Left ventricular diastolic function in children with secondary cardiomyopathies

The structure of cardiac pathology has undergone significant changes in the last decades of the last century. In Ukraine, there is a persistent tendency towards an increase in cardiovascular morbidity of non-rheumatic origin, including secondary cardiomyopathies (SCM). Their prevalence increased from 15.6% in 1994 to 27.79% in 2004.

According to the recommendations of the working group of WHO, the International Society and Federation of Cardiologists (1995), cardiomyopathies are myocardial diseases associated with dysfunction. Over the past 15 years, many studies have been conducted to clarify the pathways of myocardial dysfunction and damage, new research methods have been introduced. All this has created the conditions for revising the classification of cardiomyopathy. Thus, in 2004, Italian scientists expressed the opinion that the term "cardiac dysfunction" should cover not only a decrease in myocardial contractility and diastolic dysfunction, but also rhythm and conduction system disorders, and a state of increased arrhythmogenicity. In 2006, the American Heart Association proposed to consider cardiomyopathies as "a heterogeneous group of myocardial diseases that are associated with mechanical and/or electrical dysfunction, usually manifested by inappropriate hypertrophy or dilation of the heart planes, and arise as a result of various factors, primarily genetic. Cardiomyopathy may be limited to cardiac involvement or be part of generalized systemic disorders that lead to progressive heart failure or cardiovascular death."

One of the main manifestations of secondary cardiomyopathies is repolarization process disturbances on the ECG. The opinions on their interpretation in the literature are ambiguous and contradictory. For example, until recently it was believed that the syndrome of early ventricular repolarization (SVR) is a normal variant. However, according to many authors, SVR can be a marker of pathological conditions occurring in the myocardium.

Stable rhythm and conduction disturbances in patients with cardiac pathology in the presence of SRRV occur 2-4 times more often and can be accompanied by paroxysms of supraventricular tachycardia. In an electrophysiological study, paroxysmal supraventricular rhythm disturbances are induced in 37.9% of practically healthy individuals with SRRV.

Already in the experimental works of E. Sonnenblick, E. Braunwald, F. Z. Meerson the joint contribution of systolic and diastolic dysfunctions to the development of heart failure was proven, but later the prevailing role of systolic dysfunction in the development of heart failure was revised. It is known that a decrease in contractility and a small ejection fraction of the left ventricle (LV) do not always determine the degree of decompensation, tolerance to physical activity and prognosis in patients with cardiovascular pathology.

It has now been proven that disturbances in the diastolic properties of the myocardium usually precede a decrease in the pumping function of the LV and can, in isolation, lead to the appearance of signs and symptoms of chronic heart failure in adults with cardiac pathology.

Considering that a number of cardiovascular diseases begin in childhood, the study of the diastolic function of the myocardium in children with the most common pathology - secondary cardiomyopathy - is an important task. At the same time, in the scientific literature there are only a few publications characterizing the relaxation properties of the myocardium in children with secondary cardiomyopathy.

The aim of our study was to improve the early diagnosis of complications of secondary cardiomyopathy in children based on the determination of LV diastolic function disorders.

To assess the functional state of the cardiovascular system in patients with secondary cardiomyopathy, 65 children (46 boys and 19 girls, average age 14.9±0.3 years) were examined. Most often, secondary cardiomyopathies were detected against the background of autonomic dysfunction - in 44.62±6.2% of children, endocrine pathology - in 26.15±5.5%, chronic kidney disease of the 1st degree - in 18.46±4.9% of children. One of the criteria for inclusion in the examination group was impaired ventricular myocardial repolarization on the ECG.

The first group (40 children, 22 boys and 18 girls, average age 14.8±0.4 years) included children with non-specific repolarization process disorders (NRP) on the ECG in the form of a decrease in the amplitude and inversion of the T wave, depression and elevation of the ST segment relative to the isoline by 2 mm or more, prolongation of the QT interval by 0.05 s or more in accordance with the heart rate. The second group (25 children, 24 boys and 1 girl, average age 15.1+0.4 years) consisted of patients with SRRS on the ECG.

Among children of the 1st group, NPD were most often recorded against the background of autonomic dysfunction (45.0±8.0%) and metabolic shifts (35.0±7.6%), in particular against the background of type 1 diabetes mellitus (15.0±5.7%). Among patients of the 2nd group, children with manifestations of autonomic dysfunction predominated (44.0+10.1%), in 20.0±8.2% of those examined, NPD was recorded against the background of undifferentiated connective tissue dysplasia and chronic kidney disease of the 1st degree.

Determination of diastolic function of the heart was carried out on the basis of parameters of transmitral flow during pulsed-wave Doppler echocardiographic examination on the ultrasound device "AU3Partner" of the company "Esaote Biomedica" (Italy). The inclusion criteria in the study were the absence of mitral regurgitation, mitral valve stenosis (as factors changing the diastolic function of the LV) or tachycardia more than 110-120 beats/min in children.

To assess the LV diastolic function, the following parameters were measured: maximum flow velocity in the early diastolic filling phase of the LV (E, m/s), flow velocity in the late diastolic filling phase of the LV during atrial systole (A, m/s), flow velocity acceleration time in the early diastolic filling phase of the LV (ATE, s), flow velocity deceleration time in the early diastolic filling phase (DTe, s), and LV isovolumetric relaxation time (IVRT, s). Based on the obtained values of the velocity and time indices of the transmitral flow, the following were calculated: the ratio of velocities in the early and late diastolic filling phases of the LV (E/A), and the myocardial compliance index (MCI). MCI is the ratio of the time to reach the maximum flow velocity and the time to half the flow velocity reduction in the early diastolic filling phase (ATe/DTe/2). According to M. Johnson, IPM allows one to evaluate diastolic myocardial stiffness regardless of the heart rate.

The data obtained during the examination of a control group of 20 practically healthy children who had no cardiac complaints or organic heart diseases, and whose systolic function indicators did not differ from the normative ones, were taken as the normative indicators of diastolic function of the heart.

When analyzing the transmitral flow parameters, 78.1 ± 7.2% of the examined children of the 1st group with non-specific NPDs had diastolic dysfunction of the LV. Among the children of the 2nd group with SRRD, diastolic dysfunction of the LV was recorded in 65.0 ± 11.6% of patients. The high frequency of diastolic function disorders in the examined patients may be due to metabolic disorders in the myocardium in children with type 1 diabetes mellitus or manifestations of hypersympathicotonia in patients with autonomic dysfunction.

We have identified restrictive and pseudonormal types of LV diastolic dysfunction (Figure). No significant differences in the type of LV diastolic dysfunction were found in children of groups 1 and 2. However, it should be noted that the most unfavorable restrictive type of LV diastolic dysfunction was more often detected among children of group 1 and was accompanied by a decrease in the contractile function of the heart (50.0% of those examined, p < 0.05); moderate hypertrophy of the LV wall (75.0% of those examined, p < 0.05), which could indicate the duration or strength of the pathological process.

Pseudonormal type of LV diastolic dysfunction was more often observed in children with chronic somatic pathology (diabetes mellitus type 1, hypothalamic syndrome of puberty, dysmetabolic nephropathy). LV diastolic dysfunction at the stage of pseudonormalization of the transmitral spectrum manifests itself due to the increasing stiffness of the LV myocardium and disturbances of its relaxation, which is confirmed by the reliability of differences between the integral indicators of diastolic function.

The high percentage of LV diastolic dysfunction (65.0+11.6%) among children in group 2 with manifestations of LV diastolic dysfunction on ECG does not allow us to consider it, as previously believed, as a normal variant.

In both groups of examined children, a reliable decrease in the rate of early and late filling of the LV is revealed compared to similar indicators in children of the control group (p < 0.05 and p < 0.01, respectively). A reliable increase in the acceleration time of the diastolic flow of early filling is also noted among children of the 2nd group (0.107±0.005 s, p < 0.05) compared to the indicators of children of the 1st group and the control group.

When analyzing the IPM, its reliable decrease was revealed (IPM = 0.935±0.097, with a norm of 1.24±0.14, /> < 0.05) in 14.3% of patients in the 1st group and in 8.7% of patients in the 2nd group, which indicates a violation of the elastic properties of the myocardium. A decrease in this indicator was mainly observed in children who are professionally involved in sports sections and receive long-term physical exercise.

Thus, disturbances of repolarization processes, both nonspecific and SRRF, cannot be considered a harmless ECG phenomenon. Diastolic dysfunction of the LV is manifested in 75.0±6.06% of the examined children, in particular in 78.1±7.2% of children in group 1 and in 65.0±11.6% of children in group 2. Registration of pseudonormal and restrictive spectra of LV transmitral flow indicates pronounced disturbances of diastolic properties of the myocardium with possible further development of heart failure in patients with secondary cardiomyopathies.

I. A. Sanin. Diastolic function of the left ventricle in children with secondary cardiomyopathies // International Medical Journal No. 4 2012

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