|Double Sequential External Defibrillation in Out-of-Hospital Refractory Ventricular Fibrillation|
Attendees at the Gathering of Eagles heard about several instances where ROSC was obtained after using double sequential defibrillation.
Your patient's in v-fib, and nothing's bringing him out. You've tried everything in the arsenal-continuous compressions, repeated shocks, all the drugs; nothing breaks it. Twenty minutes pass, then 25. The tube's fine, the EtCO2 normal, the patient takes an occasional spontaneous breath, but the heart fibs on.
What do you do now? Is it time to call it a day?
Not so fast. A few U.S. systems are now permitting a novel last-gasp effort to save patients like this: double sequential defibrillation, using two AEDs to deliver a final big blast of energy before writing a victim off.
It doesn't always work. We don't know a lot about why it works when it does. There aren't many numbers to look at. But in a presentation at February's EMS State of the Sciences Conference in Dallas, former New Orleans EMS Director Jullette Saussy, MD, told of achieving several instances of return of spontaneous circulation with the measure, and even of a neurologically intact survivor to hospital discharge.
Big Easy medics employed the double defib 16 times in a year, Saussy said. Four recipients achieved ROSC sustained to the hospital. One, a 64-year-old female, ultimately went home neurologically intact.
The protocol actually originated with Wake County EMS in North Carolina where medical control docs kept getting calls from frustrated medics who had gone through their protocols for VF/PVT, then persistent VF/PVT, and couldn't get their patients out of it.
"Under the old CPR," says Brent Myers, MD, MPH, medical director of Wake County's Department of EMS, "our hunch is that the perfusion was so poor, with all the breaks everybody was taking, that these patients wouldn't stay in fib-they would deteriorate into asystole. Now, with the continuous compressions and everything else, they weren't doing that, and we didn't really have a whole lot to offer our crews. We'd go through the ACLS algorithm and look at all the correctable causes, but just not be able to get these people out of fib."
System leaders turned to local cardiologists for ideas. "The first words out of every one of their mouths," says Myers, "were, ‘Have you tried the second defibrillator yet?'"
Turns out there are some references to this in the cardiology literature. Much of it deals with refractory atrial fibrillation, though some looks at ventricular arrhythmias too. Back in 1994, a team led by New York cardiologist David Hoch looked at sequential shocks from two defibrillators after unsuccessful single shocks for refractory VF during routine electrophysiologic studies. Refractory v-fib, Hoch's team noted, can occur in up to 0.1% of EP studies, but animal studies have shown that rapid sequential shocks may reduce its threshold. Among almost 3,000 consecutive patients, only five needed the double shocks, but all five were resuscitated successfully. "This technique of rapid double sequential external shocks may have general applicability," Hoch's team concluded, "providing a simple and potentially lifesaving approach to refractory ventricular fibrillation."1
The shocks in Hoch's study were delivered 0.5–4.5 seconds apart. Wake's protocol directs the dual
defibrillation occur "as synchronously as possible," recognizing, Myers says, the limitations of a single rescuer in the field trying to activate both defibrillators simultaneously.
A 2005 Mexican study of 21 patients with paroxysmal or persistent atrial fibrillation saw 19 achieve sinus rhythm with double sequential shocks; its authors termed the intervention "safe and highly efficacious."2 In a 2004 Turkish study of 15 patients with refractory a-fib and heart disease, 13 achieved sinus after simultaneous shocks totaling 720 joules. Eleven of those maintained it six months later.3 Overall, Myers says, there's not a huge volume of literature, but what there is clearly suggests the double-shock gambit is safe.
Why It Works
Why might it work? Some hypotheses:
- It's a vector issue, where using four pads instead of two creates a broader energy vector.
- It's a duration issue, related to what is basically a single prolonged shock delivered by consecutive defibrillations. In that case, consecutive may be better than simultaneous.
- It's an energy issue, relating to the sheer number of joules delivered. In that case, simultaneous may be better than consecutive.
"Which of the three it is, we don't know," says Myers. "To me, the most likely is the broadened vector. In talking with crews and being on some of these scenes, the body habitus of the person in fib does not seem to be predictive. Some of these people have a body mass index of 30, some have a body mass index of 18-they're all over the board. So it doesn't strike me as purely an impedance thing or purely an energy thing, because the body habitus of the patients who have this problem just doesn't seem to support that. But that's very anecdotal, and I don't have any definitive evidence one way or the other."
Wake formally implemented its double sequential external defibrillation protocol in April 2010, and was waiting for a year's worth of data before assessing potential benefit. They've regained some perfusing rhythms, Myers says, but not tracked patients to hospital disposition yet. They should know more soon. In the meantime, although emphasizing the intervention's safety, Myers cautions systems about rushing ahead with it.
"I think the way to look at this is, we have this new clinical problem of persistent v-fib," he says. "With the old resuscitation techniques, people didn't make it this far in the prehospital setting, so we never had to deal with it. Now we have this new clinical entity, and we're trying to bring the best evidence we can to give people some recommendations. I can't say this is the best way. What I can say is that it's not doing any harm. We use it at a point in the resuscitation where we're running out of options. It may be a viable alternative, but a medical director has to take into account the entirety of their situation and see if it's something that makes sense in their community."
If, as Saussy noted, the alternative is calling the coroner, that's something a medical director might at least want to think about.
Double sequential defibrillation for refractory v-fib is also practiced in Ft. Worth where it's used a bit earlier in the resuscitation process.
The Emergency Physicians Advisory Board (EPAB), which provides medical oversight for the city's MedStar system, has allowed it for a few months now. MedStar's advanced-practice paramedics respond to most cardiac arrest calls, and if they get there and a patient has already been defibrillated but is still fibbing, they can call medical control and get permission to use the second defibrillator.
"If we've already defibrillated them and they're refractory, we'll go right to the increase in dose," says EPAB Medical Director Jeff Beeson, DO. "We already use the highest energy setting available on our monitors, so we can't go any higher on those. And we know the electrical phase of the arrest is time-sensitive. Other systems have picked a certain number of times to defibrillate first [five in Wake's case], but there's really no science behind that. My point is, if it didn't work once, why would you think it's going to work if you do it again?"
MedStar hasn't amassed big numbers yet, but every patient except one on whom the double defib has been used has converted out of a shockable rhythm. Around half have regained pulses. At least one survived to hospital discharge, neurologically intact, after 25 minutes of CPR and multiple shocks.
Like Myers, Beeson suspects the intervention's success is a function of the doubled defibrillation plane.
"If you have a sternal-apex approach to defibrillation, it's top to bottom and makes sense," he says. "But in most body habituses, if you draw a line between those pads, the heart's not within those lines. Not the entire heart. Part of it is. So when you do the anterior to posterior and sternal to apex, I just think you're getting a more complete defibrillation. The ultimate goal of defibrillation is attempting to get all the myocardial tissues to depolarize and reset, and I think this gives you a better chance of catching the vast majority of them."
1. Hoch DH, et al. Double sequential external shocks for refractory ventricular fibrillation. J Am Coll Cardiol 23(5): 1,141–5, Apr 1994.
2. Velázquez Rodríguez E, et al. Double sequential electrical transthoracic shocks for refractory atrial fibrillation. Arch Cardiol Mex 75 Suppl 3: S3-69–80, Jul–Sep 2005.
3. Kabukcu M, et al. Simultaneous double external DC shock technique for refractory atrial fibrillation in concomitant heart disease. Jpn Heart J 45(6): 929–36, Nov 2004.
Prehosp Emerg Care. 2015 January-March;19(1):126-130. Epub 2014 Sep 22.