Acute myocardial infarction hospital admissions and deaths in England: a national follow-back and follow-forward record-linkage study

Abstract

Background: Little information is available on how primary and comorbid acute myocardial infarction contribute to the mortality burden of acute myocardial infarction, the share of these deaths that occur during or after a hospital admission, and the reasons for hospital admission of those who died from acute myocardial infarction. Our aim was to fill in these gaps in the knowledge about deaths and hospital admissions due to acute myocardial infarction.

Methods: We used individually linked national hospital admission and mortality data for England from 2006 to 2010 to identify all primary and comorbid diagnoses of acute myocardial infarction during hospital stay and their associated fatality rates (during or within 28 days of being in hospital). Data were obtained from the UK Small Area Health Statistics Unit and supplied by the Health and Social Care Information Centre (now NHS Digital) and the Office of National Statistics. We calculated event rates (reported as per 100 000 population for relevant age and sex groups) and case-fatality rate for primary acute myocardial infarction diagnosed during the first physician encounter or during subsequent encounters, and acute myocardial infarction diagnosed only as a comorbidity. We also calculated what proportion of deaths from acute myocardial infarction occurred in people who had been in hospital on or within the 28 days preceding death, and whether acute myocardial infarction was one of the recorded diagnoses in such admissions.

Findings: Acute myocardial infarction was diagnosed in the first physician encounter in 307 496 (69%) of 446 744 admissions with a diagnosis of acute myocardial infarction, in the second or later physician encounter in 52 374 (12%) admissions, and recorded only as a comorbidity in 86 874 (19%) admissions. Patients with comorbid diagnoses of acute myocardial infarction had two to three times the case-fatality rate of patients in whom acute myocardial infarction was a primary diagnosis. 135 950 deaths were recorded as being caused by acute myocardial infarction as the underlying cause of death, of which 66 490 (49%) occurred in patients who were in hospital on the day of death or in the 28 days preceding death. AMI was the primary diagnosis in 32 695 (49%) of these 66 490 patients (27 678 [42%] diagnosed in the first physician encounter and 5017 [8%] in a second or subsequent encounter), was a comorbid diagnosis in 12 118 (18%), and was not mentioned at all in the remaining 21 677 (33%). The most common causes of admission in people who did not have an acute myocardial infarction diagnosis but went on to die of acute myocardial infarction as the underlying cause of death were other circulatory conditions (7566 [35%] of 21 677 deaths), symptomatic diagnoses including non-specific chest pain, dyspnoea and syncope (1368 [6%] deaths), and respiratory disorders (2662 [12%] deaths), mainly pneumonia and chronic obstructive airways disease.

Interpretation: As many acute myocardial infarction deaths occurring within 28 days of being in hospital follow a non-acute myocardial infarction admission as follow an acute myocardial infarction admission. These people are often diagnosed with other circulatory disorders or symptoms of circulatory disturbance. Further investigation is needed to establish whether there are symptoms and information that can be used to predict the risk of a fatal acute myocardial infarction in such patients, which can contribute to reducing the mortality burden of acute myocardial infarction.

Funding: Wellcome Trust, Medical Research Council, Public Health England, National Institute for Health Research.

Figure 1

Schematic of hospital admissions and deaths Data only include people aged 35 years and older. Deaths and admissions were from Jan 1, 2006, to Dec 31, 2010. Admissions linked to death from acute myocardial infarction within this period might have occurred up to 28 days before the start of this period and were included. Deaths linked to admissions within this period might have occurred up to 28 days after the end of the period and were included. We used a continuous inpatient spell algorithm to collapse finished consultant episodes into admissions and then collapsed them further so that admissions within 28 days of the index event were counted as part of the same event. A breakdown of the numbers in each category is available in the appendix (p 2).

Figure 2

Hospital admissions in the 28 days preceding death from acute myocardial infarction Includes 135 950 deaths with acute myocardial infarction as the underlying cause in people aged 35 years and older.

Figure 3

Diagnostic flow of patients admitted to hospital with acute myocardial infarction and those dying of acute myocardial infarction The top section shows underlying causes of death for patients with a primary acute myocardial infarction diagnosis recorded during the first physician encounter and during subsequent encounters who died within 28 days. The proportion of patients with a primary acute myocardial infraction diagnosis who remained alive are not shown here, as their number is large, but are given in the table and the appendix (p 2). The bottom section shows primary diagnoses for patients with acute myocardial infarction diagnosed as a comorbidity and for patients admitted with a cause other than acute myocardial infarction admission who died from acute myocardial infarction within 28 days. Grey bands are proportionate to the number of patients in each category. The vertical bars on the far left show the specific primary hospital diagnoses, and those on the far right show the specific causes of death for people whose primary diagnosis or cause of death was not acute myocardial infarction.

Figure 4

Age-specific event and 28-day case-fatality rates by age group Rates are for patients admitted to hospital with a primary diagnosis of acute myocardial infarction recorded during the first physician encounter or during subsequent physician encounters and patients for whom acute myocardial infarction was diagnosed only as a comorbidity. Results by sex are available in the appendix (p 1).

Figure 5

Effects of including different patient groups on national estimates of epidemiological parameters for acute myocardial infarction Bars show the relative change in national acute myocardial infarction event rate, total case-fatality rate, hospitalised case-fatality rate, and proportion of out-of-hospital deaths with incremental inclusion of additional types of patients. All comparisons are relative to patients with a primary diagnosis of acute myocardial infarction recorded during the first physician encounter.