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"Child`s Health" 7 (58) 2014

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Dynamics of heart rate variability in children with systolic dysfunction under the influence of cardiac therapy

Authors: E. Akhnazariants - Public Institution “Institution of child and adolescence welfare of National Academy of Medical Sciences of Ukraine", Kharkov, Ukraine

Categories: Pediatrics/Neonatology

Sections: Specialist manual

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Keywords

heart rate variability, myocardial dysfunction, children, treatment.

Chronic heart failure (CHF) is one of the prognostically unfavorable complications in diseases of the cardiovascular system, leading to disability and reduced life expectancy [2-4, 7, 9]. In children and adolescents, as a rule, it develops on the background of congenital and acquired heart disease, primary and secondary cardiomyopathies, rhythm and conduction disorders, after an inflammatory disease of the myocardium [4, 6]. In this regard, the development of effective approaches to the treatment of early (before the onset of the clinical picture) stages of heart failure, i.e. stages of systolic myocardial dysfunction is of great medical and social importance [2-6, 8, 9].

One of the independent prognostic factors of heart disease is the current heart rate variability (HRV) - the severity of fluctuations in heart rate in relation to its average level. The response of the autonomic nervous system (ANS) is often a trigger factor for the development of arrhythmias in patients with myocardial pathology in [5, 7, 9, 14]. Many researchers believe that autonomic dysfunction precedes the development of certain forms of organ pathology, and early diagnosis and correction of this condition allows to prevent the development or slowing the progression of the pathological process [1-3, 5, 8, 9, 12, 13]. Thus, HRV, reflecting the degree of tension of regulatory systems, determine the prognosis of myocardial pathology, influence the choice of the optimal therapeutic strategy [2, 3, 5, 7, 9, 12, 13].

In accordance with current knowledge of the pathogenesis of heart failure this condition is considered primarily as a violation of neurohormonal mechanisms regulating blood flow ( which occurs in any disease of heart) , the initial element is the increased activity of the sympathetic division of the ANS. Activation of the sympathetic-adrenal system in the early stages is compensatory in nature but with the progression of the process, appears a whole set of maladaptive reactions with subsequent activation of the renin -angiotensin- aldosterone system.

Modern tactics of the patients with myocardial pathology (MP) provides an early appointment, even at the preclinical stage of development process - at the stage of myocardial dysfunction drugs of pathogenic therapy (angiotensin converting enzyme inhibitors - ACE inhibitors and β-blockers), but in pediatric patients also retained a tradition of destination cardiometabolic funds (L-carnitine, tiotriozolin, trimetazidine) [1, 4, 6, 9-11].

The aim of the research was to study the dynamics of changes in heart rate variability in children with myocardial pathology depending on the type of therapy.

Scope and methods

The study involved 84 children and adolescents of both genders aged 11-18 with systolic myocardial dysfunction (ejection fraction less than 55 %) in various diseases of the heart (dysplastic cardiomyopathy, arrhythmias and conduction, infarction), including 42 who received pathogenetic therapy within 3 months (ACE - enalapril) and 42 - means cardiometabolic actions (tiotriozolin, trimetazidine, L-carnitine) for 30-45 days repeated courses twice a year. Examination was carried out before treatment and 1 year later. Control group consisted of 27 healthy children of both sexes aged 11-18 with normal blood pressure, ejection function and adequate response to exercise. 

HRV assessment was carried out on the results of a bifunctional daily monitoring of ECG and blood pressure using the apparatus "ES-3N/AVR" with software «CARDIOSPY» company «LABTECH» (Hungary).

For analysis of the results we were guided by standards of measurement, physiological interpretation and clinical use of HRV developed by the Working Group of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology in 1996.

HRV measurement standards include methods for estimating the time and frequency domains. They complement each other and are only different mathematical methods of analysis of the same phenomenon. Methods for assessing the time domain reflect the severity of sinus arrhythmia and consist of statistical methods that characterize normal intervals (SDNN, SDANN, SDNNi, RMSSD), and geometric methods (HRVTI), describing the geometric model of HRV.

Statistical methods include the analysis of successive NN intervals and are calculated per night: SDNN (ms) - standard deviation of all NN analyzed intervals reflects the overall tone of the ANS; SDANN (ms) - the standard deviation of the average NN intervals in 5-minute intervals, characterized by the sympathetic tone ANS; SDNNi (ms) - average value of the standard deviation of NN intervals in 5-minute intervals, calculated for 24 hours; RMSSD (ms) - the square root of the mean squares of differences between adjacent NN intervals (estimate the degree of difference of two adjacent intervals NN) displays the tone of the parasympathetic division.

Geometric methods are relatively insensitive to the quality of the analytical series NN-intervals. They are based on the construction and analysis of histograms. Thus in our study was determined only triangular index (HRVTI, cu), which is the integral density distribution (the total number of NN intervals), divided by the maximum of the density distribution. This indicator reflects the overall HRV and depends more on the low-frequency components.

Various frequency components of heart rate for the day (d) and night (n) periods were studied from methods of frequency (or spectral) area: high-frequency oscillations (HF, ms2) - fluctuations in heart rate at a frequency of 0,15-0,4 Hz, which reflect fluctuations in the parasympathetic division of the ANS (a marker of vagal effect), low-frequency oscillations (LF, ms2) - part of the spectrum in the range of 0,04-0,15 Hz, which is characterized mainly by changes in sympathetic tone VNS , very low-frequency oscillations (VLF, ms2), representing 0,003-0,04 Hz frequency range, which reflect the humoral and cerebral metabolic ergotrop influence, the index of sympathovagal interaction (LF/HF, cu), which characterizes the balance of sympathetic and parasympathetic influences, total spectral power (TP, ms2) - reflects the total activity of the autonomic effects on heart rate .

Statistical analysis was performed using the software package SPSS Statistics 17.0.

Results and discussion

In the study of temporal parameters of HRV the results that were  obtained were significantly different in children with PM compared with controls.

Note: * - indicates statistical confidence  (p < 0,01) compared with the control group; ** - indicates statistical confidence  (p < 0,02) compared with the control group; *** - indicates statistical confidence  (p < 0,05) compared with the control group.

As it can be seen from Table. 1, initially in children with PM there is a tendency to increase temporal parameters, indicating that some activation of parasympathetic effects on heart rhythm.

In assessing the wave structure of the cardiac rhythm was found that , during the day there was a significant increase in the total power spectrum (p < 0,02) by increasing high-frequency component (p < 0,01) , indicating a strengthening of vagal effects on heart rhythm. Low had a tendency to increase this parameter (p < 0,1) is also due to the high frequency component (p < 0,05). These changes entailed a decline in sympathovagal index as a day (p < 0,1) and at night (p < 0,01). Therefore, children with the PM on the stages of the systolic myocardial dysfunction noted increased parasympathetic effects on heart rhythm, especially at night.

While studying the HRV under the influence of the therapy, without taking into consideration the complex, there was not observed significant dynamics in  the group as a whole.

However, when an individual analysis showed that in the group with baseline PM 44 % of children HRV was enhanced 31 % - normal and 25 % reduced.

While the dynamics of the observation of the group the content with increased HRV was due to conservation of initially high HRV, its increasing in children with normal and one child with low baseline HRV. While 60 % of children receiving pathogenetic therapy (ACE), the ejection fraction normalized and was 60-65 %, and in patients with metabolic complex the therapy it was noted only the tendency towards normalization (55 %).

Reduced HRV dynamics of observation occurred in 48 % of children, the bulk of which consisted of persons with initially low (46,1 %) HRV, but it also included children with normal (38,5 %) and high (15,4 % ) HRV. In this group both types of treatment were used, but ejection fraction normalized in only 30 % of patients, regardless of the therapeutic complex.

Patients with systolic myocardial dysfunction under the influence of pathogenetic therapy change of vegetative maintenance of cardiac rhythm is mainly due to the activation of the parasympathetic division, which is manifested a significant increase in RMSSD and total spectral power in the daytime due to the high-frequency component.

Note: * - indicates statistical confidence  (p < 0,05) in comparison with the value before treatment; ** - indicates statistical confidence  (p < 0,01) in comparison with the value before treatment; *** - indicates statistical confidence  (p < 0,001) in comparison with the value before treatment.

Increase in vagal influences is considered as an adaptive state with economical use of heart opportunities. This is confirmed by an increase in their ejection fraction during treatment and is a proof of the adequacy of a given therapy.

On metabolic therapy a reduction in overall autonomic tone (SDNN initially 186,00 ± 12,42 ms2 in the dynamics of 166,00 ± 11,42 ms2, p < 0,05) and total power spectrum of the day (TPD initially 43,10 ± 5,75 ms2 in dynamics 31,10 ± 3,91 ms2, p < 0,05) due to the high-frequency component (HF initially 12,80 ± 3,63 ms2 in dynamics 7,40 ± 1,85 ms2, p < 0,001), indicating that the decrease in activity of the parasympathetic division and activation of the sympathetic ANS.

Reduced HRV in patients with systolic myocardial dysfunction is an independent predictor of testifying about the progression of the process. In children and adolescents with pre-clinical stage heart failure, decreased HRV also shows the progression of myocardial dysfunction and inefficiency of the therapy, as evidenced by the dynamics of clinical manifestations.

In the primary study in children with clinical manifestations of the PM did not depend on the underlying disease, and were leading cardiac complaints (60 %) and complaints of headaches (75 %).

Cardiac complaints presented as a pain, a sense of disruption of the heart and shortness of breath. Cardialgia had a stinging character, were short-term, and did not depend on the type of load, stopped at rest or after taking sedatives and soft antispasmodics. Feeling of heart outages was noted at 23 % of children. The same group also registered a complaint on a feeling of incomplete inspiration (neurotic dyspnea) in 4% of those. Shortness of breath with little exertion was found in 16 % of patients, and they did not belong to the category of “unexercised” children. Cephalalgia in these children appeared by the end of school hours or in the evening did not depend on the nature of the loads and are often noted for their meteosensitivity, sometimes accompanied by dizziness (14 %). 22 % of surveyed complaints were absent. An objective examination attracted attention asthenic constitution, pale skin, blueness under eyes. The structure of complaints changed against the background of the therapy in both groups. In the group of patients receiving ACE inhibitors pathogenetic treatment decreased the number of complaints and cardialgia heartbeat, increased the number of patients without complaints (from 19,6 % to 28,3 %). In the group receiving metabolic therapy also decreased the number of children with complaints of palpitations and cardialgia, 28 % of children in general were asymptomatic.

Thus, in children with PM of any genesis initially there is an imbalance of VNS due to the predominance of parasympathicotonia. On the background of pathogenetic therapy with ACE inhibitors it was noted further increase of level of parasympathetic division activity, thereby increasing the FAR and provided with normalization of ejection fraction.

In the group of children receiving metabolic therapy during the treatment there is a change in autonomic balance towards activation of the sympathetic component which leads to lower FAR and a tendency to increase the ejection fraction. Influence increasing of sympathetic nervous system in these children may indicate stress adaptation mechanisms with subsequent progression of systolic dysfunction that requires a review of the complex therapy.

Conclusions

1. In 48 % of children with systolic myocardial dysfunction receiving pathogenetic therapy (ACE) in dynamics of the observation the increased activity of the parasympathetic division of the ANS is noted, which is accompanied by normalization of left ventricular ejection fraction of the heart.

2. 52 % of children with pathology infarction receiving metabolic therapy in dynamics of observation the increased activity of the sympathetic division of the ANS is found, accompanied by a trend toward normalization of ejection fraction.

3. Children with systolic myocardial dysfunction of any origin is necessary to hold pathogenetic therapy of ACE inhibitors in combination with cardio nutritional long courses drugs.


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