Background The German National Cohort (NAKO) is a population-based cohort that provides in-depth information on risk factors, functions and diseases such as diabetes, cancer, cardiovascular, pulmonary, neuro-psychiatric, and infectious diseases. It was established to elucidate pathways to common diseases, and to enhance early detection and prevention. We here report first results of the electrocardiographic examination.

Methods From 2014, persons aged 20–74 years were recruited from the general population and examined at 18 study centres across Germany. Standardized examinations included an interview, self-administered questionnaires (e.g., on medical history, behavioural, psychosocial, occupational and environmental factors), collection of bio-samples (blood, urine, saliva, nasal swabs, stool), and biomedical exams, e.g. electrocardiograms (ECG), blood pressure, arterial stiffness, echocardiography, anthropometry, oral glucose tolerance tests, neurocognitive, sensory and respiratory function tests. Whole-body Magnet Resonance Imaging (MRI) focussing on brain, heart, musculoskeletal system and body fat was performed in 30,861 participants. Active and passive follow-up of study participants is ongoing using questionnaires, medical records and linkages to cancer registries and health insurances, and through mortality follow-up. In addition, all participants are re-invited for a second examination, which is expected to be completed by 2024.

Data collection is standardized, and central quality control and data cleaning is performed. For more complex data (e.g. ECGs, echocardiography, retinafotography, accelerometry), competence units process the data and derive variables on exposure, functions and disease.

For the ECG recording, electrode application is standardized using the DAL square, and computer-based ECG processing detects and possibly corrects observer errors like electrode reversal, reports quality indicators (noise and mains interference), and generates standard diagnostic interpretations and Minnesota coding.

Results Until 2019, 205,415 persons were first examined. Since 2019, 95,960 participants have been re-examined, including 14,164 MRI re-examinations. A third examination will start in 2024. Altogether, 51,588 baseline ECGs of high quality were recorded and processed, among which only 406 electrode reversals were observed (355 corrected). Overall, 1,401 myocardial infarctions (MI), 242 left ventricular hypertrophies, 193 left and 548 right bundle branch blocks, and 208 atrial fibrillations were detected. Among 60,566 processed follow-up ECGs, there were 2,245 with MI and 536 with atrial fibrillation.

Conclusion Given the large size, the in-depth repeated examinations, longitudinal information on changes in risk factor profiles, organ functions and major diseases, linkage with secondary data and high quality standards, the NAKO provides a valuable resource for epidemiologic research on determinants of population health and disease. ECGs are of high quality and provide valuable diagnostic information.