Audit of secondary prophylaxis after myocardial infarction

BMJ 1994; 309 doi: (Published 12 November 1994) Cite this as: BMJ 1994;309:1268
  1. D L Whitford,
  2. A J Southern
  1. Newcastle upon Tyne NE12 8UT, general practitioner. North Tyneside Medical Audit Advisory Group, North Shields,
  2. Tyne and Wear NE29 7BJ, audit facilitator.
  1. Correspondence to: Dr D L Whitford, 34a Wallsend Road, North Shields NE29 7BJ.
  • Accepted 22 June 1994

The effectiveness of aspirin and ß blockers in reducing morbidity and mortality after myocardial infarction is now established.1,2 Nevertheless, a study in the Northern region in 1991 showed that only 41% of patients with myocardial infarction were discharged taking the optimal drugs.3 We therefore evaluated the use of these drugs in North Tyneside.

Patients, methods, and results

Standards were set locally for the use of aspirin and ß blockers after myocardial infarction by agreement between general practitioners and physicians. Aspirin should be given to all patients except those with hypersensitivity, active peptic ulcer, or taking anti-coagulants, and treatment should be continued indefinitely in the community. ß Blockers should be given to all patients except those with active reversible airways disease, heart block, or heart failure, and treatment should be continued for at least one year and up to six years in the community.

A 50% random sample was taken of patients living in North Tyneside who had had a myocardial infarction between April 1991 and March 1992. We checked hospital notes to determine treatment on discharge and any contraindications to ß blockers or aspirin. Of the 272 patients sampled, 77 had died and four had no hospital notes available, leaving 191 patients in the study. A questionnaire was sent to 186 patients one year after their myocardial infarction, five patients having died in the time between data collection and posting the questionnaires. The questionnaire asked for details of patients' continuing drug treatment; 121 were returned completed (65% response rate).

The table shows the use of secondary prophylactic drugs on discharge from hospital and one year later in the community. There was no significant difference between the three local hospitals in the use of secondary prophylactic drugs (Fisher's exact two tailed test: aspirin, P=0.2; ß blockers, P=0.53).

Secondary prophylaxis for myocardial infarction on discharge from hospital and one year later in community. Values are numbers (percentages) of patients

View this table:


On discharge from hospital 16% of patients were treated suboptimally in that they did not receive a secondary prophylactic drug to which they had no contraindication. Thus 84% of patients were discharged from hospital taking appropriate secondary prophylactic drugs after myocardial infarction. The use of these drugs had decreased in the community one year later.

The standards we set were not reached in this retrospective audit, largely because of the underprescribing of ß blockers, already well documented.3,4 Additionally, we found that ß blockers were contra-indicated in many patients (45%). About half of these patients may have been able to take them had a therapeutic trial in hospital or in the community been undertaken. We suggest that guidelines on therapeutic trials of ß blockers in such patients be included in protocols on the use of secondary prophylaxis.

There was no evidence from the study that patients who were not prescribed these drugs in hospital later started taking them in the community. The follow up of patients after myocardial infarction in primary care should include a review of prophylactic drugs, and general practitioners should be more proactive in starting treatment when appropriate.

Our results are better than those of Eccles and Bradshaw in relation to discharge of patients taking aspirin and ß blockers.3 This may be partly due to the impact of their work over time. There were methodological differences, however. We collected our data from hospitals rather than through general practitioners, so their study may have audited communication between hospital and general practice as much as treatment on discharge. Additionally, in contrast with their study, our standards were set by local agreement between general practitioners and physicians. This led to differences in agreed contraindications (particularly to ß blockers) between the two studies, which may have further contributed to the discrepancy between our results. Audit is more likely to effect change when its development, dissemination, and implementation are as local as possible,5 and we suggest that external audit may even yield misleading results.

In conclusion, we emphasise the need to start secondary prophylactic drugs in hospital in all eligible patients after myocardial infarction and the importance of continuing treatment in the community. Our study suggests that this message is getting through but that there is still room for improvement.

We thank Carol Orr for data collection, and our standard setting group: Drs S Baillie, A Bates, S Furniss, and W Tapsfield. This study was supported by a grant from the Northern Regional Health Authority.


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