This is a prospective, single-center, non-randomized, observational study. The aim of this study is to determine the potential of a single-lead electrocardiogram monitor CardioQvark with photoplethysmography function use to evaluate systolic function of the left ventricle.

The study is conducted in the clinic of I.M. Sechenov First Moscow State Medical University (Sechenov University), Moscow, Russia. It is planned to include 400 patients. Recording of the electrocardiogram and photoplethysmogram by the monitor CardioQvark and the assessment of systolic function using echocardiography will be performed in all study participants.

The result of this study will be the identification of the parameters of the pulse wave and electrocardiogram that will correlate with systolic function of the left ventricle. It is also planned to determine the diagnostic effectiveness of this method.

The aim of this study is to determine the potential of a single-lead electrocardiogram (ECG) monitor CardioQvark (Moscow, Russia) with photoplethysmography function use to evaluate parameters systolic function of the left ventricle. Also according to the photoplethysmogram (PPG), using a special algorithm, the levels of systolic and diastolic blood pressure are calculated.

The single-lead electrocardiogram monitor CardioQvark (it is registered with the Federal Service for Health Supervision on February 15, 2019. RZN (Roszdravnadzor) No. 2019/8124) looks like an iPhone cover and records electrocardiogram (I standard lead) and photoplethysmogram (pulse wave) simultaneously.

This is a prospective, single-center, non-randomized, observational study. The investigators are planning to include in the study 400 patients with different pathologies of the cardiovascular system (coronary artery disease, hypertension, valvular heart disease, heart failure) according to the inclusion criteria.

Collection of medical history; physical examination (including inspection, palpation and auscultation, as well as determination of breathing rate, pulse rate, height, and weight) will be performed for the entire group of patients. Electrocardiogram and photoplethysmogram registration and assessment of the blood pressure using a CardioQvark monitor will be performed on all study participants at rest (the patient will sit quietly for 10-15 minutes before the examination). The reference blood pressure will be measured using a cuff-based blood pressure device ("Microlife BP AG1-10") that is worn on the upper arm according to the World Health Organization recommendations.

All subjects will undergo an echocardiography ("Dimension/Vivid 7 PRO General Electric Medical System"), the examination will be performed by an experienced doctor (the doctor will not have data on the parameters of the pulse wave and electrocardiogram). The extended protocol echocardiography will be performed according to the recommendations of European Association of Cardiovascular Imaging (EACVI) and American Society of Echocardiography (ASE). All examinations will be performed consistently within one day.

All electrocardiograms and photoplethysmograms records will be sent to the CardioQVARK server and processed by the algorithm using signal processing based on the wavelet transformation. Then engineers of "CardioQvark" (Limited Liability Company) will calculate the pulse wave parameters:

• B1 is the beginning of the wave
• B0 is the point of maximum increase of the anterior front
• SEP is the peak of the ejected pulse wave
• DER3 is the first positive peak of the third derivative
• SEPMAX is the point of the first inflection of pulse wave
• SRP is the peak of the reflected systolic wave
• DP is the peak of the diastolic wave
• End is the end of the wave
• perfusion index
• augmentation index.

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

• 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. The engineers will not have echocardiography results.

The investigators will evaluate parameters of the pulse wave (photoplethysmogram) and electrocardiogram and compare the results with echocardiography (ejection fraction, left ventricular outflow tract velocity time integral (VTI), left ventricular global longitudinal strain (GLS)).The mathematical model for determining the systolic dysfunction of the left ventricle will be built on the basis of the parameters of the photoplethysmogram and the electrocardiogram.

Intergroup analysis of significant differences, correlation analysis and Bland-Altman method will be used for statistical data analysis. All statistical analyses will be perform using a computer program for statistical processing of data SPPS (statistical package for the social sciences) Statistics Version 26.

It is planned to obtain comparative characteristics of the pulse wave and electrocardiogram parameters registered by the CardioQvark monitor and the indicators of systolic function of the left ventricle detected during echocardiography. The result of this study will be the identification of the parameters of the pulse wave and electrocardiogram that will correlate with systolic dysfunction of the left ventricle. It is planned to determine the diagnostic effectiveness of this method. The accuracy of the blood pressure measurement using the CardioQvark monitor will also be evaluated.

Thus, a quick and convenient assessment of systolic function of the left ventricle and blood pressure measurement will be available. So, study results will improve the diagnosis and treatment of cardiovascular disease.

Inclusion Criteria:

1. The presence of written informed consent of the patient to participate in the study.

2. The presence of diagnosed cardiac pathology according anamnesis (coronary artery disease (I-IV classes according Canadian Cardiovascular Society grading of angina pectoris, post myocardial infarction, patients after percutaneous coronary intervention or coronary artery bypass grafting); hypertension (stages I- III); valvular heart disease (except patients with aortic valve stenosis and mechanical prosthetic heart valve); heart failure (I-IV NYHA).

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   Exclusion Criteria:

1. Patient's reluctance to participate in the study. 2. Poor quality of ECG recording by a single-channel ECG monitor. 3. Poor visualization of the heart during echocardiography.

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Non-inclusion criteria:

1. The presence of rhythm and conduction disorders (WPW syndrome, frequent premature ventricular complexes, 2nd and 3rd degree sinoatrial block, 3rd degree atrioventricular block, complete left bundle branch block, complete right bundle branch block).
2. Patients with permanent cardiac pacemaker, cardio-resynchronization therapy (CRT), implantable cardioverter-defibrillator (ICD).
3. Conditions that can impair ECG recording quality (Parkinson's disease, essential tremor, etc.) or conditions that make it difficult to record ECG and photoplethysmogram (traumatic arm amputation)
4. Mental illness (diagnosed early)
5. Diseases with a life expected expectancy of less than 2 years.
6. Pregnancy.

Patients with different pathologies of the cardiovascular system (coronary artery disease, hypertension, valvular heart disease, heart failure) aged 18 years and older.

The research sponsor is Sechenov University. Data disclosure is not permitted by the local ethics committee. For more information about the study, you need to contact the principal investigator.