COMMUNITY HEALTH STUDIES VOLUME Vl l , NUMBER 2. 1983

THE LONG-TERM MONITORING OF CARDIOVASCULAR DISEASE IS IT FEASIBLE? R. Bonita*, R. Beaglehole+. J.D.K. North* + Department of Medicine and + Department of Community Health, School of Medicine. Auckland, New Zealand. [Mrmhrs of the ARCOS irsm who p;itiirip;iied in the stiidy inrludrd J . Cross. R. Jarkson. J . Lye. D. Mahon. K. Perry. N . Sharp. A. Strwari and S. Thnmron.]

Summary Death rates for cardiovascular disease in New

Zealand, as in many other Western industrialised countries, have been declining during the past decade. The information needed to explain this welcome, but surprising, decline is larking. In an attempt to redress the imbalance, baseline information has been collected on the occurrence and patterns of management of coronary heart disease and stroke for a large segment of New Zealand’s population. The difficulties. costs and limitations encountered in this exercise are discussed in the light of the feasibility of long-term monitoring. For diseases. such as coronary heart disease, routinely available information can, and should. be exploited. For diseases such as stroke, where a substantial proportion are managed out of the hospital setting, particular attention needs to be paid to identifying cases through sources which are not routinely available. The costs and difficulties need to be measured against the benefits to be derived from an understanding of the determinants of two of our major health problems.

Introduction Cardiovascular disease (CVD) death rates,

accounting annually for 40 per cent of all deaths, are declining in New 7aaIand.1,2 Similar changes are occurring in other western countries.3 IJnfortunately. in the absence of information on community trends in the occurrence of CVD, it is not possible to determine whether the decline in mortality reflects a change in inridenreora change in rase fatality rates.

This paper outlines the methodology and experience gained from the development of registers of myocardial infarction (MI). sudden death (SD) and cerebrovascular disease (stroke) in a large, geographically-defined area for the year beginning 1 March 1981. These registers were established to provide baseline information against which future changes in incidence or case fatality could be measured. The achievements as well as the difficulties encountered will be discussed to provide some idea of the sizeand scope of the exercise and its applicability to long-term monitoring.

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Methods Study Population

The Auckland Region Coronary or Stroke (ARCOS) study took as its study population those people normally resident in the Central Aurkland statistical area (March 1981 census population 829.464). A11 hospitalised patients 20-69 years who met the criteria of definite MI during the twelve month period from March 1981 were registered in the study. The definition and guidelines for registration of cases were moclelled on those suggested by the World Health Organisation.‘? In addition, a representative sample of home-treated MI and sudden deaths among those 20-69 years. and stroke episodes irrespective of age. were registered. A rerurrenre of an episode (stroke or coronary) was considered to have occurred if more than 28 days had.elapsed from the initial episode.

Auckland is the largest city in New Zealand, and the Central Auckland statistical area, which is coterminous with the Auckland Hospital Board region, contains one quarter of the total New laaland population. In March 1981, 10.3 per rent of the Auckland residents were aged 65 years and over and 11.5 per cent were of Maori descent. In the total New Zealand population (1981 Census). 9.9 per cent were 65 years and over and 12.2 per cent were of Maori descent6 Auckland has a relatively stable population and results from a postal survey addressed to a random sample of Auckland residents indicate that most people are able to claim a general practitioner as their source of primary care. It is served by three main public hospitals and i t is possible to identify all other sources of medical rare: an extensive system of extra-mural hospital services provides communi ty-. based services. Public hospital care is free of charge and the government subsidises rest home and private hospital care for those over the age of 65 years. Sampling Mrthods.

In order to estimate accurately the number of home-treated cases. the methodology developed by Fraser’ was used: a representative sample of Auckland’s population was defined as the accumula ted pract ice p o p u l a t i o n s of a

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geographically stratified random sample of Aurkland’s .general practitioners and only those rases occurring in the selected practice populations were included. This method of sampling is dependent on a population where most can nominate a partirular doctor as their usual general practitioner. To estimate the proportion of the population rnrolled with the selected doctors, letters were sent to 4945 people in 23 electorates on the updated elertoral roll asking them to provide the name of their usual general practitioner as well as their age decade. Follow-up letters, phone calls and visits were used to achieve a satisfactory response rate. The proportion of the replies to this survey who named one of the selected general practitioners as their usual dortor was taken as an estimate of the population for the denominator of the incidenre frartion.

Case-find ing Logistically it was possible to cope with the

patients of about 200 doctors. A random sample of 215 doctors (52 per rent of all doctors) was drawn from an updated list provided by the Department of Health of all prartising general practitioners in the three health distrirts of the Auckland region. Each was visited individually and invited to ro- operate by referring all possible coronary and stroke episodes as well as sudden deaths occurring in patients in their prartices, regardless of whether they were sent to hospital or treatedat home, for the year beginning March 1981. Careful liaison and feedback was established with the selerted doctors and each practice was phoned if four weeks had elapsed without receiving a patient referral.

Additional case-finding sources for those patients who did not reach the public hospital included regular contact with private hospitals, rest homes, medical laboratories, locum services and the extra-mural hospital. The latter provided monthly lists of all stroke patients who received domiciliary services.

Routinely available sources of case-finding included systematic searches of daily hospital admission and discharge lists of the three major hospitals, discussion with ward sisters and the follow-up of all abnormal rardiar enzyme results from the two private laboratories in Aurkland.AI1 death certificates registered in the seventeen rentres in Aurkland were rherked at least monthly and detailsof all deceased patients whomight have had a stroke or MI. either before or a t the time of death, were reviewed. Links were established with the hospital pathologist and the roroner’s office and rase-finding searches were rondurted regularly. Medical rerords offirers of all public hospitals in

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New Zealand were asked to identify Aurkland residents who had been admitted for suspected MI or stroke to hospitals outside the Aurkland region.

Data Collection Trained nurses extracted details of all patients

whose provisional diagnosis was designated as one of a wide range of presenting ronditions even vaguely suggestive of a possible heart attack or stroke, rerognisingat the same time that this would necessitate a subsequent high exrlusion rate. All notified rases rereived a pre-registration rard with details of the date of notification and the sourre of notification, for ease of “reviewing”. Onre it was established that the patient met therliniral criteria. the residential rriteria, age criteria for coronary patients and general prartitioner criteria for stroke patients, a n interview covering the mediral and social facts surrounding the attack was held with the patient or in the rase of fatal attacks or severely disabled stroke victims, with dose relatives or another suitable informant. These were completed on pre-coded interview forms as soon after the event as possible in the rase of survivors and after six weeks in rases of deaths where i t was necessary to interview a family member or close friend. Follow-up interviews were carried out at one month, and again at six months for all stroke patients, and dead or alivestatus wasestablished by phone at one year. For coronary events. dead/alive status was recorded at one month and again at one year.

T h e p r e - c o d e d q u e s t i o n n a i r e s were systematirally check coded by one observer, punched, edited and processed for statistiral analysis.

Results T h e selected general prartitioners were

rompared to the total Aurkland general practitioners for date of registration, geographical distribution and general mediral services claims (GMS). Apart from the general practitioners in the South Aurkland Health Distrirt where those selected appeared to have a slightly higher GMS inrome, the selected doctors were well matched in every respect. All but one agreed to rooperate and this doctor and his patients were excluded from the study.

When a selerted doctor left the region during the study year. the replacement doctor was coopted into the study. This orrurred on 5 occasions.

The postal survey yielded a response rate of 79 per cent to three letters and it wascalrulated that 51 per cent of the population was enrolled with the selected doctors.

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TABLE 1 Sources of all notifications (MI/SD/CVA)

Routine Sources Hospital surveillance Death Certifirate Autopsy Non-Routine Sources General prartitioner Extra-mural Hospital Rest Home/Private Hospital Other

Registered

998 96

178

436 33 30 37

Not Registered

3780 582 I24

179 269 31 58

Total

4778 678 302

615 302 61 95

1808 5023 683 1

Case- finding A total of 6831 notifications from varying

sources were reviewed (Table 1) and 26 per rent of these were registered in the study. Seventy per rent of all rases registered were from routine sources.

Table 2 summarises the reasons for exrlusion. The large number of exrlusions relates to the broad range of ronditions inrluded for review at the initial pre-registration phase. In addition, a further 49 stroke rases and 13 MI’S were excluded following registration when i t was subsequently established that the rase failed to meet the inclusion criteria.

Multiple sourres of referral allows a higher level of confidence in rompletecase-finding. Of the total number of rases registered. 34 per rent were found through more than one source (Table 3). Of the rest, routine sourres (hospital surveillanre, autopsy reports and death certification) provided most of the referrals.

An examination of those rases where only one sourre of referral was arhieved (Table 4). indicates the important contribution of non-routine sources to taw-finding: only 5 per rent of all MI’S but 22 per rent of all strokes were found through surh sourres.

Case finding rherks during and after the completion of the study were exhaustive. The extra-mural hospital servire provided the main rherk for general praritioners’ referral of home- treated strokes and an additional %rases (5 percent of ail stroke patients) were found in this manner. A sample of death rertifirates was rechecked at the end of the study and this confirmed that all eligible rases had been included. Referrals of Aurkland residents who met the study criteria from hospitals outside the Aurkland region yielded 5 MI’S but n o stroke rases. An investigation of 16,000 consultations in a two month period by urgent mediral rare servires revealed only one raw that had not already been registered. Contart with IWO-

TABLE 2 Reasons for non-registration

Failure to meet rliniral criteria Usual GP not a selerted G P Other (out of area. study year)

MI/SD CVA Total 2519 1694 4213

I64 550 714 42 57 w

2725 2301 5026

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TABLE 3

Number of sources MVSD CVA Total of referral n % n 56 n x One 806 74 378 54 1184 66 T w o 236 22 23 7 34 573 26 Three or more 45 4 90 12 145 8

1087 100 705 loo 1902 100

thirds of the rest homes and private hospitals (4932 beds) in Auckland was made throughout the study year because they were used by the selected doctors. A check of a 10 per cent random sample of the remaining rest homes and private hospitals at the end of the study did not reveal any cases which had not already been detected.

The full-time staff involved in the ARCOS study included a coordinator, three clerical, assistants and three nurse-interviewers. A total of 2640 interviews were completed, 1100 MI and SD, and 1540 stroke (including 835 follow-up) interviews. An estimated 1830 routine phone calls were made to general prartitioners and, altogether, 101.OOO kilometres were travelled to obtain the necessary information.

Discussion T h e ARCOS study has demonstrated that it is

possible to establish a comprehensive rase-finding system for estimating the number of new cases of MI and stroke in a large New Zealand population by using a sampling technique which applies to the total population. While the difficulties of developing an accurate, complete and up-to-date register have been overcome, overall surh an exerrise proved to be a time-consuming. rostly and demanding proress. In terms of providing information on a defined population, howeveF. there appears n o easier alternative to a registers

There is n o reason to believe that there wereany cases erroneously included in the ARCOS study since all questionable cases were adjudicated

TABLE 4

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One source of referral

( i ) Routine sources

( i i )

Hospital Surveillance Autopsy Reports Death Certificates Non-Routine sources General practitioner Private HospitaVRest Home Extra-mural Hospital Other

MI/SD CVA

590 173 140 14 32 33

39 105 16 33

5 4

- -

806 378

I I1 COMM(JN1TY IIEAI.TH STUDIES

rarefully. It has been demonstrated in intra- observer and inter-observer variation of the diagnosis of stroke that the cliniral diagnosis of stroke - that is. its prewnre, irrespertiveof type. or absenre - is highly consistent? Furthermore. the premise was followed that. in aetiologiral researrh, it is preferable to erroneously exclude some true rases than inrlude non-rases.IO This applied esperially to death rertifiration where, after careful verification involving discussion with the certifying doctor, 15 per rent of all thoserertifiedas having died of rerebrovasrular disease were not registered in the study because the diagnosis could not be verified. This rompares with estimates based on national mortality statistirs where 18 per rent more deaths certified as due toCVDorrurred in the Aurkland region in 1980 than was experted from estimates based on the Aurkland register. Studies elsewhere have shown that u p to 40 per rent of stroke deaths have been inrorrertly diagnosed.11

Complete rase asrertainment is the basis of a disease register.’* A majority of rases are likely to be deterted by routine sourres of rase-findingIO such as hospital admission. srrutiny of death certificates and autopsy reports. partirularly in a disease where most patients are admitted to hospital. This was certainly true for the roronary register where 95 per rent were identified in this manner. T h e stroke study, however, depended on sourres not routinely available, since only 60 per cent of the total cases registered were identified by hospital surveillance, death rertifirates and autopsy reports.

Voluntary referral by general practitioners yielded approximately two-thirds of the out-of- hospital stroke rases. The rest, found through notification by private hospitals or extra mural hospital domiriliary services. represent a small but important sertor of the total stroke study. Despite the fart that a high degree of interest and cooperation by the selected Aurkland general practitioners was maintained throughout the study. these rases might otherwise have been missed. This was not always the fault of the general practitioner, since many of these rases were seen by someone other than the general practitioner at the time of the stroke. This demonstrates the importance of a “double rherk” of home-treated rases in developing stroke registers, yet this has been beyond thescopeof most other population-based stroke studies.

It remains possible that a few mild rases who were neither notified to the study nor to extra mural hospital servires by the general practitioner may have been missed. Only a few doctors (about five) were erratic. in their notification?. The fart that 15 per rent of all rasesof stroke notified to the study by the general prartitioners wcre not treated

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in hospital and wcre suffiriently mild as to require no domiciliary servires, leads u s to believe that the number of patients missed in this way is very small. As n further measure of general practitioner ro- operation. they were the first sourreof referral in 34 per rent of all stroke rases and 18 per rent of all MI and SD cases. The experienre of a roronary heart disease register in Australia indirated that general practitioners were the main sourre of referral in only 2 per e n t of all registered rases.ls

The WHO is proposing the multi-national monitoring of trends and determinants in rardiovasrular diseases to romplement the earlier cross-sertional studies of differences in disease rates.” The experience of the ARCOS study in New Zealand suggests that surh a proposal is feasible for roronary heart disease in whirh most patients are admitted to hospital. LJse of routinely available sources would effiriently and effectively yield a majority of rases.

For strokes. however, where 30 per rent in New 7xaland are not admitted to a publir hospital during the rourse of their illness, the mechanisms for finding extra rases are rosily and elaborate. A method of identifyinga representative sampleof all stroke episodes alleviated the burden and redured the Costs of the study while effertively providingan accurate estimate of inridenre. Such a method is feasible, however. only in a population which is relatively stable and where most ramnominate a par t i rular dortor as their usual general prartitioner. Reliance on general practitioners as a sourre of rase-finding for home-treated rases is most often the only available option for studies of inridenre of a disease, yet i t has been demonstrated in this study that even when an apparent high degree of ro-operation has been established with participating doctors, without an additional system for identifying out-of-hospital rases. the inridenre of a disease, surh as stroke. is likely to be underestimated by u p to 10 per rent.

Another potential area for error ocrurs in trying to establish a diagnosis in those already frail patients over the age of 70 years, when objertive criteria are not available to confirm the diagnosis. In terms of establishing baseline data on the use of resources, i t was neressary to inrlude all rases of stroke regardless of age. sinre stroke is predominantly a disease of the elderly. To monitor all cases of stroke over time would bediffirult (even in an ideal population surh as that of the Aurkland region) and to limit stroke rases to those under 70 years would yield t o o few cdses to detert improvements in mortality or changes in therapy.

Continuous monitoring of rardiovasrular disease mortality and morbidity in rombination with the monitoring of rhanges in standard risk

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factors is the best way to determine the effects of primary prevention and to investigate the determinants of the disease. Organising and co- ordinating such a study isa major undertakingand the logistic problems should not be under- estimated. The contribution made by non-routine sources of referral, which by their nature are more

expensive, has been established. The ARCOS study, in size, scope and efficiency, establishes the feasibility of long-term monitoring of coronary heart disease by validation of routine case-finding sources. Monitoring of stroke patients, however, presents particular difficulties and limitations which need to be taken into account before attempting registration on an ongoing basis.

References

1. Bonita R, Beaglehole R, Trends in cerebrovascular disease mortality in New Zealand. NZ Med J 1982; 95: 41 1-4.

2. Beaglehole R, Hay DR. Foster FH, Sharpe DN. Trends in coronary heart disease mortality and associated risk factors in New Zealand. NZ Med J 1981; 93: 371-5.

5. Pisa Z, Uemura K, Trends of mortality for i s rhaemic heart disease and o ther cardiovascular disease in 27 countries, 1968- 1977. World Health Statistics, 1982; 35, 1: 11- 47.

4. WHO Working Party Report. Ischaemic Heart Disease Registers. Part 11, 1969.

5. Hatano S, Control of strokein thecommunity - methodologiocal considerations and protocol of WHO stroke register. WHO document No. CVD/S/73.6 Rev I , 1973.

6. 1981 Census, Department of Statistics, Wellington.

7. Fraser GE. The estimation of a disease frequency using a population sample. Int 1 of Epid, 1978: 7: 3. 277-84.

8. Weddell JM, Registers and registries: A review. Int J of Epid, 1973; 2: 3, 221-8.

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9. Hatano S. Variability of the diagnosis of stroke by clinical judgement and bya scoring method. Bull World Health Organ 1976: 54: 533-9.

10. Gillum RF. Community surveillance for cardiovascular disease: methods, problems, applications - a review.JChron Dis 1978; 31:

11. Kuller LH, Epidemiology of stroke. Adv in Neurology 1978; 19: 281-31 I .

12. Goldberg J, Gelfand HM, and Levy PS. Registry evaluation methods: a review and case study. Epidemiologic Reviews, 1980 2: 2 10-20.

13. Wheeler DJ, Flynn SJ, Leeder SR. The Hunter Valley Heart Attack Study: some methodological problems in community surveillance for acute myocardial infarction. Comm Health Studies 1981; 5, 1: 32-6.

14. Proposal for multinational monitoring of trends and determinants in cardiovascular disease and provisional protocol: Monica project, Geneva, World Health Organisation, 1981 (unpublished WHO document No. CVD/81.2/Rev. I ) .

87-94.

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