High Voltage Riata ST Defibrillator Lead Failure and Its Implications for Durata

It came from a case report published online before print in PACE from Dr. John Marenco of Tufts University in Springfield, Massachusetts:

A 60-year-old man had a single-chamber St.Jude Atlas VR defibrillator (St. Jude Medical, St. Paul, MN, USA) with a dual coil St. Jude Riata 7001 defibrillator lead (My note: this is actually a downsized, second-generation 7 Fr Riata ST model whose internal construct shares many similarities to St. Jude's currently-marketed third-generation 7 Fr Durata lead) placed in 2006 for primary prevention secondary to an ischemic cardiomyopathy and prior myocardial infarction.  All routine device interrogations, both remote and in-office, had been normal with stable sensing amplitude, lead impedances, and capture thresholds. The device was programmed with two zones: a ventricular tachycardia (VT) zone from 340 ms (176 beats/min) and a ventricular fibrillation (VF) zone from 260 ms (231 beats/min).  The VT zone had a morphology discriminator “on” with interval stability and sudden onset “passive.” Five years from implant, he presents with palpitations, light-headedness, and a single implantable cardioverter defibrillator (ICD) discharge.  He has a friend drive him to the emergency room and is found to be in ventricular tachycardia over 200 beats/min. The ventricular tachycardia terminated with intravenous amiodarone bolus before need for external defibrillation. Device interrogation demonstrated an initial rhythm of atrial fibrillation with the appropriate detection of the onset of ventricular tachycardia with a cycle length of 245 ms, within the device’s VF zone (Fig. 1). Discriminators were not activated in the VF zone, but the morphology discriminator clearly demonstrates a failure of the electrogram signal to match the template (indicated by the “x” in the marker channel). After detection of 12 intervals (interval average) within the VF zone an episode is declared and a 25-Joule (693 V) shock is delivered, failing to restore sinus rhythm.  No additional shocks are delivered despite appropriate redetection within the VF zone (Fig. 2).  After a fifth detection, the device declares “no more therapies” with VT continuing indefinitely. Device interrogation in the emergency department reveals a pacing lead impedance was 465 ohms, signal amplitude 1.8 mV, and capture threshold 0.75 V at the rate of 0.5 ms. What is the differential diagnosis of failure to deliver appropriate therapy and why did this device fail to deliver more than a single shock?

Further review of the case's figure disclosed appropriate VT detection, a high voltage impedance of 0 ohms, and an "aborted charge because of possible output circuit damage" on device interrogation after the event.  Importantly, at the time of lead revision, "there was no fluoroscopic insulation breach and no obvious insulation breach in the pocket."  Fluoroscopic screening of these leads, therefore, would not have detected pending lead failure.  Further, as far as we can tell from the report, no antecedent device alerts were triggered before this event.

This case report discloses several important issues. (1) High voltage coil damage in a 7Fr  Riata ST lead can lead to either ineffective high voltage therapy delivery, withholding of further therapies, or both despite appropriate arrhythmia detection.  St. Jude defibrillators are engineered to automatically withhold energy delivery in low high-voltage lead impedance situations to avoid excessive current delivery and device overheating in such circumstances (personal communication).  (2) This failure mechanism, while curently very rare, may affect implanters decisions regarding whether or not to replace existing Riata leads irrespective of their performance characteristics and flouroscopic appearance at the time of battery change.  Already there have been other reported high voltage failures in Riata leads with externalized wires.  Some have advocated testing the high voltage leads as part of Riata lead follow-up to screen for this failure mechanism, especially since the therapeutic implications of high voltage lead failure is much more significant and difficult to detect than low-voltage (sensing lead) failures. 

Perhaps most important for St. Jude going forward is how this case will influence implanters' choice of later-generation 7 Fr St. Jude defibrillator leads with their Optim coating but similarly-downsized inner lumen dimensions.  I look forward to St. Jude's update of their Riata Communications website regarding these recently published case reports.

-Wes

References:

Marenco JP. "Failure to Deliver ICD Shocks after a Failed Discharge Despite Redetection of Rapid Ventricular Tachycardia? What Is the Cause?" PACE DOI: 10.1111/j.1540-8159.2012.03484.x Published online 21 July 2012.

For an excellent overview of the Riata ICD lead recall by Dr. Jay Schloss: http://cardiobrief.org/2012/02/22/guest-post-more-lessons-from-the-riata-icd-lead-recall/

Defibrillators Make Top Ten Technology Hazards List

In a desperate attempt to reach an even number is seems, hospital defibrillators were added to ECRI.org's top ten health technology hazards list of devices that threaten to kill or maim patients:

The Top 10 Health Technology Hazards list is updated each year based upon the prevalence and severity of incidents reported to ECRI Institute by healthcare facilities nationwide; information found in the Institute’s medical device problem reporting databases; and the judgment, analysis, and expertise of the organization’s multidisciplinary staff. Many of the items on this year’s list are well-recognized hazards with numerous reported incidents over the years.

If one honestly looks at the number of saves versus the number of deaths from defibrillators, I wonder how many of this highly esteemed group of "multidisciplinary staff" of the ECRI might reconsider.

Clearly, most of them have never been in a code situation.

-Wes

h/t: Wall Street Journal Health Blog

News You Can Use: Sex and Your Defibrillator

Have a defibrillator and feel like getting frisky? For the first time that I can recall, there's a very helpful article published in Circulation addresses the concerns of implantable cardiac defibrillator(ICD) patients and sexual activity. There's all kinds of helpful tidbits, like this one:

A study of 1774 patients who had experienced an acute myocardial infarction showed that sexual activity was a likely contributor in fewer than 1% of cases. In fact, regular physical exertion, such as that associated with sexual activity, was associated with a decreased risk of cardiac events in patients!

Now that's helpful!

Recall that defibrillators are designed to detect rapid, potentially life-threatening arrhythmias. Most of the time, sexual activity does not lead to heart rates at a level that ICD's would consider elevated during intercourse. (This, of course is patient-specific). While your doctor can tell you the rate cut-off at which your ICD might possibly fire, watching your heart rate rise with a monitor during those moments might be a bit of a, shall we say, turn-off..

My rule of thumb: if you have a defibrillator (ICD) and can walk up two flights of stairs without getting a shock, you'll probably be okay having sex. (Be sure to check with your doctor, these are just my ballpark recommendations. Also, this rule of thumb may not apply to those involved in extramarital affairs. As we've heard, heart rates accelerate much more when a naughty, clandestine element is involved). But please be careful: if one flight of stairs makes you too exhausted or short of breath, you'd better check with your doctor first.

Now, what about the partner? What happens if the defibrillator fires and you're at the peak of passion?

First, you might give out a "yelp." That's because the shock often causes the diaphragm and vocal cords to contract. It happens very suddenly, and your partner might not mind this part, but the kids down the hall... well, that's another thing.

Second, ICD shocks won't hurt you partner. On the contrary, it might be... well, let's put it this way... interesting!

Third, if repetetive shocks occur as a result of your activities, well, sorry my friend, you've had enough and probably should head to the ER. Realize this is an infrequent event, but any time there are back-to-back shocks it means one of several things: (1) you're having a lot of rhythm problems, (2) your device might need to be reprogrammed to avoid shocks at this level of exertion, or (3) (least likely) you might have a faulty lead that needs repair.

Common sense should dictate each person's individual approach, but for the most part, ICD's needn't hold you back!

-Wes

Reference: Lauren D. Vazquez, PhD; Samuel F. Sears, PhD; Julie B. Shea, MS, RNCS, FHRS; Paul M. Vazquez, DO. "Sexual Health for Patients With an Implantable Cardioverter Defibrillator." Circulation. 2010;122: e465-e467.

How Many Times Can the Heart Be Defibrillated and Still Work?

Many, many times - like this example of 28.

But if the underlying cause for the arrhythmia isn't discovered (like the blocked artery in this man's case), the number of times that defibrillation will be successful quickly becomes limited.

-Wes

Wide and Thin or Narrow and Thick

Get your mind out of the gutter. We're talking about defibrillators here.

There's a great picture comparing the size of implantable defibrillators for the management of ventricular arrhythmias and heart failure (and a nice article on the not-so-new wireless telemetry features) over at the New York Times today.

Here's the question:

If you needed a new defibrillator and assuming all implantable devices had identicle capabilities, which would you rather have: (1) a wide and thin device (a la the "Cognis 100-D" device of Boston Scientific's), or (2) a thicker and slightly narrower device (sported by Medtronic's Consulta CRT-D and St. Jude's EPIC-HF devices)?

Go ahead and place your vote in the comments section.

For fairness, here's a side view of the three devices arranged left-to-right as in the prior picture:

(Click to enlarge)
Left: St. Jude; Middle: Boston Scientific; Right: Medtronic

(Industry reps needn't vote. Thanks.)

-Wes

Turning Off Implanted Defibrillators

End-of-life issues with implantable cardiac defibrillators (ICDs) and the need (or not) for deactivation policies is being discussed at the palliative medicine blog, Pallimed.

Shoot on over and lend your $0.02 to the discussion.

-Wes

The Rationer

Every cardiac electrophysiologist has been there: a relatively young individual in their 50’s presents to the Emergency Room short of breath, sitting bolt upright in bed and is found to be in congestive heart failure. This is not their first admission; several others have come before and each with a common theme: a positive urinary screen for cocaine.

The EKG shows left bundle branch block. Catheterizations occur, coronary disease absent or moderate, discussions held, patient recommended for defibrillator or biventricular pacing to improve their heart failure after medications have been ineffective for the past year. The person seems sincere – “No more drugs, doc, really” – a line uttered near the conclusion of every one of the patient’s prior hospitalizations, but this time, really, they mean it.

I wrestle with the ethics of the management of these patients every time I’m called to see them. Our guidelines state that ejection fractions of 15% should be treated with defibrillators, especially if no improvement on adequate, aggressive medical therapy. Our guidelines also say that patients with significant social or psychological disease that precludes careful follow-up of their device should not get a defibrillator. Outside the room the decision seems obvious; inside the room after a glance at the eyes of the desperate its another thing entirely - the suffocating feeling of heart failure having taken its toll. The family, at the patient's side, is concerned and wants to help, wondering if there’s anything that can be done.

Will the patient really quit using cocaine? My father’s voice whispers in my head: “What a person has done is an indication of what they will do.” Our business manager wonders why our volumes have slipped recently. What if they die shortly after leaving the hospital suddenly?

No matter what I decide, I will fail it seems. Is the patient sincere or playing me the fool? Can I tell? Put in the defibrillator or pacemaker perhaps it will help. But if I have guessed wrong, then resources are wasted and the patient is exposed to another risk, like infection. Don’t put in the defibrillator and I revoke a lifeline or effective therapy.

On the surface, these decisions should be easy. In reality, they are anything but.

-Wes

AED's - The Barriers to Entry

Melinda Beck of the Wall Street Jounal, did a nice piece on the need for automatic external defibrillators (AEDs) in public spaces today and started to address some of the issues of why these amazing gizmo's aren't available more widely:

Some states now require AEDs in schools; some require them in health clubs, shopping malls and golf courses. There's little uniformity; despite their foolproof nature, some businesses oppose them out of fear of being sued if something goes awry with an on-site AED. "I predict that 10 years from now, people will say, 'I'm not going to work in a building or stay in a hotel or eat in a restaurant that doesn't have an AED," says San Diego city-council member Jim Madaffer, who helped place nearly 5,000 AEDs in public facilities since 2001. They've saved 49 lives.

Schools have been a tough sell, too, largely because of cost. Some parents are raising money for AEDs themselves, often after a tragedy. Evelyn and Larry Pontbriant have donated 32 AEDs to Norwich, Conn., schools since last summer, when their 15-year-old son, an athlete with no known heart problems, suffered a fatal cardiac arrest during a running event in the local park. An AED arrived on the scene too late. "It's a good investment to have on hand in your school," says Mrs. Pontbriant. "It benefits not just the athletes, but also the teachers, coaches, referees, grandparents and siblings."

As electrophysiologists, we often get to see the "saves" made by these devices: the young boy playing baseball, struck in the chest by a fast ball ("commodio cordis") that fibrillates his heart and the police officer who responds with the AED in the trunk of his squad car to save the boy's life; or the father who collapses just outside the fire department and is rescued by their defibrillator. These event happen every day, but unfortunately as experienced in the Tim Russert case, many more are not so fortunate.

So why aren't these devices more readily available?

First and foremost: is cost. These devices are still expensive: the cheapest quoted goes for about $1300. But there are other costs not commonly discussed: like the cost of new batteries every 2-7 years (depending on the cost of the model) that can set folks back at least a $100 for each device. And what about those defibrillator patches placed on the chest? They contain a gel that improves the conductivity of the patches on the chest, making the devices more reliable at correcting the normal heart rhythm. That gel degrades and the patches must be replaced every two to seven years, too - to the tune of about $100 a set, too. These are the unspoken issues with AEDs that are never written about and schools and institutions must understand these additional costs and maintenance requirements if they are to assure the proper functioning of these devices.

Next, is the location consideration: where will these devices be used? Will they be in the office setting, car trunk, or placed next to the baseball field? Humidity, motion, and other environmental issues might require a more expensive device to be deployed without the bargain-basement price. Certainly, in the NIH-sponsored trial "Home Automated External Defibrillator Trial (HAT)," home use has not been found to be more effective than a conventional call to 911: in part because of the low incidence of events that occur in the home when a responder is present (58 patients out of 7001 studied, and only 32 had AEDs used and only 4 survived to hospital discharge).

But the cost and efficacy considerations might be offset if more defibrillators were deployed in public spaces where more responders were present and events occurred - thereby driving down the costs. I suppose it would be utopia if these devices could be deployed and maintained within 3 minutes of whereever a person traveled. But the path to implementation, especially with staffing and budget shortfalls, is a lengthy one. As a case in point: many doctors' offices, dialysis centers, and rehab units still do not have these devices and instead rely on calling 911 for a response in emergencies.

Sad, but true.

-Wes

Hang On and Shock 'em

Young cardiology fellow meets electrophysiologist after an episode of new-onset atrial fibrillation that requires cardioversion in the EP lab:

"Go ahead, hold the legs."

"Are you nuts?"

"No, I'm not nuts. You need to hold their legs so after the shock they don't bend their legs with all those catheters in them and hurt themselves."

"But you're going to use 360 Joules!"

"Yep, and you won't feel a thing."

"No way."

"Way."

"How can you be so sure?"

"Because those gloves you're wearing do not conduct electricity. Sync on? Good. Everybody clear? (No not you - you keep holding...) Go ahead."

* * * Thump * * *

"Didn't feel a thing, did you?"

"Ah, no, but now my heart is racing..."

-Wes

Reference: Lloyd MS, Heeke B, Walter PF, Langberg JJ. "Hands On Defibrillation. An Analysis of Electrical Current Flow Through Rescuers in Direct Contact With Patients During Biphasic Defibrillation." Circulation. 4 May 2008.

My Valentine's Story

It was just your routine defibrillator check at first. Then the screen showed the device had fired.

"You mean I was shocked?"

"Yep."

"When?"

"Three weeks ago, on the 23rd, at 06:38AM and 12 seconds."

"But I didn't feel anything. Just a minute, let me check my calendar." She flips through her calendar, mind scrambling. "I was in Florida. That was the day I went to the spa. I felt fine."

"Remember when you got up that day?"

Hestitating. "I'm not sure. I never had a shock before. Are you sure this thing fired?"

"Yep. Here's what the device recorded:"

(Click to enlarge)

"Why did this happen?"

"I'm not sure. As you know you have atrial fibrillation and a weak heart muscle though you were never found to have coronary artery disease (blocked arteries) - that's why the defibrillator was installed."

"Yes."

"Well, if we look at the tracings, I notice two small clues as to what happened. See those little VS notations?"

"Yes."

"Well those occur every time one of your heart beats are sensed by the device. If there's an FS, that means a heart beat was detected that was above the ventricular fibrillation cutoff rate (in other words, it was going really fast). The TF also means that the heart rate fell into a very fast ventricular tachycardia zone. A VP notation means the device paced your heart. Now, see the 'FD' as the first label on the bottom of the seond line of tracings?"

"Yes."

"Well that means that enough fast heart beats occurred to satisfy the device's algorithm to call this rhythm ventricular fibrillation - the FD stands for 'Fib Detect.' Note how the device then stops labelling the sensed ventricular beats as FS's as it charges to deliver a shock(the labels turn back to VS's but the rate still looks really fast.) Once the charge ends, a CE label is displayed. The device looks for one more fast heart beat, and when it sees it, it delivers its charge, labeled as 'Charge Delivered,' or CD on the next sensed rapid ventricular beat to reset the rhythm. That's when the shock occurs that most people feel. Then we can see your own normal ventricular sensed (VS) beats after the shock is delivered."

"Amazing."

"Yes ma'am, it is. Happy Valentine's Day."

"Oh my God, you're right! I can't believe it! I really just can't believe it!"

* * *
So what programming change was made to her device to prevent another shock? It was a single-chamber Medtronic ICD programmed with backup ventricular pacing at forty beats per minute.

Any takers?

-Wes

Addendum: For those not accustomed to viewing the information produced by interrogating a defibrillator after a shock, the top two lines on each strip represent the signal seen (1) from the tip electrode to the can of the device, simulating an EKG lead, and the lower line (2) is the signal seen locally inside the heart between closely spaced electrodes on the lead (these lines are not "on" at first until a rapid rhythm is detected). The lowest line is the "marker channel" that demonstrates how each blip on the middle signal line was interpreted by the device.

Cardiac Arrests and Hospital Staffing

Time is muscle and time is brain.

So it is not a surprise to see that hospitals that fail to apply a defibrillator shock to a cardiac arrest victim quickly while in the hospital fare worse than those who receive it early. And it was surprising to see that in-hospital deaths from cardiac arrest were higher than out-of-hospital arrest survival in areas with available AED technology.

But what was most shocking to me (pun intended) was not these findings of the study, but the accompanying editorial by Leslie Saxon, MD who advocates for centralized monitoring stations "insensitive" to staffing needs in hospitals:

The automated detection system offers advantages in that it is insensitive to staffing issues and, if centralized, can track patients anywhere in the hospital. The system also allows for quicker notification of key personnel.

Who are we kidding?

I've seen such centralized stations in action, and it was scary. First, how many monitors must one person staffing these centralized station watch? 10? 20? 100? How attentive are they? (How attentive would you be after doing this for a week or a month or a year?) Then, there's notifying the staff that there's a problem: what if no one's at the nurses station to answer the "code" phone? Also, who will check to be sure the electrodes stay applied to patients or replace the monitor's batteries when they go dead?

Can we really expect that being "insensitive" to staffing needs will save lives? If no one is there competent to execute the necessary steps for successful resuscitation (including defibrillation), then few will survive.

More effective will be the hospitalist movement, where physician staff are available in-house 24 hours per day. Additionally, simple steps, like placing every patient who undergoes any surgery, especially with conscious sedation or general anesthesia, on telemetry (and perhaps pulse oximetry). After all, not all arrests are cardiac - many are respiratory first, and then become cardiac as hypoxia ensues.

Monitoring of patients in hospitals takes people. Especially people sensitive to patients' needs. Centralized monitoring stations that remain "insensitive" to staffing issues can only spell ultimate disaster to our patients.

-Wes

Image credit.

Should Defibrillators Be In Schools?

Just in time for the back-to-school season comes this report on the epidemiology of cardiac arrest in our schools.

The report adds much to our knowledge of the epidemiology of sudden death in schools from two large counties near Seattle, WA, USA. Of 3773 episodes of cardiac arrest in a public domain over 16 years, 97 arrests occurred in 671 schools but only 12 of these occurred in children.

The incidence of sudden death among (adult) school staff was 25-fold greater than that among students. Given the additional contribution of other adults not employed by the school, greater than 90% of cardiac arrests in schools occurred among adults. The finding supports the assertion that school-based CPR and AED programs would benefit faculty and staff members, as well as visitors to the school who, because of their age, are at greater risk of cardiac arrest than the students.

And while some doctors are in favor of expanding CPR and AED distribution, others are not:

"It is estimated that over 350,000 individuals die of sudden cardiac arrest in the U.S. each year," said Dr. Gregg C. Fonarow, a professor of cardiology at the University of California, Los Angeles. "Improved cardiac arrest recognition and emergency activation, early CPR, and early defibrillation, including the use of AEDs, can significantly increase the chances of surviving sudden cardiac arrest."
This study provides important community-based data on the incidence, circumstances and outcome of cardiac arrest in the school setting, Fonarow said. "This study found that half of the student cardiac arrests were not associated with physical exertion or sports participation, and student risk was similar for elementary school, middle school, high school and college," he said.

The majority of cardiac arrests in schools occurred among adults, Fonarow noted. "The finding supports the assertion that school-based CPR and AED programs would benefit not only students, but faculty, staff members, as well as school visitors, and provides important data for considering increasing CPR training and the availability of AEDs in the school setting," he said.

Another expert disagrees. The very rarity of cardiac arrests at schools makes having AEDs available unnecessary, he said.

"Any cardiac arrest in a student, especially if it occurs on school grounds, gets a lot of media attention," said Dr. Byron Lee, an associate professor of cardiology at the University of California, San Francisco. "This has led some to call for AED in every school."

However, because cardiac arrest at schools is extremely rare, and only a minority of cardiac arrests occurs in the students, "it seems unlikely that putting an AED in every school would be cost-effective," Lee said.

But what was remarkable in this study was the unusually high success rates of public access defibrillation by lay rescuers. From the study:

Seven of the school-based cardiac arrests received lay-rescuer defibrillation. Survival to hospital discharge among cardiac arrests was 39% in school settings (46% for initial rhythm of ventricular fibrillation) compared with 27% in other public locations.

These data, in my view, make a compelling case for the wide availability of public access defibrillation. It is survival to discharge from a hospital that matters, and there is nothing that will improve survival in that setting better than a beating heart. The chest thumping of CPR, while helpful temporarily, only mildly improves the chance of survival following cardiac arrest until the coordinated contraction of the heart can be restored with defibrillation.

-Wes


Reference: Katayoun Lotfi BS, Lindsay White MPH*, Tom Rea MD, MPH, Leonard Cobb MD, Michael Copass MD, Lihua Yin MBA, Linda Becker MA, and Mickey Eisenberg MD, PhD. "Cardiac Arrest in Schools," Circulation 2007 doi:10.1161/CIRCULATIONAHA.107.698282

Image credit.

Great Poster

Click to Enlarge

My favorite poster at the Heart Rhythm Society Meeting in Denver, Colorado last week came from Dr. A. Kondur, MD et al, of the Wayne State University, Detroit Michigan and the University of Kansas Hospital, Kansas City, KS entitled "Implantable Cardiovertor Defibrillators Save Lives from Lightning Related Electrocution Too..."

They reported on a 75 year-old man who suffered a side flash injury from lightning while adjusting his radio antenna on a rainy night. A year prior he had received a biventricular implantable cardiac defibrillator for treatment of his congestive heart failure and a weakened heart muscle. It seems his scalp and right index finger were burned from the lighning strike and his heart went into ventricular fibrillation. Fortunately, defibrillators have voltage shunting circuitry (so people with such devices can have external defibrillation if necessary without fear of harming the device circuitry). Therefore, the device circuitry was not harmed by the high voltage lightning strike. The defibrillator successfully detected the abnormal heart rhythm (ventricular fibrillation) caused by the lightning and shocked his heart back to normal rhythm after the episode!

The best part of the poster, though, was the disclaimer:

"The authors do not advise implanting ICD prophylactically for lightning strikes."

You've got to love investigators with a sense of humor.

-Wes

Sudden Cardiac Death Preparedness in School Athletic Programs

Despite these new guidelines published in the April issue of the journal Heart Rhythm that addresses preparedness for cardiac arrest in high school and college athletic programs, many schools still have no automatic external defibrillators (AEDs) on site. But the guideline's lead author, Dr. Jonathan Drezner (University of Washington, Seattle), makes an important point on TheHeart.org:

"Many schools are acquiring defibrillators through donations, and while that's not a bad thing, it's solving only half the problem," said Drezner. "You have the equipment, but do you have the plan that goes with it? If the defibrillator is kept in the nurses' office in a locked cabinet, it doesn't really do you much good if a player has a cardiac arrest on the football field or the basketball court."

After communication, personnel, and equipment, the emergency action plan must be ready to work smoothly when the situation arises. "This is something that has to be practiced," emphasized Drezner. "You have to get your likely first responders, your athletic trainers, your team physicians, your school nurses, coaches, and administrators, and bring them out to the practice field and simulate a cardiac arrest. Go over that emergency practice plan, and go over it at least once a year."

But why stop with high schools and colleges? In my view, elementary schools should have a similar plan and equipment in place.

It just makes sense for our kids.

-Wes

In Cardiac Arrest, Higher Defibrillation Energies Are Better

Take any drug, give more of it, then usually you’ll see a bigger physiologic response. Most of us in medical school knew this as a dose-response curve.

As a cardiac electrophysiologist, I have always been interested (but never had the patience to test) why the American Heart Association’s guidelines were always suggesting “start low and work your way up” with defibrillation (shock) energies when a patient has the life-threatening heart rhythm disturbance, ventricular fibrillation. During ventricular fibrillation, the heart is only barely quivering and generates no effective cardiac output or blood pressure. Time is of the essence when correcting this arrhythmia to improve patient survival: without cardiopulmonary resuscitation (CPR) during ventricular fibrillation, irreversible brain injury can begin in just four to five minutes.

So it was refreshing to see the results of the effectiveness of out-of-hospital defibrillation with two different energy regimens tested side-by-side by Canadian researchers in this month’s Circulation. They compared fixed lower (150J-150J-150J) defibrillation versus higher escalating doses of defibrillation (200J-300J-360J) in 221 patients requiring more than one shock with a biphasic defibrillator during out-of-hospital cardiac arrest. Their results were predictable: higher energies work better. Much better. 25% vs. 37% better (p<0.035).

The dose-response curve held true: improved success was seen when higher defibrillation energies were applied.

Now the question becomes, why not just start delivering shocks at the maximum output of the defibrillators during cardiac arrest? If a 10% improvement was seen with escalating doses of defibrillation, could additional success be identified using a fixed maximum defibrillation energy? In animals, it has been demonstrated that ventricular fibrillation in the setting of acute ischemia (lack of blood flow to the heart) requires higher energies to achieve successful defibrillation than non-ischemic ventricular fibrillation.

I guess we’ll have to wait for another study for my answer. But for now, dial up those defibrillators when shocking ventricular fibrillation.

-Wes