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Automatic external defibrillators
SPECIAL CONTRIBUTION automatic
external
Automatic
defibrillators
External
Defibrillqtors
Early electrical therapy for patients with ventricular fibrillation and ventricular tachycardia can result in a significant increase of lives saved from sudden cardiac death. Rapid defibrillation has become a goal of prehospital and emergency department cardiac care, and the use of automatic external defibrillators can aid in reaching this objective. The history, mechanics, and implications of automatic external defibrillators are presented. [Bocka If: Automatic external defibrillators. Ann Emerg Med December 1989;18:1264-1268,]
Joseph J Bocka, MD Royal Oak, Michigan
Received Accepted
for publication for publication
INTRODUCTION
Presented Emergency in Tampa,
at the American College of Physicians Winter Symposium Florida, March 1989.
In 1984, more than 540,000 people died from coronary heart disease, the leading cause of death in the United States. The majority were sudden deaths from ventricular fibrillation (VF) and occurred outside the hospital. L2
Kouwenhouvens reported that electrical shocks applied to dogs within 30 seconds of inducing VF produced a 98% rate of resuscitation. However, those shocked after two minutes of VF had only a 27% resuscitation rate, which gives rise to the goal of early defibrillation for VF. Survival rates for manual defibrillation by emergency medical technicians (EMTs) are reported as between 5% and 23%, which compares with rates of 0% to 6% for basic CPR alone by emergency department personneld-16 In the decade since the introduction of automatic external defibrillators [AEDs), their use by EMTs and first-responders has risen dramatically. Survival rates of patients with VF who were treated with AEDs have been reported from 0% to 31%.ic-is,r6-as Theoretically, even more lives could be saved if the general public had access to and training in the use of AEDs. Emergency physicians have. a leading role in the use of AEDs and should be familiar with their application.
From the Department of Emergency Medicine, William Beaumont Hospital, Royal Oak, Michigan. April 21, 1989. August 28, 1989.
Address for reprints: Joseph William Beaumont Hospital, Emergency Medicine, 3601 Road, Royal Oak, Michigan
J Bocka, MD, Department of West 13 Mile 48072.
HISTORY In 1775, Abildgaard described a series of experiments in which he could render hens “lifeless” with electrical impulses applied through the body.zsJ6 However, he could not restore a pulse unless shocks were delivered across the chest. In 1849, Ludwig and Hoffa first described what Abildgaard had induced.27,as They originated and defined the term “fibrillation” of the ventricles. In 1900, Prevost and Batelli conducted research on VF in dogs.2s-2s They found that weak AC or DC shocks produced VF, whereas much stronger current was needed to “defibrillate.” Wiggers and Wegria27,so expanded on the work of Prevost and Battelli and described a vulnerable period of the cardiac cycle for inducing VF. They also reported that the current delivered was key to successfully performing what they termed “countershocking” of VF. Development of practical defibrillators began in the 1920s with funding from Consolidated Edison of New York in response to an increasing number of accidents and deaths resulting from electric shock.3 In 1947, Beck et alai performed the first successful human defibrillation with specially designed internal cardiac paddles. He used two 110-V, 1.5-A AC shocks to resuscitate a 14-year-old boy who had become pulseless during elective chest surgery. In 1956, Zoll et a132 performed the first successful human external defibrillation with 15-A AC producing 710 V applied across the
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1989
Annals of Emergency
Medicine
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AEDs Bocka
chest for 0.15 second. In 1961, Alexander et a]33 first described the use of AC for t e r m i n a t i n g v e n t r i c u l a r tachycardia (VT). Although Zoll et a132 had suggested the possible use of electrical therapy for VT, this was the first reported non-VF applicat i o n . 33 W o r k by L o w n and colleagues 34-3s in the early 1960s demonstrated the superiority and safety of DC over AC for defibrillation. Successful prehospital defibrillation was first performed by ambulance-transported Belfast physicians in 1966. 39 Defibrillation by EMTs without the presence of physicians was first performed in Portland, Oregon in 1969 and reported in 1972. 40 In the early 1970s, Diack and colleagues 41 (Cardiac Resuscitator Corp o r a t i o n , P o r t l a n d , O r e g o n and Secaucus, New Jersey) developed several prototype AEDs for prehospital use. Prehospital trials commenced in Brighton, England, in 1980 using the HeartAid ® AED, which weighed 28 lb and used an oral-epigastric and a precordial electrode to record ECG tracings and deliver electrical shocks. It was also capable of transcutaneously pacing the heart.17, is In 1982, the US Food and Drug Administration gave approval for EMT-defibrillation (EMT-D) clinical trials. US investigations of manual EMT-D and eventually EMT and first-responder automatic defibrillation were conducted in Washington, Iowa, Minnesota, and Tennessee. 7-24
MECHANICS Early AED models required inserting an oral-epigastric electrode and placing a second electrode on the chest. C u r r e n t AEDs require the placement of pads at the right sternal border and the cardiac apex. These electrodes serve to both monitor and defibrillate. AEDs also inform the user when there is poor lead contact, when the machine is preparing to defibrillate, and when pulses should be checked.
Fully Automatic Versus Semiautomatic AEDS Fully a u t o m a t i c AEDs shock at preprogrammed levels once VF or VT is sensed. Electrodes are placed in position, and the AED is turned on after confirming that the patient is in cardiac arrest. Turning off the AED is the only way to prevent firing once the machine is committed to dis26/1265
charge. Semiautomatic models inform the user when VF or VT is sensed and then advise defibrillation. A button must be pressed by the operator to deliver the shock. The user has the option to discharge the unit when it is deemed necessary, even if the AED is not so advising. Some models allow the operator to override the AED and d e l i v e r a u s e r - d e t e r m i n e d amount of joules.
helped increase the sensitivity for coarse VF from 62% to 96%.2o,~1 Interdevice variability in detecting VF was studied by Rosenthal et al. 42 Significant differences were found between nine HeartAid 95 ® devices in analyzing three of 12 sample VF ECGs (shock versus no shock advised). Results of further testing with newer AEDs have not been published.
AED-PACEMAKERS Rhythm Analysis Early AEDs were designed to respond primarily to a rate of more than 150 "electrical complexes" per minute and a QRS amplitude of more than 0.15 mm. 41 Presently, analysis of the ECG rhythm is done by a combination of several methods. In addition to rate and amplitude criteria, the QRS slope, morphology, power spectrum density, and time away from the isoelectric baseline for preset levels defined as abnormal are analyzed. Checks are made in two- to four-second intervals. If abnormal complexes are detected at more than twice the frequency of any other QRS for three consecutive checks, the AED will be primed to deliver a shock. Obviously, i t will take at least six to 12 seconds for the AED to commit to firing. With fully charged batteries, AEDs need about eight to 15 seconds to reach a shock level of 360 J. Thus, there will be a minimum of 15 to 30 seconds between shocks if the patient remains in VF with the AED in place. Fine VF presents the greatest detection challenge. There is a trade-off between setting the amplitude criterion low enough to detect fine fibrillation and setting it high enough to avoid shocking a patient with asystole or artifact. The sensitivity of d e t e c t i n g VF by AEDs is bet w e e n 76% and 96%. Specificity (correctly identified as not being VF) is reported to be "nearly" 100% (only one study has shown inappropriate shocks).lO-13,17-24 EMT-Ds have been reported to have a sensitivity for VF of 76% to 98% and a specificity of 94% to 100%. 4-16 Coarse VF and VT p r e s e n t e d a problem in early studies with a LifePak 100 ® prototype. Modifications were made to identify complexes with VF morphology instead of using slope and rate criteria alone; this Annals of Emergency Medicine
The use of a combined AED and transcutaneous pacemaker has been reported in two English studies using the early HeartAid ®. Jaggarao et al z7 and Heber 18 reported that three of their five survivors required both defibrillation and pacing. Gray et a124 reported no survivors but stated that immediately after his study period, one patient fully recovered after resuscitation that required both defibrillation and pacing.
AED COMPARISONS Laerdal-Cardiac Resuscitator Corporation HeartAid ®, the first mass-produced AED, was manufactured by the Cardiac Resuscitator Corporation (Table), but this unit is no longer commercially available. CRC was recently bought by the Laerdal Medical Corporation (Armonk, New York), which has taken over production of the HeartStart ® models 1000 and 2000. The HeartStart ® model 1000 (originally the HeartAid ® 1000) is the only fully AED currently available in the United States. It weighs 8 lb, is the smallest unit on the market, and retails for $4,995. A microcassette is used to record the event ECG and audio. A separate transcriber unit plays back the audio and prints out the concurrent ECG and time; this retails for $3,250. Laerdal will soon be releasing a medical control transcriber for auditing both model 1000 and model 2000; it will retail for about $3,995. Creating an event summary with either Laerdal unit requires listening to the entire tape. This is obviated by the P h y s i o - C o n t r o l and Marquette Electronics Incorporated ( M i l w a u k e e , W i s c o n s i n ) AEDs, which have magnetic card recordings. The HeartStart ® model 2000 is a s e m i a u t o m a t i c unit with a liquid c r y s t a l d i s p l a y ECG m o n i t o r . It 18:12 December 1989
TABLE. Automatic defibrillator comparisons
Manufacturer Type Weight (kg) (Ib)
HeartStart® 1000 S
HeartStart® 2000
LifePak ® 200
Responder® 1200-2"
Laerdal
Laerdal
Physio-Control
Marquette
Fully automatic
Semiautomatic
Semiautomatic
Semiautomatic
3.6 (8)
6.4 (14)
4.7 (10)
9.1 (20)
9 24 24
11 30 39
13 23 34
14 25 47
Size (cm) Height Width Depth Price (US $)
4,995
6,995
5,100
6,300
Medical control unit (US $)
3,250t
3,7501-
4,995*
*
Time to charge (sec) To 220 J To 360 J
8 10
9 15
7 12
10
Charge capacity Hours to 360 J
2 10
3.3 50
3 33
2.5 50
Temperature (C)
0
50
O - 50
0
55
O - 50
Analysis (sec)
6 - 12
6 - 12
7 - 12
8 - 12
24
24
15
16
Patch price (US $)
*Marquette manufactures four models, which are the same size (each has a solid-state magnetic event card to record ECGs -- Responder 1: no audio, needs transcriber, $5,900; Responder 2: Responder 1 plus audio, needs transcriber, $6,300; Responder 3: Responder 1 plus built-in printer, does not need transcriber, no audio, $7,300; Responder 4: Responder 3 plus audio, $7,650. tCombined transcriber soon available for models 1000 and 2000 ($3,995). *Includes computer, printer, transcriber, and software.
weighs 14 lb and retails for $6,995. Like the model 1000, it uses a microcassette to record the arrest. Both Laerdal u n i t s c o m e w i t h a user-designed factory p r e p r o g r a m m e d shock s e q u e n c e ( u s u a l l y 200, 200, 360 and 360 J). Users of the m o d e l 2000 can press a b u t t o n to i n i t i a t e defibrillation at any time or to choose s h o c k i n g at 360 J. T h e two HeartStart ® AEDs are the only units to use a p r e r e c o r d e d v o i c e c h i p to make spoken r e c o m m e n d a t i o n s .
Physio-Control Physio-Control C o r p o r a t i o n (Redmond, W a s h i n g t o n ) m a n u f a c t u r e d the LifePak ® 100, w h i c h was the unit initially used by first-responders in Seattle. During the study, i m p r o v e ments were made, and the m o d e l 100 prototype was replaced by the LifePak ® 200.20, 21 T h e L i f e P a k ® 200 weighs 10 lb and is the s m a l l e s t of the semiautomatic units available in the United States. It retails for $5,100 and uses a s t a n d a r d a u d i o c a s s e t t e and a solid-state e v e n t - d o c u m e n t a tion card to record t h e event. T h e 18:12December 1989
LifePak ® 200 does n o t have an ECG d i s p l a y . H o w e v e r , i t c a n be c o n nected to all other LifePak ® monitordefibrillator units for user ECG interpretation and defibrillation-cardioversion control. The medical control event-docum e n t a t i o n u n i t includes a M a c i n t o s h c o m p u t e r to p r o v i d e p r i n t o u t a n d s t a t i s t i c a l a n a l y s i s . It r e t a i l s for $4,995 and is discussed in detail by C u m m i n s et al. 43 It is the only u n i t able to record, analyze, and compare data from m u l t i p l e runs.
Marquette Marquette Electronics Incorporated m a n u f a c t u r e s the Responder ® series 1200 line of AEDs. All of the R e s p o n d e r ® series u n i t s are s e m i a u t o m a t i c and use a m a g n e t i c event card to r e c o r d a r r e s t ECGs; t h e s e m o d e l s are the heaviest and largest of the three AEDs. Both the Responder ® 1 and 2 m o d e l s require a separate transcript i o n u n i t for a u d i t i n g . T h e Responder ® 1 does n o t have audio-rec o r d i n g c a p a b i l i t i e s and r e t a i l s for Annals of Emergency Medicine
$5,900. T h e R e s p o n d e r ® 2 m o d e l is the Responder ® 1 m o d e l w i t h an aud i o - r e c o r d e r a n d r e t a i l s for $6,300; n e i t h e r has an ECG display. The Responder ® 3 and 4 models have ECG m o n i t o r s w i t h i m m e d i a t e p r i n t o u t capability. Using the event card, each can p r i n t o u t an i n s t a n t event summary, thereby e l i m i n a t i n g t h e n e e d for a s e p a r a t e t r a n s c r i b e r unit. T h e y also feature override cards t h a t a l l o w the d e f i b r i l l a t i o n s e t t i n g to be chosen (from 50 to 360 J). T h e R e s p o n d e r ® 3 m o d e l does n o t have a n a u d i o - r e c o r d e r a n d r e t a i l s for $7,300. T h e R e s p o n d e r ® 4 m o d e l is the Responder ® 3 m o d e l w i t h an audio-recorder and retails for $7,650.
General Essential r e q u i r e m e n t s for EMT-D programs established at the 1986 Nat i o n a l Conference on Standards and G u i d e l i n e s for EMT-D i n c l u d e d the use of a medical director, dual-channel (audio and ECG) r e c o r d i n g defibrillators, and case-by-case review. 44 It should be noted that the medical t r a n s c r i p t i o n a u d i t i n g u n i t s are n o t 1266/27
AEDs Bocka
interchangeable among manufacturers. Therefore, m e d i c a l control physicians m a y w a n t to standardize t h e A E D s in t h e i r p r o g r a m s ; t h e y also s h o u l d e n s u r e t h a t e a c h A E D has au d i o -r ec o r d in g capabilities (the M a r q u e t t e R e s p o n d e r ® 1 a n d Responder ® 3 models do not). N o n e of t h e A E D s are r e c o m m e n d e d for use at t e m p e r a t u r e s of less than 0 C to m o r e than 50 to 55 C. A l t h o u g h they take about six to 12 seconds to analyze and an additional s e v e n to 15 s e c o n d s to c h a r g e in "normal" temperature conditions, they m a y take longer in te m p e r a t u r e extremes.
AED CAUTIONS Care m u s t be taken to ensure that p a t i e n t s are m e d i c a l l y u n s t a b l e or pulseless before applying AEDs; a pat i e n t w i t h a stable VT or rapid but stable b u n d l e b r a n c h b l o c k s h o u l d not be defibrillated. This becomes increasingly i m p o r t a n t as m o r e lay personnel are given the opportunity to u s e A E D s a n d as A E D s are prog r a m m e d to shock for finer VF (and, thus, are less sensitive to artifact detection). Impedance p le th y s m o g r a p h y and breath sensors are being considered for incorporation into AEDs as m e t h o d s of c a r d i a c a r r e s t d e t e c tion.45,46 T h e u n i t s h o u l d be t u r n e d off w h e n performing CPR to prevent acc i d e n t a l s h o c k i n g of t h e operator. Additionally, AEDs should be turned off if the patient is seizing or moving. If being used on a p a t i e n t in transport, frequent stopping for pulse and A E D m o n i t o r i n g c h e c k s s h o u l d be m ad e. M o s t u n i t s are d e s i g n e d to warn w h e n m o t i o n or poor contact is detected. C h e s t s of p a t i e n t s should n o t be s h a v e d before e l e c t r o d e p l a c e m e n t but dried if wet. Water spots or nicks in t h e s k i n r e s u l t in areas of decreased resistance and could lead to local burns w i t h uneven, ineffective defibrillation. FUTURE AED USE T h e p o t e n t i a l a p p l i c a t i o n s for AEDs are vast. T h e y have been successfully used by EMTs and first-res p o n d e r s at, for e x a m p l e , t h e 1986 Seattle World's Exposition and a N e w York s h o p p i n g center, m a r i n a , and c o u n t r y club. lO-13,17-24,47,48 C u r r e n t studies are i n v e s t i g a t i n g the placem e n t of AEDs (and t r a i n i n g of the 28/1267
families) in the h o m e s of high-risk patients. 48-54 A c c e p t a n c e and i n i t i al skill quality is good. Performance retention, however, has been poor but returns to satisfactory levels after ret r a i n i n g sessions.52, 54 O n e r e p o r t l o o k e d at t h e results of placing 14 AEDs in seven high-risk locations, s4 Recognition and operation errors prevented proper AED use in the three cardiac arrests t h a t occurred during the year observed. It is yet to be determined whether family members and lay persons will be able to effectively operate AEDs during actual arrest situations. AED use has also been proposed on c o m m e r c i a l airlines. However, recent studies suggest a paucity of actual inair cardiac arrests and raise questions of cost effectiveness.55, s6 Jacobs s7 p o i n t s o u t t h a t t h e r e is greater risk of a p a t i e n t d e v e l o p i n g VF in an office building (and an even greater risk in a senior citizen or cardiac r e h a b i l i t a t i o n center) than of a fire occurring. Therefore, he speculates that in the 1990s, availability of AEDs m a y be as widespread as fire e x t i n g u i s h e r s and s m o k e detectors. However, he points out that AED use in such a setting m u s t be tested in a large c o n t r o l l e d study, and t h e res p o n s i b i l i t y for t h e cost, m a i n t e nance, q u a l i t y control, and u p k e e p m u s t be addressed before i m p l e m e n tation.
SUMMARY AEDs represent a major technological breakthrough w i t h a potential for saving hundreds of thousands of lives in the s a m e w ay that v a c c i n e s and a n t i b i o t i c s have. s7 H o w e v e r , A E D s are still in the evolutionary stage of development, and their exact role is yet to be determined. AEDs will be used by prehospital p e r s o n n e l in 43 states during 1989. E m e r g e n c y p h y s i c i a n s s h o u l d lead EMT-based programs and i m p l e m e n tation by lay persons. Two i m p o r t an t c o n c e r n s are f a m i l i a r i t y w i t h AEDs and personnel training. If used soon enough, AEDs could help resuscitate m o r e than o n e - t h i r d of all p a t i e n t s w i t h VF. A l t h o u g h s u r v i v a l has b e e n reported at 9% to 31% for some EMS systems using AEDs, there are other systems that report no surv i vo r s. 10-13,17-24 S y s t e m factors, including response t i m e and the ability of lay people to detect cardiac arrest Annals of Emergency Medicine
and activate the EMS system, must be considered before investing in and i m p l e m e n t i n g A E D s as part of an EMS system. In addition, the use of AEDs by EMTs and first-responders in EMS s y s t e m s w h e r e paramedics have response times of less than four to six m i n u t e s w o u l d not seem cost effective.
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39. Pantridge JF, Geddes JS: A mobile intensive care unit in the management of myocardial infarction. Lancet 1967;2:271-273. 40. Pantridge JF, Geddes JS: Cardiac arrest after myocardial infarction. Lancet 1966;1:807-808. 41. Diack AW, Welborn W8, Rullman RG: Use of an automatic cardiac resuscitator for emergency treatment of cardiac arrest. Med Instrum 1979; 13: 78-81. 42. Rosenthal E, Carroll D, Vincent R, et al: Automated external defibrillators: Laboratory evaluation. Int J Cardiol 1984;5:441-447. 43. Cummins RO, Austin D, Graves J, et ah An innovative approach to medical control: Semiautomatic defibrillators with solid-state memory modules for recording cardiac arrest events. Ann Emerg Med 1988;17:818-824. 44. C u m m i n s RO: EMT-de fi bri l l a t i on: National guidelines for i m p l e m e n t a t i o n . A m J Emerg Med 1987;5:254-257. 45. C ummi ns RO, Eisenberg MS, Stults KR:
Annals of Emergency Medicine
50. Hallstrom A, Eisenberg M, Bergner L: The potential use of automatic defibrillators in the home for management of cardiac arrest. Med Care 1984;22:1083-1087. 51. Moore JE, Eisenberg MS, Andresen E, et al: Home placement of automatic external defibrillators among survivors of v en tr icu lar fibrillation. Ann Emerg Med 1986;15:8tl-812. 52. Moore JE, Eisenberg MS, Cummins RO, et ah Lay person use of automatic external defibrillation. Ann Emerg Med 1987;16:669-672. 53. Eisenberg MS: A u t o m a t i c external defibrillation: Bringing it home. A m J Emerg Med 1985;3:568-569. 54. Cummins RO, 8chubach JA, Litwin PE, et ah Training lay persons to use automatic external defibrillators. A m J Ernerg Med 1989;7: 143-149. 55. Cummins RO, Schubach JA: Frequency and types of medical emergencies among commercial air travelers. JAMA 1989;261:1295-1299. 56. Speizer C, Rennie CJ, Breton H: Prevalence of in-flight medical emergencies on commercial airlines. Ann Emerg Med 1989;18:26-29. 57. Jacobs L: Medical, legal, and social implications of automatic external defibrillators. Ann Emerg Med 1986;15:863-864.
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external
Automatic
defibrillators
External
Defibrillqtors
Early electrical therapy for patients with ventricular fibrillation and ventricular tachycardia can result in a significant increase of lives saved from sudden cardiac death. Rapid defibrillation has become a goal of prehospital and emergency department cardiac care, and the use of automatic external defibrillators can aid in reaching this objective. The history, mechanics, and implications of automatic external defibrillators are presented. [Bocka If: Automatic external defibrillators. Ann Emerg Med December 1989;18:1264-1268,]
Joseph J Bocka, MD Royal Oak, Michigan
Received Accepted
for publication for publication
INTRODUCTION
Presented Emergency in Tampa,
at the American College of Physicians Winter Symposium Florida, March 1989.
In 1984, more than 540,000 people died from coronary heart disease, the leading cause of death in the United States. The majority were sudden deaths from ventricular fibrillation (VF) and occurred outside the hospital. L2
Kouwenhouvens reported that electrical shocks applied to dogs within 30 seconds of inducing VF produced a 98% rate of resuscitation. However, those shocked after two minutes of VF had only a 27% resuscitation rate, which gives rise to the goal of early defibrillation for VF. Survival rates for manual defibrillation by emergency medical technicians (EMTs) are reported as between 5% and 23%, which compares with rates of 0% to 6% for basic CPR alone by emergency department personneld-16 In the decade since the introduction of automatic external defibrillators [AEDs), their use by EMTs and first-responders has risen dramatically. Survival rates of patients with VF who were treated with AEDs have been reported from 0% to 31%.ic-is,r6-as Theoretically, even more lives could be saved if the general public had access to and training in the use of AEDs. Emergency physicians have. a leading role in the use of AEDs and should be familiar with their application.
From the Department of Emergency Medicine, William Beaumont Hospital, Royal Oak, Michigan. April 21, 1989. August 28, 1989.
Address for reprints: Joseph William Beaumont Hospital, Emergency Medicine, 3601 Road, Royal Oak, Michigan
J Bocka, MD, Department of West 13 Mile 48072.
HISTORY In 1775, Abildgaard described a series of experiments in which he could render hens “lifeless” with electrical impulses applied through the body.zsJ6 However, he could not restore a pulse unless shocks were delivered across the chest. In 1849, Ludwig and Hoffa first described what Abildgaard had induced.27,as They originated and defined the term “fibrillation” of the ventricles. In 1900, Prevost and Batelli conducted research on VF in dogs.2s-2s They found that weak AC or DC shocks produced VF, whereas much stronger current was needed to “defibrillate.” Wiggers and Wegria27,so expanded on the work of Prevost and Battelli and described a vulnerable period of the cardiac cycle for inducing VF. They also reported that the current delivered was key to successfully performing what they termed “countershocking” of VF. Development of practical defibrillators began in the 1920s with funding from Consolidated Edison of New York in response to an increasing number of accidents and deaths resulting from electric shock.3 In 1947, Beck et alai performed the first successful human defibrillation with specially designed internal cardiac paddles. He used two 110-V, 1.5-A AC shocks to resuscitate a 14-year-old boy who had become pulseless during elective chest surgery. In 1956, Zoll et a132 performed the first successful human external defibrillation with 15-A AC producing 710 V applied across the
1812
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1989
Annals of Emergency
Medicine
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AEDs Bocka
chest for 0.15 second. In 1961, Alexander et a]33 first described the use of AC for t e r m i n a t i n g v e n t r i c u l a r tachycardia (VT). Although Zoll et a132 had suggested the possible use of electrical therapy for VT, this was the first reported non-VF applicat i o n . 33 W o r k by L o w n and colleagues 34-3s in the early 1960s demonstrated the superiority and safety of DC over AC for defibrillation. Successful prehospital defibrillation was first performed by ambulance-transported Belfast physicians in 1966. 39 Defibrillation by EMTs without the presence of physicians was first performed in Portland, Oregon in 1969 and reported in 1972. 40 In the early 1970s, Diack and colleagues 41 (Cardiac Resuscitator Corp o r a t i o n , P o r t l a n d , O r e g o n and Secaucus, New Jersey) developed several prototype AEDs for prehospital use. Prehospital trials commenced in Brighton, England, in 1980 using the HeartAid ® AED, which weighed 28 lb and used an oral-epigastric and a precordial electrode to record ECG tracings and deliver electrical shocks. It was also capable of transcutaneously pacing the heart.17, is In 1982, the US Food and Drug Administration gave approval for EMT-defibrillation (EMT-D) clinical trials. US investigations of manual EMT-D and eventually EMT and first-responder automatic defibrillation were conducted in Washington, Iowa, Minnesota, and Tennessee. 7-24
MECHANICS Early AED models required inserting an oral-epigastric electrode and placing a second electrode on the chest. C u r r e n t AEDs require the placement of pads at the right sternal border and the cardiac apex. These electrodes serve to both monitor and defibrillate. AEDs also inform the user when there is poor lead contact, when the machine is preparing to defibrillate, and when pulses should be checked.
Fully Automatic Versus Semiautomatic AEDS Fully a u t o m a t i c AEDs shock at preprogrammed levels once VF or VT is sensed. Electrodes are placed in position, and the AED is turned on after confirming that the patient is in cardiac arrest. Turning off the AED is the only way to prevent firing once the machine is committed to dis26/1265
charge. Semiautomatic models inform the user when VF or VT is sensed and then advise defibrillation. A button must be pressed by the operator to deliver the shock. The user has the option to discharge the unit when it is deemed necessary, even if the AED is not so advising. Some models allow the operator to override the AED and d e l i v e r a u s e r - d e t e r m i n e d amount of joules.
helped increase the sensitivity for coarse VF from 62% to 96%.2o,~1 Interdevice variability in detecting VF was studied by Rosenthal et al. 42 Significant differences were found between nine HeartAid 95 ® devices in analyzing three of 12 sample VF ECGs (shock versus no shock advised). Results of further testing with newer AEDs have not been published.
AED-PACEMAKERS Rhythm Analysis Early AEDs were designed to respond primarily to a rate of more than 150 "electrical complexes" per minute and a QRS amplitude of more than 0.15 mm. 41 Presently, analysis of the ECG rhythm is done by a combination of several methods. In addition to rate and amplitude criteria, the QRS slope, morphology, power spectrum density, and time away from the isoelectric baseline for preset levels defined as abnormal are analyzed. Checks are made in two- to four-second intervals. If abnormal complexes are detected at more than twice the frequency of any other QRS for three consecutive checks, the AED will be primed to deliver a shock. Obviously, i t will take at least six to 12 seconds for the AED to commit to firing. With fully charged batteries, AEDs need about eight to 15 seconds to reach a shock level of 360 J. Thus, there will be a minimum of 15 to 30 seconds between shocks if the patient remains in VF with the AED in place. Fine VF presents the greatest detection challenge. There is a trade-off between setting the amplitude criterion low enough to detect fine fibrillation and setting it high enough to avoid shocking a patient with asystole or artifact. The sensitivity of d e t e c t i n g VF by AEDs is bet w e e n 76% and 96%. Specificity (correctly identified as not being VF) is reported to be "nearly" 100% (only one study has shown inappropriate shocks).lO-13,17-24 EMT-Ds have been reported to have a sensitivity for VF of 76% to 98% and a specificity of 94% to 100%. 4-16 Coarse VF and VT p r e s e n t e d a problem in early studies with a LifePak 100 ® prototype. Modifications were made to identify complexes with VF morphology instead of using slope and rate criteria alone; this Annals of Emergency Medicine
The use of a combined AED and transcutaneous pacemaker has been reported in two English studies using the early HeartAid ®. Jaggarao et al z7 and Heber 18 reported that three of their five survivors required both defibrillation and pacing. Gray et a124 reported no survivors but stated that immediately after his study period, one patient fully recovered after resuscitation that required both defibrillation and pacing.
AED COMPARISONS Laerdal-Cardiac Resuscitator Corporation HeartAid ®, the first mass-produced AED, was manufactured by the Cardiac Resuscitator Corporation (Table), but this unit is no longer commercially available. CRC was recently bought by the Laerdal Medical Corporation (Armonk, New York), which has taken over production of the HeartStart ® models 1000 and 2000. The HeartStart ® model 1000 (originally the HeartAid ® 1000) is the only fully AED currently available in the United States. It weighs 8 lb, is the smallest unit on the market, and retails for $4,995. A microcassette is used to record the event ECG and audio. A separate transcriber unit plays back the audio and prints out the concurrent ECG and time; this retails for $3,250. Laerdal will soon be releasing a medical control transcriber for auditing both model 1000 and model 2000; it will retail for about $3,995. Creating an event summary with either Laerdal unit requires listening to the entire tape. This is obviated by the P h y s i o - C o n t r o l and Marquette Electronics Incorporated ( M i l w a u k e e , W i s c o n s i n ) AEDs, which have magnetic card recordings. The HeartStart ® model 2000 is a s e m i a u t o m a t i c unit with a liquid c r y s t a l d i s p l a y ECG m o n i t o r . It 18:12 December 1989
TABLE. Automatic defibrillator comparisons
Manufacturer Type Weight (kg) (Ib)
HeartStart® 1000 S
HeartStart® 2000
LifePak ® 200
Responder® 1200-2"
Laerdal
Laerdal
Physio-Control
Marquette
Fully automatic
Semiautomatic
Semiautomatic
Semiautomatic
3.6 (8)
6.4 (14)
4.7 (10)
9.1 (20)
9 24 24
11 30 39
13 23 34
14 25 47
Size (cm) Height Width Depth Price (US $)
4,995
6,995
5,100
6,300
Medical control unit (US $)
3,250t
3,7501-
4,995*
*
Time to charge (sec) To 220 J To 360 J
8 10
9 15
7 12
10
Charge capacity Hours to 360 J
2 10
3.3 50
3 33
2.5 50
Temperature (C)
0
50
O - 50
0
55
O - 50
Analysis (sec)
6 - 12
6 - 12
7 - 12
8 - 12
24
24
15
16
Patch price (US $)
*Marquette manufactures four models, which are the same size (each has a solid-state magnetic event card to record ECGs -- Responder 1: no audio, needs transcriber, $5,900; Responder 2: Responder 1 plus audio, needs transcriber, $6,300; Responder 3: Responder 1 plus built-in printer, does not need transcriber, no audio, $7,300; Responder 4: Responder 3 plus audio, $7,650. tCombined transcriber soon available for models 1000 and 2000 ($3,995). *Includes computer, printer, transcriber, and software.
weighs 14 lb and retails for $6,995. Like the model 1000, it uses a microcassette to record the arrest. Both Laerdal u n i t s c o m e w i t h a user-designed factory p r e p r o g r a m m e d shock s e q u e n c e ( u s u a l l y 200, 200, 360 and 360 J). Users of the m o d e l 2000 can press a b u t t o n to i n i t i a t e defibrillation at any time or to choose s h o c k i n g at 360 J. T h e two HeartStart ® AEDs are the only units to use a p r e r e c o r d e d v o i c e c h i p to make spoken r e c o m m e n d a t i o n s .
Physio-Control Physio-Control C o r p o r a t i o n (Redmond, W a s h i n g t o n ) m a n u f a c t u r e d the LifePak ® 100, w h i c h was the unit initially used by first-responders in Seattle. During the study, i m p r o v e ments were made, and the m o d e l 100 prototype was replaced by the LifePak ® 200.20, 21 T h e L i f e P a k ® 200 weighs 10 lb and is the s m a l l e s t of the semiautomatic units available in the United States. It retails for $5,100 and uses a s t a n d a r d a u d i o c a s s e t t e and a solid-state e v e n t - d o c u m e n t a tion card to record t h e event. T h e 18:12December 1989
LifePak ® 200 does n o t have an ECG d i s p l a y . H o w e v e r , i t c a n be c o n nected to all other LifePak ® monitordefibrillator units for user ECG interpretation and defibrillation-cardioversion control. The medical control event-docum e n t a t i o n u n i t includes a M a c i n t o s h c o m p u t e r to p r o v i d e p r i n t o u t a n d s t a t i s t i c a l a n a l y s i s . It r e t a i l s for $4,995 and is discussed in detail by C u m m i n s et al. 43 It is the only u n i t able to record, analyze, and compare data from m u l t i p l e runs.
Marquette Marquette Electronics Incorporated m a n u f a c t u r e s the Responder ® series 1200 line of AEDs. All of the R e s p o n d e r ® series u n i t s are s e m i a u t o m a t i c and use a m a g n e t i c event card to r e c o r d a r r e s t ECGs; t h e s e m o d e l s are the heaviest and largest of the three AEDs. Both the Responder ® 1 and 2 m o d e l s require a separate transcript i o n u n i t for a u d i t i n g . T h e Responder ® 1 does n o t have audio-rec o r d i n g c a p a b i l i t i e s and r e t a i l s for Annals of Emergency Medicine
$5,900. T h e R e s p o n d e r ® 2 m o d e l is the Responder ® 1 m o d e l w i t h an aud i o - r e c o r d e r a n d r e t a i l s for $6,300; n e i t h e r has an ECG display. The Responder ® 3 and 4 models have ECG m o n i t o r s w i t h i m m e d i a t e p r i n t o u t capability. Using the event card, each can p r i n t o u t an i n s t a n t event summary, thereby e l i m i n a t i n g t h e n e e d for a s e p a r a t e t r a n s c r i b e r unit. T h e y also feature override cards t h a t a l l o w the d e f i b r i l l a t i o n s e t t i n g to be chosen (from 50 to 360 J). T h e R e s p o n d e r ® 3 m o d e l does n o t have a n a u d i o - r e c o r d e r a n d r e t a i l s for $7,300. T h e R e s p o n d e r ® 4 m o d e l is the Responder ® 3 m o d e l w i t h an audio-recorder and retails for $7,650.
General Essential r e q u i r e m e n t s for EMT-D programs established at the 1986 Nat i o n a l Conference on Standards and G u i d e l i n e s for EMT-D i n c l u d e d the use of a medical director, dual-channel (audio and ECG) r e c o r d i n g defibrillators, and case-by-case review. 44 It should be noted that the medical t r a n s c r i p t i o n a u d i t i n g u n i t s are n o t 1266/27
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interchangeable among manufacturers. Therefore, m e d i c a l control physicians m a y w a n t to standardize t h e A E D s in t h e i r p r o g r a m s ; t h e y also s h o u l d e n s u r e t h a t e a c h A E D has au d i o -r ec o r d in g capabilities (the M a r q u e t t e R e s p o n d e r ® 1 a n d Responder ® 3 models do not). N o n e of t h e A E D s are r e c o m m e n d e d for use at t e m p e r a t u r e s of less than 0 C to m o r e than 50 to 55 C. A l t h o u g h they take about six to 12 seconds to analyze and an additional s e v e n to 15 s e c o n d s to c h a r g e in "normal" temperature conditions, they m a y take longer in te m p e r a t u r e extremes.
AED CAUTIONS Care m u s t be taken to ensure that p a t i e n t s are m e d i c a l l y u n s t a b l e or pulseless before applying AEDs; a pat i e n t w i t h a stable VT or rapid but stable b u n d l e b r a n c h b l o c k s h o u l d not be defibrillated. This becomes increasingly i m p o r t a n t as m o r e lay personnel are given the opportunity to u s e A E D s a n d as A E D s are prog r a m m e d to shock for finer VF (and, thus, are less sensitive to artifact detection). Impedance p le th y s m o g r a p h y and breath sensors are being considered for incorporation into AEDs as m e t h o d s of c a r d i a c a r r e s t d e t e c tion.45,46 T h e u n i t s h o u l d be t u r n e d off w h e n performing CPR to prevent acc i d e n t a l s h o c k i n g of t h e operator. Additionally, AEDs should be turned off if the patient is seizing or moving. If being used on a p a t i e n t in transport, frequent stopping for pulse and A E D m o n i t o r i n g c h e c k s s h o u l d be m ad e. M o s t u n i t s are d e s i g n e d to warn w h e n m o t i o n or poor contact is detected. C h e s t s of p a t i e n t s should n o t be s h a v e d before e l e c t r o d e p l a c e m e n t but dried if wet. Water spots or nicks in t h e s k i n r e s u l t in areas of decreased resistance and could lead to local burns w i t h uneven, ineffective defibrillation. FUTURE AED USE T h e p o t e n t i a l a p p l i c a t i o n s for AEDs are vast. T h e y have been successfully used by EMTs and first-res p o n d e r s at, for e x a m p l e , t h e 1986 Seattle World's Exposition and a N e w York s h o p p i n g center, m a r i n a , and c o u n t r y club. lO-13,17-24,47,48 C u r r e n t studies are i n v e s t i g a t i n g the placem e n t of AEDs (and t r a i n i n g of the 28/1267
families) in the h o m e s of high-risk patients. 48-54 A c c e p t a n c e and i n i t i al skill quality is good. Performance retention, however, has been poor but returns to satisfactory levels after ret r a i n i n g sessions.52, 54 O n e r e p o r t l o o k e d at t h e results of placing 14 AEDs in seven high-risk locations, s4 Recognition and operation errors prevented proper AED use in the three cardiac arrests t h a t occurred during the year observed. It is yet to be determined whether family members and lay persons will be able to effectively operate AEDs during actual arrest situations. AED use has also been proposed on c o m m e r c i a l airlines. However, recent studies suggest a paucity of actual inair cardiac arrests and raise questions of cost effectiveness.55, s6 Jacobs s7 p o i n t s o u t t h a t t h e r e is greater risk of a p a t i e n t d e v e l o p i n g VF in an office building (and an even greater risk in a senior citizen or cardiac r e h a b i l i t a t i o n center) than of a fire occurring. Therefore, he speculates that in the 1990s, availability of AEDs m a y be as widespread as fire e x t i n g u i s h e r s and s m o k e detectors. However, he points out that AED use in such a setting m u s t be tested in a large c o n t r o l l e d study, and t h e res p o n s i b i l i t y for t h e cost, m a i n t e nance, q u a l i t y control, and u p k e e p m u s t be addressed before i m p l e m e n tation.
SUMMARY AEDs represent a major technological breakthrough w i t h a potential for saving hundreds of thousands of lives in the s a m e w ay that v a c c i n e s and a n t i b i o t i c s have. s7 H o w e v e r , A E D s are still in the evolutionary stage of development, and their exact role is yet to be determined. AEDs will be used by prehospital p e r s o n n e l in 43 states during 1989. E m e r g e n c y p h y s i c i a n s s h o u l d lead EMT-based programs and i m p l e m e n tation by lay persons. Two i m p o r t an t c o n c e r n s are f a m i l i a r i t y w i t h AEDs and personnel training. If used soon enough, AEDs could help resuscitate m o r e than o n e - t h i r d of all p a t i e n t s w i t h VF. A l t h o u g h s u r v i v a l has b e e n reported at 9% to 31% for some EMS systems using AEDs, there are other systems that report no surv i vo r s. 10-13,17-24 S y s t e m factors, including response t i m e and the ability of lay people to detect cardiac arrest Annals of Emergency Medicine
and activate the EMS system, must be considered before investing in and i m p l e m e n t i n g A E D s as part of an EMS system. In addition, the use of AEDs by EMTs and first-responders in EMS s y s t e m s w h e r e paramedics have response times of less than four to six m i n u t e s w o u l d not seem cost effective.
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eastern Minnesota. lAMA 1986;256:477-483. 17. Jaggarao NSV, Heber M, Grainger R, et ah Use of an automated external defibrillator pacemaker by ambulance staff. Lancet 1982;2:73-75. 18. Heber M: Out of hospital cardiac arrest using the "Heart Aid," an automated external defibrillator-pacemaker. Int J Cardiol 1983;3: 456-458. 19. Cummins RO, Eisenberg M, Bergner L, et ah Sensitivity, accuracy, and safety of an automatic external defibrillator. Lancet 1984;4:318-320. 20. Weaver WD, Copass MK, Hill DL, et ah Cardiac arrest treated with a new automatic external defibrillator by out of hospital first responders. A m J Cardio] 1986;57:1017-1021. 2i. Weaver WD, Hill D, Fahrenbruch CE, et ah Use of the automatic external defibrillator in the management of out of hospital cardiac arrest. N Engl J Med 1988;319:661-666. 22. Vukov LF, White RD, Bachman JW, et ah New perspectives on rural EMT defibrillation. Ann Emerg Med 1988;17:318-321.
phase of v e n t r i c u l a r systole. A m J Physiol 1940;128:500-505. 31. Beck CS, Pritchard WH, Feil SA: Ventricular fibrillation of long duration abolished by electric shock. JAMA 1947;135:985-989. 32. Zoll PM, Linenthal AJ, Gibson P, et ah Termination of ventricular fibrillation in man by externally applied countershock. N Engl J Med 1956;254: 727-729. 33. Alexander S, Kleiger R, Lown B: Use of external electric counter shock in the treatment of ventricular tachycardia. JAMA 1961;177:916-919.
35. Lown B, Neuman J, Amarasingham R, et al: Comparison of alternating current with direct current electroshock across the chest. A m J CardioI 1962;10:223-225.
49. Cummins RO, Eisenberg MS, Bergner L, et al: Automatic external defibrillation: Evaluations of its role in the home and emergency medical services. A n n Emerg Med 1984;13: 798-801.
36. Lown B: Electrical reversion of cardiac arrhythmias. Br Heart J 1967;29:469-472.
24. Gray AJ, Redmond AD, Martin MA: Use of the automatic external defibrillator-pacemaker by ambulance personnel: The Stockport experience. Br Med J 1987;294:1133-1135.
38. Lown B, Kleiger R, Wolff G: The technique of cardioversion. A m Heart J 1964;67:282-284.
27. Wiggers CJ: The mechanism and nature of ventricular fibrillation. A m Heart J 1940;20: 399-403. 28. DeSilva RA, Graboys TB, Podrid PJ, et ah Cardioversion and defibrillation. A m Heart f 1980;100:881-895. 29. Ventriglia WJ, Hamilton GC: .Electrical interventions in cardiopulmonary resuscitation: Defib rillatio n. Emerg Med Clin North A m I983;I:515-534. 30. Wiggers CJ, Wegria R: Ventricular fibrillation due to single, localized induction and condenser shocks applied during the vulnerable
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