Clinical researchIncidence of recognized and unrecognized myocardialinfarction in men and women aged 55 and older: theRotterdam StudyAnneke de Torbal, Eric Boersma, Jan A. Kors, Gerard van Herpen, Jaap W. Deckers,Deirdre A.M. van der Kuip, Bruno H. Stricker, Albert Hofman, and Jacqueline C.M. Witteman*Department of Epidemiology and Biostatistics, Erasmus MC, PO Box 1738, 3000 DR Rotterdam, The NetherlandsReceived 12 April 2005; revised 31 October 2005; accepted 8 December 2005Aims Contemporary data on the incidence of unrecognized myocardial infarction (MI) among subjectsaged 55 and older are limited.Methods and results We studied the incidence of recognized and unrecognized MI in the RotterdamStudy, a population-based cohort of men and women aged 55 and older. The baseline examinationwas performed during 1990–93, with follow-up examinations during 1994–95, and 1997–2000. Baselineand follow-up 12-lead ECGs were analysed by the Modular ECG Analysis System. The 5148 participantswho had no evidence of prevalent infarction were the subjects for analysis. Incident recognizedinfarction was defined as the occurrence of a fatal or non-fatal event coded as I21 according to theInternational Classification of Diseases, 10th edition. A repeat ECG was available in 4187 subjects. Anunrecognized infarction was considered to have occurred if there was electrocardiographic evidencein the absence of a clinically recognized event. During a median follow-up of 6.4 years, 141 incidentrecognized infarctions occurred and the incidence rate of this event was 5.0 per 1000 person years.The incidence was higher in men (8.4) than in women (3.1). The incidence rate of unrecognizedinfarction was 3.8 per 1000 person years. Men (4.2) and women (3.6) had approximately similarincidence. Hence, the proportion of unrecognized infarction was lower in men (33%) than in women(54%). This difference in proportion of unrecognized infarctions was independent of age.Conclusion A high proportion of incident MIs remains clinically unrecognized. As a history of MI isassociated with an increased risk of repeat cardiovascular complications, our data suggest a need forperiodical electrocardiographic screening to recognize (prevalent) infarctions and to install effectivepreventive treatment in those aged 55 and older.KEYWORDSMyocardial infarction;Electrocardiogram;Elderly;IncidenceIntroductionDuring the last decades, ischaemic heart disease mortalityhas considerably decreased in most countries belonging tothe Western world.1,2Changing coronary event rates is themajor determinant of this decline, whereas improvedcoronary care and secondary prevention were responsiblefor decreased event rates.3,4Despite these promising devel-opments, ischaemic heart diseases will remain a majorhealth issue during the decades ahead for several reasons.First, ischaemic heart diseases will persist to occur atearly ages in individuals with a genetic predisposition andin those with an unfavourable clinical risk profile.Furthermore, survivors of an acute coronary syndromeconstitute a population with chronic cardiac conditionsand remain at increased risk of future fatal and non-fatalcardiac events. In addition, evidence exists that patientsand doctors fail to adequately put effective preventivemeasures into practice.5Last, but not the least, it shouldbe realized that the Western world is ageing and heartdiseases come with age. This latter observation has beenthe keynote behind the Rotterdam Study, a long-termprospective cohort study in men and women aged 55 andolder,6on which we report.Myocardial infarction (MI) is the most dominant manifes-tation of ischaemic heart diseases. Although MI is usuallyassociated with severe symptoms, several cohort studieshave indicated that up to 44% of the events remain clinicallyunrecognized until routine and repeated imaging of thecardiac function is performed.7These unrecognized or‘silent’ MIs should not be considered minor events. In fact,it has been repeatedly demonstrated that patients withprevalent unrecognized MI have similar prognosis as thosewith prevalent recognized infarction.8–10Contemporary data on the incidence of unrecognized MIamong subjects aged 55 and older in the general populationare limited. Most epidemiological studies were conductedbefore the 1990s, had an upper age limit, or enrolledpatients with established coronary disease.11–20In addition,& The European Society of Cardiology 2006. All rights reserved. For Permissions, please e-mail: [email protected]*Corresponding author. Tel: þ31 10 408 8190; fax: þ31 10 408 9382.E-mail address: [email protected] Heart Journaldoi:10.1093/eurheartj/ehi707 European Heart Journal Advance Access published February 14, 2006contradictory results have been reported, with some studiessuggesting a steadily increasing incidence with age12,17andothers reporting a stabilizing or even decreasing incidencein individuals over the age of 70.8,16These differenceswere probably confounded by gender differences betweenthe studied cohorts. Against this background, we studiedthe incidence of recognized and unrecognized MI in theRotterdam Study population. We were especially interestedto learn to what extent the incidence of recognized andunrecognized MI increased with age, and if so, whether ornot differences were apparent between men and women.MethodsThe Rotterdam StudyThe Rotterdam Study is a prospective population-based cohort studyof 7983 men and women aged 55 and older. Its overall aim is toinvestigate the incidence and determinants of chronic disablingdiseases. From 1990 to 1993, all inhabitants of a suburb of thecity of Rotterdam aged 55 and older were invited to participate inthe study. The overall response rate was 78%. A trained investigatorvisited all participants at home and collected information using acomputerized questionnaire. The obtained information includedcurrent health status, medical history, drug use, and smokingbehaviour. Additionally, during two visits to the research centre,established cardiovascular risk factors were measured. TheMedical Ethics Committee of the Erasmus MC approved theRotterdam Study, and written informed consent was obtainedfrom all participants. A more detailed description of theRotterdam Study and the collection of data have been givenelsewhere.6Study populationA total of 7085 participants visited the Rotterdam Study researchcentre shortly after the enrolment interview. Living in a
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