Depression ST and nitrate tolerance. The value of ST segment depression

With regard to another criterion (as a sign of the severity of myocardial ischemia) – the magnitude of the ST segment depression – certain objections may exist. They became especially relevant when the magnitude (area) of myocardial infarction was assessed by the severity of ST segment elevation in patients in the acute stage of myocardial infarction. Indeed, it turned out that with the progression of the size of myocardial infarction, there may not be an increase, but a decrease in the degree of ST segment elevation. In addition, some drugs, in particular praktolol, having a nonspecific effect, at the same time caused a decrease in the rise of the ST segment. All this certainly limits the possibility of using such a criterion as the magnitude of the ST segment rise in patients with acute myocardial infarction to assess the effect of drugs on the size of the infarct focus. However, in our studies, this is not about recovery, but about depression of the ST segment. Of course, ST segment depression can be non-specific in many conditions, including dynamic changes in the tone of the autonomic nervous system, electrolyte disturbances, cerebrovascular diseases, mitral valve prolapse, neurocirculatory dystonia, hyperventilation, orthostasis, and large meals the amount of carbohydrates, under the influence of temperature effects, emotional stress and when taking a number of drugs (for example, cardiac glycosides). These episodes of ST segment depression are usually prolonged with a gradual onset and gradual regression. Another thing is episodes of ST segment depression in patients with typical angina pectoris that occur during, less often immediately after dosed physical activity and are well reproduced. Typical ischemic depression of the ST segment is characterized by a horizontal or downward direction. After point j, it should be 1 mm or more. As the dosed physical activity increases, the magnitude of the ST segment depression usually increases. Most often, such depression is accompanied by a typical attack of angina pectoris. With an increase in physical activity, most often in parallel with an increase in depression of the ST segment, the severity of an angina attack increases, which requires a stop of the load. The cessation of physical activity leads to a relief of the attack (sometimes it is necessary to take a nitroglycerin tablet under the tongue) and to return the ST segment to its original state. Evidence that ST segment depression may be a marker of myocardial ischemia even in case of painless episodes in patients with coronary heart disease was obtained during Holter 24-hour ECG monitoring. Additional parallel studies with Holter ECX monitoring of patients with coronary heart disease showed the possibility of an asymptomatic change in the ST segment associated with hemodynamic disturbances in the left ventricle and with a regional decrease in myocardial perfusion according to myocardial scanning with thallium, as well as in positron emission tomography with rubidium. In addition, the onset of painless ST segment depression was preceded by a regional decrease in myocardial blood flow, judging by the data of continuous monitoring of the degree of oxygen saturation in the blood of the coronary sinus. Transient asymptomatic changes in the ST segment were associated with angiographically proven coronary vasospasm. Spontaneous changes in the ST segment for more than 60 s in patients with coronary heart disease occurred only with a decrease in coronary blood flow. Therefore, in patients with coronary heart disease, even in the absence of a typical pain attack, the presence of ST segment depression, especially during exercise, can certainly be considered as a marker of myocardial ischemia.