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).