively absorbed on red blood cells. After 30 minutes, 600 MBq of 99mTc pertechnetate is injected intravenously, which is immediately connected to the absorbed red blood cells by pyrophosphate. This gives a strong connection. Notice that we first encountered the radionuclide research method, in which RFPs are "prepared" in the patient's body.

Passage of radioactive blood through the chambers of the heart is recorded in the computer's memory using an electronic device called a trigger. It "binds" the collection of information from the gamma camera detector to the electrical signals of the electrocardiograph. Collecting information about 300-500 cardiocycles (after complete dilution of the RFP in the blood, ie, stabilization of the blood pool), the computer groups them into a series of images, the main of which are the reflecting the finite-systolic and the end-diastolic phase. At the same time, several intermediate images of the heart are created during the cardiocycle, for example, every 0.1 s.

A similar procedure for the formation of medical images from a large series is necessary to obtain a sufficient "statistics of the account," in which the resulting images will have a sufficiently high quality, necessary for analysis. This applies to any analysis - both visual and computer.

In radionuclide diagnostics, as in all radiation diagnostics, the main rule of "quality of reliability" operates: collecting as much information as possible (quanta, electrical signals, cycles, images, etc.).

Using an integrated curve computer based on the analysis of the heart images, the ejection fraction, the rate of filling and emptying the ventricle, the duration of the systole and diastole are calculated. The ejection fraction (EF) is determined by the formula:

Where D0 and CO are the counting rates (radioactivity levels) in the end-diastolic and finitely systolic phases of the cardiocycle.

Ejection fraction is one of the most sensitive indicators of ventricular function. Normally, it fluctuates around 50% for the right and 60% for the left ventricle. In patients with myocardial infarction, PV is always reduced in proportion to the extent of the lesion, which has a known prognostic value. This figure is also reduced in a number of heart muscle lesions: cardiosclerosis, myocardiopathy, myocarditis, and others.

Equilibrium ventriculography can be used to detect limited violations of the contractility of the left ventricle: local dyskinesias, hypokinesia, akinesia. For this purpose, the image of the ventricle is divided into several segments, from 8 to 40. For each segment, the displacement of the ventricular wall is studied with cardiac contractions. Considerable value is represented by equilibrium ventriculography for the detection of patients who have reduced functional reserves of the heart muscle. Such people form a group of high risk of developing acute heart failure or myocardial infarction. They carry out this study under conditions of a dosed bicycle ergometric load to detect sections of the ventricular wall that do not cope with the load, although there are no abnormalities in the patient's calm state. A similar condition is called stress-induced myocardial ischemia.

Equilibrium ventriculography makes it possible to calculate the regurgitation fraction, i.e. The magnitude of the reverse emission of blood in heart defects, accompanied by a deficiency of the valve apparatus. The advantage of the method is that the study can be conducted for a long time, for several hours, studying, for example, the effect of drugs on the activity of the heart.

Radionuclide angiocardiography is a method of alternating the first passage of RFP through the chambers of the heart after a rapid intravenous injection of it into a small volume (bolus).

Typically, 99mTc-pertechnetate is used with an activity of 4-6 MBq per kg of body weight in a volume of 0.5-1.0 ml. The study is carried out on a gamma camera equipped with a high-performance computer. A series of images of the heart is recorded in the computer memory during the passage of RFP (15-20 frames within 30 seconds). Then, selecting the "zone of interest" (usually the area of the root of the lung or right ventricle), analyze the intensity of radiation RFP. Normally, the curves of passing the RFP to the right chambers of the heart and through the lungs look like one high steep peak. In pathological conditions, the curve is flattened (when the RFP is diluted in cardiac chambers) or lengthened (when RFP is delayed in the chamber).

With some congenital heart diseases, arterial blood is discharged from the left chambers of the heart to the right. Such shunts (they are called levopravshi) are with defects in the septum of the heart. On radionuclide angiocardiograms left-hand shunt is revealed as a repeated rise of the curve in the "zone of interest" of the lungs. With other congenital heart defects, the venous blood, which is not enriched with oxygen, again goes through the lungs, into the large circle of blood circulation (right-sided shunts). A symptom of this shunting on a radionuclide angiocardiogram is the appearance of a peak of radioactivity in the left ventricular and aortic regions before the maximum radioactivity is recorded in the lung region. With acquired heart defects, angiocardiograms allow to establish the degree of regurgitation through the mitral and aortic orifices.

Myocardial perfusion scintigraphy is used mainly for the study of myocardial blood flow and to a certain extent - for judging the level of metabolism in the heart muscle. It is carried out with preparations of ^99m T1-chloride and ^99m Tc-sesambi. Both RFPs pass through the vessels feeding the cardiac muscle, rapidly diffuse into the surrounding muscle tissue and are included in metabolic processes, imitating potassium ions. Thus, the intensity of accumulation of these RFPs in the cardiac muscle reflects the volume of blood flow and the level of metabolic processes in the cardiac muscle.

Accumulation of RFP in the myocardium occurs fairly quickly and reaches a maximum in 5-10 minutes. This allows you to conduct research in various projections. The normal perfusion image of the left ventricle on scintigrams looks like a uniform horseshoe-shaped shadow with a central defect that corresponds to the ventricular cavity. The zones of ischemia arising in the infarction will be displayed as areas with a lower fixation of the RFP. More vivid and, most importantly, reliable data in the study of myocardial perfusion can be obtained using single-photon emission tomography. In recent years interesting and important physiological data on the functioning of the cardiac muscle began to be obtained by using ultrashort-acting positron-decaying nuclides, for example F-DG, as the RFP. When using two-photon emission tomography. However, this is still possible only in some large scientific centers.

New possibilities in assessing the function of the heart appeared in connection with the improvement of computed tomography, when it became possible to perform a series of tomograms with short exposures against the background of a bolus injection of radiopaque substances. In a vein of the ulnar fold using an automatic syringe, 50-100 ml of non-ionic contrast substance - omnipak or ultravistine is injected. Comparative analysis of heart sections using computerized densitometry allows to determine the movement of blood in the heart cavities during the cardiac cycle.

Especially noticeably advanced computed tomography in the study of the heart in connection with the creation of electron-beam computer tomographs. Such devices allow not only to receive a large number of pictures with a very short exposure, but also to create an imitation of heart rate dynamics in real time and even perform a 3D reconstruction of a moving heart.

Another equally dynamically developing method for studying the function of the heart is magnetic resonance imaging. Due to the high magnetic field strength and the creation of a new generation of high-performance computers, it became possible to collect the information needed for image reconstruction in very short time intervals, in particular, to analyze the end-systolic and end-diastolic phase of the cardiac cycle in real time.

At the disposal of the doctor there are many ray methods for evaluating the contractile function of the heart muscle and myocardial blood flow. However, no matter how the physician strives to restrict to non-invasive procedures, a number of patients have to use more complicated procedures related to the catheterization of blood vessels and artificial contrasting of the heart cavities and coronary vessels - X-ray ventriculography and coronary angiography.

Ventriculography is necessary because it has higher sensitivity and accuracy than other methods in assessing left ventricular function. This is especially true for the detection of violations of local contractility of the left ventricle. Information on regional myocardial disorders is needed to determine the severity of coronary heart disease, assess indications for surgical interventions, transluminal angioplasty of the coronary arteries, thrombolysis in myocardial infarction. In addition, ventriculography allows you to objectively evaluate the results of exercise and diagnostic tests for ischemic heart disease (atrial pacing test, veloergometric test, etc.).

Radiopaque substance is administered in a volume of 50 ml at a rate of 10-15 ml / s and filming is performed. The film shots clearly show changes in the shadow of the contrast in the left ventricular cavity. Upon closer examination of the film frames, it is possible to notice pronounced violations of myocardial contractility: the absence of wall movement in any part or paradoxical movements, i.e. Bulging at the time of systole.

To identify less severe and local contractility disorders, it is common to perform a separate analysis of 5 to 8 standard segments of the left ventricle silhouette (for an image in the right anterior oblique projection at an angle of 30). In Fig. 111.66 shows the division of the ventricle into 8 segments. To assess the contractility of the segments proposed different ways. One of them is that from the middle of the long axis of the ventricle, 60 radii to the contours of the ventricle shadow are carried out. Each radius is measured in the end-diastolic phase and, accordingly, the degree of its shortening with contraction of the ventricle. Based on these measurements, computer processing and diagnostics of regional contractility disorders are performed.

An irreplaceable direct method of studying coronary blood flow is selective coronary angiography. Through a catheter inserted sequentially into the left and then into the right coronary artery, an X-ray contrast substance is injected by the automatic injector and filming is performed. The received images reflect both the morphology of the entire system of coronary arteries and the character of blood circulation in all parts of the heart.

Indication for coronary angiography is quite wide. First, coronary angiography is shown in all insufficiently clear cases for verification of coronary heart disease, choice of treatment method for acute myocardial infarction, differential diagnosis of myocardial infarction and myocardiopathy. As well as in combination with a repeated heart biopsy - if there is a suspicion of rejection reaction during its transplantation. Secondly, coronary angiography is used in cases of strict professional selection in case of suspicion of the possibility of coronary arteries from pilots, air traffic controllers, bus drivers and trains, as the development of acute myocardial infarction in such workers poses a threat to passengers and surrounding people.

Absolute contraindication to coronary angiography is intolerance of contrast medium. Relative contraindications are severe lesions of internal organs: liver, kidneys, etc. Coronarography can be performed only in specially equipped X-ray units that are provided with all means of restoring cardiac activity. In some cases, the introduction of contrast medium (and it must be administered several times in each coronary artery, if functional tests are used) may be accompanied by a sciatica, extrasystole, and sometimes temporary transverse cardiac blockade and even fibrillation. In addition to visual analysis of coronarograms, they are computer-processed. To analyze the contours of the artery shadow, only the outline of the artery is selected on the display. With stenosis, a stenosis schedule is constructed.