Table 1
The Minnesota codes of the electrocardiographic abnormalities.
| Electrocardiographic abnormalities Possible myocardial infarction | Minnesota Codes |
|---|---|
| Moderate Q/QS waves without ST-depression or T-wave inversion | 1-2-1 to 1-2-7 without 4-1, 4-2, 5-1, and 5-2 |
| Minor Q/QS waves with ST-depression or T-wave inversion | 1-2-8 or 1-3-1 to 1-3-6 with 4-1, 4-2, 5-1, or 5-2 |
| Probable myocardial infarction | |
| Major Q/QS waves | 1-1-1 to 1-1-7 |
| Moderate Q/QS waves with ST-depression or T-wave inversion | 1-2-1 to 1-2-7 with 4-1, 4-2, 5-1, or 5-2 |
| Q-QS wave abnormalities | 1-1-1 to 1-2-8 |
| Left ventricular hypertrophy | 3-1 |
| Wolff Parkinson White syndrome | 6-4 |
| Bundle branch block or intraventricular block | 7-1, 7-2, 7-4 or 7-8 |
| Atrial fibrillation or atrial flutter | 8-3 |
| ST-T changes | |
| ST-depression | 4-1 or 4-2 |
| T-wave inversion | 5-1 or 5-2 |
| Minor ST- codes | 4-3 or 4-4 |
| Minor T-wave codes | 5-3 or 5-4 |
Table 2
Baseline characteristics of participants with or without ECG abnormalities.
| Characteristics | Total (N = 7872) | ECG abnormalities | ||
|---|---|---|---|---|
| No (N = 5402) | Yes (N = 2470) | P value | ||
| Age, years | 57.8 ± 9.4 | 56.9 ± 9.1 | 59.7 ± 9.8 | <0.001 |
| Women, n (%) | 4899 (62.2) | 3477 (64.4) | 1422 (57.6) | <0.001 |
| Education, n (%) | <0.001 | |||
| Illiteracy | 962 (12.3) | 557 (10.4) | 405 (16.5) | |
| Primary | 1864 (23.8) | 1231 (22.9) | 633 (25.7) | |
| Secondary | 4726 (60.3) | 3370 (62.7) | 1356 (55.1) | |
| Post-secondary | 285 (3.6) | 220 (4.1) | 65 (2.6) | |
| Currently smoking, n (%) | 1612 (21.1) | 1066 (20.4) | 546 (22.7) | 0.018 |
| Currently drinking, n (%) | 816 (10.7) | 518 (9.9) | 298 (12.4) | 0.001 |
| Physical activity, MET-mins/week | 0.378 | |||
| <600, n (%) | 3142 (40.5) | 2178 (40.9) | 964 (39.5) | |
| 600–1499, n (%) | 2262 (29.1) | 1553 (29.2) | 709 (29.1) | |
| ≥1500, n (%) | 2361 (30.4) | 1595 (29.9) | 766 (31.4) | |
| Body mass index, kg/m2 | 24.9 ± 3.3 | 24.9 ± 3.3 | 25.0 ± 3.3 | 0.545 |
| Systolic blood pressure, mmHg | 141.0 ± 20.0 | 138.7 ± 19.3 | 145.8 ± 20.8 | <0.001 |
| Diastolic blood pressure, mmHg | 82.6 ± 10.4 | 82.1 ± 10.2 | 83.8 ± 10.7 | <0.001 |
| HbA1c, % | 5.8 ± 0.9 | 5.8 ± 0.9 | 5.9 ± 1.0 | 0.002 |
| Total cholesterol, mg/dL | 208.8 ± 38.7 | 204.9 ± 38.7 | 208.8 ± 38.7 | 0.057 |
| LDL cholesterol, mg/dL | 123.7 ± 34.8 | 123.7 ± 34.8 | 123.7 ± 30.9 | 0.707 |
| HDL cholesterol, mg/dL | 50.3 ± 11.6 | 50.3 ± 11.6 | 50.3 ± 11.6 | 0.004 |
| ACEI use, n (%) | 438 (5.6) | 283 (5.2) | 155 (6.3) | 0.063 |
| Hypertension, n (%) | 4651 (59.1) | 2950 (54.6) | 1701 (68.9) | <0.001 |
| Diabetes, n (%) | 651 (8.3) | 453 (8.4) | 198 (8.0) | 0.574 |
| 10-year ASCVD risk ≥10%, n (%) | 1609 (21.1) | 945 (18.1) | 664 (27.7) | <0.001 |
[i] Abbreviations: ECG, Electrocardiographic; MET, metabolic equivalent; HbA1c, glycated hemoglobin A1c; LDL, low-density lipoprotein; HDL, high-density lipoprotein; ACEI, angiotensin-converting enzyme inhibitors; ASCVD, atherosclerotic cardiovascular diseases.
Data are means ± SD for continuous variables and numbers (percentages) for categorical variables.
Table 3
Associations of ECG abnormalities at baseline with the development of cardiovascular events during follow-up.
| Without ECG abnormalities | With ECG abnormalities | Hazard Ratio (95% CI) | ||||
|---|---|---|---|---|---|---|
| Events (n, %) | Incidence rate per 1000 person-years (95% CI) | Events (n, %) | Incidence rate per 1000 person-years (95% CI) | Adjusted for TCVRFs* | Adjusted for multivariables† | |
| Overall participants (n = 7872) | ||||||
| CVD | 270 (5.0) | 10.9 (9.7, 12.3) | 194 (7.9) | 17.1 (14.8, 19.7) | 1.25 (1.03, 1.51) | 1.25 (1.02, 1.53) |
| MI or CHD death | 23 (0.4) | 0.9 (0.6, 1.4) | 29 (1.2) | 2.5 (1.7, 3.6) | 1.83 (1.04, 3.21) | 2.06 (1.15, 3.70) |
| Stroke | 248 (4.6) | 10.0 (8.8, 11.3) | 167 (6.8) | 14.7 (12.6, 17.1) | 1.19 (0.97, 1.46) | 1.16 (0.95, 1.44) |
| Participants with ASCVD risk ≥10% (n = 1609)‡ | ||||||
| CVD | 103 (10.9) | 24.5 (20.2, 29.7) | 113 (17.0) | 38.1 (31.7, 45.8) | 1.45 (1.11, 1.91) | 1.45 (1.08, 1.95) |
| MI or CHD death | 13 (1.4) | 3.0 (1.7, 5.1) | 21 (3.2) | 6.7 (4.4, 10.3) | 2.01 (1.01, 4.06) | 2.29 (1.09, 4.81) |
| Stroke | 91 (9.6) | 21.6 (17.6, 26.5) | 94 (14.2) | 31.5 (25.7, 38.5) | 1.39 (1.03, 1.86) | 1.41 (1.04, 1.90) |
| Participants with ASCVD risk <10% (n = 6007)‡ | ||||||
| CVD | 157 (3.7) | 7.9 (6.8, 9.3) | 79 (4.6) | 9.8 (7.9, 12.2) | 1.09 (0.83, 1.44) | 1.10 (0.82, 1.48) |
| MI or CHD death | 10 (0.2) | 0.5 (0.3, 0.9) | 8 (0.5) | 1.0 (0.5, 2.0) | 1.60 (0.62, 4.13) | 1.84 (0.69, 4.88) |
| Stroke | 147 (3.4) | 7.4 (6.3, 8.7) | 71 (4.1) | 8.8 (7.0, 11.1) | 1.06 (0.79, 1.41) | 1.00 (0.75, 1.34) |
[i] Abbreviations: ECG, Electrocardiographic; CI, confidence interval; TCVRFs, traditional cardiovascular risk factors; MI, Myocardial infarction; CHD, coronary heart disease; ASCVD, atherosclerotic cardiovascular diseases.
* Adjusted for traditional cardiovascular risk factors used to calculate the 10-year ASCVD risk score including age, sex, total cholesterol, high-density lipoprotein cholesterol, systolic blood pressure, smoking, and diabetes.
† Adjusted for TCVRFs and education, drinking, physical activity, low-density lipoprotein cholesterol, BMI, HbA1c and ACEI use.
‡ Of the total participants, 256 participants with missing data on any of the traditional risk factors were not included in the separate analysis in different ASCVD risk subgroups.
Table 4
The predictive abilities of ECG abnormalities for the development of cardiovascular events.
| Models | C statistic (95% CI) | C statistic change (95% CI) | IDI (95% CI) | NRI (95% CI) | ||
|---|---|---|---|---|---|---|
| Overall | Non-events | Events | ||||
| Overall participants (n = 7616)* | ||||||
| Model A | 0.699 (0.674, 0.723) | 0.002 (–0.003, 0.006) | 0.002 (0.001, 0.006) | –0.031 (–0.044, 0.046) | 0.007 (–0.004, 0.026) | –0.038 (–0.054, 0.036) |
| Model B | 0.701 (0.677, 0.725) | |||||
| Participants with ASCVD risk ≥10% (n = 1609) | ||||||
| Model A | 0.587 (0.548, 0.626) | 0.014 (–0.001, 0.035) | 0.007 (0.001, 0.019) | 0.060 (–0.022, 0.132) | 0.080 (0.002, 0.195) | –0.020 (–0.096, 0.036) |
| Model B | 0.601 (0.563, 0.639) | |||||
| Participants with ASCVD risk <10% (n = 6007) | ||||||
| Model A | 0.630 (0.595, 0.665) | 0.004 (–0.007, 0.013) | 0.000 (0.000, 0.001) | –0.012 (–0.054, 0.068) | 0.002 (–0.008, 0.012) | –0.014 (–0.049, 0.065) |
| Model B | 0.634 (0.599, 0.669) | |||||
[i] Abbreviations: ECG, Electrocardiographic; CI, confidence interval; IDI, integrated discrimination improvement; NRI, net reclassification index; ASCVD, atherosclerotic cardiovascular diseases.
Model A used traditional CVD risk factors used to calculate the 10-year ASCVD risk score including age, sex, total cholesterol, high-density lipoprotein cholesterol, systolic blood pressure, smoking, and diabetes as predictors.
Model B used traditional CVD risk factors in model A plus ECG abnormalities as predictors.
* Participants with missing data on any of the traditional risk factors were excluded for the assessment of the additional value of ECG.
Figure 1
Reclassification of individuals by adding the ECG results to the ASCVD risk predicted model with traditional risk factors*.
Abbreviations: ECG, Electrocardiography; HDL, high-density lipoprotein; ASCVD, atherosclerotic cardiovascular diseases; CVD, cardiovascular diseases.
* The traditional risk factors included age, sex, smoking, systolic blood pressure, diabetes, total cholesterol and HDL cholesterol.
Numbers are proportions of participants being reclassified.
Figure 2
Calibration plots of the models with and without ECG abnormalities.
Abbreviations: ASCVD, atherosclerotic cardiovascular diseases; ECG, Electrocardiographic.
Data points indicate expected vs observed risk by deciles of predicted risk. The bars showed the 95% confidential interval of the observed risks. The dotted lines correspond to the lines of perfect calibration on which predicted risks coincide with the observed risks.
Model A used traditional CVD risk factors used to calculate the Framingham Risk Score and the 10-year ASCVD risk score including age, sex, total cholesterol, high-density lipoprotein cholesterol, systolic blood pressure, smoking, and diabetes as predictors.
Model B used traditional CVD risk factors in model A plus ECG abnormalities as predictors.