An analysis of serial Minnesota ECG code changes in the London cohort of the WHO multinational study of vascular disease in diabetes

Aims/hypothesis. Deterioration and improvement in the electrocardiogram are important outcomes in cardiovascular disease progression assessment. We used a sample of serial records from the WHO Multinational Study of Vascular Disease in Diabetes (WHO MSVDD) to assess Minnesota coding variability. Methods. A constructed subsample of 118 of the 352 paired (baseline and follow-up) and previously Minnesota-coded ECG records from the London cohort was randomised and re-read independently of the first code (respectively 11 and 0.5 years later) by the same two coders. Detailed Minnesota codes were summary coded into groups I (CHD unlikely), 2 and 3 (CHD possible and probable, respectively). Results. Re-reading of the constructed sample for the baseline records (11 years later) generated 21 Summary code reassignments (2 unlikely to possible or probable; 19 possible or probable to unlikely) rereading for the follow-up records (0.5 years later) generated only 8 summary code reassignments (21 vs 8 p < 0.001) (3 unlikely to possible or probable; 4 possible or probable to unlikely; 1 probable to possible). Re-reading increased the estimated net ECG deterioration in the constructed sample from 11.8% to 25.4%. Consistency analysis showed most variability in marginal baseline abnormalities. Conclusion/interpretation. Coding variability is now small though re-reading suggests some time-dependent coding drift. Relative over-reading at baseline suggests that the change reported in the complete WHO MSVDD cohort at follow-up was underestimated and that almost all of the reported ECG deterioration and about half of the reported ECG 'improvement' was real.