Actual linkage rates of hospital discharge records to population register data were somewhat higher than average for the selected cases. Of all admissions in 1996–2003 for AMI age [35–74] 88.9% could be linked, for 75+ this was 93.2%. For stroke, linkage rates were somewhat lower, with 88.1% for 35–74 age category and 88.9% for those aged 75+ (Table ).
For the period 1996–2003 we included 32,990 deaths after admission for MI and 47,393 deaths after admission for stroke in our analysis. Of the MI cases 67.9% of those aged 35–74 died within the first thirty days after admission, compared to total deaths within a year. For those aged 75+ this was 66.1%. For stroke age differences were larger with 67.6% dying within 30 days for ages 35–74 and 60.2% for ages 75+. These proportions are all stable over time: no significant differences between years were detected over the period 1996–2003.
Table lists the breakdown of MI deaths in the different time of death and place of death classes and the year of admission, (given in two-year bands). Table gives a similar breakdown for stroke. Chi-squared tests were used to detect significant trends over time, these are indicated within the tables.
Dutch in-hospital mortality for myocardial infarction 1996–2003: deaths tabulated by age and place of death within 30, 90 and 365 days of admission
Dutch In-hospital mortality for stroke 1996–2003: deaths tabulated by age and place of death within 30, 90 and 365 days of admission
For MI the analysis points to a growing importance of 'other hospitals' as death location for MI, especially for 30-day mortality. In 1996–1997 about 5.9% of the 30-day mortality after MI for ages 35–74 occurred in a hospital different from that of the initial intake, in 2002–2003 this proportion had significantly risen to 10.9%. This rise was at the expense of 30-day mortality within the initial admission, the proportion of which fell from 86.8% to 79.7% over the same period. For ages 75+ a similar trend is found, but somewhat less strong, although still significant.
No significant changes were detected for MI for other death locations or different distances between time of admission and time of death, with the exception of the proportion of deaths outside the hospital for ages 35–74 within 30–89 days after admission, this fell from 48.0% in 1996–1997 (215 deaths) to 34.2% in 2002–2003 (113 deaths).
For stroke a different picture emerges. No significant changes here for deaths in a different hospital, but a significant rise for deaths outside the hospital for both age groups and all three distance to death classes. The rise is especially strong for the proportion of deaths outside the hospital within 30–89 days of admission, and seems to be concentrated in the last years included in the analysis. For instance for deaths of 75+ within 30–89 days after being admitted the proportion of deaths outside the hospital was stable at 38.4% over 1996–2001, but rose steeply to 58.9% in 2002–2003. It is important to note that the observed 30% fall in average length-of-stay for stroke patients (Table ) over the period 1996–2003 also occurred mainly in the last four years of this period.
Table (MI) and Table (stroke) list deaths for year of admission, time of death and cause of death. The patterns for both age groups are very similar, so data are presented for 35+. For admissions for MI this shows a significant (p < 0.05) decrease over time in the proportion of deaths attributed on the death certificate to MI, for all time of death classes. For deaths within 30-days of admission this decrease is accompanied by a significant rise in deaths due to other circulatory disorders and deaths due to other causes. For stroke only for deaths within 90–364 days of admission a similar pattern is found. For deaths due to stroke within 90 days of admission, no significant changes in the distribution of death cases are observed. For both MI and stroke, the diagnostic groups which contribute the most to 'other causes' are neoplasms, disorders of the endocrine system, and respiratory diseases.
Underlying cause of death in people who died after hospital admission for myocardial infarction
Underlying cause of death in people who died after hospital admission for stroke
In Table and Table , mortality rates are presented for both types of index-admissions and both age-groups. Rates were standardized using the average age and sex composition of the clinical hospital population in 2000. In addition, we estimated mortality rate changes (as absolute differences between rates) between 1996 and 2003. Most important observation is that all mortality rates have fallen over this period, but the magnitude of this fall differs. For MI, the highest reduction is observed for 30-day in-hospital mortality. After including readmission and transfer cases, this decrease is much less. For instance, hospital mortality after MI for ages 35–74 has fallen from 7.1 to 5.8 percent, over 1996–2003, a drop of 1.3%, including other 30-day hospital deaths reduces this to 0.9%. Overall 365-day mortality dropped by 1.2%, a larger amount than both 30-day overall mortality (0.8%) and 90-day overall mortality (0.8%). For ages 75+ the picture for MI is the same, but much higher absolute gains in mortality reduction are found at higher levels of mortality. The 30-day in-hospital mortality for 75+ has dropped from 24.2% to 20.2%, a drop of 4.1%. Including other 30-day hospital deaths reduces this drop to 3.1%. Again, 365-day overall mortality dropped by 3.7% further than 30-day overall mortality (3.1%) and 90-day mortality (3.4%). Observed drops in MI-mortality rates occur in most cases gradually over the entire observation period.
Mortality rates* 1996–2003 after admission for myocardial infarction, for seven different definitions of mortality, as percentage of admissions
Mortality rates* 1996–2003 after admission for stroke, for seven different definitions of mortality, as percentage of admissions
For stroke a slightly different picture emerges. Reduction of 30-day mortality within the initial admission is lower than the observed drop for 365 day mortality. For ages 35–74, 30-day mortality within the initial admission has fallen from 12.3 to 11.4%, a drop of 0.9%, while 365-day overall mortality has fallen with 1.5%. For ages 75+, 30-day mortality within the initial admission has fallen from 26.5 to 23.5%, a drop of 3.0%, while 365-day overall mortality has fallen with 3.8%. For stroke, the observed reduction occurs in the last two years of the observation period, but not before.