Quote from zambezi
I think that having one extra lead easily placed would be a good idea of the AED could automatically switch to a different lead for vericfication of asytole vs fine VF (how much longer would it take to defibrillate if the machine has to switch leads is another question) Its too bad the AED couldn't analyze two leads at once...
There would be no change in time for defibrilation if VF was obvious in Lead II(AED's do monitor lead II, right? I said Lead I earlier and that was definitely wrong now that I think about it). If asystole was detected, then the AED would go ahead and monitor Lead MCL1, or Lead I, or what have you, and if VF was found there, zap; if no VF, "No shock indicated."
(BTW-apparently the two leads monitored need to be perpendicular. So I and III? Hmm. BTW again-what the heck lead is being technically being monitored if anterior-posterior placing of the pads is used?)
Quote from zambezi
I still think in that less than ideal situation, the AED as it stands now works pretty well...it will be interesting to see how it changes as it becomes more widespread (we finally got them in all of our local schools
Most definitely AED's are a Good Thing and they are at the very least better than nothing. What I'd be interested to see is if there is an easy enough way to give the 2.5% of VFers who are occult in one lead a chance to get shocked by an AED.
Quote from zambezi
I am unsure if the coarseness of the VF waves has any effect on the ease of conversion after defibrillation...I am sure that there have been some studies done somewhere...when I have some spare time I will see if I can find anything...
I think coarser VF = more electrical activity = more electrical activity to become organized electrical activity after depolarization. Read this somewhere, but I can't give you chapter and verse on it.
An interesting paper on this is Cummins & Austin (1988) in Annals of Emergency Medicine 17(8). The abstract says:
We investigated the frequency with which a "vector of ventricular fibrillation" may exist in persons in prehospital cardiac arrest. Emergency medical technicians trained in defibrillation were directed to record the rhythm in three different monitor leads whenever they noted an initial flat line. Before these lead switches, the technicians performed a flat line protocol that included inspection of the lead connections to the patient and to the defibrillator, and checks of the calibration and battery status of the devices. They performed this flat line protocol for 127 cardiac arrest patients; 118 were in confirmed asystole after technical problems were corrected. Ventricular fibrillation was detected in only three (2.5%) when the monitor lead was switched. Initial technical problems were more frequent and were identified for ten patients (8%). The frequency of occult ventricular fibrillation (three of 118 asystolic patients) yields a 95% confidence that the true frequency is no greater than 8% to 9%. This suggests that ventricular fibrillation masquerading as asystole is rare. These data do not support protocols for empiric countershocks of patients with an initial flat line on the monitor.
I read this as saying that a policy of "shocking everything" is bad (which we agree on), but however that switching leads is important enough.
An interesting web page arguing that ACLS should drop the policy of not shocking asystole is: http://www.defib.net/asyswk.htm
ACLS '92, quoted above, says:
Rescuers should confirm asystole as the rhythm when faced with a flat line on the monitor by changing to another lead on the lead-select switch or by changing placement of the defibrillation paddles by 90(degrees). Operator errors that lead to "false asystole" are much more common than VF that masquerades as false asystole.
With reference to the above article.
What a can of worms I've opened up :stone