A United States national sample of 20,962 participants (57% women, 44% blacks) from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study provided general population estimates for electrocardiographic (ECG) abnormalities among black and white men and women. The participants were recruited from 2003 to 2007 by random selection from a commercially available nationwide list, with oversampling of blacks and those from the stroke belt, with a cooperation rate of 49%. The measurement of risk factors and 12-lead electrocardiograms (centrally coded using Minnesota code criteria) showed 28% had ≥1 major ECG abnormality. The prevalence of abnormalities was greater (≥35%) for those ≥65 years old, with no differences between blacks and whites. However, among men <65 years, blacks had more major abnormalities than whites, most notably for atrial fibrillation, major Q waves, and left ventricular hypertrophy. Men generally had more ECG abnormalities than women. The most common ECG abnormalities were T-wave abnormalities. The average heart rate-corrected QT interval was longer in women than in men, similar in whites and blacks, and increased with age. However, the average heart rate was greater in women than in men and in blacks than in whites and decreased with age. The prevalence of ECG abnormalities was related to the presence of hypertension, diabetes, blood pressure, and age. In conclusion, black men and women in the United States have a significantly greater prevalence of ECG abnormalities than white men and women at age 45 to 64 years; however, these proportions, although larger, tended to equalize or reverse after age 65.
No published data exist on the prevalence of electrocardiographic (ECG) abnormalities from national samples of black and white Americans beyond the National Health and Nutrition Examination Survey (NHANES) reports. The first of these was a sample of 25 to 74-year-old Americans from the 1971 to 1975 Health and Nutrition Study (HANES I) survey of 6,913 persons with recorded electrocardiograms. Only simple frequencies of ECG abnormalities were given, without age, race, or gender stratification. Some continuous measurements were given without heart rate correction, and the abnormalities listed did not have precise definitions, such as in the Minnesota Code, which is the primary ECG classification system for ECG findings and abnormalities in clinical trials and epidemiologic studies. The only other ECG recordings of a national sample of the United States (US) population was made for NHANES III (1988 to 1994) and was only for 6,286 white and 2,041 black persons ≥40 years old. The totality of these data has not been published but is available in reports from the US Department of Health and Human Services. Only the white prevalence, unstratified, by race and gender, have been published in a recent report comparing US white and Taiwanese Chinese populations. These reports of ECG abnormalities lack subgroup specificity and associations with relevant demographic and clinical variables. In the present study, we have characterized the full range of ECG findings and abnormalities among a national sample of 20,962 black and white men and women from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study and assessed the effect of adjustment for confounding by the clinical and demographic modifiers on observed differences.
Methods
The REGARDS study is a national, population-based longitudinal study evaluating the causes of racial and regional differences in stroke mortality. The objectives and methods of the study have been previously published. In brief, from January 2003 to October 2007, 30,239 black and white men and women aged ≥45 years were recruited by random selection of names/addresses from a commercially available nationwide list (Genesys, Daly City, California), with a 49% cooperation rate. The final sample included 21% from the stroke buckle (coastal plain of North Carolina, South Carolina, and Georgia), 35% from rest of the stroke belt area (remainder of North Carolina, South Carolina, and Georgia, and Tennessee, Mississippi, Alabama, Louisiana, and Arkansas), 44% from the other 40 contiguous states (42% black and 55% women). The demographic information and medical history were obtained by telephone interview. A brief physical examination was conducted 3 to 4 weeks after the telephone interview, including standardized measurements of the risk factors, collection of blood and urine, and recording of the electrocardiogram at rest.
The ECG recording in REGARDS was initially incorporated only to diagnose atrial fibrillation, 1 of the major risk factors for stroke. Hence, the first 8,432 REGARDS participants underwent a 7-lead ECG recording acquired by applying the standard 4-limb electrodes and a midsternal electrode. However, during the study period, it was determined that a 12-lead electrocardiogram should (and could) be recorded. Therefore, the remaining REGARDS participants (n = 21,071) underwent a standard 12-lead ECG recording. The change in the ECG protocol and the broadening of the age eligibility to include those aged 45 to 54 years occurred at approximately the same time. All electrocardiograms were read centrally at the Epidemiological Cardiology Research Center (Wake Forest University School of Medicine, Winston-Salem, North Carolina), where the electrocardiograms were coded by trained physician electrocardiographers, and all abnormalities were over-read by a second physician electrocardiographer. For the purposes of the present analysis, we excluded all participants without a 12-lead electrocardiogram and those without readable electrocardiograms. This left 20,962 electrocardiograms for the present analysis. The ECG variables include all ECG, Minnesota codes (MC) with codes 1 through 9 and continuous ECG variables: heart rate, QRS duration, QT duration (and QTI = QT/656 × [heart rate + 100]), RaVL, SV1, and SV3. Major abnormalities ( Appendix Table 2 ) included ventricular conduction defects (MC 7.1.7.2, 7.4, 7.8), major Q waves (MC 1.1, 1.2; all ≥0.03 second in duration), minor Q waves plus STT abnormalities (MC 1.3 + 4.1 or 4.2 or 5.1 or 5.2), major isolated STT abnormalities (MC 4.1 or 4.2, all with STJ of ≥0.5 mm depressed with a horizontal or downward sloping ST segment; or 5.1 or 5.2, ≥1 mm T-wave inversion), left ventricular hypertrophy plus major STT abnormalities (MC 3.1 + 4.1 or 4.2 or 5.1 or 5.2), atrial fibrillation or flutter (MC 8.3), major atrioventricular conduction abnormalities (MC 6.1, 6.2, 6.4), other major arrhythmias (MC 8.2,8.4), artificial pacemaker (MC 6.8), and major QT prolongation (QTI of ≥116).
For national prevalence estimates reflecting the sampling design of REGARDS, SAS-callable SUDAAN was used to perform all statistical analyses with sampling weights. The sampling weights were obtained using a poststratification method. There were 108 strata based on region, race, gender, and age groups. The national population was based on the 2000 census and obtained through the Centers for Disease Control and Prevention Wonder web site. National population estimates by strata and REGARDS population by strata were obtained to create selection probabilities. Sampling weights were then obtained by taking the inverse of the selection probability.
Population-weighted means and proportions were obtained to describe the distributions of continuous ECG variables and categorical variables, respectively. Logistic regression analyses were used to assess the associations between the risk factors and demographic traits with the outcome. Simple models were adjusted for demographic factors such as age, race, and gender. Full models took into account major risk factors and socioeconomic factors. After producing the weights, we were able to re-create the national population estimates using these weights.
Results
The national weighted mean age of the study sample was 59 years (56 years for black men, 58 for black women, 61 for white women, and 58 for white men). The clinical measurements of blood pressure, body mass index, and serum lipid levels and a history of diabetes, hypertension, and treatment of hyperlipidemia are listed in Table 1 . The smoking rates and blood low-density lipoprotein, high-density lipoprotein cholesterol, and triglyceride levels differed among the groups, as did the treatment of hyperlipidemia and hypertension.
| Total (n = 20,962) | White Men (n = 5,052) | Black Men (n = 2,760) | White Women (n = 7,317) | Black Women (n = 5,833) |
|---|---|---|---|---|
| Age (years) | 57.7 ± 0.04 | 55.7 ± 0.05 | 61.0 ± 0.03 | 58.1 ± 0.03 |
| Systolic blood pressure (mm Hg) | 123.6 ± 0.40 | 129.5 ± 0.56 | 120.9 ± 0.33 | 127.2 ± 0.35 |
| Body mass index (kg/m 2 ) | 28.5 ± 0.16 | 29.2 ± 0.19 | 28.2 ± 0.13 | 32.0 ± 0.16 |
| Low-density lipoprotein cholesterol (mg/dl) | 113.6 ± 0.97 | 114.5 ± 1.26 | 114.9 ± 0.68 | 118.0 ± 0.73 |
| High-density lipoprotein cholesterol (mg/dl) | 45.0 ± 0.37 | 48.8 ± 0.52 | 58.0 ± 0.33 | 56.5 ± 0.31 |
| Triglycerides (mg/dl) | 148.7 ± 3.60 | 119.1 ± 2.36 | 134.2 ± 1.77 | 105.6 ± 1.21 |
| Diabetes mellitus | 885 (13.3%) | 795 (24.0%) | 904 (9.8%) | 1,669 (23.9%) |
| Current smoker | 641 (13.7%) | 574 (26.9%) | 943 (13.5%) | 901 (19.8%) |
| Treated for hypertension ⁎ | 2,690 (36.9%) | 1,748 (50.4%) | 3,620 (40.7%) | 3,978 (59.1%) |
| Treated for hyperlipidemia † | 1,968 (27.2%) | 817 (22.2%) | 2,052 (22.7%) | 1,680 (22.1%) |
⁎ Any antihypertensive medication (diuretics, β blocker, calcium channel blocker, angiotensin-converting enzyme inhibitor, α blocker).
In Table 2 , the weighted mean values ± SE are listed for selected continuous measures of ECG variables with independent prognostic value. Each of the 4 race/gender groups was divided into age groups ≥65 and <65 years. The QRS duration increases with age and is longer in men than in women and in whites than in blacks. QTc and QTI, both heart rate-corrected measures of the QT interval, increase with age and are longer in women than in men and are similar in blacks and whites. The heart rate is also greater in women than in men but decreases with age and is greater in blacks than in whites.
| Variable | White | Black | ||||||
|---|---|---|---|---|---|---|---|---|
| Men, Age <65 yr (n = 2,394) | Men, Age ≥65 yr (n = 2,658) | Women, Age <65 yr (n = 3,909) | Women, Age ≥65 yr (n = 3,408) | Men, Age <65 yr (n = 1,592) | Men, Age ≥65 yr (n = 1,168) | Women, Age <65 yr (n = 3,361) | Women, Age ≥65 yr (n = 2,472) | |
| QRS duration | 88.7 ± 0.5 | 96.2 ± 0.6 | 84.0 ± 0.3 | 87.1 ± 0.5 | 86.7 ± 0.51 | 91.1 ± 0.7 | 82.5 ± 0.2 | 86.4 ± 0.4 |
| QTC | 406.0 ± 0.8 | 414.7 ± 0.8 | 415.4 ± 0.6 | 418.3 ± 0.8 | 409.0 ± 1.1 | 413.4 ± 1.00 | 417 ± 0.6 | 418.5 ± 0.7 |
| QTI | 98.7 ± 0.2 | 101.0 ± 0.2 | 100.4 ± 0.1 | 101.3 ± 0.2 | 98.8 ± 0.2 | 100.2 ± 0.2 | 100.6 ± 0.1 | 101.1 ± 0.2 |
| Heart rate | 64.2 ± 0.4 | 63.1 ± 0.3 | 67.0 ± 0.3 | 65.9 ± 0.3 | 68.1 ± 0.5 | 66.2 ± 0.4 | 69.7 ± 0.3 | 68.0 ± 0.3 |
The prevalence of extant ECG abnormalities is listed in Table 3 , and the significant age/race/gender associations of each of the abnormalities is given in Appendix Table 1 . Of the total population, 28.2% had ≥1 major ECG abnormality, the prevalence of which was greater in those >65 years (p <0.0001; 37% in black and white men; 35.7% in white women and 34.9% in black women). Among those <65 years, women had more abnormalities than men among the whites (25.4% vs 23.2%), and these were greater among blacks, for whom the gender proportions were more nearly equal for women and men (28.4% vs 28.8% respectively). Major Q waves were present in 11.2% of the population, with the greatest proportion (20.4%) among white men >65 years old (p <0.0001). Major Q waves more common in blacks than in whites aged <65 years. The most common abnormalities overall were minor T wave abnormalities (20.4%), and the most common major abnormalities were also T wave abnormalities (19.1%). Left ventricular hypertrophy, by Cornell voltage, was 7.4% overall and was more common in women than in men (p <0.0001) and much more in blacks than in whites (p <0.0001), reaching 19.9% in black women. Bundle branch block was most common in white men >65 years (p <0.0001): 17.1% (any MC 7 code). More persons had right bundle branch block (2.7%) than had left bundle branch block (1.2%). Atrial fibrillation was present in 1.2% of the population, with increased levels in those aged >65 years and the greatest proportion in men >65 years old. Blacks had a lower prevalence than whites, except for black men <65 years old (1.0%), who were twice as likely to have atrial fibrillation as white men <65 years old (0.4%). Atrial premature beats were more common in blacks than in whites and more common in men than in women. Overall, atrial premature beats were more common than were ventricular premature beats (5.8% vs 3.5%).
| Variable | n | % | White (12,369, 59%) | Black (8,593, 41%) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Men, Age <65 yr (n = 2,394) | Men, Age ≥65 yr (n = 2,658) | Women, Age <65 yr (n = 3,909) | Women, Age ≥65 yr (n = 3,408) | Men, Age <65 yr (n = 1,592) | Men, Age ≥65 yr (n = 1,168) | Women, Age <65 yr (n = 3,361) | Women, Age ≥65 yr (n = 2,472) | |||
| Total | 20,962 | |||||||||
| Major Q wave abnormalities (MC 1.1, 1.2) | 2,738 | 11.2 | 11.6 | 20.4 | 6.9 | 14.4 | 12.1 | 17.6 | 7.8 | 13.8 |
| Minor Q wave abnormalities (MC 1.3) | 873 | 4.1 | 3.0 | 3.9 | 3.3 | 7.1 | 4.8 | 5.6 | 4.2 | 8.5 |
| Major ST segment depression (MC 4.1, 4.2) | 1952 | 6.8 | 4.9 | 9.6 | 4.7 | 10.6 | 9.3 | 16.5 | 7.0 | 15.0 |
| Minor ST segment depression (MC 4.2, 4.4) | 2173 | 8.0 | 5.7 | 10.4 | 6.1 | 12.0 | 9.7 | 16.7 | 8.6 | 16.2 |
| Major T wave abnormalities (MC 5.1, 5.2) | 5,234 | 19.1 | 11.3 | 24.3 | 16.8 | 29.7 | 21.4 | 33.5 | 21.4 | 34.4 |
| Minor T wave abnormalities (MC 5.3, 5.4) | 5,571 | 20.4 | 11.4 | 25.3 | 18.6 | 32.4 | 21.2 | 34.0 | 22.9 | 36.1 |
| Any Q waves | 3,611 | 14.9 | 14.3 | 23.4 | 9.9 | 20.5 | 16.3 | 22.2 | 11.6 | 21.1 |
| Any ST segment depression | 2192 | 8.1 | 5.8 | 10.6 | 6.2 | 12.2 | 9.7 | 16.7 | 8.6 | 16.3 |
| Any T wave abnormalities | 5,771 | 22.6 | 12.0 | 25.6 | 20.6 | 33.3 | 21.7 | 34.2 | 24.5 | 37.5 |
| ST segment elevation in inferior leads (MC 9.2) | 15 | 0.02 | 0 | 0.07 | 0.01 | 0 | 0.07 | 0.12 | 0.19 | 0.05 |
| ST segment elevation in lateral leads (MC 9.2) | 16 | 0.08 | 0.18 | 0 | 0 | 0 | 0.57 | 0.17 | 0 | 0.01 |
| ST segment elevation in anterior leads (MC 9.2) | 161 | 0.72 | 1.3 | 0.4 | 0.01 | 0.05 | 6.3 | 1.9 | 0.5 | 0.3 |
| Left ventricular hypertrophy † | 2197 | 7.4 | 3.5 | 10.7 | 4.7 | 14.7 | 9.0 | 14.9 | 9.2 | 19.9 |
| Tall R waves | ||||||||||
| MC 3.1 or 3.3 | 1665 | 5.2 | 4.9 | 4.5 | 3.3 | 4.8 | 15.6 | 11.4 | 10.0 | 13.7 |
| MC3.1 | 1324 | 4.1 | 3.6 | 4.1 | 2.6 | 4.1 | 10.7 | 9.7 | 7.3 | 11.1 |
| MC3.3 | 341 | 1.2 | 1.2 | 0.4 | 0.8 | 0.7 | 4.8 | 1.8 | 2.7 | 2.6 |
| A-V conduction abnormalities | 998 | 3.9 | 2.6 | 14.9 | 1.0 | 5.8 | 3.6 | 12.2 | 1.6 | 4.4 |
| Any bundle branch block (MC 7.x) | 1667 | 7.4 | 6.9 | 17.1 | 4.4 | 10.1 | 6.6 | 11.0 | 2.6 | 8.4 |
| Complete left bundle branch block (MC 7.1) | 293 | 1.2 | 0.3 | 2.7 | 0.6 | 3.1 | 0.4 | 1.1 | 0.3 | 2.4 |
| Complete right bundle branch block (MC 7.2) | 726 | 2.7 | 2.8 | 9.4 | 0.6 | 3.8 | 1.8 | 7.4 | 0.7 | 4.4 |
| Incomplete right bundle branch block (MC 7.3) | 508 | 2.8 | 3.2 | 2.7 | 3.1 | 2.3 | 4.0 | 1.1 | 1.5 | 1.3 |
| Nonspecific intraventricular bundle branch block (MC 7.4) | 140 | 0.6 | 0.6 | 2.3 | 0.1 | 0.9 | 0.5 | 1.3 | 0.1 | 0.4 |
| Atrial and ventricular premature beats (MC 8.1) | 2,633 | 10.2 | 7.4 | 19.7 | 6.7 | 16.2 | 9.4 | 22.1 | 8.1 | 18.1 |
| Atrial or junctional premature beats (MC 8.1.1) | 1449 | 5.8 | 4.6 | 10.2 | 3.8 | 9.2 | 5.7 | 12.9 | 4.1 | 9.7 |
| Ventricular premature beats (MC 8.1.2) | 922 | 3.5 | 2.3 | 7.0 | 2.5 | 5.5 | 2.7 | 5.9 | 3.5 | 6.1 |
| Both atrial and ventricular premature beats (MC 8.1.3) | 252 | 0.9 | 0.5 | 2.4 | 0.5 | 1.4 | 1.0 | 3.3 | 0.5 | 2.3 |
| Atrial fibrillation (MC 8.3) | 277 | 1.2 | 0.4 | 5.2 | 0.2 | 2.6 | 1.0 | 1.8 | 0.02 | 1.0 |
| Supraventricular rhythm (MC 8.4) | 116 | 0.4 | 0.2 | 0.9 | 0.2 | 0.7 | 0.2 | 0.7 | 0.4 | 0.7 |
| Low voltage QRS (MC 9.1) | 1401 | 7.3 | 3.8 | 4.0 | 11.6 | 8.1 | 2.2 | 2.5 | 6.7 | 6.2 |
| Tall P waves (MC 9.3) | 89 | 0.4 | 0.3 | 0.2 | 0.5 | 0.3 | 1.1 | 0.6 | 0.9 | 0.5 |
| Total major abnormalities ‡ | 6,790 | 28.2 | 23.2 | 37.1 | 25.4 | 35.7 | 28.8 | 37.4 | 28.4 | 34.9 |
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