Functional State of the Myocardium and Its Geometric Model in Adolescents with Arterial Hypertension

The dissertation is devoted to the study of the functional state and geometric model of the myocardium of the left ventricle in adolescents with arterial hypertension. In the work, using echocardiographic methods, systolic and diastolic functions of the left ventricle are evaluated, morphometric dimensions of the cavity are measured, and parameters of myocardial remodeling are determined. The characteristics of the circadian profile of blood pressure in adolescents at various degrees of severity of hypertension and different variants of the geometric model of the left ventricle are investigated, and the relationship between echocardiographic and electrocardiographic data is established. The results obtained allow for the refinement of diagnostic criteria and the justification of the advisability of including additional parameters in the standard echocardiographic examination of adolescents with arterial hypertension.

RELEVANCE OF THE PROBLEM

The results of scientific research and practical medicine over the past decades present an increasing amount of data on the extraordinarily early onset of hypertension, pertaining to childhood and adolescent age [2, 138, 149]. The World Health Organization, in its Atlas of Heart Disease and Stroke (2004), pointed out that "high blood pressure (BP) is one of the most important preventable causes of premature death worldwide" [46]. Among diseases of the cardiovascular system, which occupy the leading place in the structure of causes of mortality, arterial hypertension (AH) holds a special place not only due to its high prevalence. It substantially affects the state of health, duration, and quality of life of patients, as it is the principal factor in the development of cardiovascular complications: ischemic heart disease, atherosclerosis, vascular catastrophes, and heart insufficiency [19]. Having begun as a functional disturbance, AH leads to organic impairments and the death of the patient [12]. The heart, brain, and kidneys participate in the pathogenesis of AH and simultaneously serve as the target organ [86]. The majority of patients with AH have a low quality of life, which is associated with the severity of the somatic disease exerting a pronounced influence on their psychological and social spheres of life [63].

The pediatric aspect of arterial hypertension presents a real epidemiological and clinical problem [75]. The detection, treatment, and prevention of AH specifically in childhood are more effective compared with the adult contingent of patients. Although AH is quite easily detected among the adult population, diagnosing it at early, often asymptomatic stages can be difficult [6, 47, 118]. Special difficulties arise during the differential diagnosis of neurocirculatory dystonia presenting with a hypertensive type and hypertension stage I in adolescents [53, 57, 122, 142]. In these diseases, the degree of fitness for military service, the possibility of referral to labor associations, and admission to educational institutions differ substantially [2].

Research of recent years has demonstrated that changes in functional and structural-geometric indicators of the left ventricle closely correlate with the severity of clinical manifestations [43]. The link between the presence of left ventricular hypertrophy and the increase in cardiovascular risk has been clearly proven. It has been shown that a decrease in the degree of left ventricular hypertrophy leads to a whole range of favorable consequences, the result of which is an improvement in the patient's prognosis, and vice versa. Finally, it has been established that certain classes of antihypertensive drugs can contribute to the regression of left ventricular hypertrophy [27, 92].

The association of left ventricular hypertrophy with a high risk of cardiovascular complications is explained by several mechanisms. First and foremost — the ability of hypertrophy to impair the filling of the heart with blood during diastole, leading to the development of congestive heart failure.

Given that the influence of left ventricular hypertrophy on the prognosis is more significant at a young age [39], the investigation of the geometric model and functional capabilities of filling and relaxation of the left ventricle in adolescents with arterial hypertension is of interest.

OBJECTIVE OF THE INVESTIGATION: To assess the state of systolic and diastolic functions of the left ventricle, morphometric dimensions of the cavity, and the geometric model of the left ventricle in adolescents with arterial hypertension.

TASKS OF THE INVESTIGATION:

1. To investigate the characteristics of the circadian profile of blood pressure in adolescents at various degrees of severity of arterial hypertension and different geometric models of the left ventricle.

2. To conduct an analysis of the state of diastolic function of the left ventricle, morphometric dimensions of the left ventricular cavity, and its contractile capacity depending on age, sex, and degree of severity of arterial hypertension.

3. To assess the geometric model of the myocardium of the left ventricle in adolescents suffering from arterial hypertension and to identify the frequency of occurrence of various types of remodeling.

4. To establish the relationship between electrocardiographic data and the results of echocardiographic investigation.

SCIENTIFIC NOVELTY: For the first time in adolescents with arterial hypertension, echocardiographic assessment of diastolic and systolic functions of the left ventricle with calculation of its dimensions and volumes has been conducted, and functional and morphometric changes of the heart have been determined.

For the first time in adolescents, indicators of left ventricular geometry have been analyzed and variants of remodeling encountered against the background of arterial hypertension have been identified, and the relationship between parameters of geometry and diastolic function of the myocardium of the left ventricle has been established.

For the first time, the characteristics of the circadian profile of blood pressure in adolescents at various degrees of severity of arterial hypertension and different geometric models of the left ventricle have been investigated.

A reliable association of echocardiographic indicators of the left heart chambers with the Cornell voltage criterion for left ventricular hypertrophy has been obtained.

PRACTICAL SIGNIFICANCE: On the basis of the results of the conducted investigation, the frequency of occurrence of risk factors of arterial hypertension and concomitant pathology among adolescents with arterial hypertension has been determined.

The results of the work have demonstrated the advisability of including the following parameters in the standard echocardiographic investigation in adolescents with arterial hypertension: calculation of the mass of the myocardium of the left ventricle, the mass of the myocardium indexed to body surface area, and myocardial stress at the meridian in systole. For patients with excess body weight, it is advisable to index the mass of the myocardium of the left ventricle to height raised to the power of 2.7.

On the basis of the conducted investigation, echocardiographic features distinguishing the state of the myocardium of the left ventricle in patients with labile arterial hypertension from stable forms of hypertension have been determined.

The advisability of using the Cornell voltage criterion as an electrocardiographic sign for the diagnosis of left ventricular hypertrophy has been confirmed.

POSITIONS SUBMITTED FOR DEFENSE:

1. Changes in the state and morphometry of the myocardium of the left ventricle in adolescents suffering from arterial hypertension include an increase in the mass of the myocardium of the left ventricle, its dilation, a change in the size and geometry of the walls of the left ventricle, and the appearance of a tendency toward impairment of active diastolic relaxation and diastolic filling.

2. Echocardiographic indicators of systolic and diastolic functions of the left ventricle have distinctive features at various degrees of arterial hypertension, which can be used as diagnostic criteria.

3. The overwhelming majority of adolescents with arterial hypertension have a normal geometric model of the left ventricle. The process of myocardial remodeling occurs in 26.1% of adolescents against the background of arterial hypertension. The most common variant is concentric remodeling.

PRESENTATION AND IMPLEMENTATION OF THE RESULTS:

The materials of the investigation were reported at a scientific session of students and young scientists of SGMU (Arkhangelsk, 2003); at the conference "Actual Problems of Modern Rheumatology and Cardiology" (Volgograd, 2004); at the VI All-Russian Symposium "Diagnosis and Treatment of Disorders of Rhythm and Conduction of the Heart in Children" (St. Petersburg, 2004); at a scientific session of students and young scientists of SGMU (Arkhangelsk, 2004); at the regional conference of young scientists dedicated to the 293rd anniversary of the birth of M.V. Lomonosov (Arkhangelsk, 2004); at the regional scientific-practical conference of pediatricians of the Arkhangelsk Region (Arkhangelsk, 2005); at a scientific session of students and young scientists of SGMU (Arkhangelsk, 2005); at the VI All-Russian seminar of pediatric cardiologists in memory of Professor N.A. Belokon' (Tomsk, 2005); at the VII International Slavic Congress "Cardiostim" (St. Petersburg, 2006); at the II All-Russian scientific-practical conference "Arterial Hypertension in the Practice of a Therapist, Neurologist, Endocrinologist, and Cardiologist" (Moscow, 2006).

Based on the dissertation, 12 printed works have been published, including the development of methodological recommendations for physicians titled "Echocardiographic Parameters of Remodeling of the Left Ventricle in Adolescents with Arterial Hypertension." The results of the investigation have been implemented in the work of MUZ "Children's Polyclinic No. 1" and MUZ "City Polyclinic No. 2" (implementation act dated 15.02.2006), as well as in the educational process at the pediatric faculty and the Faculty of Advanced Training and Retraining of Physicians at Northern State Medical University (implementation act dated 15.02.2006).

The work was carried out within the framework of the NIR "Health of the Population of the European North" (state registration number 01200500222).

STRUCTURE AND SCOPE OF THE WORK: The dissertation is presented on 134 pages of typed text and consists of an introduction, 7 chapters (literature review, objects and methods of investigation, results of investigation), discussion of the results of investigation, conclusion, conclusions, practical recommendations, and a list of references. The work is illustrated with 20 tables and 19 figures. The list of references includes 100 works by domestic and 55 by foreign authors.