Revista Española de Cardiología (English Edition) Revista Española de Cardiología (English Edition)
Rev Esp Cardiol. 2002;55:337-46 - Vol. 55 Num.04

Epidemiology of Ischaemic Heart Disease in Spain: Estimation of the Number of Cases and Trends from 1997 to 2005

Jaume Marrugat a, Roberto Elosua b, Helena Martí b

a Unidad de Lípidos y Epidemiología Cardiovascular. Universitat Autònoma de Barcelona.
b Unidad de Lípidos y Epidemiología Cardiovascular. Institut Municipal d'Investigació Mèdica (IMIM). Barcelona.

Keywords

Epidemiology. Heart disease. Myocardial infarction. Unstable angina.

Abstract

Introduction and objectives. The large amount of information on rates of acute coronary syndrome accumulated in Spain over the last two decades is summarized in this paper, which also estimates the number of cases expected in 2002 and the trend for 1997 to 2005. Methods. Published information on the situation in the 90's was reviewed and summarized. We present the incidence of acute myocardial infarction (AMI), and an estimate of the absolute number of patients expected for various acute coronary syndromes in each autonomous community in Spain in 2002, along with the trend for 1997 to 2005. Results. Approximately 68,500 patients will suffer AMI in 2002 and 40,989 of them will be hospitalized, while the rest will die before admission. A further 24.9% of admitted patients will not survive 28 days. Slightly less than half will be younger than 75 years old, an age with a better prognosis (28-day mortality 38.8%). Approximately 33,500 patients with unstable angina will be admitted, and 4.5% of them will die within 3 months of admission. Assuming the incidence of AMI remains stable, the absolute number of cases will increase by 2.28% yearly (9,847 cases in total) and hospitalizations for acute coronary syndromes will increase by 1.41% (8,817 cases in total) between 1997 and 2005. Conclusion. Ischaemic heart disease generates increasing demand for health care in Spain. Case fatality is high among the approximately 68,500 AMI patients, given that scarcely two thirds will have been hospitalized in 2002.

Article

INTRODUCTION

In the last decade, a lot of information has been compiled on the dimensions of the problem of ischemic heart disease (IHD) and its risk factors in Spain. IHD continues to be the primary cause of death in men and the third most important cause of death in women, being responsible for 11% and 10% of deaths in men and women, respectively, in 1997.1

The incidence of acute myocardial infarction (AMI) (number of new cases/100 000 inhabitants and year) in the Spanish population age 35 to 64 years is among the lowest in the world and seems to have stabilized in the last 10-15 years.2,3 These data contrast with the perception shared by many doctors that the number of patients being seen for IHD in hospitals is increasing. This impression is confirmed by the findings of hospital morbidity statistics, which indicate that the number of patients discharged alive or deceased with the diagnosis of IHD passed from 30 032 in 1977 to 94 124 in 19934 (Figure 1).

Fig. 1. Evolution of admissions for ischemic heart disease (IHD) between 1977 and 1993 in Spain, according to the national survey of hospital morbidity (Instituto Nacional de Estadística, 1999).

On the other hand, IHD tends to appear in the fifth decade of the life and increases in frequency with age and the coexistence of risk factors. Since Spain will become the most «elderly» country in the world in few decades,5 we can expect to see an increase in morbidity and mortality due to chronic diseases, including IHD.

The aim of this review is to examine what is known about the frequency of IHD and to estimate the absolute number of cases that will occur in Spain and its autonomic communities in 2002. We also propose to study the trend in the total number of cases of AMI in the population and hospitalizations for AMI or unstable angina between 1997 and 2005.

METHODS

The source of the data used for this review is based was scientific articles on the dimensions of the IHD problem published in peer-reviewed journals in the last decade. Studies with a population base obtained from adequate sample sizes were selected.

Mortality and estimation of the number of patients with AMI in Spain

The number of cases of AMI that occur in the Spanish population age 25 to 74 years and the number deaths in the first 28 days after AMI were calculated using the data from three population studies: MONICA-Cataluña,3 REGICOR,2 and IBERICA6,7 (Table 1). The raw rates per decade of age (25-34, 35-44, 45-54, 55-64, and 65-74 years) and sex were used. In autonomic communities that do not have a population registry of the incidence of AMI in persons age 25 to 74 years, the specific mean rate per decade of age was extrapolated from the IBERICA study. The same calculation was made in the population over 74 years-old using the raw rates for the age group over 74 years of REGICOR for the period 1996-19978 in men and women (Table 1).

Hospitalization and mortality at 28 days and one year due to AMI

The number of people seen in hospitals for AMI was calculated based on the percentage of patients that reach the hospital in relation to the total number of cases of AMI that occur in the general population according to the population studies mentioned above2,3,6,8 (Table 1).

The number of patients with AMI treated in hospitals who die in the first 28 days was calculated using raw data from the IBERICA study7 for patients under 75 years, and data from the REGICOR study for those over 74 years.8 It has been assumed that lethality increases by 4% at one year of follow-up among survivors of the acute phase in patients under 74 years, as indicated by a 12-year follow-up study of patients under 74 years,9 and by 11% in patients over 74 years, as found in a specific analysis made using data from the PRIAMHO study10 (Table 1).

Hospitalization and mortality at 3 and 6 months for unstable angina

To estimate the number of patients who are attended in hospitals in Spain for unstable angina, it was assumed that the number of admissions for unstable angina is equal to the number of first infarctions. This assumption is based on the results of the RESCATE study, in which all patients hospitalized for acute coronary syndromes (AMI and unstable angina) between 1994 and 1996 in 4 hospitals of Catalonia were registered. In this study it was observed that the number of patients hospitalized for these two acute pathologies was very similar.11,12 In accordance with the findings of the IBERICA study, 82% of hospital AMI were considered first AMI.

The 3-month lethality was based on the results of the PEPA study, the unstable angina register of 18 hospitals of Spain, 13 and the number of readmissions within 6 months from the RESCATE data12 (Table 1).

Prevalence of angina in the Spanish population

The number of people with self-declared angina in the population age 45 to 74 years was calculated according to the results of the PANES study.14,15

Reference population

The number of cases per autonomic community and in Spain overall was estimated using the projection of the National Institute of Statistics for the years 1997 to 2005 as the reference population.16

Presentation of results

The estimates of the number of coronary events are presented by age groups, sex, and autonomic community with the 95% confidence interval (CI).

Validation of the estimates

The estimates made were validated by calculating the ratio between the estimated number of cases of mortal IHD and the number of deaths due to IHD in each autonomic community according to official statistics on mortality.1 The official figures for mortality correspond to 1997; therefore, to calculate this ratio the number of cases of mortal IHD were estimated using the 1997 population.

RESULTS

Estimates of the expected number of patients with AMI in Spain in 2002 by autonomic community, sex, and age group, as well as the expected number of cases of mortal AMI are shown in Tables 2 and 3. It has been estimated that 68 494 cases of AMI will take place in Spain in 2002 (95% CI, 65 723-71 264), and that 38 700 patients will die in the first 28 days (56.5%). In the population over 74 years, the estimated number of cases is 33 269 (48.6%). Of the mortal cases, 24 906 (64.4%) will occur in persons over 74 years. More than half of all the cases in Spain will take place in the autonomic communities of Catalonia, Andalusia, Madrid, and Valencia.

Of the total number of AMI, 40 989 patients (95% CI, 38 871-43 107) will receive hospital care (59.8%) and the rest, 27 505 (40.2%), will die without it. Of the patients with AMI who reach the hospital, 12 785 (31.2%) will pass away within a year and 10 191 (24.9%) in the first 28 days after the onset of symptoms.

It is also estimated that 77.6% of the patients 25 to 74 years old with AMI will receive hospital care and that 15.1% will die within 28 days and 19.1% within one year. Nevertheless, in the population over 74 years, only 41.0% will receive hospital care, of which 44.3% will die within 28 days and 55.3% within one year (Tables 4 and 5).

It has been estimated that 33 529 patients (95% CI, 31 613-35 444) in the population over 24 years will be hospitalized for unstable angina. Of the total number of patients with unstable angina hospitalized, 1497 (4.5%) will have died within 3 months of admission and 6693 (20.0%) will be readmitted for some reason in the next 6 months of follow-up (Tables 6 and 7).

It was estimated that 956 000 persons in the population 45 to 74 years old would suffer angina in 2002. There are no data on the population under 45 years or over 74 years.

In Table 8 is shown the ratio of the estimated number of mortal cases in 1997 and the official number of deaths due to IHD in the same year, which was 0.95 (1.02 in men and 0.86 in women). This ratio is less than 0.70 in the Canary Islands, in both men and women, and in Andalusia and Melilla, in women.

The estimated trend in the total number of AMI that occur in the Spanish population, the number of patients hospitalized for this cause, and the number of patients hospitalized for AMI and unstable angina between 1997 and 2005 is shown in Figure 2. These numbers will increase by 2.28% a year (9847 cases between 1997 and 2005), to 1.41% (4850 cases) and 1.41% (8817 cases), respectively.

Fig. 2. Estimate of the total number of patients with acute myocardial infarction (AMI) in the Spanish population, and of the number of patients with AMI and acute coronary syndromes (myocardial infarction + unstable angina) hospitalized between 1997 and 2005.

DISCUSSION

The estimations made of the dimensions of the IHD problem between 1997 and 2005 indicate that the aging of the population in itself will increase the number of cases of AMI and unstable angina in Spain.

It has been estimated that in 2002 between 65 700 and 71 200 cases of symptomatic AMI will take place in Spain and that, of these patients, 56.5% will die in the first 28 days. This high rate of lethality is surprising from the perspective of hospitals because rates of lethality of 4-7% have been described in the hospital setting in clinical trials17 and 15%-18% in hospitals.7,10,11 It must be considered that patients are highly selected and generally low-risk in clinical trials, which explains the low lethality observed.18 Population registers have shown that two-thirds of all patients with AMI in the 25 to 74-year age group die before reaching the hospital. This fact, together with the high lethality observed in patients over 74 years, explains the high lethality of AMI in the population.

On the other hand, in the Framingham heart study it was observed that up to 30% of the AMI that occur in the community are silent; which is to say, that they were detected by the appearance of specific changes in periodic electrocardiograms made in the absence of symptoms or medical care.19 This means that the figure of AMI in Spain could rise to approximately 98 000 cases if the Framingham figure were to prove extrapolatable to Spain. The 28-day lethality would then decrease to 39.5%.

The acute coronary syndrome has generated an increasing demand for care in recent years, as indicated by the evolution of the number of hospital discharges with this diagnosis (Figure 1).4 This increased demand for care could be related to a larger number of cases of AMI in the population. The incidence of AMI in the 25-74 year-old population remains stable. Nevertheless, the increased life expectancy and decreased birth rate in Spain are producing a progressive aging of the population that is translated, in turn, into an increased frequency of chronic diseases like IHD. The incidence, mortality, and lethality of AMI in patients over 74 years are much greater than in patients between 25 and 64 years,8 and most cases of AMI take place after 64 years.20 The greater demand for care could also be due to the greater incidence of recurrent acute coronary syndromes due to the decreasing lethality observed in patients hospitalized in the last two decades, which is related to therapeutic improvements.9,21 This greater demand for care is also reflected in an increase in the number of admissions for heart failure.22

The discrepancy between the figures of the survey of the hospital discharge diagnoses4 and those estimated in this study derives from the fact that this survey includes not only acute coronary syndromes but also admissions related to programmed diagnostic procedures.

The increase in the number of interventionist procedures in the last decade, as is evident in the registry of interventions of the Section of Hemodynamics and Interventionist Cardiology of the Spanish Society of Cardiology, is another indicator of the increase in healthcare activities related to IHD. In this registry, a mean annual increment of 14% has been observed in the last decade in the number of coronariographies and of 20% in the number of non-surgical revascularization procedures.23 The possibility that the practice of these procedures has prevented a potential increment in the incidence of AMI cannot be excluded, although its impact on the population presumably would have been small.

According to the estimate made, 74 500 people will be admitted to Spanish hospit al centers for an acute coronary syndrome in 2002, 55% for AMI and the rest for unstable angina. If this incidence remains stable, in 2005 the number of patients hospitalized for acute coronary syndromes will reach 78 000 admissions.

Study characteristics and limitations

The calculations were made using the results of population surveys and hospital registries made in Spain in the last decade. Most of these registries carried out quality control procedures to guarantee data quality and their internal validity. In some autonomic communities, local population data were used because local population registries were available. In the rest, average values were extrapolated from the IBERICA study,6 which monitored an approximate population of 4 800 000 people age 25-74 years in 8 regions (20% of the Spanish population of that age group). Therefore, this population can be considered reasonably representative (external validity) of the general population of Spain. The rates in the population over 74 years come from the province of Girona and correspond to 1996 and 1997.8 The extrapolation of data from this province to the country as a whole may be questionable. Nevertheless, the data corresponding to the population age 25 to 74 years of Girona is very similar to the average values obtained from the IBERICA study, so it can be accepted, with the necessary reservations, that the data for the population over 74 years-old are also a good estimate. On the other hand, these are the only data on population incidence in this age group in Spain.

All these estimates are mere approaches to reality, and cannot be known with the accuracy that one would wish. In any case, confidence intervals and indirect validations are presented whenever possible. In particular, the study of validity indicates that the estimates come close to the official figures for mortality due to IHD. In any case, the estimated number of mortal cases is lower than the number of cases declared in death certificates, especially in women and in two autonomic communities, the Canary Islands and Andalusia. Although the official statistics generally overestimate mortality due to IHD slightly,24 in the specific case of these two communities the number of estimated cases could be lower than that of real cases. The Canary Islands and Andalusia are the two autonomic communities with the highest official mortality due to IHD,1 which is probably related to a higher incidence of AMI. The use of the mean incidence of the IBERICA study could lead to underestimation of the number of real cases, especially in the Canary Islands.

On the other hand, the new definition of AMI based on troponin values25 should lower the «diagnostic threshold». One overall effect should be to increase the number of AMI by approximately 25% in patients hospitalized with indicative symptoms26 and, possibly, to reduce its lethality and the number of cases of unstable angina, although the number of patients will remain the same for purposes of healthcare.

To estimate the number of people who present angina pectoris in the Spanish population, the data of the PANES study have been used.14,15 These results probably overestimate the number of people with angina, due to the limited sensitivity and specificity of the questionnaire, as well as the sampling method used in this study, which was not a random sampling of the population but by itineraries. The number of people with angina in Spain probably does not surpass 600 000.

Definitively, the dimension of the problem of IHD in Spain in 2002 is not very different from that of the past decade in terms of incidence. About 68 500 patients will have symptomatic AMI, of which two-thirds will be admitted to hospitals. The rest will die before being seen in an adequate setting. Just under half of the patients will be under 74 years old. Our estimates indicate that both hospital activity related with acute coronary syndromes and the total number of cases in the population will grow by more than 10% between 1997 and 2005.


Correspondencia:
Dr. J. Marrugat.
Unitat de Lípids i Epidemiologia Cardiovascular.
Institut Municipal d'Investigació Mèdica (IMIM).
Dr. Aiguader, 80. 08003 Barcelona. España.
E-mail: jmarrugat@imim.es"> jmarrugat@imim.es

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1885-5857/© 2002 Sociedad Española de Cardiología. Published by Elsevier España, S.L.U. All rights reserved

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