Electrocardiographic left ventricular hypertrophy by five criteria among civil servants in Benin City, Nigeria: prevalence and correlates

International Journal of Cardiology 70 (1999) 1–14

Electrocardiographic left ventricular hypertrophy by five criteria among civil servants in Benin City, Nigeria: prevalence and correlates a, b c,d e Sara L. Huston *, Clareann H. Bunker , Flora A.M. Ukoli , Pentti M. Rautaharju , Lewis H. Kuller b a

Cardiovascular Health Branch, Health Promotion Section, Division of Community Health, North Carolina Department of Health and Human Services, P.O. Box 29605, Raleigh, NC 27626 -0605, USA b Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, USA c Department of Community Health, University of Benin Teaching Hospital, Benin City, Edo State, Nigeria d Cancer Center, Howard University, Washington, DC, USA e EPICARE Center, Department of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, NC, USA Accepted 7 January 1999

Abstract Although increasing hypertension rates have been reported in several African populations, little is known about the frequency of resulting hypertensive complications in these populations. We recorded the electrocardiograms of 482 male and 284 female civil servants in Benin City, Nigeria. Five different criteria were used to detect the presence of electrocardiographic left ventricular hypertrophy. Associations between electrocardiographic left ventricular hypertrophy and demographic, anthropometric and blood pressure characteristics were assessed. The prevalence of electrocardiographic left ventricular hypertrophy ranged from 3 to 29% in the total population, depending on the criteria used, with four of the five criteria resulting in prevalence estimates of less than 10%. The prevalence of electrocardiographic left ventricular hypertrophy was significantly greater among those with hypertension (19% of the total population), ranging from 11 to 49%. The prevalence of electrocardiographic left ventricular hypertrophy increased with blood pressure level in both normotensives and hypertensives. Among hypertensives with systolic blood pressure $180 mmHg or diastolic blood pressure $110 mmHg, the prevalence exceeded 50% by four of the five criteria. We conclude that left ventricular hypertrophy may be affecting many hypertensives in this Nigerian population, potentially resulting in a substantial future burden of cardiovascular disease and death.  1999 Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords: Left ventricular hypertrophy; Epidemiology; Electrocardiography; Blacks; Nigeria; Blood pressure; Anthropometry

1. Introduction Despite reports of increasing blood pressure and hypertension prevalence among African populations, little information is available on the burden of resulting cardiovascular disease and mortality in these populations. Historically, hypertension and cardiovascular disease were extremely rare in African *Corresponding author.

populations [1–4]. More recent surveys, however, have reported higher mean blood pressures and greater hypertension prevalence than previously recorded in some African populations [5–8], particularly in urban areas. Hypertension prevalence is typically higher in urban African populations than in rural populations [6,9], sometimes approaching levels seen in the United States [5,6,8–10]. Several studies in Nigeria have suggested that blood pressure may also be positively correlated with socioeconomic

0167-5273 / 99 / $ – see front matter  1999 Published by Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 99 )00061-3

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status [5,11,12]. These African populations may be in transition towards higher blood pressure levels as they adopt more ‘Westernized’ lifestyles (for example, sedentary lifestyle, increased dietary fat and sodium consumption) [5,11,13–15]. If blood pressure levels and hypertension rates are indeed on the rise in these populations, a subsequent rise in hypertensive disease and cardiovascular disease events may become evident. Left ventricular hypertrophy is one such adverse outcome of hypertension that can result in an increased risk of cardiovascular morbidity and mortality. Left ventricular hypertrophy is an increase in the muscle mass of the left ventricle resulting from a chronic pressure or volume overload of the circulatory system, and is frequently a result of hypertension. Left ventricular hypertrophy is a major independent risk factor for subsequent death due to cardiovascular disease and ischemic heart disease in both blacks and whites in the United States [16–19]. In addition, persons with left ventricular hypertrophy are at increased risk of developing ischemic heart disease, heart failure, stroke and intermittent claudication, independent of the effect of blood pressure level [16–18]. In the Framingham study [16], the risk of a lethal coronary attack, including sudden death, was also increased among those with left ventricular hypertrophy; 40% of those with prior left ventricular hypertrophy died during their initial coronary event. Electrocardiography and echocardiography are the two most commonly used methods of detecting left ventricular hypertrophy. Although the echocardiogram is considered the gold standard, electrocardiography is still widely used. Among African Americans, the prevalence and incidence rates of electrocardiographic left ventricular hypertrophy are more than twofold those among whites, even after adjusting for differences in age and blood pressure [20– 25]. Reports of echocardiographically diagnosed left ventricular hypertrophy are inconsistent, with some showing greater left ventricular mass and greater prevalence of left ventricular hypertrophy among blacks compared with whites, and some showing no race differences [26–31]. Information on left ventricular hypertrophy in African populations is scarce. Several reports on electrocardiographic patterns in Africans were published in the 1960s and 1970s; however, the authors sought more to characterize these patterns in different

population groups than to examine left ventricular hypertrophy specifically [32–34]. More recent reports have examined hypertensive heart disease among Nigerian hypertensives, but these rely on small numbers of selected patients and focus primarily on detailing the clinical manifestations and assessing the validity of electrocardiography in diagnosing left ventricular hypertrophy [35–38]. This report presents baseline results from the Nigerian Civil Servant Study, a prospective cohort investigation of hypertension and cardiovascular disease among approximately 800 civil servants in Benin City, Nigeria. This is a relatively healthy working population representing a broad range of the socioeconomic spectrum. In addition, previous study has shown that this population of civil servants is undergoing a transition, with the prevalence of hypertension increasing among those of higher socioeconomic status [5]. This report describes the baseline prevalence of electrocardiographic left ventricular hypertrophy by five criteria in this population, and examines patterns in these prevalence estimates by demographic factors, anthropometric measurements and blood pressure.

2. Materials and methods

2.1. Study protocol The study protocol was approved by the Biomedical Institutional Review Boards of both the University of Pittsburgh and the University of Benin Teaching Hospital. Informed consent was obtained from all participants at the beginning of their first visit. Pregnant women were excluded from the study. Participants found to have high blood pressure or other health problems were referred for follow-up care.

2.2. Study population The target study population consisted of all on-site employees of the Edo State Ministries of Education and Information, and all on-site female employees of the Ministry of Agriculture, in Benin City, Nigeria. We included all female employees from this one Ministry (Agriculture) to ensure an adequate number

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

of women in the study for sex-specific analyses, since the number of women in the Nigerian Civil Service was relatively small. In addition to the use of staff lists provided by the Ministries, we carried out a chair-to-chair census of each workspace to determine the total target population.

2.3. Data collection The study was conducted in rooms provided at each ministry. Data were collected in three visits for each participant. Demographic and physical activity information was obtained through questionnaires administered by trained interviewers. Height and weight measurements were made while the subject was lightly clothed and not wearing shoes. Body mass index was calculated by dividing the individual’s weight (in kilograms) by the height (in meters) squared. Body mass index was classified as low, normal or high using the fifteenth and eightyfifth percentile cut-off points of body mass index among men and women aged 20–29 years in the United States Second National Health and Nutrition Examination Survey [39]. For women, these cut-off points are 19.1 and 27.3 kg / m 2 , and for men they are 20.7 and 27.8 kg / m 2 . The past year’s physical activity data were collected using the leisure and occupational activity questionnaire developed and validated in the Pima Native American population [40]. This questionnaire was customized during a pilot study in the Nigerian civil servant population to include activities common in Nigeria, and was designed to allow the addition of uncommon activities reported during data collection. Occupational activity included walking and bicycling to and from work, along with all activity done at work. Leisure activity included all activities done outside the workplace, including household work activities such as farming and walking to the market, and recreational activities such as calisthenics and table tennis. Each activity was weighted by its intensity relative to the resting metabolic rate (one MET), and physical activity totals are reported in MET hours per week, averaged over the past year.

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tion Trial protocol [41]. Three blood pressure measurements were obtained at each of the three visits after a 5-min seated rest period. Systolic blood pressure was recorded at the first of two successive Korotkoff sounds (onset of Phase I), and diastolic blood pressure was recorded at the last Korotkoff sound. The average systolic and diastolic blood pressures were calculated by averaging the second and third blood pressure measures over all three visits. These averages were used to classify blood pressure level according to the guidelines set by the Sixth Report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure [42]. Hypertension was defined as an average systolic blood pressure of at least 140 mmHg, or average diastolic blood pressure of at least 90 mmHg, or current use of anti-hypertensive medications. High normal blood pressure was defined as an average systolic blood pressure of between 130 and 139 mmHg (inclusive) or average diastolic blood pressure of between 85 and 89 mmHg (inclusive), and no current use of anti-hypertensive medications. Normal blood pressure was defined as an average systolic blood pressure of less than 130 mmHg and an average diastolic blood pressure of less than 85 mmHg and no current use of anti-hypertensive medications. Individuals with hypertension who were currently taking anti-hypertensive medications and had blood pressures less than 140 mmHg systolic and 90 mmHg diastolic were classified as having controlled hypertension. All other hypertensives were classified as having uncontrolled hypertension. Those with uncontrolled hypertension were further classified by stage of hypertension [42]. Briefly, Stage 1 hypertension includes those with systolic blood pressure of 140–159 mmHg or diastolic blood pressure of 90–99 mmHg; Stage 2: systolic blood pressure of 160–179 mmHg or diastolic blood pressure of 100–109 mmHg; and Stage 3: systolic blood pressure $180 mmHg or diastolic blood pressure $110 mmHg. When systolic and diastolic blood pressures fell into different categories, the higher category was used.

2.4. Blood pressure

2.5. Electrocardiograms

Blood pressure was recorded by technicians certified according to the Multiple Risk Factor Interven-

Standard 12-lead supine electrocardiograms were recorded using a battery-powered portable electro-

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cardiograph machine (MACPC, Marquette Electronics, Milwaukee, WI, USA). Special care was taken in consistently placing the chest electrodes; a special device (Heart Square, Heartware, Edmonton, Alberta, Canada) was used to produce two critical measurements that documented the locations of electrodes V3 , V4 , V5 and V6 [43]. This electrode placement procedure also provided two anthropometric measurements of chest size. Chest width was measured as the distance from the midsternal line to the left lateral chest wall, and chest depth was measured as the distance from the anterior chest wall to the left midaxillary line. The digitized electrocardiogram files were analyzed by the EPICARE Center (Wake Forest University School of Medicine, Winston-Salem, NC, USA) using the Novacode software [44] designed specifically to process electrocardiograms for epidemiological studies. The electrocardiographic amplitude measurements on which the left ventricular hypertrophy criteria were based were taken from selective averages of normally conducted complexes contained in the recordings of 10-s duration after drift

correction and rejection of artifacts and ventricular ectopic complexes.

2.6. Electrocardiographic criteria The electrocardiographic criteria used in this study are listed in Table 1. The primary conventional electrocardiographic criteria used for left ventricular hypertrophy are based on various categories of the 1982 version of the Minnesota Code [45] and the gender-specific Cornell Voltage criteria [46]. The Minnesota Code is a standard classification scheme for electrocardiographic abnormalities that is often used in epidemiologic studies. The Minnesota Codes 3.1 and 3.3 reflect high amplitude R and S waves, while codes 5.1 through 5.3 indicate T-wave abnormalities. The Cornell Voltage criteria are based upon R and S wave amplitudes only. In addition, the Novacode electrocardiogram software estimated left ventricular mass index through multivariate algorithms [19,44]. These algorithms are sex-specific, and they are race-specific for women only; the algorithm used for men was developed in white men. Novacode

Table 1 Selected electrocardiographic criteria for left ventricular hypertrophy [19,44–46] Minnesota Codes [45] 3.1: 3.3: 5.1: 5.2:

5.3:

Cornell Voltage [46] Men: Women: Novacode [19,44] Men:

Women:

a b

R amplitude.2600 mV in either V5 or V6 , or .2000 mV in any of leads I, II, III or aVF, or .1200 mV in lead aVL. As measured only on the penultimate complete normal beat. R amplitude.1500 mV but # 2000 mV in lead I, or R amplitude in V5 or V6 plus S amplitude in V1 .3500 mV. As measured only on the penultimate complete normal beat. T amplitude negative 500 mV or more in any of leads I, II, V2 , V3 , V4 , V5 ,V6 , or in lead aVL when R amplitude is $ 500 mV, or in lead aVF when QRS is mainly upright. T amplitude negative or diphasic (positive–negative or negative–positive type) with a negative phase of at least 100 mV but not as deep as 500 mV in any of the leads I, II, V2 , V3 , V4 , V5 , V6 , or in lead aVL when R amplitude is $ 500 mV, or in lead aVF when QRS is mainly upright. T amplitude zero (flat), or negative, or diphasic (negative–positive type only) with ,100 mV negative phase in leads I, II, V3 , V4 , V5 , V6 , or in lead aVL when R amplitude is $500 mV.

R amplitude in aVL plus S amplitude in V3 .2800 mV. R amplitude in aVL plus S amplitude in V3 .2000 mV. Electrocardiographic left ventricular mass index .150 g / m 2 , where electrocardiographic left ventricular mass index5236.410.103R(V5 )10.0203S(V1 )10.0283S a (III)10.1823T neg (V6 )20.1483 T pos (aVR)11.0493QRS duration.b Electrocardiographic left ventricular mass index .120 g / m 2 , where electrocardiographic left ventricular mass index5222.310.0223R(aVL)10.0183[R(V6 )1S(V2 )]20.0143R(V2 )20.0693S a (V5 )1 0.1993T neg (aVL)10.7463QRS duration.b

S or Q or QS, whichever is larger. Amplitudes (absolute values) are in mV; QRS duration is given in ms.

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

electrocardiographic left ventricular hypertrophy prevalence was estimated using cut-off points set at the upper normal limits for echocardiographic left ventricular mass index according to the American Society of Echocardiography standards [47], which are 150 g / m 2 for men and 120 g / m 2 for women. The Novacode criteria for left ventricular hypertrophy were strong predictors of subsequent cardiovascular disease mortality in the first National Health and Nutrition Examination Survey follow-up study [19]. In the interest of brevity, electrocardiographic left ventricular hypertrophy will hereafter be simply referred to as left ventricular hypertrophy.

2.7. Statistical analysis Data analysis was carried out using SAS version 6.08 (SAS Institute, Cary, NC, USA). Frequencies of left ventricular hypertrophy according to the five criteria were compared across sex, age, body mass index and blood pressure classification groups using the chi-square test (with continuity correction) or Fisher’s exact test when appropriate. Sex-specific frequencies of left ventricular hypertrophy were also compared across age, blood pressure and body mass index classification groups using the chi-square test (with a continuity correction) or Fisher’s exact test. We also examined the influence of anthropometric and physical activity measures on the left ventricular hypertrophy prevalence estimates. We limited this part of the analysis to men because the sample size of women was too small for meaningful analysis. Using logistic regression, we compared the likelihood of left ventricular hypertrophy between extreme quartiles of each anthropometric and physical activity measure while adjusting for systolic blood pressure and age (both entered as continuous variables). The Minnesota Code 3.1 or 3.3 criteria yielded high prevalence estimates compared with the other criteria, especially among those with normal blood pressure. We tried to gain some insight into the reasons for this by comparing the age, blood pressure, physical activity and anthropometric measurements of normotensive men with Minnesota Codes 3.1 or 3.3 to those without. The Student’s t-test (the MannWhitney U test for the physical activity data) was used for this analysis.

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3. Results

3.1. Participation Of the 960 employees on the staff and census lists at the three ministries, 809 (84.3%) participated in the study, 77 (8.0%) refused to participate and 74 (7.7%) could not be found at the workplace. The participation rate was 91% of those who could be found at the workplace and 84% overall, with rates of 79 to 97% across sites. After the study was completed, study staff returned to the sites and collected demographic data, blood pressure- and anthropometric measurements for 122 (81%) of the 151 nonparticipants (those who previously refused or could not be found at the workplace). The nonparticipants were similar to the participants with respect to the proportion who were hypertensive, and in mean age and mean body mass index. Electrocardiograms were obtained for 781 (96.5%) of the 809 participants. The electrocardiograms of 15 participants were excluded from the analysis due to inadequate electrocardiogram quality, missing electrocardiogram leads or ventricular conduction defects that prevented the assessment of left ventricular hypertrophy criteria. The resulting population of 766 (94.7% of the total) used in this analysis did not differ from the total population of 809 with respect to age, systolic and diastolic blood pressure, body mass index or sex distributions.

3.2. Population description Men comprised 63% of the population. Using Nigerian Civil Service salary grade categories, Senior Staff (primarily administrators and other professionals) and Junior Staff (e.g. messengers, drivers, groundskeepers), as a proxy for socioeconomic status, 58% of this population were of low socioeconomic status. The mean age of the participants was 41 and the mean length of residence in an urban area was 30 years. The prevalence of hypertension and the proportion overweight in this population were lower than those among African Americans in the Third National Health and Nutrition Examination Survey, a comprehensive health survey of a nationally representative sample of United States’ residents [48]. In this

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population of Nigerian civil servants, the prevalence of hypertension was 19.3% among men and 9.9% among women (Table 3) compared with 33.5% of African–American men and 27.5% of African– American women [48]. The proportion of the population considered to be overweight was 6.0% among men (Table 4) and 24.9% among women (Table 5) in this Nigerian population compared with 32.4% of African–American men and 48.6% of African– American women [48].

mates of less than 10% in the total population (Table 2). The Minnesota Code 3.1 or 3.3 criteria resulted in a prevalence estimate of 29%, which was about threefold higher than estimates yielded by the other criteria. Left ventricular hypertrophy prevalence by the Minnesota Code 3.1 or 3.3 and Minnesota Code 3.1 was significantly higher in men than women, and men also had a slightly higher prevalence of left ventricular hypertrophy by the Novacode criteria. Likewise, mean systolic blood pressure and hypertension prevalence were higher among men than women (Table 3). Left ventricular hypertrophy prevalence by any criteria did not show any significant trend with age in the total population (Table 2), although both mean systolic blood pressure and hypertension prevalence

3.3. Electrocardiographic left ventricular hypertrophy prevalence and associated factors Four of the five electrocardiographic criteria for left ventricular hypertrophy yielded prevalence esti-

Table 2 Prevalence (%) of electrocardiographic left ventricular hypertrophy according to five criteria by sex, age group, blood pressure and body mass index among civil servants, Benin City, Nigeria, 1992 n

Novacode %

Minnesota Code

Odds ratio (95% CI)

a

Cornell Voltage

3.1 or 3.3

3.1

%

Odds ratio (95% CI)a

%

Total

766

8.2

2

29.1

2

Sex Male

482

9.8

36.3

5.6

2.80 (1.92–4.09) Referent

13.7

284

1.81 (0.97–3.40) Referent

Age 20–34 35–44

178 319

8.4 8.2

9.0 8.5

45–54

229

8.7

55–64

40

5.0

Referent 0.91 (0.59–1.39) 1.10 (0.71–1.73) 0.68 (0.28–1.63)

Blood pressure Normal High normal

574 71

5.4 11.3

Hypertension

121

19.8

Body mass index b Low 219

7.3

Female

Normal High a

444 99

9.7 3.0

16.9

Referent 0.97 (0.48–1.99) 1.04 (0.49–2.21) 0.57 (0.06–2.63)

29.8 27.6

Referent 2.22 (0.90–5.33) 4.33 (2.35–7.99)

24.2 35.2

0.74 (0.39–1.38) Referent 0.29 (0.06–0.94)

31.9 22.5

48.8

36.5 29.7 11.1

Referent 1.70 (0.97–2.96) 2.98 (1.95–4.55) 1.36 (0.95–1.94) Referent 0.30 (0.14–0.59)

9.9

3.5

13.1 7.5

6.6 14.1 23.1

13.7 10.1 1.0

(3.1 or 3.3)1(5.1–5.3) Odds ratio (95% CI)a

%

%

Odds ratio (95% CI)a

Odds ratio (95% CI)a

2

3.1

2

4.2

2

4.35 (2.12–9.16) Referent

2.9

0.82 (0.34–2.02) Referent

4.1

0.98 (0.45–2.17) Referent

Referent 0.94 (0.47–1.89) 1.53 (0.77–3.05) 0.82 (0.15–3.09)

2.8 1.9

Referent 0.67 (0.17–2.81) 1.91 (0.61–7.06) 0.89 (0.02–8.26)

4.5 3.8

Referent 1.87 (0.77–4.40) 2.31 (1.02–5.12)

1.0 2.8

Referent 2.74 (0.27–15.70) 14.43 (5.18–45.80)

3.0 2.8

1.41 (0.83–2.37) Referent 0.09 (0.00–0.55)

3.5

5.2 2.5

13.2

3.7 3.4 1.0

1.08 (0.41–2.77) Referent 0.29 (0.01–1.94)

4.2

4.4 5.0

10.7

4.6 4.3 2.0

Referent 0.84 (0.31–2.29) 0.97 (0.34–2.76) 1.12 (0.11–5.92) Referent 0.95 (0.01–4.14) 3.94 (1.75–8.85) 1.07 (0.45–2.47) Referent 0.46 (0.05–1.97)

CI: confidence interval. Body mass index (kg / m 2 ): Low: #19.1 for women, #20.7 for men; Normal: 19.2–27.2 for women, 20.8–27.7 for men; High: $27.3 for women, $27.8 for men. b

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Table 3 Mean systolic blood pressure and hypertension prevalence by sex, age group, and body mass index among civil servants, Benin City, Nigeria, 1992 n

Systolic blood pressure (mmHg)

Hypertension

Mean

(s.d.)a

%

(n)

Odds ratio (95% CI)b

Total

766

117.4

(17.6)

15.8

(121)

2

Sex Male Female P

482 284

120.3 112.4 t-test: 0.0001

(18.1) (15.5)

19.3 9.9

(93) (28)

2.19 (1.36–3.52) Referent X 2 : 0.0008

Age 20–34 35–44 45–54 55–64 P

178 319 229 40

111.6 114.8 122.9 132.2 ANOVA: 0.0001

(16.0) (15.8) (18.0) (18.7)

3.9 11.0 27.1 42.5

(7) (35) (62) (17)

Referent 3.01 (1.28–8.20) 9.07 (3.98–24.07) 18.06 (6.18–56.11) X 2 trend: ,0.0001

Body Mass Index c Low Normal High P

219 444 99

114.8 118.2 119.3 ANOVA: 0.0294

(17.8) (17.7) (16.2)

10.0 17.8 20.2

(22) (79) (20)

0.52 (0.30–0.88) Referent 1.17 (0.65–2.09) X 2 trend: 0.0070

a

s.d.: standard deviation. CI: confidence interval. c Body mass index (kg / m 2 ): Low: #19.1 for women, #20.7 for men; Normal: 19.2–27.2 for women, 20.8–27.7 for men; High: $27.3 for women, $27.8 for men. b

did increase with age (Table 3). Likewise, no significant trends in left ventricular hypertrophy with age were seen in either men or women (Tables 4 and 5). As the level of body mass index increased, both mean systolic blood pressure and hypertension prevalence increased (Table 3), but left ventricular hypertrophy prevalence showed a different pattern. The left ventricular hypertrophy prevalence estimates were lower among those with high body mass index compared to those with a normal body mass index (Table 2). Although this effect was not always statistically significant, the pattern was consistent in both men and women (Tables 4 and 5) and in both normotensives and hypertensives (data not shown). Those with low body mass index often had a higher proportion with left ventricular hypertrophy compared with those with a normal body mass index, but this effect was neither statistically significant nor consistent across criteria (Tables 2, 4 and 5). Hypertension was strongly associated with the presence of electrocardiographic left ventricular hypertrophy by all five criteria (Table 2). Four of the five criteria resulted in prevalence estimates of 11– 23% among those with hypertension. Again, the Minnesota Code 3.1 or 3.3 criteria resulted in a much

higher prevalence estimate (49%) than the others. Although those with high normal blood pressure generally had higher left ventricular hypertrophy prevalence estimates than those with normal blood pressure, these differences were not statistically significant. The pattern of greater left ventricular hypertrophy prevalence in those with hypertension remained consistent in both men and women when the data were stratified by sex (Tables 4 and 5). Among those with normal or high normal blood pressure, the prevalence of left ventricular hypertrophy by both the Minnesota Code 3.1 criteria and the 3.1 or 3.3 criteria increased with each increasing quartile of systolic blood pressure (Table 6). Left ventricular hypertrophy by the Novacode criteria also increased with increasing quartile of systolic blood pressure, but only the highest quartile had a significantly greater prevalence than the lowest quartile. Left ventricular hypertrophy by the Cornell Voltage and the Minnesota Code (3.1 or 3.3)1(5.1–5.3) criteria showed no trend with systolic blood pressure quartiles. The association between left ventricular hypertrophy and diastolic blood pressure was weaker than that with systolic blood pressure (Table 6). The prevalence of left ventricular hypertrophy increased

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Table 4 Prevalence (%) of electrocardiographic left ventricular hypertrophy according to five criteria by age group, blood pressure and body mass index among male civil servants, Benin City, Nigeria, 1992 n

Novacode %

Odds ratio

93 185

12.9 9.2

45–54

167

9.6

55–64

37

5.4

Blood Pressure Normal High normal

337 52

7.1 13.5

Hypertension

93

17.2

Body mass index b Low 179

7.3

Normal High a b

273 29

11.7 6.9

Cornell Voltage

3.1 or 3.3

3.1

%

Odds ratio (95% CI)a

%

Odds ratio (95% CI)a

%

Odds ratio (95% CI)a

Referent 0.68 (0.29–1.61) 0.72 (0.30–1.70) 0.39 (0.04–1.88)

39.8 37.8

Referent 0.92 (0.54–1.59) 0.83 (0.47–1.44) 0.49 (0.19–1.23)

16.1 11.9

Referent 0.70 (0.33–1.51) 0.96 (0.46–2.03) 0.46 (0.08–1.79)

3.2 2.2

Referent 0.66 (0.11–4.63) 1.12 (0.23–7.07) 0.83 (0.02–10.79)

6.5 3.2

Referent 2.03 (0.70–5.21) 2.71 (1.30–5.62)

32.0 44.2

Referent 1.68 (0.89–3.17) 1.90 (1.16–3.12)

10.1 17.3

Referent 1.87 (0.77–4.40) 2.93 (1.56–5.49)

1.2 1.9

Referent 1.63 (0.03–16.90) 8.92 (2.40–40.33)

3.3 1.9

(95% CI) Age 20–34 35–44

Minnesota Code

a

0.59 (0.28–1.21) Referent 0.56 (0.06–2.41)

35.3 24.3

47.3

39.1 37.4 10.3

1.08 (0.72–1.62) Referent 0.19 (0.04–0.66)

15.6 8.1

24.7

16.2 13.6 0.0

(3.1 or 3.3)1(5.1–5.3)

1.23 (0.70–2.16) Referent Undefined (Undef.–0.76)

3.6 2.7

9.7

3.9 2.6 0.0

1.55 (0.48–5.00) Referent Undefined (Undef.–4.35)

%

Odds ratio (95% CI)a

3.6 5.4

8.6

3.9 4.4 3.4

Referent 0.49 (0.13–1.88) 0.54 (0.14–2.09) 0.83 (0.08–4.93) Referent 0.58 (0.01–4.16) 2.79 (0.94–7.87) 0.89 (0.31–2.47) Referent 0.78 (0.02–5.63)

CI: confidence interval. Body mass index (kg / m 2 ): Low: #20.7; Normal: 20.8–27.7; High: $27.8.

with increasing quartiles of diastolic blood pressure only when the Minnesota Code 3.1 or 3.3 criteria were used. Among those with uncontrolled hypertension, stage of hypertension was associated with the prevalence of left ventricular hypertrophy (Table 7). By all criteria except Minnesota Code 3.1 or 3.3 and 5.1–5.3, those with Stage 3 hypertension had significantly greater left ventricular hypertrophy prevalence than those with Stage 1 hypertension. Four of the five criteria estimated that more than 50% of those with Stage 3 hypertension had left ventricular hypertrophy. After adjusting for age and systolic blood pressure, left ventricular hypertrophy prevalence by the three Minnesota Code criteria was still associated with body mass index and chest depth among men (Table 8). Men in the lowest quartile of body mass index were significantly more likely to have left ventricular hypertrophy by any of the Minnesota Code criteria than those in the highest quartile. In addition, those in the lowest quartile of chest depth were significantly more likely to have left ventricular hypertrophy by

the Minnesota Code 3.1 or 3.3 or Minnesota Code 3.1 criteria than those in the highest quartile. High levels of physical activity, however, did not consistently affect the likelihood of left ventricular hypertrophy among men (Table 8). Those in the highest quartile of leisure time physical activity were slightly (P5 0.093) more likely to have left ventricular hypertrophy by the Minnesota Code 3.1 or 3.3 criteria compared with those in the lowest quartile. The data suggested, however, that physical activity above the median was associated with an increased likelihood of left ventricular hypertrophy by some criteria. When we used the same multivariate logistic regression method (adjusting for age and systolic blood pressure) to compare the two highest quartiles of leisure physical activity to the two lowest quartiles, the odds ratio for Minnesota Code 3.1 or 3.3 was 1.49 (95% confidence interval51.01–2.20, P50.046). Likewise, those in the two highest quartiles of occupational physical activity were more likely to have left ventricular hypertrophy by the Novacode criteria compared with those in the two lowest quartiles (odds

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

9

Table 5 Prevalence (%) of electrocardiographic left ventricular hypertrophy according to five criteria by age group, blood pressure and body mass index among female civil servants, Benin City, Nigeria, 1992 Novacode n

%

Odds ratio

85 134

3.5 6.7

45–54

62

6.5

55–64

3

0.0

Blood pressure Normal High normal

237 19

3.0 5.3

Hypertension

28

28.6

Body mass index b Low

40

7.5

171 70

6.4 1.4

Normal High a b

Cornell Voltage

3.1 or 3.3

3.1

%

Odds ratio (95% CI)a

%

Referent 1.97 (0.47–11.60) 1.89 (0.30–13.30) Undefined (Undef.–91.15)

18.8 13.4

Referent 0.67 (0.30–1.49) 1.26 (0.52–3.03) Undefined (Undef.–11.19)

1.2 3.7

Referent 1.83 (0.04–15.51) 13.14 (3.38–45.90)

13.1 10.5

Referent 0.78 (0.08–3.56) 7.67 (3.09–19.14)

1.7 5.3

1.18 (0.20–4.77) Referent 0.21 (0.00–1.51)

25.0

(95% CI) Age 20–34 35–44

Minnesota Code

a

22.6 0.0

53.6

17.5 11.4

1.57 (0.64–3.79) Referent 0.61 (0.24–1.48)

6.5 0.0

17.9

2.5 4.7 1.4

(3.1 or 3.3)1(5.1–5.3) Odds ratio (95% CI)a

%

Referent 3.26 (0.35–155.79) 5.79 (0.55–288.61) Undefined (Undef.–1105.00)

2.4 1.5

Referent 3.24 (0.06–34.80) 12.66 (2.48–67.19)

0.8 5.3

0.52 (0.01–4.10) Referent 0.30 (0.01–2.28)

9.7 0.0

25.0

2.5 4.7 1.4

%

(95% CI)a

Odds ratio (95% CI)a Referent 0.63 (0.05–8.85) 4.45 (0.75–46.12) Undefined (Undef.–177.08)

2.4 4.5

Referent 6.53 (0.11–129.11) 39.17 (6.67–396.17)

2.5 5.3

0.52 (0.01–4.10) Referent 0.30 (0.01–2.28)

Odds ratio

6.5 0.0

17.9

7.5 4.1 1.4

Referent 1.95 (0.34–20.10) 2.86 (0.39–32.39) Undefined (Undef.–177.08) Referent 2.14 (0.04–19.12) 8.37 (1.84–35.32) 1.90 (0.30–8.78) Referent 0.34 (0.01–2.73)

CI: confidence interval. Body mass index (kg / m 2 ): Low: #19.1; Normal: 19.2–27.2; High: $27.3.

Table 6 Prevalence (%) of electrocardiographic left ventricular hypertrophy according to five criteria by quartiles of systolic and diastolic blood pressure among civil servants with normal or high normal blood pressure, Benin City, Nigeria, 1992 n

Total

645

Novacode

Minnesota Code

%

Odds ratio

3.1 or 3.3

3.1

(95% CI)a

%

Odds ratio (95% CI)a

%

2

25.4

2

13.3 24.2

Referent 2.07 (1.12–3.86) 2.67 (1.46–4.90) 3.50 (1.92–6.42)

6.0

Systolic blood pressure (mmHg) 84–103 157 2.5 Referent 104–110 165 6.1 2.47 (0.69–10.98) 111–119 168 6.0 2.42 (0.68–10.77) 120–139 154 9.7 4.13 (1.27–17.42) Diastolic blood pressure (mmHg) 51–66 158 3.8 Referent 67–71 157 7.6 2.10 (0.70–6.98) 72–77 180 4.6 1.49 (0.48–5.11) 78–89 150 7.3 2.00 (0.66–6.77) a

CI: confidence interval.

29.2 35.1

16.5 24.8 28.9 31.3

Referent 1.68 (0.93–3.03) 2.06 (1.18–3.63) 2.32 (1.30–4.14)

Cornell Voltage (3.1 or 3.3)1(5.1–5.3)

%

Odds ratio (95% CI)a

Odds ratio (95% CI)a

%

Odds ratio (95% CI)a

7.4

2

1.2

2

2.9

2

1.9 7.3

Referent 4.03 (1.05–22.58) 5.40 (1.50–29.39) 6.37 (1.78–34.47)

1.3 1.8

Referent 1.44 (0.16–17.38) 0.46 (0.01–9.02) 1.02 (0.07–14.23)

1.9 4.2

Referent 2.27 (0.51–13.84) 1.25 (0.21–8.68) 1.72 (0.33–11.27)

9.5 11.0

3.8 7.6 11.7 6.0

Referent 2.10 (0.70–6.98) 3.35 (1.26–10.38) 1.62 (0.50–5.66)

0.6 1.3

0.6 1.3 1.7 1.3

Referent 2.03 (0.10–120.27) 2.66 (0.21–140.57) 2.12 (0.11–125.95)

2.4 3.2

1.9 4.5 3.3 2.0

Referent 2.41 (0.54–14.68) 1.78 (0.37–11.18) 1.05 (0.14–8.00)

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

10

Table 7 Prevalence (%) of electrocardiographic left ventricular hypertrophy according to five criteria by stage of hypertension among civil servants with uncontrolled hypertension, Benin City, Nigeria, 1992 n

Novacode %

Odds ratio

111

20.7

Hypertension Stage Stage 1 77 14.3 Stage 2 23 21.7 Stage 3 a

11

63.6

Cornell Voltage

3.1 or 3.3

3.1

%

Odds ratio (95% CI)a

%

Odds ratio (95% CI)a

%

Odds ratio (95% CI)a

2

48.6

2

24.3

2

12.6

2

9.9

2

Referent 1.67 (0.40–6.05) 10.50 (2.16–55.37)

40.3 60.9

Referent 2.31 (0.81–6.68) 6.68 (1.24–66.26)

15.6 39.1

Referent 3.48 (1.09–11.16) 6.50 (1.37–30.90)

11.7 13.0

Referent 1.13 (0.18–5.13) 1.68 (0.15–10.18)

3.9 8.7

Referent 2.35 (0.18–21.72) 29.60 (4.36–221.40)

(95% CI) Total

Minnesota Code

a

81.8

(3.1 or 3.3)1(5.1–5.3)

54.5

18.2

%

Odds ratio (95% CI)a

54.5

CI: Confidence Interval,

ratio52.73; 95% confidence interval51.38–5.39; P5 0.004). Among men with normal blood pressure, those with left ventricular hypertrophy according to the Minnesota Code 3.1 or 3.3 criteria had higher systolic blood pressure (113.5 compared with 110.1 mmHg; P50.0009) than those without left ventricular hypertrophy. Age, diastolic blood pressure, physical activity levels, body mass index and chest dimensions were similar between the two groups (data not shown; all P-values.0.20).

4. Discussion This report is one of the first to describe the epidemiology of left ventricular hypertrophy in an African population. We examined the prevalence of, and factors associated with, electrocardiographic left

ventricular hypertrophy according to five different criteria among civil servants in Benin City, Edo State, Nigeria. Among the total population of civil servants, four of the five electrocardiographic criteria for left ventricular hypertrophy resulted in prevalence estimates of between 3 and 10%. Of the factors examined in this study, blood pressure level and hypertension status were most strongly and consistently associated with electrocardiographic left ventricular hypertrophy. The prevalence of electrocardiographic left ventricular hypertrophy among those with hypertension (who made up 19% of the total population) was substantial, ranging from 11 to 49%. Furthermore, among those with Stage 3 hypertension (10% of hypertensives), four of the five criteria estimated the prevalence of left ventricular hypertrophy to be greater than 50%. The estimates of left ventricular hypertrophy prevalence by the Minnesota Code 3.1 criteria among hypertensives in this popula-

Table 8 Odds ratios (95% confidence interval in parentheses) for electrocardiographic left ventricular hypertrophy by five criteria associated with anthropometric and physical activity measures after adjusting for systolic blood pressure and age among male civil servants, Benin City, Nigeria, 1992 Novacode

Minnesota Code 3.1 or 3.3

a

Body mass index Chest width a Chest depth a Occupational activity b Leisure activity b Total activity b a

0.52 (0.20–1.39) 0.97 (0.39–2.43) 1.20 (0.54–2.64) 2.19 (0.85–5.66) 0.68 (0.25–1.86) 2.13 (0.85–5.29)

2.03 (1.12–3.67)* 1.59 (0.85–2.96) 2.18 (1.29–3.67)† 1.09 (0.63–1.89) 1.64 (0.92–2.91)§ 0.87 (0.50–1.51)

Odds ratios are for the lowest quartile compared to the highest quartile. Odds ratios are for the highest quartile compared to the lowest quartile. § P,0.10; *P,0.05; **P,0.01; † P,0.005. b

Cornell 3.1 †

4.81 (1.87–12.37) 1.76 (0.68–4.56) 2.20 (1.04–4.65)* 1.27 (0.57–2.80) 1.83 (0.79–4.23) 1.07 (0.48–2.40)

(3.1 or 3.3)1(5.1–5.3)

Voltage

11.29 (1.21–105.8)* 0.94 (0.08–10.93) 2.18 (0.44–10.79) 0.60 (0.10–3.65) 3.93 (0.71–21.81) 1.10 (0.15–8.15)

1.14 (0.32–4.11) 0.79 (0.14–4.50) 0.71 (0.23–2.19) 1.68 (0.47–5.97) 0.37 (0.07–1.91) 1.05 (0.25–4.35)

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

tion were 24.7% in men and 17.9% in women, which were much higher than the prevalence of Minnesota Code 3.1 among white hypertensives (men: 9.6%; women: 6.2%) and approaching that among black hypertensives (men: 31.0%; women: 20.5%) in the Hypertension Detection and Prevention Follow-up Study [23]. Our results suggest that left ventricular hypertrophy may be a serious public health problem affecting hypertensives in this Nigerian population. Men generally have been found to have a greater incidence and prevalence of left ventricular hypertrophy than women [17,49–51]. In this population, men had a significantly higher prevalence of left ventricular hypertrophy than women according to only two of the criteria (Minnesota Code 3.1 and Minnesota Code 3.1 or 3.3), although hypertension prevalence was significantly higher among men. In addition, the prevalence of left ventricular hypertrophy among hypertensives was higher among women than men according to four of the five criteria, contrary to the pattern often reported among hypertensives [22,23]. The prevalence estimates among all men in this population (range: 2.9–36.3%) generally were intermediate to those reported among black men (range: 8.3–36.6%) and white men (range: 1.9–15.4%) in other populations using similar criteria [19,50,52]. The prevalence estimates among all women in this population (range: 3.5–16.9%) were similar to those reported among black women (range: 5.3–17.4%) and white women (range: 1.8–20.1%) in other populations [19,50,52]. Although systolic blood pressure and hypertension prevalence increased with age in this population, the prevalence of left ventricular hypertrophy did not. In fact, the prevalence estimates often appeared to decrease with age. While left ventricular hypertrophy has been reported to increase with age in some populations [17,21,23], another study among Nigerians found that QRS voltages decreased significantly with age [38]. A study of the Second National Health and Nutrition Examination Survey data also found that some voltage criteria increased with age while others decreased [24]. The lack of an association between left ventricular hypertrophy and age in this Nigerian population may be due to variations in the validity of these criteria across age groups or may be due to limitations of the study design. For example, as this was a survey of working

11

individuals, older people with left ventricular hypertrophy may be too ill to work and so may not have been well represented. The main limitation of this study is the lack of a validity standard; unfortunately, we were not able to collect echocardiograms at the baseline visit. Electrocardiographic criteria have generally been reported to have adequate specificity, but low sensitivity for detecting left ventricular hypertrophy when compared to echocardiographic or necropsy measurements. In addition, one study of five electrocardiographic criteria for left ventricular hypertrophy among United States blacks and whites found that the specificity of these criteria was considerably lower among blacks, while sensitivity was equally low in both blacks and whites [28]. A recent report from the Charleston Heart Study, however, concluded that the accuracy of the Cornell Voltage and Novacode criteria among African Americans was comparable to the accuracy among whites [53]. Earlier reports of unusually high electrocardiographic left ventricular hypertrophy prevalences among people of African descent suggested that leanness, small chest dimensions and high levels of physical activity in the populations studied may have affected the validity of electrocardiographic criteria [32,54,55]. Although we were not able to examine the effect of these factors on validity through the use of a ‘gold’ standard, we did examine the associations of these factors with electrocardiographic left ventricular hypertrophy by five criteria. While increased physical activity was associated with increased prevalence of left ventricular hypertrophy by some criteria in this population, the effect was weak and inconsistent. The associations between body size and electrocardiographic left ventricular hypertrophy prevalence, however, were quite interesting. Obesity has been associated with increased prevalence and incidence of left ventricular hypertrophy [17,51,56]. The validity of certain electrocardiographic criteria for left ventricular hypertrophy, however, has also been reported to vary with body size. For example, obesity decreases the sensitivity of some voltage criteria [57,58]. Greater subcutaneous fat in the upper body may cause increased impedance of the electrical signal and increased distance between the heart and the electrode, thereby attenuating the wave amplitudes in the precordial leads [24,57].

12

S.L. Huston et al. / International Journal of Cardiology 70 (1999) 1 – 14

Likewise, some electrocardiographic criteria for left ventricular hypertrophy may not be accurate for very thin individuals. A shorter distance between the heart and the precordial electrodes in those with either little body fat or small chest size may result in increased wave amplitudes and decreased specificity of voltage criteria relative to those of ‘average’ build [59–61]. In this Nigerian population, although body mass index was positively associated with both mean systolic blood pressure and hypertension prevalence, a high body mass index was associated with a decreased prevalence of left ventricular hypertrophy. Furthermore, men in the lowest quartile of body mass index had a significantly higher prevalence of left ventricular hypertrophy by each of the Minnesota Code criteria compared with men in the highest quartile, independent of age or systolic blood pressure. In addition, men in the lowest quartile of chest depth had a significantly higher prevalence of left ventricular hypertrophy by the Minnesota Code 3.1 and Minnesota Code 3.1 or 3.3 criteria than men in the highest quartile. Given these findings, we raise the possibility that any true positive effect of obesity on left ventricular hypertrophy prevalence may not have been observed in this population simply because there were so few obese individuals (only 45, 6%, had a body mass index $30.0 kg / m 2 ); in addition, any true positive effect may have been attenuated by a negative effect of increased body mass index on the sensitivity of the electrocardiographic criteria. We are also concerned that, in an unusually lean population such as this one, the Minnesota Code criteria in particular may be inappropriate for estimating left ventricular hypertrophy prevalence due to its apparent decreased specificity among lean individuals; of the five criteria examined in this study, the three Minnesota Code criteria were significantly associated with low body mass index after adjusting for age and systolic blood pressure. Indeed, the Minnesota Code 3.1 or 3.3 criteria resulted in prevalence estimates consistently and profoundly higher than those generated by the other criteria. Certainly, if we assume that the cases of electrocardiographic left ventricular hypertrophy among those with normal blood pressure are false positives, then the Minnesota Code 3.1 or 3.3 criteria would have the lowest specificity of the criteria examined here. We have recently recorded echocardiograms on a subsample of this population that will help to answer

some of these validity questions. Analysis of these echocardiographic data will allow us to estimate left ventricular hypertrophy prevalence more accurately and to assess the validity of electrocardiographic criteria for left ventricular hypertrophy in this population. In addition, we are currently following this population to detect subsequent morbidity and mortality, which may be the most meaningful validity standards. In spite of the ostensible reduced specificity of some electrocardiographic criteria used, we conclude that left ventricular hypertrophy may be affecting many hypertensives in this Nigerian population, potentially leading to a substantial future burden of cardiovascular disease and death. The potential impact of increasing hypertension prevalence and accompanying left ventricular hypertrophy may be of particular concern in Nigeria, where many people with hypertension remain undiagnosed or untreated, and often do not seek out medical treatment until the late stages of heart failure [35]. Even in this urban employed population, only 39% of the hypertensives were aware of their condition, only 24% were taking anti-hypertensive medications, and only 8% had their blood pressure under control (compared with 68, 54 and 27% in a United States national sample [42]). Although we cannot generalize these findings to other populations in Nigeria or Africa, hypertension (and the lack of adequate treatment for hypertension) in African populations may be resulting in significant cardiovascular disease, including left ventricular hypertrophy. Now that several reports have documented substantial prevalence rates of hypertension and increased blood pressures relative to historical levels in some African populations, information on the effects of this change is needed. In addition, hypertension prevention and treatment intervention programs among African populations in transition from low to high blood pressure levels are required to prevent the potential burden of cardiovascular disease.

Acknowledgements This research was supported in part by Research Grant [HL44413 from the National Heart, Lung, and Blood Institute of the National Institutes of Health, USA.

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