Electrocardiograph

As of May 2013, 162 hospitals have agreed to participate in the China PEACE-Retrospective AMI Study (Figure 3). Of the 13 that did not participate, 7 did not have admissions for AMI and 6 declined participation. Examination of patient databases from participating hospitals yielded 31,601 hospitalizations for AMI (3,859 in 2001, 8,863 in 2006, and 18,879 in 2011). Of these, we sampled 18,631 for the China PEACE-Retrospective AMI Study (2,801 in 2001, 5,199 in 2006, and 10,631 in 2011). Of these 18,631 sampled hospitalizations, we acquired medical records for 18,110 (97.2%) and began data abstraction in August 2012. Medical records from 95% (154) of study sites contained all expected sections and represent 89% of all hospitalizations in the China PEACE-Retrospective AMI Study. In the remaining 8 study sites, we did not have access to daily progress notes due to local administrative policies of hospital archives departments. However, these records were considered adequate for inclusion in the study. The use of electronic medical records increased with time: 0% of hospitals used electronic medical records in 2001, 7% of hospitals used electronic medical records in 2006, and 46% of hospitals used electronic medical records in 2011. We will code hospital-level variables for the presence of daily progress notes and electronic medical records to better understand whether these factors introduce bias into study results.
To verify the accuracy of principal discharge diagnoses, we randomly selected 300 medical records and examined concordance between principal discharge diagnosis and electrocardiographic findings consistent with the subtype of AMI (STEMI versus NSTEMI). We found concordance in 95% of cases.

Standard 12-lead ECGs were recorded at baseline and at the year 4 visit in the resting supine position and using strictly standardized procedures in all clinical centers. Electrocardiograms were sent electronically to an ECG core laboratory at St Louis University Medical Center, St Louis, Missouri. Each ECG was reviewed by 2 trained coders and discordant results were adjudicated by a senior coder. Electrocardiograms were coded according to the Minnesota Code (MC).¹⁹ Independent data entry operators entered data twice in an electronic database and data were adjudicated by a supervisor. Among a random sample of 5% of baseline ECGs, κ values for the categorization described were 0.90 for major, 0.71 for minor, and 0.82 for no ECG abnormalities.
Electrocardiographic abnormalities were divided into major and minor abnormalities on the basis of the MC and according to previous publications.^{7 (link),8 (link),10 (link)} Criteria for major prevalent ECG abnormalities were any of the following: Q-QS wave abnormalities (MC 1-1 to 1-2-8); left ventricular hypertrophy (MC 3–1); Wolff-Parkinson-White syndrome (MC 6-4-1 or 6-4-2); complete bundle branch block or intraventricular block (MC 7-1-1, 7-2-1, 7–4, or 7–8); atrial fibrillation or atrial flutter (MC 8–3); or major ST-T changes (MC 4–1, 4–2, 5–1, and 5–2). Criteria for minor prevalent ECG abnormalities were minor ST-T changes (MC 4–3, 4-4, 5–3, and 5–4). Participants with both major and minor abnormalities were classified as having major abnormalities. Participants without minor or major ECG abnormalities were classified as having marginal or no abnormalities and their ECG was considered normal.
At 4 years, we analyzed repeat ECG data among 1670 of the participants who had not had any CHD events during the first 4 years of follow-up. From the base-line sample of 2192 participants, we excluded 424 participants without ECG data at 4 years and 98 participants who had had a CHD event during the first 4 years of follow-up. These 522 participants were more likely to be older, of black race, smokers, have hypertension and less education, be less physically active, and have an increased creatinine level than the participants included in the repeat ECG analyses at 4 years. For these analyses, participants were classified according to the presence of any (major, minor, or both) abnormalities at baseline and follow-up. These participants were then categorized as abnormalities at baseline only, persistent abnormalities (both baseline and follow-up), incident abnormalities (follow-up only), and no abnormalities (neither baseline nor follow-up).