It is a prospective, controlled, single-center, non-randomized, observational study.

From September 2019 to December 2020, the study plans to prospectively include 400 patients aged 18 to 90 years.

The goal of study is reveal single parameters of the electrocardiogram, which a good correlation with left ventricular diastolic dysfunction (LV DD), discovered during echocardiography.

Investigators plan to assess the diagnostic effectiveness of the spectral analysis of electrocardiograms obtained using a single-lead portable ECG monitor.

All subjects will undergo an echocardiographic examination of the heart with a determination of diastolic dysfunction of the left ventricle and will be divided into 2 main groups: with diastolic dysfunction of the left ventricle, confirmed by the results of the echocardiography and without.

At the same time, for all patients single-lead ECG will be recorded (in turn of leads I) for 3 minutes with further spectral analysis of the data obtained.

A single-lead ECG monitor CardioQvark is designed as an iPhone cover. It is registered with the Federal Service for Health Supervision on February 15, 2019. RZN No. 2019/8124.

Then a spectral analysis of the electrocardiogram will be performed using a continuous wavelet transform, the principles of which are based on the Fourier transform.

The analysis implies an assessment of the following parameters (the parameters listed below will be calculated as the median of the tact-cycle):

• TpTe - time from peak to end of the T-wave
• VAT - time from the beginning of the QRS to the R-peak
• QTc - corrected QT interval.
• QT / TQ - the ratio of QT length to TQ length (from the end of T to the beginning of the QRS of the next complex).
• QRS_E - the total energy of the QRS wave based on the wavelet transform
• T_E - T-wave total energy based on wavelet transform
• TP_E- energy of the main tooth of the T-wave based on the wavelet transform
• BETA, BETA_S - T-wave asymmetry coefficients (simple and smooth versions)
• BAD_T - flag of T-wave quality (whether expressed in the current lead
• QRS_D1_ons - energy of the leading edge of the R-wave (based on the "first derivative" wavelet transform)
• QRS_D1_offs - energy of the trailing edge of the R-wave (based on the "first derivative" wavelet transform)
• QRS_D2 - peak energy of the R-wave (based on the "second derivative" wavelet transform)
• QRS_Ei (i = 1,2,3,4) - QRS-wave energy in 4 frequency ranges (2-4-8-16-32 Hz) based on wavelet transform
• T_Ei (i = 1,2,3,4) - T-wave energy in 4 frequency ranges (2-4-6-8-10 Hz) based on wavelet transform
• HFQRS - the amplitude of the RF components of the QRS wave

Additionally used parameters:

• TpTe, VAT, QTc - are duplicated to control the correctness of the record processing (the value of the UCC should be approximately equal to the median of the tick-by-bar).
• QRSw - QRS width.
• RA, SA, TA - the amplitudes of the R, S, T-waves, respectively, are used to normalize the parameters listed above.

Statistical processing of results: SPSS Statistics Version 26 is a computer program for statistical processing of data.

The result of this study will be the identification of ECG parameters that will correlate with LV diastolic dysfunction, and by which it will be possible to determine its presence and degree in the future.

Investigators also plan to analyze ECG parameters characteristic of patients with LV diastolic dysfunction in different population groups:

• patients suffering from high blood pressure with patients without the above pathology
• patients with zones of a- and hypokinesis according to echocardiography as a result of a coronary circulation disorder
• patients suffering from atrial fibrillation with patients without this pathology
• men / women
• patients of different age groups

During statistical processing of the data, the following will be calculated: sensitivity, specificity, prognostic value of positive and negative results, likelihood ratio, area under ROC - curve, correlation coefficient. it is planned to obtain data on the diagnostic effectiveness of the proposed approach, as well as on individual parameters of the electrocardiogram in the diagnosis of diastolic dysfunction of the left ventricle.