Congestive heart failure (CHF) is a disorder of the heart when structural or functional heart disease impairs the heart's ability to work properly. In developed countries, the prevalence of CHF in the general population is around 1-2% (depending on the definition used) and the prevalence of CHF in people aged 70 years and older is ≥ 10%. The cumulative 5-year mortality of patients with CHF is about 50%.

According to different studies, the prevalence of the early repolarization pattern (ERP) in the 12-lead electrocardiogram (ECG) in the general population is 2-31%. Although ERP in ECG have been considered as benign finding for many years, an increasing number of studies have been conducted in recent years to demonstrate an association of ERP in ECG with sudden cardiac death, mainly through ventricular arrhythmias in previously healthy individuals or those with structural cardiac pathology. New studies are also being performed to support the association of ERP with the progression of CHF.

Although the prevalence of ERP in the general population is not very high, the knowledge that ERP lead to a higher risk of sudden cardiac death and development of CHF lets physicians tailor patient care and follow-up, and treatment at a very low cost because ECG is a cheap, simple, and widely available diagnostic test.

Impedance cardiography (ICG) is another safe, non-invasive, cheap, routine diagnostic method based on the detection of changes in thoracic bioimpedance during heartbeat.

The aim of the present study is to evaluate the diagnostic and prognostic significance of ICG and ERP in congestive heart failure patients and to compare it with other non-invasive CHF diagnostic methods. The investigators hypothesize that ERP and changes in ICG readings may be used as a cheap, safe, non-invasive and widely available diagnostic and prognostic methods in patients with congestive heart failure witch help physicians tailor their patient follow-up and treatment accordingly.

The participants of the study are those who are hospitalized due to the flare-up of congestive heart failure. All of the participants will undergo routine tests. They will also undergo an ICG witch is not a routine test in the research center.

Congestive heart failure (CHF) is a disorder of the heart when structural or functional heart disease impairs the heart's ability to fill with blood or pump it out properly. In developed countries, the prevalence of CHF in the general population is around 1-2% (depending on the definition used) and the prevalence of CHF in people aged 70 years and older is ≥ 10%. The cumulative 5-year mortality of patients with CHF is about 50%. In 2018 in Lithuania CHF accounted for 5.64 hospitalizations per 1000 people in general population. Mortality rate was 155.17 per 1,000 patients and the average length of in hospital stay was 26.64 days.

In order to improve the diagnosis, treatment and financial costs in patients with CHF it is important to search for diagnostic methods that are cheap, effective, preferably non-invasive, as well as those that have reliable prognostic significance for patients with CHF.

According to different studies, the prevalence of early repolarization pattern (ERP) in the 12-lead electrocardiogram (ECG) in the general population is 2-31%. This may be due to different ERP definitions used by different authors. Although ERP in ECG have been considered as benign finding for many years, an increasing number of studies have been conducted in recent years to demonstrate an association of ERP in ECG with sudden cardiac death, mainly through ventricular arrhythmias in previously healthy individuals or those with structural cardiac pathology. New studies are also being performed to support the association of ERP in ECG with the progression of CHF. ERP, which has been first described in 1936 by Shipley and Hallaran, is generally defined as J-point (J-p) elevation with QRS notching or slurring in the terminal part of the QRS complex in at least two adjacent inferior (II, III, and aVF) and / or lateral leads (I, aVL, and V4-V6) detected by the standard 12-lead electrocardiogram. The amplitude of the J point must be at least 1 mm (0.1 mV) and the J-p must appear as an additional positive wave in the S wave (QRS notching) or the J-p may appear as a faint transition of the high R wave to the ST segment without Jp-QRS slurring, QRS duration should be <120 ms and anterior precordial leads (V1-3) are not included in the description of ERP because such changes in these leads may be due to Brugada syndrome or right ventricular dysplasia. Although the prevalence of ERP in ECG in the general population is not very high, the knowledge that ERP in ECG lead to a higher risk of sudden cardiac death and development of CHF lets physicians tailor patient care and follow-up, and treatment at a very low cost because an ECG is a cheap, simple, and widely available diagnostic test.

Impedance cardiography (ICG) is another safe, non-invasive, cheap, routine diagnostic method based on the detection of changes in thoracic bioimpedance during heart cycle. A lot of research has been carried out in recent years which examines the possibilities of ICG in CHF patients in various aspects: diagnostics, treatment, prognosis. A good correlation between ICG, cardiac ultrasound and invasive diagnostic methods was observed in most studies.

Evaluating CHF patients, it is important to evaluate thoracic fluid content (TFC) that can be used to diagnose a flare-up of CHF, its degree, to evaluate the effectiveness of treatment, as well as the prognosis of patients. ICG evaluate the TFC and its index. In clinical practice, it is important to predict the flare-ups of CHF, to predict the outcome of CHF patients, and to provide appropriate treatment to patients timely. Various prognostic indicators are studied: ICG parameters (TFC, TFC index, cardiac output (CO), CO index, systolic time ratio, etc.), brain natriuretic peptide (BNP), New York Heart Association (NYHA) classes. The current data are quite controversial, with most studies reporting positive ICG data as a predictor of CHF.

The aim of the present study is to evaluate the diagnostic and prognostic significance of ICG and ERP in ECG in CHF patients and to compare it with other non-invasive CHF diagnostic methods. The investigators hypothesize that ERP in ECG and changes in ICG readings may be used as a cheap, safe, non-invasive and widely available diagnostic and prognostic methods in patients with CHF witch help physicians tailor their patient follow-up and treatment accordingly.

The participants of the study are those who are hospitalized due to the flare-up of CHF. All of the participants will undergo routine tests. They will also undergo an ICG witch is not a routine test in the research center.

Inclusion Criteria:

• patients hospitalized due to a flare-up of congestive heart failure;
• early repolarization pattern in a 12-lead ECG;
• free from mental disorders;
• participants signed the informed consent form.

Exclusion Criteria:

• septic shock;
• high grade aortic valve regurgitation;
• high grade aortic valve stenosis;
• ventricular septal defect;
• prosthetic aortic valve;
• uncontrolled hypertension (mean arterial pressure >130 mmHg);
• heart rate > 200 bpm;
• height <120 cm or >230 cm;
• weight <30 kg or >155 kg;
• intra-aortic balloon counterpulsation;
• pacemaker with a minute ventilation sensor;
• restless patient;
• patient refuses to participate.

All individual participant data that underlie results in a publication.

Data will be available from 2022-08-01 through 2027-08-01.

Data will be shared with other principal investigators in the field of congestive heart failure research. Requests should be submitted to study's principal investigator MD Andrius Ališauskas at: andrius.alisauskas@lsmu.lt