Should cardiac patients buy an automatic external defibrillator?

Have you got a fire extinguisher at home? I haven't but I know they are quite popular. I guess my perception of the risk of a house fire is low enough for me not to have been concerned to have gone out and bought one. But what about a defibrillator? Should cardiac patients consider buying one of these devices. I have never been asked this question until two weeks ago and since then another patient also wanted to discuss the topic. Until the question arose I hadn't really given it much thought. We know that some people with cardiac disease are at high risk of a ventricular arrhythmias and for these people we implant an internal cardiac defibrillator (ICD). But what of the bulk of patients who are not at high enough risk to warrant an ICD but who want to give themselves the best chance of survival should cardiac arrest occur. The Resuscitation Council Advanced Life Support protocol re-enforces that early access to defibrillation is key to survival when ventricular fibrillation occur. So if you have an automatic external defibrillator (AED) at home and someone who knows how to use it, you would by definition get earlier access to this treatment. Provided the treatment did not harm you then the benefit could be as important as the difference between life and death.

But is there any evidence that having a AED at home is of benefit? A study published in the New England Journal of Medicine 6 years ago sought to try and answer this question. The investigators recruited 7001 patients with previous anterior wall heart attacks who did not fulfil the criteria for an ICD. The patients were randomly assigned to one of two groups. The first receive standard care and their partners were trained to respond to cardiac arrest by calling 911 and performing cardiopulmonary resuscitation (CPR). In the second group the partners were trained to use an AED followed by calling 911 and performing CPR. The study outcome was the number of deaths in each group.

Patients were studied for 3 years and during that time 450 patients died, 228 (6.5%) in the standard care group and 222 (6.4%) in the defibrillator group. There were no significant differences overall or in any subgroups they examined.

Of the 450 deaths, 160 were though to be due to sudden cardiac arrest and of these 117 occurred at home. Of the home deaths 58 were witnessed and the AED used in 32. Of these 32 patients 14 received an appropriate shock and 4 survived to hospital discharge. There was no evidence that the AED gave any inappropriate shocks or harmed people.

So why didn't the trial show a difference between the two groups? The rate of cardiac arrest was much lower had the investigators been predicted based on historical studies. This is because the treatment of heart attacks is very good due to primary angioplasty and better drug prevention therapies. The study had a very smaller number of cardiac arrests and was underpowered to detect any effect of the AED. The partners were all trained in CPR and this may also have reduced the effect of the AED. Access to the AED therapy is important and less than half the patients with sudden cardiac arrest at home had a witnessed event, and not all of the witnessed ones had the AED applied. This is perhaps greatest limitation of the AED namely that someone else has to to deliver the treatment.

On the positive side however the successful use of the AED in 14 patients and in 4 neighbours resulted in long-term survival for 6 people and this confirms that an AED in the home used by the general public with minimal training is feasible, corrects ventriculal fibrillation and carries no risk of inappropriate shock.

So what is my recommendation to patients who ask me "Should I buy a home defibrillator?" I will say that the device is safe and will not harm you. The likelihood of needing to use it is very low but if a cardiac arrest does occur the device will correct the heart rhythm and this may be beneficial and improve the survival of the victim. Whatever they decide the partner should consider attending a basic life support course as defibrillation needs to be combined with CPR. I guess if your the sort of person who has a burglar alarm, smoke alarm and fire extinguisher then your attitude to risk might lead you to purchase an AED, it's a personal decision. The devices cost around £1000 to buy but some would say What price a life!

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