The validity of hospital discharge register data on non-ST-elevation and ST-elevation myocardial infarction in Finland

Objectives. To examine the validity of ST-elevation myocardial infarction (STEMI) and non-ST-elevation myocardial infarction (NSTEMI) diagnoses in Finnish nation-wide hospital discharge register (HDR). Design. In the first stage of the study, we sampled 180 patients treated in 1996-2012 for MI in three different hospitals, Oulu university hospital, Turku university hospital and North Karelia Central hospital, 60 patients in each hospital. A cardiology resident classified the patients on the basis of ECG finding into following categories: NSTEMI, STEMI or not classifiable myocardial infarction (NCMI). In the second stage of the study, we sampled altogether 270 additional patients i.e. 90 patients per hospital. Patients were treated between 2012-2014 for STEMI (n = 3 × 30), NSTEMI (n = 3 × 30), and NCMI (n = 3 × 30). The ECGs of these patients were independently evaluated by the cardiology resident and a senior cardiologist and compared with the HDR diagnosis. Results. In the first stage of the study, the agreement between the ECG coding of the cardiology resident and the HDR diagnoses was poor (Cohen's kappa coefficient 0.38 (95% CI 0.10-0.32). In the second stage, the agreement remained at the same poor level (Cohen's kappa = 0.22 (95% CI 0.11-0.03)). The agreement between the cardiology resident and the senior cardiologist was, however, good (Cohen's kappa = 0.75 (95% CI 0.65-0.85)). Conclusions. Our results show that the division of MI diagnoses to STEMI and NSTEMI is not reliable in the Finnish HDR. These diagnoses should not be used as outcomes in scientific research without additional verification from the original ECGs.