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Distal (microvascular) stenocardia or syndrome of X is the stenocardia caused by functional and organic insolvency of distal department of a coronary bed at angiographically intact and not spazmirovanny large (epicardial) coronary arteries.
Allocation of this form of stenocardia became possible only after implementation in clinical practice of the selection koronaroangiografiya. Use of coronary angiography allowed to establish that at 10 — 20% of patients with stenocardia coronary arteries of an intaktna. According to the Kemp (1973) offer, the stenocardia developing in the absence of a spasm and koronarografichesky signs of defeat of large (epicardial) coronary arteries began to call a syndrome of X.
Now in connection with establishment of the major role of disturbances of a microcirculator bed of a myocardium in development of this form of stenocardia, the bigger preference is given to the term microvascular stenocardia. The place of this form of stenocardia among other ischemic heart diseases forms finally is not defined. About it there are two points of view. Some cardiologists consider microvascular stenocardia as the ischemic heart disease special form with insolvency of a microcirculator bed of a myocardium, others consider this form of stenocardia not as kind ischemic heart disease of atherosclerotic genesis, but the independent disease of an unknown etiology which is shown clinic of stenocardia at normal large coronary arteries. As it will be visible from a further statement, the second point of view is considerably more reasoned.
Etiology and pathogeny
The etiology of microvascular stenocardia (syndrome of X) is unknown. At the heart of a pathogeny, according to opinion of most of cardiologists, pathology of small coronary arteries — microvascular dysfunction therefore often this stenocardia is called an illness of small vessels (small vessel disease) lies.
Insolvency of a microcirculator bed of a myocardium is caused by a combination of functional and organic factors. The following is considered as pathogenetic mechanisms of microcirculator stenocardia now.
Narrowing and insufficient ability prearteriol a myocardium to expansion
Masen and soavt. (1991) subdivided an arterial segment of a microcirculator bed of a myocardium on a functional sign into arterioles (they provide a coronary reserve) and prearteriola (possess resistive function). Prearteriola have the size 100 — 250 microns, and 25% of function of resistance to a coronary blood-groove fall to their share. Even small decrease in their gleam causes sharp increase of vascular resistance and disturbance of a coronary blood-groove. It is supposed that the main pathogenetic link of microvascular stenocardia is dysfunction prearteriol. Narrowing prearteriol in various sites of a myocardium of various extent and expressiveness develops, at the same time ability prearteriol considerably decreases to extend. Distalny a narrowing site prearteriol myocardium ischemia at rest can develop or at increase of need of a myocardium for oxygen during an exercise stress. Kompensatorno is observed increase of products of adenosine in ischemic sites, in a certain measure it leads to dilatation of arterioles which owing to uneven expressiveness promotes intra myocardial redistribution of a blood-groove and development of a syndrome of burglarizing of certain sites of a myocardium. Compensatory increase of concentration of adenosine in a myocardium promotes emergence of pain in heart as adenosine is a mediator of a painful attack.
prearteriol in a myocardium the raised products of endothelin and a neuropeptid of Y are a proximate cause of narrowing. Products of an endothelial vazodilatiruyushchy factor of nitrogen of oxide are at the same time broken that promotes strengthening of a spasm prearteriol and reduce their ability to dilatation. Confirmation of disturbance of a vazodilatation at the level prearteriol in a microcirculator bed of a myocardium are results of dipiridamolovy test. Normal in response to intravenous administration of Dipiridamolum there is an increase in a blood-groove in a coronary bed. At microcirculator stenocardia after introduction of Dipiridamolum the coronary blood stream does not increase, and, on the contrary, decreases in connection with existence of a phenomenon of intramiokardialny (intercoronary) burglarizing.
There is also an opinion on a role of increase of a tone of a sympathetic innervation and a hyperreactivity prearteriol in response to sympathetic hyper activation. In these conditions easily develops prearteriol.
Morphological changes of a microcirculator bed of a myocardium
Morphological changes in system of microcirculation of a myocardium at a microcirculator form of stenocardia are studied absolutely insufficiently. There are separate messages on morphological studying of intravital bioptat of patients (Mozeri and soavt., 1990), and also about results of a computer and magnetic and resonant tomography of heart at microvascular stenocardia. By means of the specified methods the following morphological changes are revealed:
swelling and degeneration of endothelial cells;
giperplasticheskoyefibdomyshechny thickening of walls of small arteries;
reduction of a gleam of a sosudovmikrotsirkulyatorny bed; the centers of a degeneration of myofibrils and inclusion of lipofuscin in them (at a submicroscopy of intravital bioptat of a myocardium).
Mechanisms of development of morphological changes in a microcirculator bed of a myocardium are not known yet, but these changes, undoubtedly, promote development of microvascular stenocardia.
Increase of aggregation of thrombocytes and erythrocytes, disturbance of a hemorheology
The detailed researches conducted in the Belarusian scientific research institute of cardiology (N. L. Tsapayeva, 1999), revealed substantial increase of aggregation of thrombocytes and erythrocytes, and also viscosity of blood at patients with microcirculator (distal) stenocardia. The specified changes promote disturbances of hemoperfusion of a myocardium and development of stenocardia.
Reduction of the threshold of painful sensitivity
Change of perception of pain is considered to be as one of the most important factors of a pathogeny of microvascular stenocardia. Reduction of the threshold of painful sensitivity at this disease is established. It is supposed that it is connected with decrease in products of endogenous opiate connections — endorphines.
It is supposed that in development of microvascular stenocardia disturbances of a metabolism in a myocardium play a role. With microvascular stenocardia during an exercise stress are found the high level of potassium in blood and increase of concentration of a lactate in comparison with healthy people in patients. These changes can demonstrate reduction of activity of aerobic metabolic processes in a myocardium (V. I. Metelitsa, 2002).
However it is not excluded that these metabolic changes arise for the second time, in response to disturbance of hemoperfusion in a myocardium.