Articles

Greater Incidence of Hospitalized Myocardial Infarction Among Mexican Americans Than Non-Hispanic Whites

The Corpus Christi Heart Project, 1988-1992

David C. Goff, Milton Z. Nichaman, Wenyaw Chan, David J. Ramsey, Darwin R. Labarthe, Carmen Ortiz
https://doi.org/10.1161/01.CIR.95.6.1433
Circulation. 1997;95:1433-1440
Originally published March 18, 1997

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Abstract

Background Since Mexican Americans have adverse patterns of risk factors for myocardial infarction relative to non-Hispanic whites, the incidence of myocardial infarction should be greater among Mexican Americans than among non-Hispanic whites. This expectation conflicts with reports generated from death certificate registries.

Methods and Results Data regarding myocardial infarction attacks and incident events were collected for a 4-year period in the Corpus Christi Heart Project, a population-based surveillance project for hospitalized coronary heart disease events. For both women and men, Mexican Americans experienced greater hospitalization rates for both attacks and incident events than non-Hispanic whites. Age-adjusted attack rate ratios comparing Mexican Americans with non-Hispanic whites were 1.59 (95% CI, 1.05 to 2.41) and 1.31 (95% CI, 1.18 to 1.45) among women and men, respectively. Corresponding incidence ratios were 1.52 (95% CI, 1.28 to 1.80) and 1.25 (95% CI, 1.10 to 1.42).

Conclusions This is the first report documenting greater incidence of hospitalized myocardial infarction among Mexican Americans than among non-Hispanic whites, a biologically plausible finding given the risk factor patterns observed in the Mexican-American population. Public health planners and clinicians should be aware of the importance of myocardial infarction as a health problem in the Mexican-American population. Culturally appropriate prevention strategies should be developed for and tested in Mexican-American populations.

On the basis of their cardiovascular risk factor profiles, Mexican Americans would be expected to have a greater incidence of myocardial infarction than non-Hispanic whites.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Preliminary results of the Corpus Christi Heart Project (CCHP) supported this expectation; however, that report was based on data regarding a combined end point of incident and recurrent myocardial infarction hospitalizations during a 12-month period.20 To examine this hypothesis more rigorously, age-adjusted and sex-specific rates and rate ratios for hospitalization for first myocardial infarction are compared between these two ethnic groups over a 48-month period.

Only very limited information is available concerning the natural history of coronary heart disease among US Hispanics, the nation’s second largest minority group, of which Mexican Americans constitute a large component. On the basis of vital statistics studies, mortality from coronary heart disease has been reported to be lower among Mexican Americans than among other Hispanic and non-Hispanic populations in the United States.21 22 23 24 25 26 27 28 29 Reported trends in mortality rates for coronary heart disease and acute myocardial infarction are inconsistent. Several reports indicated that mortality may have declined less among Mexican Americans than among non-Hispanic whites.24 27 28 However, at least one report showed similar declines for both ethnic groups.29 Two studies of the prevalence of myocardial infarction have indicated similar or lower prevalence among Mexican Americans than among non-Hispanic whites30 31 ; however, comparisons based on prevalence could reflect ethnic differences in myocardial infarction case-fatality. Early results from the CCHP indicated greater 28-day case-fatality after myocardial infarction among Mexican Americans than among non-Hispanic whites32 33 ; therefore, lower prevalence in Mexican Americans does not necessarily indicate lower incidence.

To investigate the apparent inconsistency between the expected higher rate of incidence of myocardial infarction based on risk factor distributions and observations from vital statistics registries, a community surveillance system for coronary events was established. The CCHP was designed to elucidate certain critical components of the natural history of coronary heart disease as it occurs in two distinct and contrasting populations, Mexican Americans and non-Hispanic whites, within the single community of Corpus Christi/Nueces County, Texas. In this report, hospitalization rates for incident myocardial infarction are examined to determine whether Mexican Americans have greater incidence of myocardial infarction than non-Hispanic whites. In addition, we report attack rates for hospitalized myocardial infarction, including both incident and recurrent events.

Methods

Study Population

The target population of this surveillance program is all residents of Nueces County, Texas, 25 to 74 years old. The data for this report were collected during the period May 1, 1988, through April 30, 1992. Nueces County, located on the Texas Gulf Coast, had an estimated population of ≈291 145 in 1990, with ≈95% of the county population residing within the central city of Corpus Christi.34 Of the total population, 43% were non-Hispanic whites, 52% were persons of Hispanic origin (of these, 92% were Mexican-Americans), and 5% were African Americans or of other races. In the target population 25 through 74 years old, 51% were non-Hispanic whites and 45% were of Hispanic origin. The more detailed data from the 1990 US Census35 showed marked sociodemographic differences between the two major ethnic groups in Nueces County. Mexican Americans had fewer years of formal education (50% of Mexican-American adults were high school graduates versus 85% of non-Hispanic whites). Furthermore, a greater percentage of Mexican Americans, 29%, than non-Hispanic whites, 10%, reported incomes below the poverty level.

Medical care in Nueces County is self-contained, a situation that is essential to the accurate population-based ascertainment of cardiac events. At the beginning of this 48-month period, there were seven acute-care hospitals whose combined catchment areas included the entire resident population of the county. As a result of hospital closure and construction, by the end of this period, there were six acute-care hospitals in Corpus Christi. Surveillance occurred at all times in all hospitals in operation. Each of the hospitals maintained dedicated special-care units, although facilities for specialized cardiac procedures, such as angiography and aortocoronary bypass surgery, were available only at the three largest hospitals. San Antonio, the nearest urban center with medical care rivaling the quality available locally, is >150 miles from Nueces County; therefore, the likelihood of referral outside the county even for care on a nonemergency basis is low. This contention has been supported by a review of coronary heart disease–related discharges of Nueces County residents from the Veterans Administration hospital and other large private hospitals in San Antonio and Houston (data not shown).

Case Ascertainment and Data Collection

Potentially eligible patients were ascertained on a concurrent basis during the period May 1, 1988, through April 30, 1992, by monitoring of admissions to special-care units at the seven hospitals. This process is similar to the “hot pursuit” procedure used in the World Health Organization’s Monitoring of Trends and Determinants of Cardiovascular Disease (MONICA) Project.36 Special-care units were monitored on a regular basis to identify patients admitted with diagnoses possibly indicative of coronary heart disease. To ensure complete ascertainment of cases of hospitalized myocardial infarction, lists of discharges with selected coronary heart disease–related diagnoses were obtained from each hospital. Those hospitalizations that had not already been identified through the concurrent procedures described above were reviewed. This procedure allowed the identification of patients with definite or possible myocardial infarctions who were hospitalized outside of the special-care units. By capture-mark-recapture techniques, completeness of ascertainment has been estimated to be 97.9%; estimated completeness of ascertainment did not differ by sex or ethnicity (unpublished data). For all potential cases, hospital records were abstracted when first available for review, usually at least 4 to 6 months after discharge. Data were collected on the course and care of the patient during the hospital stay, as well as on ethnicity, sociodemographic factors, medical history, ECGs, drugs prescribed at discharge, and discharge diagnostic codes.

Classification of Ethnicity and Events

During the first 24 months of ascertainment, the main method of classification of ethnicity was by self-identification during an in-hospital interview as to “Spanish origin” and for the subcategory of “Mexican origin,” as adopted in the 1980 US Census, supplemented by medical record abstraction.37 Ethnicity of study subjects who were not interviewed was obtained from the hospital records. Among 683 individuals interviewed during the first 24 months of the project, the medical record and the interview data concerning ethnicity were in agreement in 94.1% (643/683) of cases (κ=0.90, P<.001). During months 25 through 48, classification of ethnicity was based solely on medical record data.

Classification of cases as definite or possible myocardial infarction or no infarction was done in accordance with criteria recommended by Gillum and others,38 as modified in the Cardiovascular Community Surveillance Project.39 These criteria, based on ECGs, cardiac enzymes, and cardiac pain as routinely available in clinical records, permit classification of coronary events as definite or possible according to the degree of specificity of the criteria that were met (“Appendix”). In this report, the measure of interest is the combined occurrence of definite and possible myocardial infarction. This measure is a sensitive indicator of the burden of myocardial infarction in a population; as such, this is the preferred measure to examine for surveillance purposes. The theoretical disadvantage to using this measure is the inclusion of noncases. Since ethnicity is not part of the classification scheme, inclusion of noncases would bias the observed ethnicity-related rate ratios toward the null; therefore, this is a conservative approach. The definite myocardial infarction category, when considered alone, comprises a subset of cases of greater specificity but of substantially lower sensitivity for myocardial infarction. That is, many true cases are excluded. Thus, examination of the subclass of definite myocardial infarction has been proposed as more appropriate for testing questions of prognosis than for testing questions of differential incidence.38 The theoretical disadvantages of using the definite myocardial infarction subclass to examine questions of differential incidence include a loss of power due to reduced sample size and decreased generalizability related to the exclusion of true cases.38 Only those enzyme data and ECG tracings that were obtained within 72 hours of admission or after onset of an in-hospital acute event were used. ECGs were classified on site by study staff certified in the application of the Minnesota Code.38 ECGs were examined for a pattern of evolving myocardial infarction; for those cases, the ECG evidence was classified as “evolving diagnostic.” When evidence of evolution was not seen, ECG evidence was ranked in the highest category met by any single recording, that is, “diagnostic,” “equivocal,” or “other.” Enzyme data were treated similarly, being classified as “abnormal,” “equivocal,” “normal,” or “incomplete.” Abnormal enzymes were considered equivocal in the presence of nonischemic causes for elevated values, such as defibrillation, surgery, liver disease, or trauma. Pain that was described as having all of the following characteristics was classified as being of cardiac origin: (1) it occurred anywhere in the anterior chest, left arm, or jaw and might also involve the back, shoulder, right arm, or abdomen on one or both sides, and (2) it had a duration of >20 minutes or multiple doses of nitrates were self-administered without relief, and (3) it had no definite noncardiac cause. Similar criteria were previously tested extensively in the Community Cardiovascular Surveillance Program and elsewhere and are currently in use in the Minnesota Heart Health Program, the Stanford Five-City Project, and the Pawtucket Heart Health Program.39 40 41 42 A computer algorithm for application of the criteria has been used in the Minnesota Heart Study, the Community Cardiovascular Surveillance Program, and the current CCHP.

In these analyses, all hospitalizations that met criteria for definite or possible myocardial infarction were included as attacks. An incident, hospitalized myocardial infarction was defined as a hospitalization of a person without a history of previous myocardial infarction, as determined from a review of the medical record and from record linkage with data in our surveillance files. That is, we checked our surveillance files to determine whether or not a person met our criteria for hospitalized myocardial infarction previously during the study period. We had no access to surveillance data before May 1, 1988; thus, this criterion introduced the possibility that we might have overestimated incidence in our earlier data relative to that found when more recent data were used. We examined this potential bias from two perspectives. In study year 1 (May 1, 1988, through April 30, 1989), 68.5% (526/768) of myocardial infarction hospitalizations were classified as incident events; in study years 2, 3, and 4, respectively, 60.4% (430/712), 61.0% (426/698), and 61.0% (423/694) were identified as incident events. In study year 1, 8.3% (64/768) of myocardial infarction hospitalizations were identified as recurrent events solely on the basis of surveillance record linkage; that is, there was no indication of a previous history of myocardial infarction in the medical records of these individuals, yet there was a previous hospitalization for definite or possible myocardial infarction according to our surveillance data. In study years 2, 3, and 4, 12.2% (87/712), 13.8% (96/698), and 14.8% (103/694) of myocardial infarction hospitalizations were identified as recurrent events solely on the basis of surveillance record linkage. Both perspectives show attainment of a plateau essentially by study year 2; thus, these data support the conclusion that the estimates of incidence reported here may be more valid beginning in study year 2 than in study year 1. The attack rates were not affected by this limited, early misclassification.

Data Analysis

Midyear population estimates for each year 1988 through 1991 for Nueces County were obtained in 10-year ethnicity- and sex-specific groups from the Texas Department of Health to use as denominators in the calculation of 1-year age-specific hospitalization rates for attacks and incident myocardial infarction. The possibility that age-by-ethnicity interactions might be present for either attack rates or incidence was examined by linear regression of the natural logarithm of the age-specific rates (attacks or incidence) on study year, age group, ethnicity, and an age-by-ethnicity interaction term separately for women and men. Age-adjusted rates of hospitalization for incident myocardial infarction for the two ethnic groups, by sex, were calculated by the direct method using the Texas population (25 to 74 years old) in 1990 as the referent. Trends in hospitalization rates were examined by linear regression of the logarithm of the rate versus time. Annual estimates of ethnicity- and sex-related rate ratios were calculated by use of the age-adjusted rates described above. Linear regression of the natural logarithm of the annual rate ratios versus study year was performed to obtain overall estimates of ethnicity- and sex-related rate ratios and corresponding 95% CIs at the midpoint of the study period. These overall estimates were used to test the hypotheses that Mexican Americans would have a greater incidence of hospitalization for myocardial infarction than non-Hispanic whites for both women and men and that women would have a lower incidence of hospitalization for myocardial infarction than men for both Mexican Americans and non-Hispanic whites.

Results

During 4 years of ascertainment (May 1, 1988, through April 30, 1992), we identified 2872 hospitalizations for myocardial infarction among Mexican-American and non-Hispanic white women and men; 1805 (62.8%) of these were classified as incident events. The “Appendix” includes a description of the criteria met by the 2872 hospitalizations. The age-specific rates and numbers of hospitalizations by ethnicity, sex, age, and study year are shown for incident myocardial infarctions in the Table⇓. With rare exceptions for both sexes, the age-specific rates for incident events were higher among Mexican Americans than among non-Hispanic whites. There was no evidence of an age-by-ethnicity interaction for incident events (results not shown); therefore, meaningful age-adjusted rates could be calculated for ethnic comparisons. Similar results were seen for attacks (not shown). Ethnicity- and sex-specific, age-adjusted rates for attacks and incidence are shown in Figs 1⇓ and 2⇓, respectively. The highest attack rates were observed among Mexican-American men, followed in order by non-Hispanic white men, then Mexican-American women, and finally, non-Hispanic white women. Attack rates declined over the 4-year period in both groups of women and in Mexican-American men; a slight increase was observed among non-Hispanic white men (Fig 1⇓). The declining trend in attack rates was statistically significant only in Mexican-American women (P<.05 for log[attack rate] regressed on study year). The highest incidence rates were also observed among Mexican-American men, followed in order by non-Hispanic white men, then Mexican-American women, and finally, non-Hispanic white women. Also, as for attack rates, the incidence of hospitalized myocardial infarction declined in both groups of women and in Mexican-American men; incidence did not change appreciably in non-Hispanic white men (Fig 2⇓). Again, only in Mexican-American women did this declining trend reach statistical significance (P<.05 for log[incidence rate] regressed on study year). The steepest declines in incidence were seen between years 1 and 2, especially in women. Since we had concerns about the accuracy of classification of incident cases in year 1, our examination of trends was based on years 2 through 4. Between year 2 and year 4, incidence decreased among Mexican Americans, but no appreciable change was observed among non-Hispanic whites. None of the 3-year trends in incidence were statistically significant. With only 4 years of data regarding trends, we had limited power to compare trends among ethnicity- or sex-specific groups. At present, the declines in both attacks and incidence appear to be more rapid in Mexican Americans than in non-Hispanic whites, for both women and men, and more rapid in women than in men of both ethnic groups.

View this table:
Table 1.

Age-Specific Rates1 and Number of Incident Hospitalizations for Definite or Possible Myocardial Infarction by Ethnicity and Sex Among Mexican-American and Non-Hispanic White Women and Men Residing in Corpus Christi/Nueces County, Texas, May 1, 1988, Through April 30, 1992

View this table:
Table 2.
Figure 1.
Figure 1.

Annual age-adjusted attack rates for hospitalized definite or possible myocardial infarction by ethnicity and sex, May 1, 1988, through April 30, 1992: the Corpus Christi Heart Project. MA indicates Mexican-American; NHW, non-Hispanic white.

Figure 2.
Figure 2.

Annual age-adjusted incidence rates for hospitalized definite or possible myocardial infarction by ethnicity and sex, May 1, 1988, through April 30, 1992: the Corpus Christi Heart Project. Abbreviations as in Fig 1⇑.

As the primary analysis for this report, we examined and compared rates of myocardial infarction attacks and incidence between Mexican Americans and non-Hispanic whites and between women and men on the basis of 4 years of data. Annual estimates of rate ratios for ethnic and sex comparisons of myocardial infarction attacks and incidence are shown in Figs 3⇓ and 4⇓, respectively. In every study year and for both women and men, Mexican Americans experienced greater hospitalization rates for both myocardial infarction attacks and incidence than non-Hispanic whites. Age-adjusted attack rate ratios at the midpoint of the 4-year study period comparing Mexican Americans with non-Hispanic whites were 1.59 (95% CI, 1.05 to 2.41) and 1.31 (95% CI, 1.18 to 1.45) among women and men, respectively. Corresponding incidence ratios were 1.52 (95% CI, 1.28 to 1.80) and 1.25 (95% CI, 1.10 to 1.42). In every study year and for both Mexican Americans and non-Hispanic whites, women experienced lower hospitalization rates for both myocardial infarction attacks and incidence than men. Age-adjusted attack rate ratios of myocardial infarction comparing women and men were 0.58 (95% CI, 0.50 to 0.68) and 0.48 (95% CI, 0.35 to 0.66) among Mexican Americans and non-Hispanic whites, respectively. Corresponding incidence ratios were 0.61 (95% CI, 0.50 to 0.74) and 0.50 (95% CI, 0.39 to 0.63).

Figure 3.
Figure 3.

Annual age-adjusted attack rate ratios for hospitalized definite or possible myocardial infarction by ethnicity and sex, May 1, 1988, through April 30, 1992: the Corpus Christi Heart Project. Abbreviations as in Fig 1⇑.

Figure 4.
Figure 4.

Annual age-adjusted incidence rate ratios for hospitalized definite or possible myocardial infarction by ethnicity and sex, May 1, 1988, through April 30, 1992: the Corpus Christi Heart Project. Abbreviations as in Fig 1⇑.

Discussion

This is the first report documenting greater incidence of hospitalized myocardial infarction among Mexican Americans than among non-Hispanic whites. This finding was observed for both women and men and confirms our previously published results based on data regarding total hospitalizations for myocardial infarction, including both incident and recurrent events, in the first year of the study.20 This ethnic difference in incidence of hospitalized myocardial infarction may be due to the adverse pattern of cardiovascular risk factors in Mexican Americans compared with non-Hispanic whites. Although we have no risk factor data specific to the Corpus Christi population, others have reported on differences in cardiovascular disease risk factors between Mexican Americans and non-Hispanic whites. Mexican Americans reportedly have higher blood concentrations of cholesterol2 8 and triglycerides2 12 and lower concentrations of HDL cholesterol2 4 than non-Hispanic whites. Mexican Americans have smaller (potentially more atherogenic) LDL particles.13 Conversely, Mexican Americans have lower lipoprotein(a) levels.14 Mexican Americans also have diminished insulin sensitivity and insulin response3 and greater prevalence and incidence of diabetes4 7 9 15 and diabetic complications, including retinopathy and nephropathy.43 44 45 Mexican Americans also have greater prevalence of obesity2 4 10 and similar or only slightly lower prevalence and incidence of hypertension.4 11 16 17 18 The prevalence of cigarette smoking is similar in the two groups of men but substantially lower among Mexican-American women than among non-Hispanic white women; in both sexes, the number of cigarettes smoked per day is substantially lower among Mexican Americans.4 Mexican Americans are also less likely to receive treatment for diabetes,7 hypercholesterolemia,8 and hypertension.6 18 In summary, the available data support the impression that the cardiovascular disease risk factor pattern among Mexican Americans is adverse relative to that of non-Hispanic whites, and there is no obvious reason to doubt the generalizability of these data to the Corpus Christi population. On this basis, our findings of greater incidence of hospitalized myocardial infarction among Mexican Americans were expected.

Conversely, our findings of greater incidence of hospitalized myocardial infarction among Mexican Americans than among non-Hispanic whites conflict with analyses of death certificate data that suggest lower coronary heart disease mortality rates in Mexican Americans than in non-Hispanic whites, at least among men.21 22 23 24 25 26 27 28 29 We have analyzed Nueces County mortality data (unpublished data) and found the same ethnic pattern as we reported for Texas29 ; thus, the inconsistency is not due to local factors operating in Nueces County. These results also contradict two reports based on prevalence of myocardial infarction. In a report from the San Antonio Heart Study, Mexican-American women had nonsignificantly higher prevalence and Mexican-American men had significantly lower prevalence of myocardial infarction than their non-Hispanic white counterparts.30 In a report from the San Luis Valley Diabetes Study, ethnic comparisons of the prevalence of myocardial infarction appeared to differ by sex and diabetic status; however, none of the ethnic comparisons reached statistical significance. Among participants who did not have diabetes, Hispanic women had lower prevalence of myocardial infarction than non-Hispanic whites, and Hispanic men a similar prevalence. Among diabetic participants, Hispanic women had similar prevalence and Hispanic men lower prevalence than non-Hispanic whites.31

The inconsistency in ethnic comparisons of myocardial infarction rates based on hospitalizations versus deaths could be explained by any of three leading considerations. Each is addressed here, in turn: (1) inadequacies in the completion of death certificates, (2) incomplete ascertainment of myocardial infarction in our surveillance data collection, and (3) real and large ethnic differences in out-of-hospital sudden cardiac death rates or silent myocardial infarction rates. Differential enumeration of the population of Nueces County by ethnicity cannot explain this inconsistency because hospitalization rates and mortality rates were calculated from the same population estimates.

1. Inadequacies in the certification of cause of death seem the likeliest explanation. Death certificates are completed by health professionals who may not be fully aware of the research uses of these data. Furthermore, ethnic differences in access to medical care and misclassification of ethnicity on death certificates may lead to spurious ethnic differences in the certified cause of death. The combined effect of these potential biases is difficult to predict and requires additional attention. On the basis of our findings of greater myocardial infarction hospitalization rates and posthospitalization case-fatality rates,33 we would expect greater community-level coronary heart disease mortality rates in Mexican Americans than in non-Hispanic whites. This implies the existence of a substantial degree of misclassification of cause of death and/or ethnicity on death certificates. Such misclassification could include overdiagnosis of myocardial infarction deaths among non-Hispanic whites, underdiagnosis among Mexican Americans, and/or misclassification of Mexican-American decedents as being non-Hispanic white. We are currently collecting death certificates and supporting data for out-of-hospital coronary heart disease–related deaths in Nueces County with which to examine these and other issues.

2. As noted above, we have estimated that our completeness of ascertainment of hospitalized myocardial infarction is ≈98% with the capture-mark-recapture methodology. This estimated completeness of ascertainment did not differ by sex or ethnicity; therefore, our data on hospitalized myocardial infarction do not appear to be biased by differential ascertainment by ethnicity or sex. We have also examined the issue of potential ethnicity-related differences in the validation of myocardial infarction. In a comparison of validated cases with clinically diagnosed cases, ie, those given a discharge diagnostic code of 410, we observed no ethnicity-related difference in sensitivity, specificity, or predictive values in either women or men (unpublished data).

3. The results presented here do not include data regarding out-of-hospital cardiac deaths. It is possible that both the death certificate–based mortality estimates and these hospitalization estimates are correct. If so, then an opposing and substantial ethnic difference must exist in out-of-hospital myocardial infarction deaths. The magnitude of the excess incidence of hospitalized myocardial infarction among Mexican Americans was substantial, 25% for men and 50% for women in this study. Out-of-hospital cardiac deaths are generally believed to account for ≈25% of myocardial infarctions. If this latter statement is assumed to be true and the total myocardial infarction rates (the sum of hospitalized myocardial infarctions and out-of-hospital myocardial infarction deaths) are assumed to be equal between the ethnic groups, the out-of-hospital myocardial infarction mortality rate ratios comparing Mexican Americans with non-Hispanic whites must be 0.5 and 0.25 among men and women, respectively. It seems unlikely that ethnic differences in out-of-hospital sudden cardiac death rates could be large enough to account for the inconsistency between ethnic comparisons of myocardial infarction rates on the basis of hospitalizations versus deaths. This contention is further supported by reports indicating that the risk factors for sudden cardiac death are similar to those for myocardial infarction46 ; therefore, one would expect similar ethnic patterns for hospitalized myocardial infarction and out-of-hospital sudden cardiac death. One would expect greater, not lesser, out-of-hospital myocardial infarction mortality among Mexican Americans than among non-Hispanic whites. We believe that the mortality rate ratios are likely to be similar to those reported here for hospitalizations. Nevertheless, additional attention to the issue of out-of-hospital death is warranted. Data regarding silent myocardial infarction can be obtained best from cohort studies; however, for the same reasons as given above, ethnic differences in the occurrence of silent myocardial infarction that oppose and are large enough to offset the pattern observed for hospitalized myocardial infarction seem unlikely.

The inconsistency between these incidence data and other prevalence data, such as those reported from the San Antonio Heart Study,30 can be explained by differential survival after myocardial infarction. Prevalence is related to both incidence and survival. Therefore, a group with greater incidence of myocardial infarction and greater case-fatality, such as Mexican Americans, can have lower prevalence of myocardial infarction than a group with both lower incidence and better post–myocardial infarction survival, such as non-Hispanic whites. We have reported greater short- and long-term mortality after myocardial infarction among Mexican Americans than among non-Hispanic whites.32 33 As expected, the greater mortality observed among Mexican Americans after myocardial infarction was related, in part, to the greater prevalence of diabetes among Mexican Americans hospitalized for myocardial infarction.33 47 This ethnic difference in survival after myocardial infarction might explain the inconsistency in ethnic comparisons on the basis of prevalence and incidence data. Additional data regarding ethnic differences in the incidence of myocardial infarction from other studies of these ethnic groups could help resolve the inconsistencies identified in this report.

As expected, rate ratios comparing myocardial infarction incidence and attack rates between women and men were consistent with results from many other studies in showing substantially lower rates among women than among men in both ethnic groups. These expected results add further strength to the validity of our inferences related to ethnic differences.

Our present analysis of trends in myocardial infarction incidence and attack rates has limited power because of its short duration to date (4 years). Even so, the trends seem to be declining more rapidly among Mexican Americans than among non-Hispanic whites and more rapidly among women than among men. These findings are related primarily to flat trends for both incidence and attack rates among non-Hispanic white men. Whether these flat trends are harbingers of an end to the decline in coronary heart disease mortality rates in non-Hispanic white men and eventually other sex and ethnic groups remains to be seen.

As indicated above, this study is limited by lack of data regarding out-of-hospital cardiac deaths and silent myocardial infarctions; plausible frequencies of these occurrences do not explain our results. In addition, this study has several important strengths. First, this study is population-based, at least in terms of hospitalizations for myocardial infarction. All of the acute-care hospitals in Nueces County were participating in this surveillance program. According to estimates of completeness of ascertainment, almost every person residing in Nueces County who was hospitalized with a myocardial infarction in Nueces County during the study period was included in this analysis. Furthermore, Nueces County is relatively isolated from other centers of medical care. Few patients leave Nueces County for acute medical care; thus, the effects of selection bias regarding sources of care outside the community should be minimal. Second, the Mexican-American population in Nueces County is large enough to provide stable estimates of incidence; thus, chance is an unlikely explanation of our results. This contention is supported by the relatively narrow 95% CIs associated with the reported rate ratios. Finally, the Hispanic population studied, Mexican Americans, is the largest subgroup of Hispanics in the United States; thus, these results have substantial public health importance.

These findings confirm our previously published results based on 1 year of case ascertainment of total myocardial infarction20 and support the contention that Mexican Americans have a greater incidence of myocardial infarction than non-Hispanic whites among both women and men. Furthermore, this finding is biologically plausible, given the risk factor patterns observed in the Mexican-American population. Because of both immigration and natality, the Mexican-American population in the United States is younger and growing more rapidly than the non-Hispanic white population. Over the next several decades, one can predict that an increasing number of Mexican Americans will be entering the age range in which coronary heart disease in general and myocardial infarction in particular are the leading health problems. Public health planners and clinicians should be aware of the importance of myocardial infarction as a health problem in the Mexican-American population. Culturally appropriate prevention strategies should be developed for and tested in Mexican-American populations.

Appendix A1

A more detailed description of criteria for myocardial infarction is available from the authors on request.

Acknowledgments

This investigation was supported by grant HL-38429 awarded by the National Heart, Lung, and Blood Institute. The authors thank the Corpus Christi Advisory Committee, the administrators and staffs of the participating hospitals, and the Corpus Christi–Nueces County Department of Public Health for their support of this project.

Footnotes

  • Guest editor for this article was Charles H. Hennekens, MD, Brigham and Women’s Hospital, Boston, Mass.

  • Received May 29, 1996.
  • Revision received October 30, 1996.
  • Accepted November 12, 1996.

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  • Greater Incidence of Hospitalized Myocardial Infarction Among Mexican Americans Than Non-Hispanic Whites
    David C. Goff, Milton Z. Nichaman, Wenyaw Chan, David J. Ramsey, Darwin R. Labarthe and Carmen Ortiz
    Circulation. 1997;95:1433-1440, originally published March 18, 1997
    https://doi.org/10.1161/01.CIR.95.6.1433
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