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Cobb LA, Fahrenbruch CE, Olsufka M, Copass MK. Changing Incidence of Out-of-Hospital Ventricular Fibrillation, 1980-2000. JAMA. 2002;288(23):3008–3013. doi:10.1001/jama.288.23.3008
Context Recent reports from 2 European cities and an earlier observation from
Seattle, Wash, suggest that the number of patients treated for out-of-hospital
ventricular fibrillation (VF) has declined.
Objective To analyze the incidence of cardiac arrest and to examine relationships
among incidence, sex, race, age, and first identified cardiac rhythm in Seattle.
Design, Setting, and Patients Population-based study of all cardiac arrest cases with presumed cardiac
etiology who received advanced life support from Seattle Fire Department emergency
medical services during specified periods between 1979 and 2000. United States
Census data for Seattle in 1980, 1990, and 2000 were used to determine incidence
rates for treated cardiac arrest with adjustments for age and sex.
Main Outcome Measures Changes in incidence of cardiac arrest and initial recorded cardiac
Results The adjusted annual incidence of cardiac arrest with VF as the first
identified rhythm decreased by about 56% from 1980 to 2000 (from 0.85 to 0.38
per 1000; relative risk [RR], 0.44; 95% confidence interval [CI], 0.37-0.53).
Similar reductions occurred in blacks (54%; RR, 0.45; 95% CI, 0.26-0.79) and
whites (53%; RR, 0.47; 95% CI, 0.38-0.58) and was most evident in men (57%;
RR, 0.43; 95% CI, 0.35-0.53), in whom the baseline incidence was relatively
high. When all treated arrests with presumed cardiac etiology were considered,
that incidence decreased by 43% (RR, 0.58; 95% CI, 0.49-0.67) in men but negligibly
in women, for whom a relatively low incidence of VF also declined but was
offset by more cases with asystole or pulseless electrical activity.
Conclusion We observed a major decline in the incidence of out-of-hospital VF and
in all cases of treated cardiac arrest presumably due to heart disease in
Seattle. These changes likely reflect the national decline in coronary heart
The number of patients in Seattle, Wash, treated for out-of-hospital
cardiac arrest with ventricular fibrillation (VF) as the first recorded rhythm
has decreased since 1980.1 Such a change might
be anticipated in view of the overall reduction in coronary heart disease
mortality in the United States.2 Since out-of-hospital
deaths contribute substantially to coronary heart disease mortality,3 it follows that the incidence of out-of-hospital cardiac
arrest may be reduced concomitantly.
Kuisma and colleagues4 recently described
a marked decrease in the incidence of out-of-hospital VF from 1994 to 1999
in Finland. Herlitz et al5 reported a modestly
decreased incidence of VF cases during a 17-year period in Sweden but no appreciable
change in the total number of treated cardiac arrests.
The purpose of this report is to analyze the changing pattern of out-of-hospital
cardiac arrest in Seattle during the past 20 years in terms of incidence,
relationship to initially recorded cardiac rhythm, and sex and race of patients.
The Seattle Fire Department's emergency medical services (EMS) system,
Medic One, has been described previously.1,6 This
system is the sole provider within the city for medical emergency response
dispatched for 911 calls and it is 2-tiered, with mean initial responses by
emergency medical technicians of 3.5 to 4.0 minutes and paramedic responses
of 7.5 to 8.0 minutes following dispatch. Since 1970, details of all cardiac
arrests attended by Medic One in Seattle have been entered into a comprehensive
database that includes age, sex, race, initial cardiac rhythm, treatment,
and EMS parameters relevant to patient outcome.
The patients described in this report were consecutive cases of cardiac
arrest who received advanced life support by Seattle Fire Department paramedics,
including patients (9.2%) whose cardiac arrests were witnessed by EMS personnel.
In this report, advanced life support is defined as the application by a paramedic
of 1 or more of the following: tracheal intubation, precordial shock for VF
or ventricular tachycardia, intravenous line placement, and administration
of medication. Patients whose arrest was apparently not due to cardiac causes
(eg, trauma, exsanguination, drug overdose) were excluded from this analysis.
Three patients with VF, all in 1990, received 1 or more precordial shocks
but no further EMS interventions. Because of end-of-life instructions or cardiac
arrest in a hospital, these 3 patients were not included as treated and were
not considered in the present analysis.
The primary source of these data was the medical incident report submitted
by fire department paramedics for all patients attended. Each report was reviewed
to identify treated cardiac arrests and edited for omissions or inconsistencies.
Any missing data were obtained from death certificates or hospital admission
forms. During the years covered in this report, we adopted several procedures
to ensure identification of all cases, primarily formal periodic checks against
fire department records for complete ascertainment. After 1990, we accounted
for cases by tabulation of all sequentially numbered reports and after 1998
by additional electronic verification. Use of automated external defibrillators
(AEDs) by first responders, begun in 1984 and phased in completely by 1990,
provided another cross-check. Receipt of AED tapes and telephone notification
of each instance of AED use were checked against the medical incident reports
identified as cases of cardiac arrest. Beginning in 1994, 2 screeners identified
cases by reviewing duplicate sets of forms. Such efforts have ensured that
few, if any, cases were missed and would be expected, if anything, to enhance
the identification of cardiac arrests in later years. The data are presented
in 3 periods, each including a US Census year: 1979-1980, 1989-1990, and 1999-2000.
During the earliest period, the determinations of initial cardiac rhythm
were obtained from defibrillator monitors used by paramedics who typically
arrived on the scene approximately 4 minutes after the first responders. During
the latter 2 periods, the initial rhythm was usually based on tracings obtained
with AEDs used by the first responding emergency medical technicians.7 In view of the small number of patients with ventricular
tachycardia and cardiac arrest (ie, 1% of those found with VF), patients with
ventricular tachycardia are counted with those whose first recorded rhythm
Because of the small number of cardiac arrests among persons younger
than 20 years, they were excluded; accordingly, the census information was
also restricted to those aged 20 years or older. Race-specific incidence rates
were calculated for whites, blacks, and Asians/Pacific Islanders; the latter
were combined to provide comparable racial classification across the 3 census
periods. The numbers of cases and population size were limited for other racial
groups, so they were not considered separately in this report. In calculating
age- and sex-adjusted annual incidence rates, we counted the events during
periods of 2 years and halved the resultant (2-year) rates. The incidence
rates in persons aged 20 years or older in the earlier 2 periods were adjusted
for age and sex to those of the 2000 Seattle census and the US 2000 census
for all periods.8
The significance of linear trends for incidence over the 3 periods was
estimated according to the Mantel-Haenszel test of linear association, and
2-tailed P values are reported.9 Relative
risks (RRs) and their 95% confidence intervals (CIs) are reported for the
rates in 1999-2000 using 1979-1980 rates as the baseline.10 We
used 1-way analysis of variance and the resulting linearity significance level
to examine trends in mean ages. P<.05 was considered
significant for all analyses.
Since 1980, the number of VF cases treated annually has declined, with
an approximate 50% reduction in the number treated each year (Figure 1). Although the population of Seattle aged 20 years or older
increased modestly from 1980 to 2000, the total number of treated cardiac
arrests per year decreased by 31%, related to a substantial decline in patients
whose first recorded rhythm was VF (Table
1). The overall adjusted incidence rate for all treated arrests
with presumed cardiac etiology declined by 34% (RR, 0.66; 95% CI, 0.58-0.75).
The rate declined for men (43%), but only to a minor extent for women (10%).
After age and sex adjustment to the 2000 US population, the annual incidence
of VF in Seattle declined by 56% (RR, 0.44; 95% CI, 0.37-0.53) during this
20-year span. Reductions in VF incidence rates were evident in both men and
women (57% and 51%, respectively). Among patients with VF, declining incidence
rates were evident in virtually all age strata (data not shown). The incidence
of VF in men far exceeded that of women, and the ratio of male-female incidence
rates decreased only from 4.0 to 3.5 in 20 years.
The incidence of asystolic arrests and the overall incidence of patients
treated for pulseless electrical activity (PEA) did not demonstrate consistent
changes over the study period (Table 1).
In men, the incidence of treated cardiac arrests with asystole or PEA tended
to decrease, whereas in women, these rates tended to increase. The overall
changes in rhythm-specific incidence rates in Seattle over the 3 periods are
shown in Figure 2.
The incidence of VF cardiac arrests decreased significantly in blacks
and whites but not in Asians/Pacific Islanders over the study interval. Whites
experienced a decrease of 53% (RR, 0.47; 95% CI, 0.38-0.58), from 0.85 to
0.40 per 1000. Blacks had a similar 54% decrease in VF incidence (RR, 0.45;
95% CI, 0.26-0.79), but that decline was offset by an increase in the incidence
of arrests with asystole (0.45-0.81 per 1000) (Table 2). Reduction in the overall incidence of treated cardiac
arrests was apparent in whites but was less prominent or not observed among
blacks and Asians/Pacific Islanders, the latter group having relatively few
cases. However, the proportion of patients with cardiac arrest discharged
alive from the hospital did not change whether the initial rhythm was VF,
PEA, or asystole.
In Seattle, a city with a population of about 560 000, there has
been a marked reduction in the incidence of treated out-of-hospital cardiac
arrest, particularly in cases in which the initial recorded rhythm was VF.
The decline began in about 1980 and persisted to 2000. This is not an isolated
observation; decreases in the incidence of VF cardiac arrests have also been
reported in Göteborg, Sweden,5 and Helsinki,
Although the incidence of VF cardiac arrests was reduced among men,
women, blacks, and whites, the basis for the declining incidence of VF is
only speculative. It seems likely, however, that this reflects the general
reduction in age-adjusted mortality attributed to coronary heart disease.2,11 Further clarification is required
to determine the relative influences of primary and secondary preventive measures
as well as improved medical/surgical outcomes.12
In searching for alternative explanations for the declining incidence
of treated VF, we considered the possibility that compared with 10 or 20 years
earlier, more patients in recent years were found dead and without indication
for attempted resuscitation. We were able to examine this possibility with
339 untreated patients aged 20 years or older from a 12-month case series
in 1989 and 730 patients from 1999-2000. All were declared dead on arrival
without obvious cause, except for a small group with end-of-life instructions.
Slightly more than half of patients in these groups were men, deaths were
unwitnessed in 98%, and 98% occurred at home or in a nursing home. The age-
and sex-adjusted (US Census, 2000) annual incidence of these events was 0.85
per 1000 aged 20 years or older in 1989 and 0.87 in 1999-2000. Thus, the limited
available data do not support this alternative explanation.
An additional explanation might be that patients with symptoms of acute
myocardial infarction in latter years of the study incurred less delay in
seeking care than those in earlier years. In that scenario, the site of VF
might be transferred from the out-of-hospital setting to the hospital. However,
there is little reason to believe that this has occurred, particularly in
the past decade. Efforts to reduce patient delay in reacting to symptoms of
myocardial infarction, including a program in the Seattle area, have met with
little or no success.13,14 Additionally,
national trends over a recent 4-year period showed only minor, nonsignificant
decreases in delay in seeking care and unchanged median delay times at 2.1
Although we noted a reduction in the incidence of treated cardiac arrest
with VF as the initial rhythm, we did not observe a concomitant decrease in
the incidence of asystole or PEA. The reasons for this discrepancy are uncertain;
however, we believe it is likely that an appreciable proportion of those with
nonshockable rhythms developed cardiac arrest from noncardiac causes or developed
circulatory arrest from cardiac pump failure without an arrhythmic event.
Whereas the vast majority of VF cardiac arrests are related to an underlying
cardiac disorder, our impression is that cardiac causes are less frequent
in persons with asystole or PEA, even after excluding obvious noncardiac causes
such as drug overdose, trauma, exsanguination, and primary respiratory failure.16-18 Patients with asystole
or PEA were, on average, older than those with VF; many could well have died
from conditions not affected by the improvement in nationwide coronary mortality.
There are areas for potential inaccuracy in the reporting of these trends.
First, US Census data are not free of error.19 Race
as tabulated in 2000 is not directly comparable with prior enumerations because
persons may be counted as combinations of 2 or more races rather than according
to the first race listed, as in prior census years.20 The
number of black Seattle residents aged 20 years or older who were counted
as of "single race" in 2000 declined in comparison with the 1990 population
(33 725 vs 34 730), while 22 880 persons aged 20 years or older
were counted in 2000 as being of 2 or more races. This may provide evidence
that potential underreporting is not proportional across the 3 racial groupings.
The effect of underreporting by race in 2000 would be to diminish a decline
in incidence by that race; this possibility may play a role in the apparent
increase in asystole reported for black patients in 2000 (Table 2).
Second, the incidence rates may be spuriously elevated by including
cardiac arrests among nonresidents in Seattle or lowered by not including
city residents who developed cardiac arrest elsewhere. For cardiac arrest
cases in 1999 and 2000, 92 (12%) of the 744 were nonresidents of Seattle.
Nonresident men with treated cardiac arrest were appreciably younger than
residents: mean, 59.1 (SD, 12.8) years vs 70.1 (SD, 14.5) years. However,
the mean ages of female residents and nonresidents were similar (72.5 and
71.9 years, respectively). The 1990 census described a net influx of about
89 000 commuters into Seattle (113 000 in 1980), and it is likely
that our calculated incidence rates are modestly overestimated by using the
Seattle population denominators.21,22 Comparable
census data are not yet available for 2000. However, it also seems most probable
that our reported trends over time are minimally, if at all, affected by travel
into or out of Seattle.
Although unlikely to significantly affect our findings and conclusions,
we note that the means for recognizing VF in Seattle changed after about 1985.
At that time, the determination of initial rhythm began to shift to review
of recordings from AEDs7 rather than from paramedic
observations, which had been carried out a mean of 4 to 5 minutes later in
the course of resuscitation. However, tracings obtained later in the course
of the cardiac arrests, as in 1979-1980, most likely would serve to identify
fewer cases of VF compared with those in which first-arriving EMS personnel
applied AEDs (as in the latter 2 periods), thereby tending to obscure any
decrease in incidence over a span of time. Of course, any changes in the identification
of VF could not affect the overall incidence of cardiac arrest.
Extrapolation of the 2000 incidence rates of cardiac arrest for persons
aged 20 years or older in Seattle to a national level suggests that approximately
184 000 treated cardiac arrests due to presumed cardiac causes could
be anticipated in the United States each year. Of these, about 76 000
would have VF as the initially recorded rhythm. These numbers contrast with
the estimated 400 000 to 460 000 sudden cardiac deaths in the United
States.3 This difference is related to the
substantial number of all-cause out-of-hospital deaths that were not treated
and to the considerable likelihood of overestimation of sudden cardiac deaths
when relying on data from death certificates.23,24 Furthermore,
suddenness of death does not equate treatable arrhythmic events. From an EMS
perspective, the number of treatable VF cardiac arrests are most relevant;
these may represent only about one fifth of so-called sudden cardiac deaths.
A caveat in this extrapolation is to recognize the potential limitations of
our use of a population sample from a single geographic site that represents
only about 1/500 of the US population.
In summary, the incidence of cardiac arrest due to VF has substantially
declined in Seattle. Since 2 European communities have also reported declining
numbers of cases, we conclude that arrhythmogenic cardiac arrests are less
commonly encountered now than 10 to 20 years ago.
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