Análisis plano de la historia

2.4.1.1 Need for a symptom-based, standardised definition

Rose considered that a symptom-based definition o f CHD was necessary for use in research studies for three main reasons: (i) to obtain a greater yield o f cases than that obtained by resting ECG alone, (ii) to identify different forms o f CHD (in particular angina, which often is not associated with ECG abnormalities), and (iii) to give a measure o f disease that was independent o f the reading variability o f the EGG.^^ ’'"^ By requiring specific defined criteria, the questionnaire was intended to provide a standardised definition o f angina that would overcome the subjectivity and lack o f inter-observer agreement associated with the clinical interview ,'’"^ and therefore enable more reliable comparisons between and within populations.

2.4.1.2 Derivation of the Rose chest pain questionnaire

The questionnaire was developed from a research study at St M ary’s Hospital, London, which included: i) 36 consecutive patients with ‘unequivocal angina’ (the majority o f whom had ischaemia on resting ECG), ii) 15 consecutive patients with proven MI but not angina, and iii) 23 consecutive patients with chest pain considered, after full hospital investigation, not to be due to heart disease. All subjects were asked open-ended questions about the characteristics o f their pain. The angina questionnaire was derived from the responses o f the 36 angina cases, compared with the other two groups (Table 2.1). O f the different aspects o f chest pain that Rose considered, four characteristics were used in the final angina definition: the site o f pain, the relation to exertion, the subjects’ response to pain, and the time to relief on resting. Other characteristics (such as severity and quality o f pain) were considered insufficiently discriminatory o f cardiac pain to permit their use. The specific requirements for angina are shown in Table 2.2, together with the original questionnaire. Rose used a ‘relatively strict’ definition as he considered specificity to be important for an epidemiological instrument. O f the 36 patients with unequivocal angina, 29 (81%) fulfilled all the Rose criteria, compared to 2 (9%) patients with non-cardiac chest pain. Rose also proposed “one or more attacks o f severe pain across the front o f the chest lasting for 30 minutes or longer” as a definition o f “possible myocardial infarction” (PMI). Thirteen o f 15 infarction patients and 2 ‘controls’ fulfilled this criterion. Based on such exceptionally small numbers o f patients, the precision o f the estimates shown in Table 2.1 is extremely low. Each criterion was considered in isolation, and there was no justification regarding the selection o f one criterion above another, and no description o f how many cases fulfilled several but not all criteria.

2.4.1.3 Use of the Rose chest pain questionnaire

R ose’s definition o f angina, derived from this very small hospital-based study, has remained the standard questionnaire definition throughout four decades o f cardiovascular epidemiology. The chest pain -questionnaire was originally intended to be administered, with strict instructions given for its use,^^’” "* but it was subsequently modified for self-administration (see Table

2 2) 62,70 administered and self-administered versions continue to be used extensively in

numerous different countries, languages, and among different age and ethnic groups, primarily to measure the prevalence o f angina.” ^’’^^ The Rose questionnaire has been used in the BRHS and the other major British cardiovascular studies: the Whitehall Studies^^, the Caerphilly and Speedwell S t u d y t h e Scottish Heart Health S t u d y , t h e Renfrew and Paisley Study, and the annual Health Surveys for E n g l a n d a n d Scotland.’^’ Rose angina has also been used as an ‘outcome’ measure in clinical trials,^^^’^^^ case-control,'^'*"'*’^ longitudinal'^^ '^^’'^^ and cross- s e c t i o n a l s t u d i e s . Rose angina is used far more frequently than Rose’s definition o f possible MI (PMI). This is probably because traditionally accepted definitions o f clinical MI are not purely symptom-based, including ‘objective’ ECG and enzyme criteria, whereas this is not the case for clinical angina.

2.4.1.4 Modifications to the Rose angina questionnaire

Although few alternatives to the Rose angina questionnaire have been proposed, many studies have made modifications to the original wording and/or to the precise definition o f angina. By far the most common modification involves the site o f pain criterion specified by Rose as “the sternum or the left anterior chest and left arm” . This criterion has been omitted altogether,

changed to “the sternum or the left arm”,^^'*'^^^ “the sternum or the left chest or the left or “the sternum or the left anterior chest” . T h e angina definition used in the BRHS differs from the original in several ways. First the questionnaire itself had minor wording modifications, which are detailed in chapter 3 (3.5.1.1 and Table 3.3). Second, two categories o f angina were defined from the outset.^* ‘Definite angina’ used the Rose criteria except that the site criterion was “the sternum or the left anterior chest” (results pertaining to Rose’s original site criterion are also presented in this thesis.) ‘Possible angina’ was defined as chest pain on exertion that did not fulfil all the remaining criteria for ‘definite angina’.

2.4.1.5 Prevalence of Rose angina and possible MI

Use o f the Rose questionnaire has revealed a substantial prevalence o f angina and ‘possible MP (PMI) in Britain and other industrialised countries, with the prevalence o f Rose angina among women often shown to be similar to that among men. Table 2.3 presents estimates o f prevalence from the major British studies;^^’^^’'^^''^^’’^’’’^^'’*° age-specific comparisons are presented and discussed in relation to the BRHS findings in chapter 4. It can be seen from the BRHS and other studies'^' ’"^^ ’^^’’^^ that modifications to the questionnaire or angina definition such as those described above can make a substantial difference to the number o f subjects classified as positive for angina symptoms. There is also some evidence that the method o f administration can affect the yield o f cases: A randomised comparison o f administration method in the Whitehall study suggested that the postal questionnaire yielded twice the number o f angina and PMI cases as the administered version;’® a similar finding was reported in a Finnish-Norwegian study.