METHODS
Study population
The study population comprised participants from the Seventh Tromsø Study (Tromsø7) in Norway and the Know Your Heart (KYH) study in Russia, which are cross-sectional population-based studies. The Tromsø7 study was conducted between March 2015 and October 2016 in the Tromsømunicipality, Norway and the KYH study was conducted from 2015 to 2018 in Arkhangelsk, Novosibirsk, Russia. Both studies were designed and conducted in parallel using harmonized questionnaires, health examinations, biological sample collection, and echocardiography protocols.
In the Tromsø7 study, the inclusion age range was 40 years and older without an upper limit, whereas the KYH study included participants aged 35–69 years. Speckle-tracking analysis was performed to compare both populations (20), and echocardiograms were selected from approximately equal-sized age and sex groups from both populations (40–49, 50–59, and 60–69 years). The final sample for the present study comprised about equal sized groups from Norway and Russia, with 46% from Tromsø and 27% each from Arkhangelsk and Novosibirsk. Figure 1 shows a flowchart of the number of participants included and excluded from this study and their division into study groups.
Normal ranges
To define normal ranges in healthy individuals, atrial S/SR-based parameters were investigated in selected individuals. For this purpose, participants were excluded if one or more of the following criteria were met: moderate-to-severe valvular heart disease and history or objective indicators of previous coronary artery disease (classes 1.1 – 1.2.7 of the Minnesota Code), myocardial diseases, electrocardiogram (ECG) with a QRS complex more than 130 ms, ejection fraction (EF) less than 50%, hypertension, antihypertensive medication, history of AF, AF on ECG, or elevated NT-proBNP.
Hypertension was defined as a systolic blood pressure (BP) more than 140 mmHg and/or diastolic BP more than 90 mmHg during the visit, regular intake of anti-hypertensive drugs, or a reported history of hypertension. All study participants were asked about their current medications, and the data was coded using the Anatomical Therapeutic Chemical (ATC) classification system. Any medication within the ATC classes C02, C03, C07, C08, or C09 was regarded as an antihypertensive. Elevated NT-proBNP values were homogenized between the Norwegian and Russian study groups (21), and a cutoff value of 250 ng/ml was chosen according to the average upper normal range (99 percentile) based on a study in the Tromsø7 population (22).