The Minnesota Code (MC) and Novacode (Nova) are the most widely used electrocardiographic (ECG) classification systems. The comparative strengths of their classifications for Q- and ST-T–wave abnormalities in predicting coronary heart disease (CHD) events and total mortality have not been evaluated separately by gender. We studied standard 12-lead electrocardiograms at rest from 4,988 participants in the Cardiovascular Health Study. Average age at baseline was 73 years, 60% of participants were women 85% were white, and 22% had a history of cardiovascular disease or presence of ECG myocardial infarction by MC or Nova. Starting in 1989 with an average 17-year follow-up, 65% of participants died and 33% had incident CHD in a cohort free of cardiovascular disease at baseline. Of these, electrocardiograms with major Q-wave or major ST-T abnormalities by MC or Nova predicted increased risk for CHD events and total mortality with no significant differences in predictability between men and women. The study also found that women had fewer major Q-wave changes but more major ST-T abnormalities than men. However, there were no gender differences in predicting CHD events and total mortality. In conclusion, ECG classification systems for myocardial infarction/ischemia abnormalities by MC or Nova are valuable and useful for men and women in clinical trials and epidemiologic studies.
Electrocardiographic (ECG) criteria for myocardial infarction and ischemia have been used as evidence for coronary heart disease (CHD) in epidemiologic studies and clinical trials and are a powerful index for assessment of cardiovascular disease (CVD) risk and an important predictor for total mortality. Comparative strengths of their classification by the Minnesota Code (MC) and the Novacode (Nova), have not been evaluated separately by gender. The present study evaluated the value of current MC and Nova for myocardial infarction/ischemia for prediction of incident fatal and nonfatal cardiac events and total mortality and compared the predictive power of each coding system in men and women.
Methods
The Cardiovascular Health Study (CHS) is a population-based prospective cohort study of risk factors for CHD and stroke in men and women ≥65 years of age in 4 United States communities that started in 1989. Eligible participants were sampled from Medicare-eligibility lists in each area. Details of the study design have been described previously. Eligible participants gave informed consent, and study protocols were approved by institutional review boards at participating institutions. Of 5,888 ECG recordings available from baseline examinations of the CHS cohort, those with incomplete data or inadequate quality and QRS duration ≥120 ms were excluded. The remaining 4,988 participants at baseline were classified into 2 groups, a CVD group (n = 1,113) and a CVD-free group (n = 3,875). CVD at baseline was defined by the presence of ECG myocardial infarction evidence by MC or Nova, a history of clinical myocardial infarction, angina pectoris that was confirmed by retrospective review of hospitalization medical records, or self-report of coronary angioplasty or bypass surgery. Average follow-up was 17 years (maximum 18). Three outcomes were considered in the present analysis: incident CHD events (fatal and nonfatal), CHD death, and all-cause mortality. After baseline, deaths and hospitalization events were ascertained by semiannual follow-up telephone calls to cohort members, review of vital records, and community surveillance of hospitalized and fatal events. The CHS mortality review committee reviewed and adjudicated all fatal events.
Identical electrocardiographs (MAC PC, Marquette Electronics, Inc., Milwaukee, Wisconsin) were used in all clinic sites. Standard 12-lead electrocardiograms at rest were recorded in all participants using strictly standardized procedures. All electrocardiograms were processed in a central laboratory (Epidemiologic Cardiology Research Center, Wake Forest University, Winston-Salem, North Carolina) and were classified by the Nova and MC using the 2001 version of the GE Marquette 12-SL program. ECG classification criteria for myocardial infarction/ischemia by Nova/MC in the present study were the same as previously described. Nova myocardial infarction was identified by Nova codes 5.1 to 5.4 and ECG major Q/ST-T changes by Nova was identified as Nova codes 5.1 to 5.6. Similarly, MC myocardial infarction was identified by categories C.1 to C.4 to match Nova myocardial infarction. ECG major Q/ST-T change by MC was identified as categories C.1 to C.6 ( Table 1 ).
| Category | Novacode | Minnesota Code ⁎ |
|---|---|---|
| Major Q waves | 5.1 | C.1 |
| Moderate Q waves with ST-T abnormalities | 5.2 | C.2 |
| Moderate Q waves without ST-T abnormalities | 5.3 | C.3 |
| Minor Q waves with ST-T abnormalities | 5.4 | C.4 |
| Isolated/major ST abnormalities | 5.5 | C.5 |
| Isolated/major T wave abnormalities | 5.6 | C.6 |
| Minor Q waves | 5.7 | C.7 |
| Minor ST-T abnormalities | 5.8 | C.8 |
| No significant Q waves or ST-T | 5.0 | C.0 |
| Electrocardiographic myocardial infarction by Novacode and Minnesota Code | 5.1–5.4 | C.1–C.4 |
| ECG major Q or major ST-T abnormalities by Novacode and Minnesota Code | 5.1–5.6 | C.1–C.6 |
⁎ C standard for combined code of Minnesota Codes 1, 4, and 5 to match hierarchical codes in Novacode 5.
CVD and CVD-free groups at baseline were analyzed separately. Cox proportional hazards regression models were used to test and compare the MC and Nova for myocardial infarction/ischemia and ECG abnormality classifications as predictors of each of the 3 study end points after adjustment for demographic and clinical variables. Clinical and demographic characteristics that were significantly associated with risk of CHD event or total mortality were included in the multivariate model to determine if ECG predictors for risk of CHD events and total mortality differed between women and men and between CVD and CVD-free groups at baseline, which are listed in Tables 2 and 3 . All analyses were performed with SAS 9.1.3 (SAS Institute, Cary, North Carolina).
| Characteristics | Total(n = 4,988) | Prevalent CVD Group | CVD-Free Group | ||||
|---|---|---|---|---|---|---|---|
| Women | Men | p Value ⁎ | Women | Men | p Value ⁎ | ||
| (n = 561) | (n = 552) | (n = 2,416) | (n = 1,459) | ||||
| Age (years) | 73 ± 6 | 74 ± 6 | 74 ± 6 | 0.5846 | 72 ± 5 | 73 ± 6 | 0.0001 |
| Body mass index (kg/m 2 ) | 27 ± 5 | 27 ± 5 | 27 ± 4 | 0.0414 | 27 ± 5 | 26 ± 4 | 0.0364 |
| Systolic blood pressure (mm Hg) | 136 ± 22 | 141 ± 24 | 135 ± 21 | <0.0001 | 136 ± 22 | 135 ± 21 | 0.5097 |
| Diastolic blood pressure (mm Hg) | 71 ± 11 | 69 ± 12 | 71 ± 11 | 0.0416 | 70 ± 11 | 73 ± 11 | <0.0001 |
| African-American | 15.4% | 20.7% | 10.0% | <0.0001 | 15.7% | 14.9% | 0.5563 |
| Current smoking | 12.2% | 13.0% | 9.1% | <0.0001 | 12.8% | 12.0% | <0.0001 |
| Hypertension | 57.8% | 72.7% | 61.4% | <0.0001 | 56.4% | 52.9% | 0.0356 |
| Diabetes mellitus | 15.6% | 20.6% | 25.5% | 0.0542 | 12.2% | 15.5% | 0.0030 |
| Total mortality | 64.9% | 73.8% | 83.3% | 0.0001 | 56.5% | 68.3% | <0.0001 |
| Coronary heart disease death | 15.6% | 22.1% | 29.7% | 0.0037 | 10.6% | 16.2% | <0.0001 |
| Incident coronary heart disease † | 32.6% | 28.9% | 38.6% | <0.0001 | |||
| Myocardial infarction/ischemia by Novacode/Minnesota Code ‡ | |||||||
| Myocardial infarction by Novacode/Minnesota Code | 8.9% | 35.7% | 44.0% | 0.0043 | |||
| Major Q wave by Novacode/Minnesota Code | 6.7% | 24.2% | 35.7% | <0.0001 | |||
| Major ST-T change by Novacode/Minnesota Code | 15.2% | 35.1% | 29.4% | 0.0396 | 10.7% | 9.7% | 0.3484 |
| Major Q/ST-T change by Novacode/Minnesota Code | 20.2% | 52.6% | 56.5% | 0.2085 | 10.7% | 9.7% | 0.3484 |
| Major Q/ST-T change by Novacode ‡ | |||||||
| Myocardial infarction by Novacode | 6.3% | 23.5% | 33.0% | 0.0005 | |||
| Major Q wave by Novacode | 4.1% | 13.4% | 23.0% | <0.0001 | |||
| Major ST-T change by Novacode | 14.4% | 33.7% | 28.8% | 0.0789 | 9.6% | 9.5% | 0.9160 |
| Major Q/ST-T change by Novacode | 17.5% | 43.5% | 47.1% | 0.2271 | 9.6% | 9.5% | 0.9160 |
| Major Q/ST-T change by Minnesota Code ‡ | |||||||
| Myocardial infarction by Minnesota Code | 7.8% | 31.2% | 39.0% | 0.0067 | |||
| Major Q wave by Minnesota Code | 6.4% | 23.7% | 33.7% | 0.0002 | |||
| Major ST-T change by Minnesota Code | 12.2% | 28.9% | 22.8% | 0.0212 | 8.9% | 7.2% | 0.0564 |
| Major Q/ST-T change by Minnesota Code | 17.8% | 49.0% | 52.5% | 0.2411 | 8.9% | 7.2% | 0.0564 |
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