Aim
To provide an overview of risk to patients diagnosed with acute myocardial infarction.  It should serve as a useful starting point to highlight issues or raise questions about acute myocardial infarction survival, which might merit further investigation.
 

Period of coverage
Data are presented for patients admitted in each of the years ending 30th June 1999 to 30th June 2008.

Deprivation data are used in the calculation of standardised survival rates (see below).  For Scottish Clinical Indicators on the web, published from January 2005 onwards, deprivation quintiles are based on the Scottish Index of Multiple Deprivation (SIMD), derived from the 2001 census data.  Full information on the SIMD can be found on the Scottish Executive website; report here and the dataset here.
 

These codes include myocardial infarction specified as acute or with a stated duration of 4 weeks or less from onset.
  
Patient basis of the indicator
Each patient admitted with an AMI is counted once within each year no matter how many times the patient is admitted for AMI within that period.  The aim is to avoid any double counting of the same patient.

Emergency admissions
From the July 2009 update the definition for selecting emergency admissions in SMR01 data has been revised. The previous definition selected old type of admission recorded as emergency. The new definition can be found here. There may be changes to figures if comparing this update to previous updates.

Definition of outcome
Outcome is defined as survival for at least 30 days after admission.  Mortality is established on the basis of linkage to the GROS death records and so takes account of any deaths occurring after discharge from hospital.
 

Standardisation
Results are indirectly standardised for age, sex and deprivation (SIMD) quintile.  The reference population in terms of which the rates are standardised is the total of AMIs included for Scotland over the entire period.  The rates are thus standardised over time as well as between Hospitals/NHS Boards.  For a more detailed explanation of the indirect standardisation process, please refer to annex 7 of the May 2002 Clinical Outcome Indicators Report (Clinical Outcomes Working Group, 2002)
 

Presentation at NHS Board and hospital level
The indicators are presented at NHS Board and hospital level. Data for NHS Argyll & Clyde totals are presented separately for NHS Argyll & Clyde (H) and NHS Argyll & Clyde (GG). All hospitals are included in NHS Board and Scotland totals. However, data for individual NHS Boards and hospitals are presented only if the total number of AMIs included in the indicator was greater than 50 in the year ending30th June 2007 or the year ending 30th June 2008.  The threshold for inclusion was chosen partly for confidentiality reasons and partly to show most of the major organisations within acute care.
 

Figures at NHS Board and hospital level are available here as a series of downloadable excel files.
 

Interpreting the figures: general points
Interpretation of indicators presented by single year should be carried out with caution.  Statistically hard and fast rules cannot be provided for such interpretation - it is a matter of common sense. In particular, very little should be read into data for a single year, especially when this consists of a deviation from an established pattern.
 

The SMR01 source data is 99% complete for year ending June 2008 at Scotland level; however further data may still be submitted by some hospitals.  Therefore, any apparent fall in the figures for 2008 as compared with previous years, must be viewed with caution. SMR data completeness by NHS Board can be found at here.
   

Death records from the GRO are final up to December 2007 and 2008 data are provisional. Final data from the GRO does not tend to vary a great deal from provisional data.
  

Confidence intervals for the data for individual years have not been presented.  This is not only to keep the presentation simple but also to avoid looking at individual years data and instead focus attention on the long-term trends.  The Clinical Outcome Indicators Report of July 1999 (p20-27) contains a detailed discussion of the kinds of inference it is legitimate to draw from patterns of apparent change and stability in the indicators.
 

In terms of the annual trends presented here, the larger, longer lasting and more stable the difference between the indicator for a NHS Board and the Scottish mean, the more likely it is that this represents a real difference in outcome rather than a chance difference reflecting random variation over time.
 

Most importantly, however, even when a large, stable and long-lasting difference in outcome is apparent, the caveat, which has been stressed throughout the publication of such survival indicators, applies equally here.  No direct inferences about quality of care should be drawn from the data presented here.  However, it should serve as a useful starting point to highlight issues or raise questions about outcomes in this area, which might merit further investigation. The effects of any differences between hospitals in aspects of case mix for which we have been unable to standardise, such as mean severity on admission or differing diagnostic thresholds, may be just as significant as any differences in quality of care. 
 

Interpreting the figures: specific points
Previous Clinical Outcome Indicators Reports (pdf versions are available here) have discussed at length the necessity of recognising the extent to which apparent differences in outcome may be due to differences between hospitals in the case mix of patients admitted.  Such 'case mix' factors may reflect differing admission thresholds, differing diagnostic procedures or differing coding conventions.  In recent years however a specific issue has emerged in the context of the diagnosis of acute myocardial infarction.

The introduction of more sensitive tests for the diagnosis of acute coronary ischaemia - e.g. troponin -, and the incorporation of troponin (and other biomarkers) levels in definitions of acute myocardial infarction (AMI), may have affected the recording of AMI over recent years. Since it is likely that cases previously undiagnosed would now be correctly determined as AMI, it may be that the size of downward trends in the incidence of AMI has been understated in the SMR01 data. Variations in the definition, recording and coding of AMI may affect inter-hospital and inter-Health Board comparisons of post AMI survival.

ISD issued coding guidance in June 2007 covering the recording of troponin levels in acute coronary syndromes- see Coding Guidelines Number 20
 

The introduction of a joint European and American definitions of acute myocardial infarction using biomarker (including troponin) levels by the American College of Cardiology and the Europrean Society of Cardiology in 2000 is set out in: Myocardial infarction redefined: a consensus document of the Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction. Eur Heart J 2000; 21:1502–13
 

References

Clinical Outcomes Working Group (1999)  Clinical Outcomes Indicators July 1999. Edinburgh: The Scottish Executive.
 
Clinical Outcomes Working Group (2002) Clinical Outcomes Indicators May 2002. Edinburgh: The Scottish Executive.
 
Kendrick, S and Clarke, J (1993), “The Scottish record linkage system”, Health Bulletin 51(2): 72-79.
 
McKenna, CJ and Forfar, JC (2002) Was it a heart attack? Troponin positive acute coronary syndrome versus myocardial infarction. BMJ 324:377-378