Published 23 March 2009, doi:10.1136/bmj.b876
Cite this as: BMJ 2009;338:b876

Head to Head

Should doctors recommend automated external defibrillators for use at home after myocardial infarction? No

¹ University of Pennsylvania Health System, Philadelphia, PA 19104, USA

Should people at risk of reinfarction have defibrillators available at home? Michael F O’Rourke thinks that enthusiasm is an important factor (doi:10.1136/bmj.b874); Mathew Hutchinson and David Callans say at home defibrillators do not save additional lives (doi:10.1136/bmj.b876)

Few diseases have such disparate clinical outcomes in the absence of definitive treatment as sudden cardiac death. Many studies have shown excellent outcomes in patients resuscitated after sudden cardiac death who receive early defibrillation, so it is logical for doctors to seek to extend this powerful treatment to other populations at high risk. Unfortunately, the trials that have sought to protect individual patients with automated external defibrillators have been overwhelmingly unsuccessful. In light of the fortuitous convergence of circumstances that leads to a successfully resuscitated out of hospital cardiac arrest, the task of broad application of this treatment seems indeed daunting.

First, defibrillation works only for patients presenting with ventricular tachyarrhythmia. The current incidence of out of hospital cardiac arrest in the United States is 0.55 per 1000 people—about 160 000 events a year.¹ Of these arrests, only 20-38% will have ventricular tachycardia or ventricular fibrillation at presentation; thus most sudden cardiac arrests in the general population are due to pulseless electrical activity, bradyarrhythmia, or asystole.² Although the proportion of arrests caused by ventricular tachycardia or ventricular fibrillation may be higher in selected populations, the concept is important. Furthermore the overall incidence of ventricular tachyarrhythmia as a cause of sudden cardiac death is decreasing: undoubtedly a reflection of improvements in the treatment of coronary heart disease.¹ The proportion of sudden cardiac deaths not attributable to ventricular tachycardia or ventricular fibrillation is steadily increasing and has a uniformly poor outcome even when the arrests occur in the hospital with ready access to advanced life support systems. The reduction in rates of sudden death related to tachyarrhythmia is further underscored by the lower than expected event rates in trials of automated external defibrillators (2.2% over 37 months from the randomised, controlled Home Automated External Defibrillator Trial (HAT)).³

Events need to be witnessed

Next, it seems intuitive that the successful resuscitation of sudden cardiac death requires the event being witnessed. Unfortunately less than 20% of out of hospital arrests occur in public locations. In the community based, randomised, controlled Public Access Defibrillation (PAD) trial, 95% of cases of sudden cardiac death who were dead on arrival at the emergency department had unwitnessed arrests.⁴ In HAT, only 36% of the sudden deaths due to ventricular tachycardia or ventricular fibrillation occurring at the patient’s own home were witnessed. From this same study, neighbours or visitors to the study patient’s home were twice as likely to survive to hospital discharge from a "shockable" rhythm (2/4, 50%) than the study patients themselves (4/15, 27%). A particularly disturbing finding in HAT was the substantial number of cases of witnessed arrests in which family members did not even attach the defibrillator.

The most important factor for successful resuscitation of ventricular tachycardia or ventricular fibrillation is rapid defibrillation. The efficacy of rapid defibrillation is best assessed by time from onset of arrhythmia to termination, but most events are not witnessed, so many trials index the time from recognition of the arrest to defibrillation. A recent observational study by Chan and colleagues found that even in hospitalised patients who were defibrillated within two minutes of diagnosis, only 39% survived to hospital discharge, and 40% had at least moderate neurological disability.⁵ The biases of in-hospital mortality studies notwithstanding, these results are both provocative and disappointing.

The study which evaluated the best case scenario for out of hospital resuscitation was the observational, casino based defibrillation study by Valenzuela et al. This study benefited from its highly public settings, strategic placement of defibrillators (to minimise the time to first defibrillation), and operators trained in basic life support and using defibrillators. In this study, arrests were witnessed in 86% of the patients and the mean time to the first shock was 4.4 (SD 2.9) minutes. Patients who were defibrillated within three minutes of their arrest had a 74% survival rate to hospital discharge.⁶ To achieve such a rapid and consistent response for the typically unwitnessed arrest in a patient’s home seems unrealistic.

Mortality benefit?

Given the above discussion, it is not surprising that HAT failed to show a mortality benefit with home use of defibrillators. At first glance the HAT participants would seem to be an ideal population to study, given their high prevalence of Q wave anterior infarctions (64%) and mild left ventricle dysfunction. However, even in the higher risk ischaemic population from MADIT II (the randomised, controlled Second Multicenter Automated Defibrillator Implantation Trial) who were treated with implantable defibrillators, divergence of the survival curves did not begin until nine months after implantation.⁷ Furthermore, DINAMIT (the randomised, controlled Defibrillator in Acute Myocardial Infarction Trial) showed no mortality benefit for implantable cardioverter defibrillators in patients immediately after infarction. The high rate of non-arrhythmic death in the implantable defibrillator arm of DINAMIT further suggests that the dominant mechanism of mortality in post-infarction patients with important left ventricular dysfunction is heart failure, not ventricular defibrillation.⁸

In summary, the incidence of arrhythmic sudden death in post-infarction patients is steadily decreasing. The prophylactic use of defibrillators, either implanted or external, have not been proven effective in reducing overall mortality immediately post infarction. The high prevalence of unwitnessed sudden cardiac death and the dramatic reduction in patient survival with delayed defibrillation makes the routine recommendation of home defibrillators impractical. Further investigation is required to identify higher risk subgroups of patients who will benefit from implantation.

Cite this as: BMJ 2009;338:b876

---

Competing interests: None declared.

Provenance and peer review: Commissioned; not externally peer reviewed.

References

1. Rosamond W, Flegal K, Furie K, Go A, Greenlund K, Haase N, et al. Heart disease and stroke statistics—2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 2008;117:e25-146.[Free Full Text]
2. Cobb LA, Fahrenbruch CE, Olsufka M, Copass MK. Changing incidence of out-of-hospital ventricular fibrillation, 1980-2000. JAMA 2002;288:3008-13.[Abstract/Free Full Text]
3. Bardy GH, Lee KL, Mark DB, Poole JE, Toff WD, Tonkin AM, et al. Home use of automated external defibrillators for sudden cardiac arrest. N Engl J Med 2008;358:1793-804.[Abstract/Free Full Text]
4. Becker L, Eisenberg M, Fahrenbruch C, Cobb L. Public locations of cardiac arrest. Implications for public access defibrillation. Circulation 1998;97:2106-9.[Abstract/Free Full Text]
5. Chan PS, Krumholz HM, Nichol G, Nallamothu BK, American Heart Association National Registry of Cardiopulmonary Resuscitation Investigators. Delayed time to defibrillation after in-hospital cardiac arrest. N Engl J Med 2008;358:9-17.[Abstract/Free Full Text]
6. Valenzuela TD, Roe DJ, Nichol G, Clark LL, Spaite DW, Hardman RG. Outcomes of rapid defibrillation by security officers after cardiac arrest in casinos. N Engl J Med 2000;343:1206-9.[Abstract/Free Full Text]
7. Moss AJ, Zareba W, Hall WJ, Klein H, Wilber DJ, Cannom DS, et al. Prophylactic implantation of a defibrillator in patients with myocardial infarction and reduced ejection fraction. N Engl J Med 2002;346:877-83.[Abstract/Free Full Text]
8. Hohnloser SH, Kuck KH, Dorian P, Roberts RS, Hampton JR, Hatala R, et al. Prophylactic use of an implantable cardioverter-defibrillator after acute myocardial infarction. N Engl J Med 2004;351:2481-8.[Abstract/Free Full Text]

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    StumbleUpon    Technorati    What's this?

Relevant Articles

Should doctors recommend automated external defibrillators for use at home after myocardial infarction? Yes

Michael F O’Rourke
BMJ 2009 338: b874. [Extract] [Full Text]

Should doctors recommend automated external defibrillators for use at home after myocardial infarction? No

Mathew D Hutchinson and David J Callans
BMJ 2009 338: b876. [Extract] [Full Text]

Online poll

Find out more on doc2doc >>