In-Hospital Defibrillation

This piece was written in response to an article in the November 1995 Annals of Emergency Medicine which criticized the FDA for misunderstanding AED technology.  I thought the authors' critique had problems as well. The editors of Annals  declined to publish my piece, so I'm free to publish it here. The content is a bit outside my chosen area of interest (in-hospital defibrillation).

A perspective on the automatic external defibrillator controversy

John A. Stewart, RN, MA
December 1995

The article "Ventricular fibrillation, automatic external defibrillators, and the United States Food and Drug Administration: Confrontation without comprehension" [November 1995;26(5):621-631 (Cummins, et al).] criticizes a number of recent actions by the Food and Drug Administration (FDA) regarding automatic external defibrillator (AED) technology. There has been much disagreement between the FDA and device manufacturers in recent years, with the American Heart Association (AHA) generally defending the manufacturers on the basis of AED technology's importance for public health. This dispute between the FDA and a number of respected physicians on the AHA's Emergency Cardiac Care Committee sends mixed messages to emergency care providers and is therefore cause for concern from everyone committed to decreasing the toll of sudden cardiac death.

FDA representatives exhibit confusion over limitations and appropriate use of AED technology, but lack of clarity and logic is also apparent in the statements of many ardent advocates of AEDs. Confusion surrounds this technology largely because AEDs have been designed and evaluated without a clear and convincing rationale for their clinical use.

The authors believe that the FDA has subjected AED technology to special scrutiny which has negatively affected public health. The FDA counters that problems exist which should be addressed now, for the long-term benefit of the public. However, it seems clear that halting production of devices which indisputably save lives clearly harms patients, at least in the short term--if effective alternatives are not available.

EMT-Defibrillation programs started with manual defibrillators, but both the FDA and its critics now appear to accept that AED technology, either at its present level of development or with future refinements, will be the foundation of all early-defibrillation programs. The AHA in recent years has almost completely equated early defibrillation with use of AEDs-- even in the hospital setting, where manual defibrillators are immediately available [1]--and the authors of the present article treat use of AEDs and early defibrillation as synonymous and inseparable. With this widespread perception, it is indeed true that impeding the production of AEDs has "the potential to blunt the recent momentum of the early-defibrillation movement."

However, the assumptions supporting the wide adoption of this technology may be flawed. Widespread use of AEDs may represent the unnecessary application of a complex technology to a relatively simple clinical problem.

Try a simple test: look at the two sets of tracings presented in the article. Is it not clear that the first case exhibits ventricular fibrillation (VF) and that the second case shows an organized rhythm after the first shock? I think you will agree that these are not tough calls. How long did it take you to decide? It was probably a matter of one or two seconds at most. Although most readers of the Annals have had advanced training in arrhythmia analysis that they could draw upon if necessary, what is involved here is simple visual pattern discrimination--distinguishing between order and chaos--a skill that comes easily to most people without advanced training.

Judging from the rhythm strips, the first pattern was analyzed by a Laerdal AED for about fifteen seconds and the second for more than twenty seconds, but in both cases the devices clearly made wrong decisions. Yet, as the authors discuss at some length, the devices operated "precisely as [they were] designed to operate."

What do these two examples tell us? They do not indicate that Laerdal's or any other brand of AED is defective, poorly designed, or a significant threat to public health. However, they do suggest that this sort of pattern discrimination is easy for humans but difficult for computers, even with sophisticated algorithms developed over many years. Computers work well for some things but not for others. Wide application of AED technology without adequate consideration of the clinical alternatives and implications has led both to the FDA's stance that devices are "defective" because they can't match human performance, and to the authors' curious appeal to have clinical decisions evaluated "from the perspective of the AED."

The vast majority of studies on the efficacy of AEDs compare AED treatment to treatment without early defibrillation, the apparent assumption being that manual defibrillation is out of the question. The only studies which have directly compared AED defibrillation with manual defibrillation have concluded only that outcomes were not demonstrably worse with AEDs than with manual defibrillators [2-4]. (Two of the studies [2, 3] also reported a one-minute improvement in time to first shock with AEDs; however, the third study, using a more reliable method of determining time intervals, failed to confirm this [4].)

The main rationale for the wide promotion of AED technology is the presumed brevity and ease of training, which will in theory make early defibrillation available to more people. "No worse" clinical performance would clearly be better if the technology also made training significantly easier. However, no training advantage of AEDs has ever been demonstrated in a meaningful side-by-side comparison against manual defibrillators. Automated rhythm analysis has been assumed to be a major advance in ease of use, perhaps largely because rhythm analysis in this context represents a diagnostic decision and as such is part of the traditional province of the physician. Implantable defibrillators obviously require automated shock decisions, but the need for automatic rhythm analysis with external defibrillation is unclear because a human operator must be present in any case to identify cardiac arrest and connect the device. There is no good evidence to my knowledge that distinguishing shockable rhythms is a major problem in defibrillation training, and my own training experience argues otherwise [5]. Although the 1994 Textbook of ACLS states that AEDs, in contrast to manual defibrillators, require only "brief, convenient training sessions and minimal continuing education," the sole reference cited for this statement is actually a rather persuasive refutation of it [6]. The referenced study compares a four-hour manual defibrillation course with a ten-hour course and finds no significant difference in test results or subsequent performance between the two groups, concluding that much of the material in the longer manual defibrillation course is irrelevant to performing the skill. The description of the longer course (with a large portion of extraneous material related to identification of specific arrhythmias) is typical of those courses routinely compared (unfavorably) to "brief, convenient" AED training [2, 7].

The perceived need for AEDs also rests on assumptions about the relative importance of specificity versus sensitivity. Perfect sensitivity is easy to achieve by "blind" defibrillation of all pulseless patients with manual defibrillators. Therefore, the need for AEDs (or accurate identification of a shockable rhythm by a human operator) is based largely on the perceived need for high specificity. However, the importance given to specificity by most AED algorithms is hard to justify clinically: shocks given to pulseless patients not in VF have never been shown to be harmful [8], and survival rates are dismal in these cases with or without shocks. The present article cites a single study to suggest that shocking asystole is dangerous, but that study was retrospective and did not find statistical significance in multiple tests [9]. The 1992 ACLS Guidelines, which strongly endorse AED technology, also (for the first time) offer an argument against shocking asystole--but that argument also fares poorly upon close examination [10].

ECG artifact is an additional problem with both manual defibrillators and AEDs. "Troubleshooting" for artifact delays manual defibrillation, and artifact can entirely block shock delivery by AEDs. However, the authors of the present article treat artifact as an excuse for incorrect decisions by AEDs rather than as a real clinical problem.

"Occult" VF--VF that "masquerades" as asystole in one monitoring lead but is clearly visible in another lead --represents a seemingly intractable problem for AEDs, though the ACLS Guidelines address it only in relation to manual defibrillation. Fine VF may appear as asystole in a single lead, and high-amplitude VF may look like fine VF or asystole [11]. With an AED's dual-function adhesive pads, it is difficult to imagine a workable way to identify occult VF in additional leads, as the ACLS Guidelines recommend for manual defibrillation. Current AED design therefore appears to ensure that some patients in VF--even coarse VF--will not be defibrillated.

The most plausible danger of nonspecific defibrillation is that a shock to a perfusing rhythm will precipitate VF. Though the practical danger of this is very small (and the problem would seem to be easily correctable with a defibrillator in hand) [12], due caution should be exercised to avoid the possibility. But looking to AEDs to provide a secondary check for pulselessness (by means of the surface ECG), as is sometimes advocated to justify use of AEDs, is an indirect and needlessly complex approach. Misdiagnoses of cardiac arrest due to inadequate pulse checks may be a significant problem in emergency cardiac care [13]; if so, the problem has broad significance for all basic and advanced life support providers and should be addressed directly with improved training.

AEDs are commonly seen as devices that facilitate early defibrillation, and this is undeniably true when no other defibrillation alternative is available. However, in light of the high value AEDs place on specificity--by blocking at least a few appropriate shocks in order to minimize shocks to pulseless patients not in VF--it can be argued (keeping in mind the alternative of 100% sensitivity with blind defibrillation) that AEDs are shock prevention devices. Determining their proper role in emergency cardiac care will require a fresh perspective.

The FDA should not hold AEDs to an unrealistic standard of performance but should instead recognize that though the technology is not perfect, it can play an important role in providing defibrillation to the community--particularly in facilitating public access defibrillation, where preventing inappropriate use and intentional misuse would be impossible with manual defibrillators. EMS physicians and the AHA also should recognize the limitations of present AED technology. AEDs are great when compared to no defibrillation, but in the hands of professional first responders, more aggressive use of manual defibrillators might achieve better results at less cost.

The AHA's AED Task Force states that

because the outcomes of cardiac arrest due to pulseless electrical activity or asystole are dismal and VF can masquerade as asystole, it can be argued that it is reasonable from a public health standpoint to use defibrillation in every instance that appears to be clinical cardiac arrest.[14]

They continue by alluding briefly to ethical and medicolegal drawbacks of this approach and go on to say that "fortunately, electrocardiographic (ECG) waveform analysis . . . has been used effectively since the early 1980s." This sequence of reasoning implies that the question of blind defibrillation has been rendered moot by the availability of AED technology.

But to whom is this technology available? It is estimated that only 30% of ambulances in the US are equipped with AEDs [14], and the devices are found on the nursing units of only a handful of U.S. hospitals (not to mention the wide world beyond our national borders). Aside from AED technology's recognized limitations, it is not a viable option when one doesn't have AEDs.

Support for early defibrillation should not mean exclusive support for a single approach. The AED remedy is appealing in part because conforms to a traditional physician-directed model of medical care, with a computer algorithm (designed in collaboration with "defibrillation experts") standing in for the physician. But to repeat the words of the AHA AED Task Force, "it can be argued that it is reasonable from a public health standpoint to use defibrillation in every instance that appears to be clinical cardiac arrest." This alternative, like all others, should be openly discussed and investigated. There are indeed ethical and legal ramifications to this or any approach to early defibrillation, but the primary consideration should be achieving the best overall outcome--i.e., saving the most lives over time. Because the basic elements of the medical problem--that early defibrillation saves lives and that survival from nonshockable presenting rhythms is dismal--are both easy to grasp and beyond dispute, specialized medical expertise is largely irrelevant to these decisions. The challenge of providing early defibrillation is an important social and public health issue. Pertinent discussions and decisions should take place in a more public and less contentious way than through politicized quarrels among AHA physicians, device manufacturers, and the FDA.

1. American Heart Association. Textbook of Advanced Cardiac Life Support. 1994; American Heart Association: Dallas.  

2. Stults KR, Brown DD, Kerber RE. Efficacy of an automated external defibrillator in the management of out-of-hospital cardiac arrest: validation of the diagnostic algorithm and initial clinical experience in a rural environment. Circulation. 1986;73:701-709.  

3. Cummins RO, Eisenberg MS, Litwin PE, Graves JR, Hearned TR, Hallstrom AP. Automatic external defibrillators used by emergency medical technicians: a controlled clinical trial. JAMA. 1987;257:1605-1610.

4. Schneider T, Mauer D, Diehl P, Eberle B, Dick W. Quality of on-site performance in prehospital advanced cardiac life support (ACLS). Resuscitation. 1994;27:207-213.  

5. Stewart JA. Evaluation of a defibrillation training program for noncritical care nurses [master's thesis]. Dallas: Southwestern Graduate school of Biomedical Sciences, University of Texas Southwestern Medical Center at Dallas, 1989.   

6. Bradley K, Sokolow AE, Wright KJ. A comparison of an innovative four-hour EMT-D course with a "standard" ten-hour course. Ann Emerg Med. 1988;17:613-619.   

7. ECRI. Early defibrillation and the role of automated external defibrillators. Health Devices. 1995;24(8-9):300-302.

8. Kern KB, Ewy GA. Clinical defibrillation: optimal techniques. In Tacker WA Jr. Defibrillation of the Heart: ICDs, AEDs, and Manual. Mosby-Year Book, St. Louis, 1994.

9. Martin DR, Gavin T, Bianco J, Brown CG, Stueven H, Pepe PE, Cummins RO, Gonzalez E, Jastremski M. Initial countershock in the treatment of asystole. Resuscitation 1993;26(1):63-68.

10. Stewart JA. Questions remain about shocking asystole. Am J Emerg Med. 1996; 14(3): 337-338. Letter.   

11. Ewy GA. Ventricular fibrillation masquerading as asystole. Ann Emerg Med. 1984;13(9 part 2):811-812.  

12. Stewart JA. A more effective approach to in-hospital defibrillation. J Cardiovasc Nurs. 1996; 10(4): 37-46.   

13. Flesche CW, Breuer S, Mandel LP, Breivik H, Tarnow J. The ability of health professionals to check the carotid pulse. Circulation. 1994;90 (4 part 2):I-288. Abstract.  

14. Automatic External Defibrillation Task Force, Weisfeldt ML, et al. American Heart Association report on the Public Access Defibrillation Conference December 8-10, 1994. Circulation. 1995;92:2740-2747.  

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