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What we commonly think of as a "heart attack" is Myocardial Infarction. This is the death of muscle cells in the heart because of lack of circulation and resultant hypoxia(low oxygen). Angina is the chest pain caused by a temporary lack of circulation without damage to the heart itself, it is relieved by nitroglycerin (or supplemental oxygen) which dilates the coronary artery which branchs from the aorta to provide blood supply to the heart itself.
The atria (upper chambers of the heart, the LUB when you listen to heartbeat) pump blood to ventricles (lower chambers, the DUB) to ''preload''. Ventricular fibrillation is "Disorganized, ineffective quivering of the ventricles" the cells of the heart are contracting individually or in small groups. A defibrillator works by stopping all contractions in hopes that one of the normal pacemakers of the heart will take control when contractions resume. There are several pacemakers in the heart, the normal ones are toward the top and pace at 60-80 per minute. In the middle is the SA (sino-atrial) node which acts as a delay in conducting the nerve impulse from atriums to ventricles allowing the atrium to fill ventricle. If rate drops below 50-60 which is inherent pace of SA node it takes over and paces at that rate. That being said:
40% of AMI (acute myocardial infarction) patients never reach the hospital, about 1/3 of patients never seek medical attention due to denial or absence of pain. A few patients may experience no pain (elderly & diabetics). A variety of lethal and non-lethal arrhythmias (irregular heartbeat) may follow usually within 1 hour. PVCís (premature ventricular contractions) are most common which are the ventricles contracting too soon not allowing complete filling and resultant ineffective contraction which begins cycle again. Follow up care includes intravenous administration of Lidocaine reducing Ďirritabilityí of the ventricles as well as Bicarb to correct acid imbalance of blood due to hypoxia, and other drugs to increase the strength of the contractions.
Cardiogenic shock can occur immediately or as late as 24 hours after onset of AMI, CHF (congestive heart failure) occurs when ventricles can no longer keep up with return flow from atria due to extent of damage, usually within first few hours to first few days of AMI.
So, defibrillation is effective only for AMI leading to V Fib not for a myriad of other cardiac dysfunctions, and immediate follow up care is required. I have used AEDís on 7 patients, all were transported to a hospital within 15 minutes and none survived. Iíve used portable defibrillators on hundreds of patients many of whom survived the initial incident but did not prosper following the event. AEDís do save lives but the odds are really stacked against you even when close to a hospital.
For these reasons I believe best course is to make sure everyone on board (at least us OLD guys) takes 1 baby aspirin per day, ( acts as blood thinner, aids in preventing blockages). If you already have EPIRBís, great lifejackets, Liferaft etc. and got some money left over it couldnít hurt to have an AED but itís way down the list of essential equipment.
Sorry I was so wordy but didnít know how to say that AEDís are good and save lives but the chances of saving a life far from help with one are very low.
Might I suggest the book ďEmergency Care and Transportation of the Sick and InjuredĒ from the American Academy of Orthopedic Surgeons from Jones and Bartlett Publishers.
Iím not a doctor, I was a Paramedic in late 70ís and have supervised paramedics since then, Iím now certified as EMT and have been certified at least at that level since 1971.
Bet this is more than you EVER wanted to know on this subject.