The state of the left heart chambers in patients with type 2 diabetes mellitus combined with arterial hypertension

The dissertation is devoted to the study of the structural and functional state of the left heart chambers in patients with type 2 diabetes mellitus in combination with arterial hypertension. The work aims to assess morphofunctional changes of the left ventricular myocardium, as well as to analyze heart rate variability and the character of rhythm and conduction disturbances in this category of patients. Particular attention is paid to the capabilities of tissue Doppler imaging in the early diagnosis of subclinical myocardial dysfunction.

The study compares the identified changes in patients with normal and elevated arterial pressure, which makes it possible to evaluate the mutual influence of diabetes mellitus and arterial hypertension on the cardiovascular system. The obtained data are of importance for optimizing the prevention of chronic heart failure and cardiovascular complications in patients with type 2 diabetes mellitus.

According to WHO data (2002), cardiovascular diseases account for no less than half of human mortality. A substantial contribution to this structure is made by diabetes mellitus (DM), the prevalence of which in developed countries among the adult population tends to double every 15 years. It is recognized that 85% of patients with diabetes identified in various countries have type 2 DM, which thus continues to be one of the major problems of clinical medicine in the 21st century.

Numerous experimental, pathomorphological, epidemiological, and clinical studies indicate that DM leads to functional, biochemical, and morphological changes of the heart even when arterial hypertension (AH), coronary heart disease (CHD), and any other known cardiovascular diseases are absent (Kannel W.B. et al., 1974; Regan T.J. et al., 1977; Galderisi M. et al., 1991; Devereux R.B. et al., 2000). It can be stated that there is real evidence for the possibility of forming an independent form of cardiac damage directly associated with the presence of DM, now termed diabetic cardiomyopathy (Rubler S. et al., 1972).

It should be noted that, despite the numerous publications addressing the structural and functional state of the left heart chambers in patients with DM, certain aspects of the problem under consideration remain unresolved or require clarification. Thus, there is no unanimous opinion regarding the state of systolic and diastolic myocardial function in patients with DM. Some authors believe that the contractile capacity and diastolic compliance of the left ventricular (LV) myocardium deteriorate only with a prolonged course of the disease (Hiramatsu K. et al., 1992; Annonu A.K. et al., 2001).

Other researchers consider that myocardial changes can be detected already in its early phases (Beljic T. et al., 1994; Gough S.C. et al., 1995; Pitale S.U. et al., 2000; Poirier P. et al., 2001). The timely detection of early myocardial changes can be facilitated by tissue Doppler imaging (TDI), a new method of non-invasive evaluation of myocardial function.

It is known that the state of autonomic regulation significantly affects cardiac function. The most informative and accessible method for assessing the influence of the autonomic nervous system on the myocardium is recognized as the study of heart rate variability (HRV). However, despite the fact that an imbalance is found in patients with DM, the obtained results concerning HRV are highly heterogeneous: the issues of the sequence of HRV changes, its dependence on disease duration, as well as on the state of compensation of metabolic disturbances and structural and functional cardiac changes remain insufficiently resolved. In addition, current literature data on the nature and frequency of various cardiac rhythm disturbances in patients with DM are also insufficient.

It has been established that the high risk of cardiovascular complications in DM is associated with AH (Hayden M. et al., 1999), the detection rate of which in the diabetic population is 50–80% (Epstein M., 1997; The Guidelines Subcommittee of the WHO/ISH Mild Hypertension Liaison Committee, 1993; Reaven G.V., 1985). Cardiovascular mortality in DM with concomitant AH is 8 times higher than against a background of normal arterial pressure (BP) (Kannel W.B. et al., 1974). These factors determine the relevance of studying the state of the cardiovascular system in the combination of DM with AH.

These considerations provided the basis for undertaking the present study.

Aim of the study: to investigate the structural and functional state of LV myocardium in patients with type 2 DM against the background of AH.

Objectives:

1. To evaluate structural and functional changes of LV myocardium in patients with type 2 DM with normal and elevated arterial pressure.

2. To study the frequency and character of rhythm and conduction disturbances, as well as heart rate variability, in patients with DM with normal BP as well as with concomitant AH.

3. To clarify the relationship between heart rate variability and structural and functional changes of LV myocardium in patients with type 2 DM with normal BP and in those with AH.

Scientific novelty:

1. It has been shown that in patients with DM without concomitant CHD and AH, the use of TDI makes it possible to detect signs of subclinical systolic and diastolic dysfunction caused by damage to the longitudinal myocardial fibers of the LV.

2. The combination of DM with AH leads to a more pronounced impairment of LV systolic and diastolic functions in both longitudinal and radial directions.

3. The combination of DM with AH is accompanied by disturbance of cardiac autonomic control: a decrease in sympathetic and parasympathetic modulations of sinus node activity and the presence of such cardiac rhythm disturbances as high-grade ventricular premature beats, paroxysmal atrial fibrillation, as well as transient first- and second-degree atrioventricular block.

Practical recommendations:

1. For the early diagnosis of cardiac damage in patients with DM, echocardiographic examination is recommended, including, when possible, tissue Doppler imaging.

2. The use of TDI as a diagnostic test for the subclinical stage of diabetic cardiomyopathy makes it possible to identify patients at increased risk of developing chronic heart failure before the development of global LV dysfunction and/or the appearance of its symptoms, and to optimize the prevention of cardiovascular complications of DM.

3. The identified structural and functional LV changes combined with significant rhythm disturbances in patients with DM against the background of AH substantiate the need for early preventive measures, including both non-pharmacological and pharmacological interventions.