Reducing the Symptom to Reflow Interval in Acute Myocardial
Infarction
By Mic Gunderson
Acute myocardial infarction (AMI) is high risk and time sensitive condition where EMS
can have a significant influence on patient outcome. This session of the NAEMSP Dialog
reviewed the EMS challenges and related healthcare system issues in caring for AMI
patients from the time of symptom onset to the time that coronary reflow is restored.
The approximately 200 members of the NAEMSP Dialog discussion group were joined by
several invited participants. Christopher Lee, MD was the lead author of a paper
published in Prehospital Emergency Care entitled 'Early Cardiac Cath Lab Activation by
Paramedics for Patients with STEMI on Prehospital 12 Lead ECGs.' paper recently
published in Prehospital Emergency Care (see the 'Papers and Resources' section below).
Chris is a clinical instructor in emergency medicine at the Yale University School of
Medicine and recently completed his fellowship in EMS and is pursing a PhD in
investigative medicine at Yale. Also from Yale and co-authoring the paper were Carin
Van Gelder, MD and David Cone, MD. Other invited participants included Nick Nudell,
REMT-P. Nick is the founder of the popular EKG Club online discussion group. For the
last few years, he has traveled the country as a Senior Field Clinical Engineer for Angel
Medical Systems providing support services the cardiologists involved in clinical trials of
a medical device designed to detect precursors to acute myocardial infarctions.
Tom Bouthillet, REMT-P is a Lieutenant / Paramedic with Hilton Head Island Fire &
Rescue who also serves on the EMS Advisory Committee of the South Carolina Chapter
of the AHA's Mission: Lifeline, and is the editor of the Prehospital 12 Lead ECG blog.
Rounding out the invited participants group was David Carter, RN, MBA, who has
worked as a paramedic, RN, managed numerous EMS programs, and is currently the Site
Administrator of Sarasota Memorials new free standing ER and health care center in
North Port Florida. David has been very active with Society of Chest Pain Centers,
serving on its Board of Trustees and their Accreditation Review Committee.
12 Lead ECG
The technical, operational and financial challenges associated with 12 lead ECG capture
and transmission were considered.
It was asked if 12 lead ECG transmission has become a “million dollar solution to a 5
cent problem.” Transmission capability in many communities requires thousands of
dollars of computer equipment, expensive modems, recurring monthly subscriptions,
restrictive licensing agreements, and a lack of interoperability.
There was strong support for the idea of an open source data and/or communications
protocol that is compatible with all manufacturers and all ePCR systems. It is hoped that
this would reduce costs and
improve interoperability.
EMS systems in the European Union are considering use of the Digital Imaging and
Communications in Medicine (DICOM) format
(http://en.wikipedia.org/wiki/Digital_Imaging_and_Communications_in_Medicine) and
transmitted to existing Picture Archiving and Communication System
(http://en.wikipedia.org/wiki/Picture_archiving_and_communication_system) already
in place in many hospitals. Another option is the CAPTURE method (CAmera Phone
Transmission and Universal Routing of prehospital Electrocardiograms) where
paramedics simply take a photograph of a diagnostic quality 12-lead ECG and email it to
a dedicated email account at the receiving hospital for the cost of a minimum cell phone
data plan.
Other technology issues cited included the desirability and utility of not having to
repeatedly press the button to acquire serial 12 lead recordings. Instead, it should be
possible to schedule them to run at specified time intervals and/or continuously
monitor ST segments. It was also suggested that equipment suppliers design EMS
equipment that transmits patient data allow it to meets national patient labeling
standards for instant integration into the hospital record and thereby eliminating the
need for an ED 12-lead to accomplish this same goal.
Even if the technology for capturing and transmitting 12 leads is available in an EMS – it
must be applied. There was discussion of the problem of crews not capturing 12 leads
on many patients who should have received one. One suggestion was to have BLS first
responders trained and equipped to apply the ECG leads thereby reducing time to
application and serving as a visual reminder to arriving ALS ambulance crews to acquire
the 12 lead.
The idea of having EMT-Bs capturing 12 lead ECGs and using the machine interpretation
to declare STEMI alerts and guide destination decisions (i.e. go to an ED at a PCI hospital
vs. a closer ED at a non- PCI hospital). The AHA study that condemned the lack of 12lead availability did not take into consideration that 12 lead ECG is, for the vast majority
of the US, only provided by paramedic services. Paramedic services are concentrated in
the urban and suburban areas where access to PCI centers is highest. Therefore, the
greatest potential impact of prehospital 12 leads may be in the BLS areas.
False Positives
Beyond the challenges of transmitting, the need for transmission was also discussed.
The typically stated purpose of transmission from the field is to reduce the number of
false positives - which may lead to unnecessary cath lab team activations or
unwarranted diversions to PCI capable hospitals.
Part of the problem is that there isn't consensus on what a false positive is. It could
mean that the ED physician or a cardiologist may have disagreed with the STEMI
interpretation or that the patient was catheterized and had a culprit artery that was not
identified. Perhaps the patient did not go to the cath lab but ended up with a discharge
diagnosis of AMI / NSTEMI. It may also be that a STEMI Alert is declared by EMS but the
patient, or their families, may decide against cardiac catheterization due to chronic
illness, age, or debility. Which of these cases should be counted as a false positive? A
helpful parallel was drawn to trauma alerts, where the criteria, from an EMS perspective,
is if the crew correctly categorized the patient as having met the Trauma Alert criteria,
regardless of any later decision by the trauma surgeon on taking that patient into
surgery. That is consistent with the suggestion that a distinction be made between
inappropriate activation and a false positive catheterization. An inappropriate activation
is where the medic incorrectly makes a STEMI interpretation when the patient did not
actually meet the STEMI criteria. A false positive would be a patient that met the STEMI
criteria but was not found to have a culprit artery. EMS cannot directly influence the
false positive catheterization rate short of making changes to the criteria to be more
sensitive and specific. Otherwise, EMS only has control over correct use of the criteria.
Clarity in such definitions are sorely needed.
Another part of the problem identified was the education and quality assurance
feedback in 12 lead interpretation, which varies widely from system to system. The
intensity of training and the degree of feedback on actual cases were cited as additional
factors impacting the false positive rate.
Another problem cited was the lack of feedback on patient outcome. Cardiologists have
a distinct advantage by having the opportunity to compare their ECG findings with
patient presentation and outcomes – and refine their decision-making process
accordingly. EMS only see patients for a short period of time before handing them off.
While some systems can provide abbreviated information about what happened to the
patient after hand-off, it is far from universal. Too often, hospital staff inappropriatelty
claim that HIPAA regulations prevent them from talking to EMS about patients that
were previously under the care of EMS.
There was brief discussion of other technologies to potentially help reduce the false
positive rate, such point-of-care cardiac enzyme testing. It was mentioned that it might
not be necessary to require positive cardiac biomarkers for patients who present with
an obvious STEMI on the initial 12-lead ECG. On the other hand, for an acutely ill patient
with a non-diagnostic ECG, ST-depression, T-wave inversion, or baseline abnormalities
that obscure the diagnosis of AMI, point-of-care cardiac enzyme testing might help with
the triage decision.
Some 12 lead monitor defibrillators may also be equipped with software that uses the
Acute Cardiac Ischemia Time-Insensitive Predictive Instrument (ACI-TIPI) score (Daudelin
DH, Selker HP: Medical error prevention in ED triage for ACS: use of cardiac care
decision support and quality improvement feedback. Cardiol Clin. 2005;23:601–14.) as
an adjunct to the 12 lead alone. It was suggested that this may be something to further
aid an EMT only system in making transport destination decisions
An important point was made that all the attention is currently places on false positives,
but we're eventually going to have to figure out how to measure false negatives.
Funding
The cost of 12 lead programs was cited as a barrier to more commonplace prehospital
screening for AMI. A 2009 AHA EMS Survey was cited as showing that only 50% of EMS
units across the US have 12 lead capability on at least 75% of their units. Many EMS
agencies are struggling just to meet basic operational needs and cannot afford 12 lead
programs without some way to pay for it. Currently, EMS user fee payments are limited
to an all inclusive fee schedule under CMS which does not allow itemized charges such
as a 12 lead screening. Therefore, EMS typically incurs the costs for a 12 lead program
without revenue to offset those additional costs. However, the hospital reaps the
potential savings associated with a shorter hospital stay as a consequence of the EMS 12
lead reducing the symptom to balloon interval - which leads to reduced myocardial
damage – which leads to the shorter hospital stay. Some recognition of this situation
needs to made in order to align incentives to help facilitate funding for more prehospital
12 lead programs.
Regarding cost relative to BLS services, there are some BLS services that have developed
a 12 lead program by purchasing used ALS monitor/defibrillators with 12 lead capability.
This is overkill since the vast majority of the device’s capabilities are not within the
scope of the BLS provider. A PC laptop based 12 lead device was mentioned that
connects to the USB port. If the laptop has an wireless data card, it can send the ECG to
the receiving hospital or simply transmit the ECG over the radio. The cost was
about 3K. There may be a significant market opportunity offering for a BLS level AED
with 12 lead capture capabilities.
Also with regard to funding, the financial implications of EMS bypassing the closest or
patient preferred hospital in favor of PCI hospital for STEMI patients was discussed.
Issues may include: Conflicts of interest between competing hospitals and physician
groups; Loss of revenue to non-PCI hospitals by not receiving financially lucrative STEMI
patients (and perhaps, at some point in the future, NSTEMI patients).
Patient Factors
Several of the issues discussed related to factors under the control of patients, rather
than EMS or other healthcare system providers. The biggest issue here was the problem
of delays from the time AMI symptoms begin to the time that care is sought. These
delays can be several hours or more and often dwarf the delays between steps once 91-1 is contacted.
Public education is the obvious answer but it is a complex issue that will probably
require an entire series of efforts to be effective. For example, the period of fear that
may be displayed during transport and acute care may be ‘teachable moment’ where
advice from healthcare professionals may be more likely to be heeded. But, that will be
for the next incident – not the present one.
Cost was cited as another reason why patients may avoid calling 9-1-1 sooner than later.
The consequences of an ambulance bill, ED bill, hospital bill, and lost income from
missing work are very likely to give someone pause in calling 9-1-1 or going to the ED in
the face of symptoms they recognize as very suggestive of AMI.
A useful schema was offered that identified four key milestones in the symptom onset
to accessing care interval:
1) Onset of problem
2) Patient recognizes their symptoms
3) Patient decides symptoms are worthy of evaluation
4) Patient accesses care (e.g., by calling 9-1-1 or going to a medical facility)
There are many studies that have tried to find the causes of delays between these
milestones. There is probably not much that can be done for delays between 1 and 2.
Delays between 2 and 3 and between 3 and 4 could be influenced by education efforts.
There is a lot of conjecture in the literature about symptoms in patients with diabetes,
neuropathies, advanced age, or other conditions that could complicate the sensing of
ischemic angina (interval between 1 and 2), but the evidence shows these
considerations are not limited to this sub-group.
Performance Measures
One of the key elements of improving any process of care is being able to measure and
monitor its performance. Discussion took place regarding intermediate or final outcome
measures as well as any process performance measures. The suggestions included:
 % of cases with ST improvement from EMS arrival to arrival at ED
 Frequency of getting an S-T segment seen on the prehospital 12 lead that
decreases or disappears by the time the patient arrives at the receiving hospital.
 % discharged alive
 LV ejection fraction following STEMI
 length of hospital stay
 % of patients who should have received an aspirin that actually received one
from EMS
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EMS false positive rate for STEMI alerts
% of patients who should have received a 12 lead that actually received one from
EMS
% of cases with appropriate capture of serial 12 lead ECGs
Time interval from patient contact to 12 lead capture
A metric that would reflect ECG data quality
STEMI protocol compliance rate (overall and by individual steps)
% of STEMI patient transported to PCI center
% of NSTEMI patient transported to PCI center
% of STEMI patients presenting to ED with transmural injury (with prehospital
non-Q wave STEMI)
Scene arrival to en rout to hospital interval
9-1-1 access to hospital arrival interval
12 lead acquisition to "STEMI alert" or Cath Lab activation interval
Non-STEMI Cases
The challenges in dealing with presumed acute coronary syndrome (ACS) case types
other than STEMI were discussed. The conversation centered on how to handle cases
where EMS has captured a 12 lead that does not show a STEMI, yet the
presentation is otherwise consistent with AMI.
This was considered to be a major issue from the perspective of the smaller hospitals
that do not offer PCI. If those hospitals are told that EMS plans to divert the true STEMI
patients to regional PCI centers, but still transport all of the other chest pain patients to
the closest facility, or facility of pt's choice, the non-PCI hospital were thought to be
likely to be accepting og that policy. The numbers of true-STEMI cases are likely small
enough that the smaller hospitals will not panic about revenue loss. However, if EMS
policies start diverting non-STEMI but ‘likely ACS’ cases away to the PCI center, the
smaller hospitals may be less enthusiastic.
A major concern in many hospital communities is that EMS policies will direct all chest
pain patients to PCI facilities. Some field medics may have tendencies to base such
decisions on "just in case, maybe we should" and "if we can, we should". It's not only a
financial concern for the non-PCI facilities, but also has implications for taking patients
away from their "home" hospitals and medical records and their own physicians. Such
policies may also take local response capability away. I could also mean overloading the
already busy PCI facilities (that often also house other limited resource capabilities) and
potentially negatively impacting their ability to appropriately handle not only the true
STEMI patients, but also other critical patients.
The discussion thread and resource list for this session of the NAEMSP Dialogue may be
viewed at http://groups.google.com/group/naemsp-dialog/web/topic-3---ems-role-inreducing-symtom-to-reflow-interval-in-ami.