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| Journal of the New Zealand Medical Association,
01-June-2007, Vol 120 No 1255
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The pre-hospital phase of acute myocardial
infarction: a national audit is needed in New Zealand
Robin Norris
The outcome of acute myocardial infarction (AMI) is usually
settled before the patient reaches hospital. Indeed, two-thirds to
three-quarters of deaths happen outside hospital, and there is an inverse age
gradient for out-of-hospital death1,2—for
victims of heart attack who are under 55 years of
age,2 this proportion is over
90%.2
Although a large proportion of these deaths are truly sudden
and not caused by putative infarction, it has been shown that for cases in which
the presence or absence of premonitory symptoms leading up to death can be
determined from relatives or bystanders, more than 70% do have a premonitory
symptom, usually chest pain.3 Hospitals can
treat only a population of survivors, particularly for younger patients.
Could the burden of out-of-hospital death be reduced if
patients came under care earlier than they do at present? We carried out a study
during 1994–95 involving 2213 patients in three UK centres; 1829 (83%) of
the patients arrived at the hospital by ambulance, and delay times were known or
could be estimated in 1791 (98%).4 We found
that for patents coming under ambulance care within 1 hour of onset of symptoms
(about one-third of those coming to hospital by ambulance), death could be
prevented for up to 30 days after the event in about 14% of cases; for those
coming under care within 1 to 2 hours, the proportion was about 10%. The
proportion of survivors decreased rapidly when care occurred after 2 hours
however (Figure 1).
About 80% of this salvage was due to defibrillation from
ventricular fibrillation (VF), and the remaining 20% was estimated to have been
due to thrombolytic treatment.5,6 Because VF
can be treated as well by ambulance as by hospital personnel, and 35–40%
of successful defibrillations were carried out by the Ambulance
Service,4,7 the key to survival for these
patients was as short as possible delay to coming under ambulance rather than
hospital care.
The benefits of early care are much greater than the
benefits shown from randomised clinical trials carried out in hospitals since
the introduction of thrombolytic treatment (Figure 2). Patient salvage was shown
from use of a fibrin-specific instead of a non-fibrin-specific thrombolytic drug
in the GUSTO Trial involving 41,021 patients;8
over 1 year from revascularisation of patients with two or three vessel disease
who had recovered from unstable angina or non-Q wave infarction in the FRISC II
Trial of 2057 patients;9 and from addition of a
novel anti-platelet drug to aspirin during the hospital phase in the Chinese
COMMiT Trial which recruited 45,852
patients.10
Figure 1. Deaths prevented per 1000 patients
treated according to delay between onset of symptoms and coming under ambulance
paramedic care (N=1791 patients)4
 Numbers inside the histograms indicate percentages of
total patients and bars indicate 95%CI. Clear portions of the histograms
indicate deaths prevented by defibrillation and shaded portions deaths estimated
to have been prevented by thrombolytic
treatment5
The patient and the ambulance service are the keys in
reducing delay in care. Potential patients (the public) need to be educated to
do two things:
The
patients in our study who called their general practitioner arrived at hospital
about 2 hours later than those who called the
ambulance,4 and other researchers have reported
similar findings.11 The ambulance service needs
to respond in emergency mode to calls for chest pain and to be highly proficient
in advanced life support. The New Zealand ambulance service (St Johns and
regional services in Wellington, Taranaki, and Nelson) has an excellent
reputation, but performance indicators for ambulance services are not explicitly
set out, as has been done in the UK.12 Possible
regional differences in performance and opportunities for improvement could be
shown only through a national audit.
Figure 2. Deaths prevented per 1000 patients
treated resulting from improvements shown by clinical
trials8–10 in obtaining or maintaining
infarct artery patency; for description, see text
 Audit of the pre-hospital phase of
infarction should assess both patient and ambulance performance (Figure 3). For
patient performance, we need to know the time of onset of the most severe pain,
the time of call for help, who was called, or, if the patient brought him or
herself to hospital, the time of hospital arrival.
Ambulance performance should record
the time of receipt of the call, the time of arrival at the scene and at
hospital, and whether or not cardiac arrest occurred. If an arrest did occur,
the time, place (home, public place, or ambulance), the presenting rhythm (VF,
asystole, or electromechanical dissociation), and the outcome (survived to reach
hospital, death in hospital, or discharge with or without neurological deficit)
need to be recorded. Electronic recording and transmission of data would
facilitate the process, and data would need to be collated and analysed at some
central point, possibly at ambulance headquarters or attached to a
hospital.
Figure 3 Components of performance by the
patient, the ambulance service, and the hospital
 What would be the advantages of
such an audit? First, it would be an important international contribution to
knowledge about the pre-hospital phase of AMI. Of the various
national,13–16 and
international,17,18 audits reported, none
(except the UK Myocardial Infarction National Audit Project
[MINAP])16 records full details of the
pre-hospital phase. The principal thrust of MINAP so far has been to examine the
delivery of thrombolytic treatment rather then
resuscitation,19 but it is intended to analyse
the pre-hospital data at a later stage (JS Birkhead, Personal Communication;
2007).
Second, the major importance of an
audit for New Zealand medicine would be the opportunity to examine (and
hopefully improve) ambulance and patient performance.
The greatest problem is to make
people aware of the potential serious import of new prolonged chest pain;
stressing they seek help urgently from the ambulance service and not from the
GP; and allaying their possible feelings of guilt if the call turns out to be a
“false alarm”
Unfortunately, media campaigns
encouraging patients to seek help earlier have been generally
disappointing,20,21—although some
individual campaigns22,23 have shown a
reduction in delay. No reduction in hospital case fatality was shown from these
campaigns; indeed none would be expected, because the population of patients
seeking help earlier would include those most at risk. The yardstick for success
should be deaths prevented, principally by defibrillation, but also increasingly
by early thrombolytic treatment started within the “golden
hour”.6
In contrast, education to seek help
from the ambulance service rather than from the GP has had some success. In the
UK, 10 years ago, only one-third of patients admitted to hospital with AMI had
called the ambulance,4,11 but (as documented by
MINAP), the proportion calling the emergency number has risen to more than
two-thirds.19
New attempts to influence patient
behaviour are needed, although in New Zealand it might be more logical to audit
delay times for a period to establish a baseline. Nevertheless, plans for public
education would need to be made in advance. Most of the unsuccessful campaigns
have relied mainly on the media,20,21 and have
continued at the most for 2 years.
First, as with campaigns to stop
smoking, education might have to be continued for a longer period. Second,
alternatives to media advertising should be considered. These could involve
display of posters and distribution of pamphlets from general
practitioners’ surgeries—this can improve public
knowledge.24 Third, more than 40% of patients
presenting with AMI have had previous symptoms of coronary heart disease, either
angina or infarction.
Part of the treatment for these
patients should be explicit advice on what to do should they have a prolonged
attack of pain. It is true that these patients delay for as long as those with
no previous history;25,26 the reason is not
clear, but may well be because they have not had the necessary explicit advice.
Many clinicians, the writer included, have felt that such advice would cause
unnecessary anxiety. This is probably wrong.
What are the possible problems of a
pre-hospital audit? Most of the data would be provided by ambulance officers,
and we would need to be assured that the data were reliable. In the
writer’s experience, and from conversation with colleagues, ambulance
personnel are conscientious and reliable in recording times and events, and
would be keen to help with this new initiative.
An easy-to-use electronic
system—with entry of data on a palm-top computer and downloading onto a
computer at ambulance headquarters—would make the task easier.
Ascertainment of the final diagnosis and hospital outcome would need access to
the patient’s hospital case notes, but this is now relatively easy with
electronic records. Furthermore, confidentiality issues would have to be
addressed.
What is the present situation in
New Zealand? Two recent small studies suggest that all is not well. The median
delay from onset to arrival in a single hospital was 3 hours 41
minutes,27 but the study included only 100
patients of whom 16 had ST elevation. Another recent
study28 also showed long delays, but the times
stated were means—thereby possibly skewed by referrals from distant
regions or community hospitals.
But there is better news.
Concurrently with the publication of this article, delay times are being
recorded in a repeat of a previous 2-week national
audit.13 (C Ellis, Personal Communication;
2007). This should give a general indication of the situation regarding delay in
New Zealand and will be useful to establish methods. Hopefully this will set the
stage for the continuous audit that will be necessary for comparisons of
performance among different regions and to establish temporal trends such as
might hopefully follow a public educational programme.
As described 40 years
ago,29 defibrillation remains the most
important lifesaving treatment for AMI, but the necessity for defibrillation is
greatest before admission to hospital—and the circumstances, treatment,
and outcome of VF attacks do not figure in most national and international
audits. There is a natural tendency for hospital clinicians to regard
opportunities for treatment as starting on admission to hospital, but this is
surely wrong.
A national audit of the
pre-hospital course and treatment of AMI would be an important contribution to
New Zealand medicine.
Competing interests: None.
Author
information: Robin Norris was cardiologist in charge of the
Coronary-Care Unit at Green Lane Hospital and Honorary Professor of
Cardiovascular Therapeutics at the University of Auckland School of Medicine
until 1992. After 1992 he was an honorary consultant cardiologist at the Royal
Sussex County Hospital, Brighton, UK from where he directed the UK Heart Attack
Study and helped to set up the UK Myocardial Infarction National Audit Project
(MINAP). He is now retired.
Correspondence: Dr
Robin Norris, 17 Aberdeen Rd, Castor Bay, Auckland. Email: robinnorris@orcon.net.nz
References:
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