PROGNOSIS OF A
DEFIBRILLATOR SHOCK IN A PATIENT WHO HAS HEART FAILURE.
You are listening to ReachMD XM 157, the channel for
medical professionals. Welcome to the clinician's roundtable. I am your host
Dr. Matthew Sorrentino from the University of Chicago Medical Center and with
me today is Dr. Jeanne Poole. Dr. Poole is the professor of medicine and the
director of the Arrhythmia Service in the Division of Cardiology, Department of
Medicine at the University of Washington, Seattle, Washington. Today, we will
discuss a recent paper called prognostic importance of defibrillator shocks in
patients with heart failure. This is a report from the sudden cardiac death
and heart failure trial reported recently in the September 4, 2008, issue of
the New England Journal of Medicine.
Dr. Poole, welcome to the show.
Thank you it is my pleasure.
I would like to start first by going over the SCD-HeFT trial
(the sudden cardiac death and heart failure trial). What type of patients were
studied in that trial?
Those were patients who were identified based upon New York
Heart Association Class for moderate symptoms of heart failure, so they needed
to be New York Heart Association Class II or III and also a left ventricular
ejection fraction of 35% or less and no prior history of life-threatening
So these were symptomatic patients in a large part, but not
Correct, so they were not the sickest, which would be
considered a class IV patient neither were they the most healthy as you will
heart failure patient the class I patient.
And what type of procedures were done in the trial? How
were patient's randomized to different therapies?
They were randomized in equal proportions to either receive
an implantable cardiac defibrillator or to receive amiodarone compared to
placebo drugs, so the amiodarone was double blinded with placebo, so there were
three arms to the trial. One-third got amiodarone blinded, one-third got a
placebo pill, and the other third received an implanted defibrillator.
Now, you mentioned that these were symptomatic heart failure
patients. Did it matter what the underlying etiology of the heart failure was,
ischemic versus dilated cardiomyopathy?
No, patients could have either etiology of heart failure to
be included in this trial.
And how many patients were ischemic versus not ischemic, do
Yes, it was about 50% split for ischemic and nonischemic out
of the total of 2521 patients.
I know that this was one of the pivotal ICD trials. What
was the overall result of the trial, which group did better?
The group did best who has received the implantable
defibrillator. They had a marked and significant reduction in all cause
mortality. On the other hand, the amiodarone arrhythmic drug did not benefit
patients at all. Their mortality was the same as those who were given the
So your paper now is looking at this group a little bit
differently. What was the main issue that you want to look at in your
subpopulation of this trial?
We were interested in looking at just the patients who
received the implantable defibrillator and we were asking the question now that
we had the implanted this device into people who have never had ventricular
tachycardia or ventricular fibrillation, what does the group of patients look
like who then go on to have one of those rhythms treated by the device. Are
they a higher risk group of patients compared to those who never had a rhythm
abnormality over the course of the followup in this trial, which was very
long. It was about 4-1/2 years, the longest clinical ICD trial that has been
completed to date. So, really our question is now that patients have an
abnormal rhythm, are they are a higher risk subpopulation?
No, in the trial some patients had what were called an
appropriate shocks and others had what was called an inappropriate shock. What
do you mean by that difference?
Well, we want defibrillators to only treat life-threatening
arrhythmias, so ventricular arrhythmias. However, some times the patients can
have arrhythmias that are coming from the atrium such as atrial fibrillation a
common rhythm problem in heart failure patients and these rhythms can also go
fast enough that it triggers therapy from the device. The device is
functioning normally, but treats this rhythm abnormality that we would prefer
to treat in another way and not with the shock, that is probably the most
common cause for what we term an inappropriate shock. There are, however, some
other instances where the device again can be functioning as it is asked to do
so, but it is picking up other signals. So, for instance, if a patient gets
too close to some sort of external electrical interference, those signals may
be picked up by the device and interpret it as an arrhythmia and then the device
will deliver a shock to the patient.
So in another words, if a patient has atrial fibrillation
that causes the heart rate to go very fast, it goes faster than the limit that
the ICD is meant to detect and that is what delivers the shock?
That is correct.
So how many of the patients in your population received an
appropriate shock, how many an inappropriate shock?
Hundred and eight two of the patients that had the device
implanted, which was a total of 811 had an appropriate shock and a total of 141
patients received an inappropriate shock.
Does that seem like a high number of inappropriate shocks?
Well, it is too high for all of us who would wish that it
was not treating these other rhythms. However, if you compare to other trials,
it is very similar. So, in all clinical trials that had been done, the rate of
inappropriate shocks vary somewhere between about 14% and 18% depending upon
the length of followup in the trials, so certainly longer the followup the more
of these events you are going to identify, but I think all of us that are in
this business would agree that an inappropriate shock rate that is in that
range is certainly much higher than what we would like to see.
Now in looking at the patients who received an appropriate
shock was there someway to determine who was more likely to get an appropriate
That was not part of this study; however, we have looked at
those kinds of characteristics in patients. We have also seen data that came
out of other trials such as the MADIT II trial that have looked at predictors
of shock and certainly patients who have atrial fibrillation heading into this
trials are a group of patients that are more likely to have an inappropriate
shock and it turns out that this is often a predictor for appropriate shocks.
Also, we might wonder why that might be, but we know that atrial fibrillation
is in itself a risk factor of poor outcome in heart failure patient. Also,
patients who are not treated with beta-blocker therapy are a group of patient
in whom we have identified are more likely to have an appropriate shock as well
as an inappropriate shock.
So, patients who are receiving shocks I guess in general can
be considered sicker patients would you say?
They can be and I think that has been a consistent finding
also amongst the number of these trials and again that was not part of this
specific study, but patients who have lower ejection fractions and worse heart
failure such as a higher class New York Heart Association class III versus
class II in some trials are the group that have a higher shock rate.
So, let us talk about the results of your trial, what is the
prognosis of patients after receiving a shock?
Well, the groups are at a significantly higher risk of
future death compared to patients who did not receive any shock at all and that
was to for both patients who had an appropriate shock as well as those patients
who had an inappropriate shock.
How much higher is their risk of death compared to those who
did not get a shock?
For patients who had any appropriate shocks compared to
those who did not over the course of the trial the risk was 5 times greater.
For patients with inappropriate shocks, it was about 2 times greater than those
who had had no inappropriate shock over the course of the followup of the
trial, so that is a significant increased risk.
So, you mention there is as much as 5 times increased risk
of future death if you have received a shock. Is this again just a way of
identifying a sicker group of patients or could the shock have led to worsening
heart failure and leading to the outcome down the road.
The primary reason for the increased risk is likely to be
the arrhythmias. We know that patients with heart failure who develop
ventricular tachycardia or ventricular fibrillation are a higher risk group,
that has been known for a long time. The study that we did gave us the ability
to really assess how much greater that risk is, so if we try to say do the
shocks for patients, I think the answer would be overwhelming a small
percentage of patient if that all are actually harmed by a shock because if
patients were harmed, then we would not have multiple clinical trials that have
now proven and substantiated that implantable defibrillator stabilize because
the primary modality for these devices to save patients is shock therapy.
Having said that, is there some instance in which a shock itself might be
danger? Perhaps in a very rare instance if somebody has end-stage heart
failure, one could imagine the shock might be harmful to that patient, but
overall the most reasonable approach to thinking about this study and these
results is that the rhythms are the marker of increased risk and the ICD shock
is the simply the therapy being delivered to that patient.
I guess, I am still concerned about the patients who
received only an inappropriate shock. In those patients, they did not have
ventricular tachycardia or ventricular fibrillation and yet they have a 2-fold
increased risk of death further on in the trial. Is that surprising or again
is it the atrial fibrillation that you think is the signal here?
Well, the numbers are small to really completely sort that
out, but at least half of the patients who had an inappropriate therapy, a
shock therapy, had it because of atrial fibrillation. So, I think it is a
reasonable assumption that if the atrial fibrillation that is the increased
marker of subsequent increased mortality. Again, it is hard to know whether or
not in an end-stage situation, shocks themselves might be harmful to an
individual. Probably, it is the atrial fibrillation. Often times, the atrial
fibrillation was also occurring around the same timeframe as a ventricular
arrhythmia. Some of those patients were in the group in our study that
actually did not live longer than 24 hours after their therapy was delivered
and if you then look at the risk for patients who had inappropriate shocks that
if survive longer than 24 hours; the increased risk is much smaller. So, it
makes you wonder about that particular group of patients. Where they
particularly high-risk group at the end stage of their heart disease or where
they perhaps even dying from other terminal diseases? and we simply do not have
enough clinical information on that group of patients to really sort that out
at this time.
Well, I want to thank Dr. Jeanne Poole who is the
professor of Medicine in the Division of Cardiology at the University of
Washington, Seattle. We have been discussing a recent paper about the
prognosis of a defibrillator shock in a patient who has heart failure. I am
Dr. Matthew Sorentino. You have been listening to the Clinician's Round Table
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