Lecture: Analysis of heart rate variability Mr. A.P. Kulaichev. Computer electrophysiology and functional diagnostics. Ed. 4th, rev. and add. – M .: INFRA-M, 2007, p.
The analysis of heart rate variability (HRV) is a rapidly developing section of cardiology, in which the capabilities of computational methods are most fully realized. This direction was largely initiated by the pioneering work of the famous Russian researcher R.M. Baevsky  in the field of space medicine, who first put into practice a number of complex indicators characterizing the functioning of various regulatory systems of the body.
The heart is ideally able to respond to the slightest changes in the needs of numerous organs and systems. A variational analysis of the heart rhythm enables a quantitative and differentiated assessment of the degree of tension or tone of the sympathetic and parasympathetic divisions of the ANS, their interaction in various functional states, as well as the activities of the subsystems that control the work of various organs.
HRV methods are not intended for the diagnosis of clinical pathologies, where, as we saw above, traditional means of visual and measuring analysis work well. The advantage of this section is the ability to detect the most subtle deviations in cardiac activity, therefore, its methods are especially effective for assessing the general functional capabilities of the body in the norm, as well as early deviations, which, in the absence of the necessary preventive procedures, can gradually develop into serious diseases.
The initial material for the analysis of HRV is short single-channel ECG recordings (from two to several tens of minutes), performed in a calm, relaxed state or with functional tests. At the first stage, sequential cardiointervals (CIs) are calculated from such a record, and R-teeth are used as the reference (boundary) points of them, as the most pronounced and stable ECG components.
HRV analysis methods are usually grouped into the following four main sections:
- variational pulsometry;
- spectral analysis;
- correlation rhythmography.
Other methods. For the analysis of HRV, a number of less commonly used methods are also involved in constructing three-dimensional scattergrams, differential histograms, calculating autocorrelation functions, triangulation interpolation, and calculating the St. George index . In the evaluation and diagnostic plans, these methods can be characterized as scientific-search, and they practically do not bring fundamentally new information.
Holter monitoring Long-term monitoring of the ECG according to Holter involves many hours or many hours of single-channel continuous recording of the ECG of a patient who is in his usual life conditions. Recording is carried out by a portable wearable recorder on a magnetic medium. Due to the long time period, the subsequent study of ECG recordings is carried out by computational methods.
Intervalography This section mainly uses methods of visual analysis of graphs of changes in sequential KI (intervalogram or rhythmogram). This allows you to assess the severity of various rhythms (primarily respiratory rhythm, see Fig. 6.11) to identify violations of the variability of CI (see Fig. 6.16, 6.18, 6.
Fig. 6.11. Intervalogram of deep breathing
Fig. 6.16. Fibrillation intervalogram
Fig. 6.19. Intervalogram of a patient with normal health, but with obvious violations in HRV
The intervalogram allows you to identify important individual features of the action of regulatory mechanisms in reactions to physiological tests. As an illustrative example, consider the opposite types of reactions to a breath-holding test. Fig. 6.22 shows the reaction of accelerating heart rate during breath holding.
However, in the test subject (Fig. 6.22, a) after the initial sharp decline, stabilization occurs with a tendency to a certain lengthening of the CI, while in the test subject (Fig. 6.22, b) the initial sharp decline continues with a slower shortening of the CI, with variability being manifested CI with a discrete nature of their alternation (which for this subject was not manifested in a state of relaxation). Figure 6
Fig. 6.23. Intervalograms for breath holding samples with prolongation of KI
Variational pulsometry In this section, descriptive statistics are mainly used to assess the distribution of CI with histogram construction, as well as a number of derived indicators characterizing the functioning of various regulatory systems of the body, and special international indices.
Bar chart. Recall that a histogram is a graph of the probability density of a sample distribution. In this case, the height of a particular column expresses the percentage of cardio intervals in the ECG record of a given range of duration. The horizontal scale of the duration of the KI for this is divided into successive intervals of equal magnitude (bins). For comparability of histograms, the international standard sets the bin size to 50 ms.
Normal cardiac activity is characterized by a symmetrical, dome-shaped and solid histogram (Fig. 6.24). During relaxation with shallow breathing, the histogram narrows, while deepening the breathing, it broadens. If there are omissions of contractions or extrasystoles, separate fragments appear on the histogram (respectively, to the right or left of the main peak, Fig. 6.25).
The asymmetric shape of the histogram indicates the arrhythmic nature of the ECG. An example of such a histogram is shown in Fig. 6.26, a. To find out the reasons for this asymmetry, it is useful to refer to the intervalogram (Fig. 6.26, b), which in this case shows that the asymmetry is determined not by pathological arrhythmia, but by the presence of several episodes of a change in normal rhythm, which can be caused by emotional causes or changes in depth and respiratory rate.
Fig. 6.24. Symmetric Bar Graph
a is a histogram; b – intervalogram
Indicators. In addition to the histographic representation, variational pulsometry also computes a number of numerical estimates: descriptive statistics, Baevsky indicators, Kaplan indices, and a number of others.
Indicators of descriptive statistics additionally characterize the distribution of CI:
- sample size N;
- variation range dRR – difference between honey maximum and minimum KI;
- the average value of RRNN (the norm in terms of heart rate is: 64 ± 2,6 for ages 19–26 years and 74 ± 4,1 for ages 31–49 years);
- SDNN standard deviation (norm 91 ± 29);
- coefficient of variation CV = SDNN/RRNN * 100%;
- asymmetry and excess coefficients characterizing the symmetry of the histogram and the severity of its central peak;
- Mo mode or CI value, halving the entire sample, with a symmetric distribution, the mode is close to the average value;
- AMo mode amplitude is the percentage of CI falling into the modal bin.
- RMSSD – the square root of the average sum of squares of the differences of the neighboring CIs (practically coincides with the standard deviation SDSD, norm 33 ± 17), has stable statistical properties, which is especially important for short records;
- pNN50 – the percentage of neighboring cardio intervals that differ from each other by more than 50 ms (norm 7 ± 2%) will also change little depending on the length of the recording.
The indicators dRR, RRNN, SDNN, Mo are expressed in ms. The most significant is AMo, which is distinguished by its resistance to artifacts and sensitivity to changes in the functional state. Normally, in people under 25 years old, AMo does not exceed 40%, with age it increases by 1% every 5 years, exceeding 50% is regarded as a pathology.
Indicators R.M. Baevsky:
- the index of autonomic equilibrium IVR = AMo/dRR indicates the relationship between the activity of the sympathetic and parasympathetic divisions of the ANS;
- vegetative rhythm indicator PPR = 1/(Mo * dRR) allows you to judge the vegetative balance of the body;
- the indicator of the adequacy of the regulatory processes PAPR = AMo/Mo reflects the correspondence between the activity of the sipathic part of the ANS and the leading level of the sinus node;
- voltage index of regulatory systems IN = AMo/(2 * dRR * Mo) reflects the degree of centralization of heart rate control.
The most significant in practice is the IN index, which adequately reflects the total effect of cardiac regulation. The limits of the norm are: 62,3 ± 39,1 for ages 19–26 years. The indicator is sensitive to increased tone of the sympathetic ANS, a small load (physical or emotional) increases it by 1,5-2 times, with significant loads, the growth is 5-10 times.
Methods for determination
A cardiological study of heart contractions determined the best methods of HRV, their characteristics in various conditions.
The analysis is carried out on the study of the sequence of intervals:
- RR (electrocardiogram abbreviations);
- NN (intervals between normal contractions).
Statistical methods. These methods are based on obtaining and comparing the “NN” gaps with the assessment of variability. The cardiointervalogram obtained after the examination shows a set of “RR” intervals repeating one after another.
Indicators of these gaps include:
- SDNNs reflect the sum of HRV indices at which deviations of NN intervals and variability of RR intervals are highlighted;
- RMSSD sequence comparison of NN intervals;
- PNN5O shows the percentage of NN gaps that differ by greater than 50 milliseconds over the entire study period;
- CV score for magnitude variability.
Geometric methods are distinguished by obtaining a histogram that shows cardio intervals with different durations.
These methods calculate the variability of the heart rate using certain values:
- Mo (Fashion) refers to cardio intervals;
- Amo (Fashion Amplitude) – the number of cardio intervals that are proportional to Mo as a percentage of the selected volume;
- VAR (variational range) is the ratio of the degree between cardio intervals.
Autocorrelation analysis evaluates heart rate as a random development. This is a dynamic correlation graph obtained by gradually shifting by one unit of a dynamic series in relation to its own.
This qualitative analysis allows us to study the influence of the central link on the heart and determine the latency of the periodicity of the heart rhythm.
Correlation rhythmography (scatterography). The essence of the method is to display the following cardio intervals in a graphical two-dimensional plane.
During the construction of the scatterogamma, a bisector is distinguished, in the center of which there is a set of points. If the points are deflected to the left, you can see how much the cycle is shorter, an offset to the right shows how much longer the previous one.
The region corresponding to the deviation of NN intervals is highlighted on the obtained rhythmogram. The method allows to identify the active work of the autonomic system and its subsequent effect on the heart.
HRV research methods
International medical standards define two methods for studying heart rate:
- Registration record of “RR” intervals – for 5 minutes is used to quickly assess HRV and conduct certain medical tests;
- Daily recording of “RR” intervals – more accurately assesses the rhythms of the vegetative registration of “RR” intervals. However, when decoding the record, many indicators are evaluated by the five-minute interval of HRV registration, since segments are formed on the long record that interfere with the spectral analysis.
To determine the high-frequency component in the heart rhythm, a recording of about 60 seconds is needed, and for the analysis of the low-frequency component, 120 seconds of recording are required. For a correct assessment of the low-frequency component, a five-minute recording is required, which is chosen for the standard HRV study.
HRV of a healthy body
Variability of the middle rhythm in healthy people makes it possible to determine their physical endurance according to age, gender, time of day.
For each person, HRV indicators are individual. Women have a more active heart rate. In childhood and adolescence, the highest HRV is observed. High- and low-frequency components decrease with age.
The effect on HRV is the weight of a person. Reduced body weight provokes the power of the HRV spectrum, in obese people the opposite effect is observed.
Sport and light physical exertion have a beneficial effect on HRV: the power of the spectrum increases, heart rate becomes less frequent. Excessive loads, on the contrary, increase the frequency of contractions and reduce HRV. This explains the frequent sudden deaths among athletes.
Using methods for determining heart rate variation allows you to control your workout, gradually increasing the load.
If HRV is reduced
· Coronary and hypertensive diseases;
· Taking some drugs;
HRV studies in medical activities are simple and affordable methods that evaluate the autonomic regulation in adults and children with a number of diseases.
· Assess the visceral regulation of the heart;
· Determine the overall work of the body;
· Assess the level of stress and physical activity;
· Monitor the effectiveness of drug therapy;
· Diagnose the disease at the initial stage;
· Helps to choose an approach to the treatment of cardiovascular diseases.
Therefore, when examining the body, do not neglect the methods of research of heart contractions. HRV indicators help determine the severity of the disease and choose the right treatment.
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