Download Delaying shock for cardiopulmonary resuscitation

Delaying shock for cardiopulmonary resuscitation:
does it save lives?
Jason Beguea and Thomas Terndrupb
Purpose of review
Out-of-hospital cardiac arrest claims more than 450 000
lives annually in North America. Many communities have
dedicated significant resources to provide rapid
defibrillator response for patients in ventricular fibrillation. In
spite of these efforts, mortality from out-of-hospital cardiac
arrest has not improved significantly. Emerging evidence
suggests some patients in ventricular fibrillation arrest may
be harmed by immediate defibrillation.
Recent findings
Recent laboratory studies have shown benefit in performing
a period of chest compressions (cardiopulmonary
resuscitation) prior to defibrillation in models with more
than 4 minutes of induced ventricular fibrillation. During the
initial 4 minutes the heart is more amenable to electrical
defibrillation. Between 4—
—10 minutes, chest compressions
create some coronary perfusion and fill the left ventricle
to prepare the heart for electric shock. These findings,
in conjunction with most emergency medical service
response times reported to be 5—
—8 minutes, have prompted
human investigation into a strategy of chest compression
first. A recent randomized controlled trial reported a fivefold
increase in survival for patients with more than 5 minutes of
VF who received 3 minutes of chest compressions prior to
defibrillation compared with those who had not.
Summary
Current guidelines call for rapid defibrillation as the most
important ‘link’ in the ‘chain of survival’. For most ventricular
fibrillation patients who have professional rescuers arrive
after 5—
—8 minutes of ventricular fibrillation, however,
immediate defibrillation is likely to be ineffective.
Counterintuitively, these patients may benefit from a period
of chest compressions prior to being shocked.
Keywords
defibrillation timing, out-of-hospital cardiac arrest,
ventricular fibrillation
Curr Opin Crit Care 11:183—
—187. ª 2005 Lippincott Williams & Wilkins.
a
Department of Emergency Medicine and bCenter for Emergency Care and
Disaster Preparedness, University of Alabama at Birmingham, Birmingham,
Alabama, USA
This study was supported through a cooperative agreement with the National
Heart, Lung and Blood Institute (U01.2000268) including contributions from the
National Institute of Neurological Disorders and Stroke, Institute of Circulatory and
Respiratory Health of the Canadian Institutes of Health Research, Defense
Research and Development Canada, Heart and Stroke Foundation of Canada, and
the U.S. Army Medical Research & Materiel Command.
Correspondence to Jason Begue, Assistant Professor, Department of Emergency
Medicine, University of Alabama at Birmingham, 619 19th St South, JT N275,
Birmingham, AL 35249-7013, USA
Tel: 205 975 7866; fax: 205 975 4662; e-mail: [email protected]
Current Opinion in Critical Care 2005, 11:183—
—187
Abbreviations
AED
CPR
EMS
OOH-CA
PAD trial
ROSC
SCD
VF
automated external defibrillator
cardiopulmonary resuscitation
emergency medical system
out-of-hospital cardiac arrest
Public-Access Defibrillation and Survival After Out-of-Hospital
Cardiac Arrest
return of spontaneous circulation
sudden cardiac death
ventricular fibrillation
ª 2005 Lippincott Williams & Wilkins.
1070-5295
Introduction
Sudden cardiac death (SCD), defined as deaths occurring
out of the hospital or in emergency departments due to cardiac disease, claims approximately 450 000 lives per year
in the United States [1]. Despite reduction in overall mortality from cardiovascular disease, SCD rates remain elevated, especially in certain regions and populations of the
United States [1]. Some resources have been dedicated
to improving outcomes from SCD and out-of-hospital cardiac arrest (OOH-CA). Advanced life support units have
increased their ability to quickly respond and apply more
advanced care on scene. Basic life support units have been
empowered to provide emergent cardiac care including
cardiopulmonary resuscitation (CPR) and defibrillation
using automated external defibrillators (AEDs). With increasing importance placed on rapid defibrillation and bystander CPR comes the implementation of telephoneassisted CPR and public access AEDs. In spite of these
efforts, however, survival from OOH-CA is generally poor.
Most areas report little improvement in SCD mortality,
with survival still hovering around 3–5% [1].
Studies of the effectiveness of improving the interventions have mixed results. In Seattle and Kings County,
Washington, which by many is considered an OOH-CA
success story, investigators reported an observed increase
in survival to hospital discharge in the late 1970s–1980s
from 7–17% [2]. This came after efforts in CPR training
for the public and increasing the number of emergency
medical system (EMS) responder defibrillation-capable
units. These results have been duplicated in few other
communities (exception Rochester, MN) [3]. In New
York City, survival is dismal, around 1.4% [4]. Ontario,
Canada, is only slightly better with 2.5% survival [5].
When looking at studies of other locations, unfortunately
the Seattle experience seems to be the outlier, not New
York and Ontario. Further evaluation in Seattle showed
that outcome improvements were not sustained [6]. Although it is true that epidemiologic studies in this area
183
184 Cardiopulmonary resuscitation
are difficult to compare because of statistical variations
and definitions of SCD [7•], the efforts to improve results
simply were not living up to the promise.
Why haven’t the millions of dollars in time and resources
been effective in improving outcomes? Since the block
grants of the 1970s, EMS response times were decreased
and intervention capabilities were increased, in part for
OOH-CA situations. Over the past decade several promising interventions have been studied, with modest overall
impact. One that has shown promise, both in animals and
preliminary human studies, has been to provide chest
compressions prior to defibrillation for patients in a prolonged period of cardiac arrest. An increasing amount of
clinical and laboratory evidence supports delaying defibrillation when cardiac arrest time is greater than 5 minutes.
These early studies have shown significant mortality benefit for patients with prolonged ventricular fibrillation (VF)
prior to defibrillation attempts. This paper addresses the
question of whether it is better to delay shocking a person
in VF until CPR can be performed.
Rapid defibrillation
Current clinical guidelines and clinical practice greatly
emphasize the importance of rapid defibrillation for all patients with SCD in a shockable rhythm. The American
Heart Association ‘chain of survival’ considers defibrillation to be the most important intervention and the ‘strongest link’ in the chain of survival for VF cardiac arrest
intervention. The philosophy that ‘the earlier that the defibrillation is performed, the better the rate of survival’ is
based on a small number of case series [1]. Based on these
guidelines, rapid defibrillation is being taught to EMS providers as the most important intervention, possibly at the
risk of suboptimal chest compressions. ‘Quick look’ defibrillator/monitor paddles allow the paramedic to determine whether a patient is in a ‘shockable’ rhythm and to
provide that shock as a single intervention upon arrival
at the patient’s side. In places where defibrillation can
be nearly immediate, this approach has met with success.
This was shown by a survival rate of 53% for people who
collapsed with VF in a casino (74% for those who received
the first shock within 3 minutes) [2] and 21% survival in a
US airport when care was provide by teams of on-site personnel providing rapid defibrillation [3].
Delays in defibrillation
The main difference between the care from on-site rescuers (i.e., casino security guards or airport rescue crews)
and the EMS agencies is the response time. The success
of the casino and airport defibrillation strategies can be related to response times in the 2-minute to 3-minute range
[5,6]. Even at their best, EMS response times are much
longer. Ontario, Canada, reports an average response time
of 7.8 minutes [4], Seattle, Washington 7.7 minutes [2],
and Tucson, Arizona ;8 minutes [5]. Outside North
America, these times were consistent in cities studied —
Taipei 7.4 minutes [6] and Helsinki 7.0 minutes [7•] —
until arrival of EMS with defibrillator capability. Of note,
the times reported in Seattle were after the improvements made in EMS aimed at decreasing response times.
The time response difference of 2–3 minutes for the onsite providers vs the 7–8 minutes for EMS services, and the
differences in outcomes, have prompted public and work
force access to AEDs. This has also had mixed results,
however. In Miami, publicly accessed AEDs improved
time to first shock to 4.88 minutes from 7.64 [8], with improvement in survival from 9 to 17% for patients in VF.
The recently published New England Journal of Medicine
Public-Access Defibrillation and Survival After Out-ofHospital Cardiac Arrest (PAD) trial, large multicenter
study, showed a 9% absolute risk reduction and a twofold
increased probability of survival for SCD patients who collapsed in a location with an AED available. An interesting
finding from the study was the control group survival rate
of almost 15% of definite cardiac arrests, although limitations in proportional interpretation are clear. The control
group personnel were all trained and maintained in CPR
[9]. For the study group with AEDs, the time until first
rhythm assessment averaged more than 6 minutes. The
PAD trial showed the benefit of AED placement and
training lay persons in CPR, but also the difficulty and expense in placing AEDs and training people to use them to
decrease the time to shock. The PAD study was unable to
achieve response times of the casino or airport studies.
Importance of cardiopulmonary resuscitation
The studies looking at rapid (<3 minutes) on-site defibrillation (like the casino study) are limited in that they
exclude the places where most arrests occur: residential
facilities and private homes. The AED/CPR infrastructure
of trained bystanders tested by PAD also excludes the vast
majority of these residential dwellings. Several studies
have shown the clinical benefit of CPR, either bystander
or EMS provider. A multivariate analysis by Wilcox-Gok
[10] showed a significantly higher probability of survival
related to shorter elapsed time from collapse to initiation
of CPR.
Animal studies have shown the importance of uninterrupted CPR of good quality. In a swine study by Kern
[11], following 3 minutes of untreated VF, pigs were
grouped to receive either standard 15:2 compression-toventilation ratio vs continuous chest compressions. The
15:2 group had only 16 seconds/min of hand-off time
(i.e., no compression). Neurologically intact survival was
reported in two of 15 for the 15:2 group, vs 12 of 15 for
the continuous chest compression group [11]. Yu et al.
[12] studied time delay for AED waveform analysis. In
swine with VF, return of spontaneous circulation (ROSC)
was achieved in five of five among those who had a pause
of 3 seconds vs zero of five for those with a pause of more
Delaying shock Begue and Terndrup 185
than 15 seconds. Even delays for applying rescue breaths
were shown to be hemodynamically detrimental to swine
receiving CPR [13].
During a resuscitation attempt, many factors detract from
performance of chest compressions. Attaching the monitor, the pulse check, establishing an airway, establishing
intravenous access, rhythm evaluation, medication administration, and ventilation are just some of the distractions
from continuous chest compressions. These interruptions
of chest compressions may decrease successful defibrillation and ROSC [14,15,18]. During EMS resuscitations,
chest compressions were done for less than 50% of the resuscitation. In a study of first-responder AED use, handsoff time programmed by the AED accounted for 40% of
the time the AED was applied to the patient [21]. The
amount of hands-off time can also be related to the probability of ROSC [20]. Studies in Memphis and Hong Kong
with similar findings have helped to add to the evidence of
the importance of CPR [16•,17].
Cardiac arrest
Looking at the pathophysiology of no-flow cardiac arrest
gives some answers as to why VF shocked after 2–3
minutes responds much better than VF shocked at 7–8
minutes. VF and cardiac arrest are much more than just
electrical phenomena. The mechanical, metabolic, and electrical deterioration of the heart during prolonged VF is incompletely understood [4,18]. The oxygen supply deficit
of the high-energy-requiring myocytes and the ensuing
depletion of metabolic substrates contribute greatly to
the circulatory demise. During the first 15–30 seconds after cardiac arrest, carotid and coronary artery blood flow
drop precipitously. During this initial period, the intravascular volume redistributes into the venous and right-sided
heart system. As the right side of the heart distends and
the left side empties, a low-pressure gradient continues in
providing some small amount of coronary and carotid flow.
After this first 4–5 minutes, however, the left side of
the heart empties and the flow stops [1,2]. It is during
this initial 4–5 minutes, termed the electrical phase [3]
by Weisfeldt and Becker, that the fibrillating heart is most
responsive to electrical defibrillation. Once the left side of
the heart empties and flow stops (the circulatory phase),
the chance of restarting an empty, metabolically starved,
fibrillating heart into an organized rhythm is remote [25].
Chest compressions restore some of the pressure gradient
between the left and right sides of the heart, thus allowing
the left side to fill and create some small but beneficial
flow in the coronary and carotid arteries. CPR has been
shown to provide about 30% of the normal cardiac output.
In pigs, Steen [25] was able to produce coronary artery
perfusion pressures of 12–18 mmHg with CPR after 6.5
minutes of induced VF (up from 0 mm Hg). Klouche
et al. [4] had similar results from their swine experiments,
with coronary perfusion pressures ranging from 9–28 mm
Hg with mechanical chest compressions after 7 minutes of
untreated VF. Videos of the swine heart during fibrillation
and resuscitation show the empty left side of the heart being shocked into an organized sinus rhythm. With no blood
to pump, however, and therefore no flow and no coronary
perfusion pressure, clinically we have pulseless electrical
activity. The left ventricle, even partially filled with blood
from CPR, when defibrillated into an organized electrical
rhythm, would enable a return of pulsatile flow and perfusion, returning the circulation to a self-sustaining state
[25].
Cardiopulmonary resuscitation first
Based on the above pathophysiologic model of cardiac arrest, it is easy to understand why the results for the on-site
providers, who had response times of less than 4 minutes,
were so much better than those with average response
times of greater than 6 minutes. This provides a structure
for determining why performance of CPR would be beneficial during the circulatory phase prior to defibrillation.
Does it work in practice?
Several studies of animals have shown significant benefit
for the CPR first idea. Yakaitis [5] reported that after
5 minutes of VF, dogs that received 1 minute of CPR had
an 80% resuscitation rate vs 30% of those who underwent
defibrillation immediately after the 5-minute period of VF.
In his study on dogs, Niemann [6] demonstrated that following 7.5 minutes of VF, a 20% rate of ROSC for dogs that
underwent immediate defibrillation vs 60% ROSC for animals that had 5 minutes of CPR plus epinephrine prior to
defibrillation [6]. Niemann also reported that of swine
that had been resuscitated from 5 minutes of VF, those
that had immediate defibrillation had 64% ROSC vs
95% for those that received 90 seconds of CPR preceding
the defibrillation. [7•]. These studies provide significant
physiologic evidence of the importance of CPR to ‘prime
the pump’ prior to reorganizing the electrical activity.
In humans, the clinical data are, of course, not as precise,
but they are still very promising for CPR first. There have
been several studies of prehospital cardiac arrest and the
impact of a CPR-first strategy (Table 1). A Swiss study
compared outcomes of SCD after providing AED capabilities, decreasing defibrillation times from 15.6 minutes to
5.7 minutes. Outcomes worsened, however, with 1-year
survival dropping from 17.9 to 9%. They concluded that
their paramedics could not respond quickly enough to provide immediate defibrillation and that the CPR provided
by the earlier BLS unit may have actually helped save
more lives [8]. In Seattle, the addition of AEDs to the first
responders did not improve outcomes, even though defibrillation times had dropped. One interpretation is that
defibrillation was performed when the heart was empty.
Based on the animal data above, the Seattle EMS protocol
186 Cardiopulmonary resuscitation
Table 1. Recent papers evaluating a ‘delayed defibrillation’ approach
Study
Type, n
Level of
evidence
Niemann,
et al. [31], 2000
Swine, 31
6
Niemann,
et al. [30], 1992
Canine, 28
6
Cobb,
et al. [6••], 1999
Human (observational,
prospective,
population based),
1117
Retrospective chart
review-before and
after, 168
Human (randomized
controlled trial; subgroup
analysis of response
times >5 mins), 200
3
90 s of CPR prior to
defibrillation
4
EMS defibrillation capable
(emphasis shift from CPR
to rapid defibrillation)
3 min of CPR prior to
defibrillation
Stotz,
et al. [32], 2003
Wik,
et al. [33••], 2003
2
Intervention
Outcome, control
5 min of VF1 min of CPR prior
to defibrillation
7.5 min of VFepi + CPR
64% ROSC
(immediate
defibrillation)
21% ROSC
(immediate
defibrillation)
7% survival to
hospital d/c
(immediate
defibrillation)
23.7% (average
defibrillation at
15.6 min)
2/41 (4%) survival
to hospital d/c
(immediate
defibrillation)
Outcome,
experimental
95% ROSC
65% ROSC
17% survival
to hospital d/c
14.1% (average
defibrillation
at 5.7 min)
14/41 (24%) survival
to hospital d/c
Level of Evidence, selected: Level 2 Randomized clinical trials with smaller or less significant treatment effects Level 3 Prospective, controlled,
nonrandomized, cohort studies Level 4 Historical, nonrandomized, cohort, or case-control studies Level 5 Case series: patients compiled in serial
fashion, lacking a control group Level 6 Animal studies or mechanical model studies CPR, cardiopulmonary resuscitation; EMS, emergency medical
system; ROSC, return of spontaneous circulation; VF, ventricular fibrillation.
now provides 90 seconds of chest compressions prior to
performing defibrillation. Again, comparing before and after implementation, the addition of 90 seconds of chest
compressions improved overall survival from 24 to 30%,
with 78% of the survivors having favorable neurologic status, up from 71% [6]. The biggest improvement came in
patients who had a delay of greater than 4 minutes until
defibrillation, increasing from 17 to 27%. In Norway, Wik
et al. [9] performed a randomized controlled trial comparing the effects of a CPR-first strategy. Patients who had
out-of-hospital VF were randomly assigned to receive either standard care with immediate defibrillation or 3
minutes of chest compressions prior to defibrillation. Although overall there was no benefit to the CPR strategy,
a subgroup analysis of patients whose response times were
longer than 5 minutes had ROSC of 58% compared with
38%, and there was a 1-year survival of 20 vs 4% in the immediate defibrillation group. These studies showed the
potential benefit of the application of a CPR-first strategy
for patients in prolonged VF.
The question that is raised, however, is how to determine
which patients are in the ‘electrical phase’ and need immediate defibrillation and which are in the ‘circulatory
phase’ and would benefit from some period of CPR prior
to attempting defibrillation. The human studies performed show immediate defibrillation to be beneficial
in cases in which time to defibrillation is less than approximately 3 minutes. The precise time of onset of OOH-CA
is unknown in the vast majority of cases, however.
Bystander CPR, if performed properly, has been shown to
be beneficial [10,11]. In a recently published abstract,
Vilke et al. [12] report significantly higher survival in
patients with down times of 4–10 minutes if they received
bystander CPR. Even CPR performed by untrained laypersons given instructions by the EMS dispatcher has
been investigated [13,14]. The quality of bystander
CPR and therefore its benefit can be highly variable, however. Witness reports of time intervals are often unreliable
and many patients have unwitnessed arrest. The ability to
determine the phase of cardiac arrest and predictability of
defibrillation response based upon the electrical pattern
of the fibrillation waveform have been examined in animal
models and humans. Amman et al. [15] retrospectively
compared data to determine this predictability based on
a combination of fibrillation wave mean frequency and
amplitude, with promising results. With only a single 5second waveform reading of waveform angular velocity,
Sherman et al. [16•] were able to identify with a 90% sensitivity the swine that had less than 5 minutes of VF vs
those that had more than 5 minutes of VF. In an evaluation
of the human VF waveforms from the previously discussed
randomized, controlled trial, Effestol [17] reported that
several predictors of ROSC defibrillation success were improved after 3 minutes of CPR.
Conclusion
Rapid defibrillation is a mantra that pervades nearly
all EMS organizations, as an extrapolation from welldemonstrated immediate defibrillation success. Since the
time intervals for most OOH-CA victims usually produce
delayed defibrillation, performing CPR first may refill the
left ventricle and optimize the chances for defibrillation,
allowing development of a pulsatile rhythm. Any change to
the current emergency-and-rescue culture regarding defibrillation would require additional, compelling data from a
formal hypothesis-testing trial. A large, randomized, multicenter, hypothesis testing study is needed to confirm
or refute the reproducibility and generalizability of
Delaying shock Begue and Terndrup 187
a CPR-first strategy. We envision that future cardiac arrest
guidelines will include these strategies, as well as techniques that evaluate information ‘hidden’ in the VF waveform,
that would guide the rescuers to perform immediate shock
or optimized CPR for a period until defibrillation would be
expected to produce ROSC and increased survival.
Acknowledgements
The authors thank members of the writing group from the Resuscitation
Outcomes Consortium, especially Drs Clifton Callaway, James Christenson, Daniel P Davis, and Ian Stiell.
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Papers of particular interest, published within the annual period of review, have
been highlighted as:
•
of special interest
•• of outstanding interest
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