ls Europace (2000) 2, 263–269
doi:10.1053/eupc.2000.0104, available online at http://www.idealibrary.com on
Is electrical storm in ICD patients the sign of a dying
heart?
Outcome of patients with clusters of ventricular tachyarrhythmias
M. Greene, D. Newman, M. Geist, M. Paquette, D. Heng and P. Dorian
Division of Cardiology, St Michael’s Hospital, Toronto, and the Department of Medicine, University of Toronto,
Toronto, Canada
Background Electrical storm in patients with implanted
cardioverter defibrillators (ICDs) is purported to carry an
ominous prognosis.
Methods and Results We retrospectively compared 40
patients with electrical storm (defined as three or more
episodes of ventricular arrhythmia requiring ICD therapy
in a 24 h period) with those only having isolated appropriate ICD therapy (n=57) and with patients having no or
only inappropriate ICD therapy (n=125). All patients
received ICDs for documented sustained VT or VF. There
was no significant difference in age, sex, ejection fraction,
total follow-up time, or underlying heart disease between
any of the three groups. Patients who had electrical storm
received their first appropriate ICD therapy 275369 days
post-implant (35% had storm as their first event) with storm
Introduction
Electrical storm, defined by Kowey et al.[1], as frequent
or incessant ventricular fibrillation (VF) or haemodynamically destabilizing ventricular tachycardia (VT),
may be associated with a poor prognosis. Storm tends to
occur in the presence of acute myocardial infarction
or worsening heart failure, and in patients without
implanted cardioverter defibrillators (ICDs) a protracted period of time may pass from arrhythmia onset
until treatment is delivered. This temporal factor is likely
to make some contribution to the unfavourable outcome. In patients with ICDs, however, these lifethreatening ventricular tachyarrhythmias can be
terminated by antitachycardia pacing or shock therapy
Manuscript submitted 15 June, 1999 and revision accepted
1 March 2000.
Correspondence: Paul Dorian, St Michael’s Hospital, 30 Bond
Street, Toronto, Ontario, Canada M5B 1W8.
1099–5129/00/030263+07 $35.00/0
occurring an average of 599710 days post-implant.
Patients had 1·51·0 storms in total (median=1), with
5591 episodes per storm. There were no significant
differences in actuarial survival at 5-year follow-up between
the three groups. Eighty percent of storm patients were
alive 5 years post-implant.
Conclusion Storm is a common occurrence in ICD
patients, can occur at any time during the follow-up period,
and does not independently confer increased mortality.
(Europace 2000; 2: 263–269)
2000 The European Society of Cardiology
Key Words: Implantable cardioverter defibrillators,
survival, antiarrhythmia agents, electrical storm.
before they sustain haemodynamic compromise, and as
a result the outcome may be better.
There is limited information regarding this phenomenon in ICD patients. Villacastin et al.[2] found that
multiple consecutive appropriate ICD discharges were
an independent predictor of cardiac and arrhythmic mortality, but this study was done in patients
implanted with earlier generation ICDs that did not
have complete data logging and electrogram storage
capabilities and in whom frequent VT/VF events were
not always aggressively treated. Furthermore, few
patients in this study received new or changed antiarrhythmic therapy at the time of frequent ICD discharges. In contrast, Credner et al.[3] found that ICD
patients with frequent device therapy for recurrent
VT/VF did not have a worse mortality when compared
with ICD patients receiving isolated VT/VF therapy. It
is not clear whether electrical storm is an early sign of
inexorable cardiac deterioration and portends a poor
prognosis, or is merely an exclamation mark in a
variable clinical course.
2000 The European Society of Cardiology
264
M. Greene et al.
Table 1 Characteristics of ICD patients receiving no or only inappropriate ICD therapy; patients receiving
appropriate ICD therapy, and patients experiencing one or more electrical storms
No therapy or
inappropriate therapy
(n=125)
Appropriate
ICD therapy
(n=57)
Electrical
storm
(n=40)
60·613·0
85%
38·317·5
59·215·1
79%
37·016·7
60·213·9
68%
33·813·3
Heart disease
CAD (%)
CM (%)
Other (ARVD, valvular or congenital heart disease)
None (%)
68%
10%
9%
13%
67%
11%
17%
5%
78%
10%
12%
0%
Presenting rhythm
VT (%)
VF (%)
Syncope (%)
None (%)
42%
49%
6%
3%
74%
26%
0%
0%
65%
25%
10%
0%
350·9537·6
275·4368·9
Age (years)
Sex (% male)
EF (%)
Time to first ICD therapy (days)
EF=ejection fraction; CAD=coronary artery disease; CM=cardiomyopathy; ARVD=arrhythmogenic right ventricular dysplasia;
VT=ventricular tachycardia; VF=ventricular fibrillation.
Intravenous (i.v.) amiodarone has been shown to be
very effective in treating electrical storm in patients
without ICDs[4–6]. However, some controversy exists
around the use of amiodarone in patients with ICDs
because of its claimed effect of increasing defibrillation
threshold (DFT)[7–9], or decreasing VT pace terminability[10]. The effect of a policy of liberal amiodarone use
in patients with electrical storm is not well understood.
We, therefore, examined whether certain ICD patients
were more likely than others to develop electrical storm,
the frequency and timing of its occurrence, and finally
the outcome and prognosis for ICD patients with storm.
Materials and Methods
Patient population
The charts of 227 patients with ICDs implanted from
February 1986 to May 1998 followed at St Michael’s
Hospital in Toronto, Ontario, Canada were reviewed
and all patients who had received appropriate ICD
therapy were selected. Of this group, any patient who
had had one or more episodes of electrical storm
(defined below) became the study population. All
patients were followed up to the end of the study period;
patients who subsequently underwent cardiac transplantation had their follow-up date censored at the day of
transplantation. Patients were followed at a minimum of
6 month intervals; no patient was lost to follow-up. Each
detected arrhythmia episode was individually reviewed
and prospectively classified as either ‘appropriate’ (treatment for ventricular arrhythmia) or ‘inappropriate’
(treatment for other reasons). Only therapies deemed
appropriate (i.e. for ventricular arrhythmia) based
on intra-cardiac electrograms, R-R intervals, and
Europace, Vol. 2, July 2000
symptoms were included for analysis. The primary endpoint for this study was death or survival to May 1998.
Patients were divided into three groups: Group (1) No
appropriate ICD therapy, Group (2) appropriate ICD
therapy but no storm, Group (3) electrical storm (see
Table 1).
Definition of electrical storm
Electrical storm was defined for the purpose of this
study as three or more episodes of VT or VF requiring
ICD therapy (either antitachycardia pacing (ATP) or
shock) in a 24-h period. Storm was considered to have
ended if a 2-week period passed with no arrhythmia
episodes recorded.
ICDs included and operative approach
Patients were implanted with devices and lead/patch
systems manufactured by Guidant Inc., St Paul, MN
(models Ventak, Ventak PRx, Ventak PRxII, Ventak
Mini II, Ventak AV-DDD or AV-DDDR), Medtronic
Inc., Minneapolis, MN (models 7217, 7218, 7219, 7220,
7221, 7223, 7271), Telectronics Pacing Systems, Denver,
CO (models 4204, 4210, 4211, 4215, 4310, 4310HC), or
Ventritex, Sunnyvale, CA (models V-100, V110, V-145,
V-175, V-190). All of these ICDs had some form of
datalogging capability, either intracardiac electrograms
or R-R intervals or both. Epicardial lead systems (n=52)
were implanted via either median sternotomy or left
thoracotomy with leads tunnelled to a generator positioned in the abdomen. Transvenous lead systems
(n=175) were implanted via the subclavian or cephalic
Outcome of ICD patients with electrical storm
Table 2
265
Characteristics of storm patients who have died
Patient
number
1
2
3
4
5
6
7
8
9
10
Heart
disease
Sex
EF
(%)
Antiarrhythmic
medication at
initial discharge
Time to
first storm
(days)
Time to death
from last storm
(days)
Cause
of death
CAD
CAD
CAD
CAD
CAD
CAD
CAD
CAD
CAD
CAD
M
M
M
F
M
M
M
F
M
M
23
35
37
24
46
26
18
23
29
19
Sotalol
Sotalol
Sotalol
-blocker
-blocker
Amiodarone+sotalol
Amiodarone
Sotalol
Sotalol
-blocker
425
43
399
237
990
604
2131
942
739
28
473
30
1642
11
17
46
370
29
190
613
COPD
COPD
CHF
Sepsis
CHF
CHF
CHF
SCD
CHF
CHF
654619
342506
Mean(standard deviation)
289
CAD=coronary artery disease; M=male; F=female; COPD=chronic obstructive pulmonary disease; CHF=congestive heart failure;
SCD=sudden cardiac death.
vein and were either tunnelled to the pulse generator in
the abdomen or in the left or right pectoral region.
in the zone or following unsuccessful ATP therapy. In
14/61 (23%) storms all episodes of VT were successfully
treated with ATP.
Statistics
Continuous variables were expressed as mean
standard deviation (SD). Continuous variables were
compared with Student’s t-test, and differences between
categorical variables were tested by Chi-square analysis.
Survival curves were calculated according to the
Kaplan–Meier actuarial method and compared using
the log-rank test.
Results
The clinical characteristics of the three groups of
patients are listed in Table 1. Clinical characteristics are
similar for all three groups, although in the appropriate
ICD therapy group indication at implant was ventricular tachycardia (VT) more often than the no appropriate
ICD therapy group (who had a greater proportion of
patients with ventricular fibrillation (VF) or syncope as
an indication) (P=0·001, see Table 1). There was no
difference in mean follow-up time among the three
groups.
Arrhythmias documented during storm and
resultant ICD therapy delivered
Of the 61 storms which occurred in 40 patients, all
storms had therapy delivered for sustained monomorphic VT (cycle length range 400–200), except two,
where therapy was delivered for polymorphic VT which
occurred in the context of ischaemia. The majority of
episodes occurring during storm were successfully
treated by shock, either as the only programmed therapy
Mortality and heart transplantation in the
electrical storm group
Total mortality in the group of 227 patients was 12·3%
(n=28) after 2·92·6 years of follow-up (average
annual mortality over 5 years was 2·1%). Ten of 40
storm patients (25·0%) died over a mean of 3·62·6
years with an average annual mortality rate (over
5 years) of 4·5%, nine of 57 patients receiving appropriate therapy died (15·8%) over an average of 3·62·6
years with an average mortality rate over 5 years of
3·0%; and nine of 125 (7·2%) of patients who did not
receive therapy died over 2·22·3 years (average annual
mortality 1·1%). None of the mortality differences is
statistically significant (see Fig. 2).
Of the storm patients who died, one of them died
suddenly but did not have a tachyarrhythmic episode
recorded in her ICD datalogs at the time of her death
(suggesting death due to bradyarrhythmia or pulseless
electrical activity), one died of sepsis following a long
illness, six patients died of progressive heart failure and
two died of end-stage chronic obstructive pulmonary
disease (see Table 2 for details).
Of the total storm group, four patients have subsequently had heart transplants (storm termination to
transplant 213189 days (median 229 days); two of
these patients had electrical storm treated with intravenous amiodarone followed by an oral maintenance
dose and spent an arrhythmia-free year prior to heart
transplantation for worsening heart failure. One transplant patient had two storms early after ICD implantation associated with medication non-compliance, and
a subsequent 110 days arrhythmia free prior to transplant. The final patient had short periods where he was
Europace, Vol. 2, July 2000
266
M. Greene et al.
Other illness
5%
Unknown
29%
New or
worse CHF
15%
Medication change
or non-compliance
20%
Post-op
13%
Psychological
stress 10%
ETOH
8%
Figure 1 Presumed causes of electrical storm in a cohort
of 40 patients. Cause assignment was made by clinicians
at time storm occurred. See text for further discussion.
ETOH=ethanol; CHF=congestive heart failure.
No obvious aetiological factors were evident at onset
of storm in 18 (29%) patient storms. Eight patients
(13%) had storm occurring immediately following either
ICD implant or in one patient following percutaneous
transluminal coronary angioplasty (in whom repeat
angiography revealed the angioplastied vessel to be
patent). Worsening heart failure was evident in nine
(15%) VT storms. Three (5%) storms occurred in the
context of other illnesses. Five patient storms (8%)
occurred during and around periods of excess ethanol
consumption; while six (10%) storms followed periods of
unusual stress (departure on long-distance trip, driver’s
license suspension, extended family visits, stressful
phone conversation). Twelve (20%) patient storms were
associated with either non-compliance or adjustment of
antiarrhythmic medication (see Fig. 1). In 14 (35%) of
the storm patients, the first ever delivered therapy was
for electrical storm; and the remainder had isolated
therapies delivered prior to storm.
electrically stable, but had frequent storms prior to his
transplant.
Factors possibly contributing to storm onset
The 40 patients had a total of 61 storms (a mean of 1·5
storms each, median one storm, and a range of one to six
storms). The mean time to first storm was 599·1710·3
days (1·64 years) with an annual average incidence of
0·42 storms per year.
Seasonal occurrence
The majority of the 61 storms (25, 40·9%) occurred
during the winter (December, January and February),
six (9·8%) storms occurred in the spring (March, April
and May), 17 (27·9%) in the summer (June, July and
August) and 13 (21·4%) in the fall (September, October
and November) (P=0·006). When we eliminated from
the analysis those storms that occurred immediately in
1·0
0·9
Cumulative survival
0·8
0·7
0·6
0·5
0·4
0·3
0·2
P = 0·24
0·1
0
1
2
3
4
5
23
19
15
14
15
9
(day of implant)
N (no Rx)
=
N (App Rx) =
N (Storm) =
125
57
40
67
51
35
48
33
37
25
26
20
Follow-up (years)
Figure 2 Survival of ICD patients with electrical storm (· · ·) compared to patients
with appropriate ICD therapy (– – –) and patients with no or only inappropriate
therapy (——). There were no significant differences in survival between the three
groups. See text for further discussion.
Europace, Vol. 2, July 2000
Outcome of ICD patients with electrical storm
Table 3
267
Characteristics of patients with electrical storm
n=40
Mean # of storms (range)
Mean # of episodes of arrhythmia per storm (range)
Storm end to follow-up (days)
Storm end to heart transplant (days, n=4)
1·51·0
55·190·6 (4–465)
548·0493·6 (0–2334)
213·5189·4 (0–395)
the post-operative period, the winter and summer
preponderance remained.
relatively good prognosis with an overall survival at
2 years of 95% and at 6 years of 77·5%.
Antiarrhythmic therapy pre and post
electrical storm
Comparisons with previous studies
Prior to the onset of the patient’s first storm, 18 (45%)
were treated with sotalol, 10 (25%) with amiodarone
alone (n=6) or in combination with other antiarrhythmics, seven (17·5%) with metoprolol, and five (12·5%)
were receiving no antiarrhythmic drugs.
Following the first storm, 15 of 30 patients not
previously on amiodarone received i.v. (n=10) or oral
amiodarone immediately upon diagnosis. Three of these
patients (20%) subsequently had further storms. Of the
15 patients not treated with amiodarone, eight (53%)
had further episodes of storm and five received amiodarone after subsequent episodes. Among the 10
patients already on amiodarone at the time of storm,
four patients received additional amiodarone (two i.v.,
two oral); none of the 10 had further episodes of storm.
Thus, of 25 patients on amiodarone during, and after
storm, three of 25 (12%) had storm recurrence, whereas
eight of 15 (53%) of those not treated with amiodarone
had storm recurrence (P<0·001). All patients who were
aware of the storm were given counselling and offered
treatment by a psychiatrist. The majority were prescribed a benzodiazepine for a period of time following
their storm. One patient went on to have a radiofrequency ablation of his VT focus, and following
this procedure, he has had no further tachyarrhythmia
episodes.
Discussion
Major findings
Electrical storm in ICD patients occurs frequently
and unpredictably, and often occurs late post-implant.
The occurrence of electrical storm did not confer an
increased mortality in our study and no single clinical
characteristic predicted which ICD patients were more
likely to experience storm during the course of their
follow-up. No statistically significant differences were
found in any of the clinical characteristics between storm
patients and those receiving only isolated appropriate
ICD therapy. In addition, VT storm patients had a
Overall mortality in our VT storm patients was 2·5%,
5% and 12·5% over the first 1, 2 and 3 years after
implantation. This compares favourably with the mortality in ICD patients in other prospective randomized
trials with ICDs, including the AVID trial[11]. Trials
investigating multiple consecutive discharges or ‘cluster
shocks’ in ICD patients found that the mortality rates in
these patients was higher than in this study[2,13–15]. Some
of these studies (Khono et al.[12], Kluger et al.[13]
and Greenberg et al.[15], included patients who had
storm for reasons other than VT (a.fib, sinus tachycardia, electrical noise). In a study looking at complications following ICD implant, Nunain et al.[14], found
15·1% patients died over 15·39·7 months of follow-up.
We examined differences between our patients and
those described in other studies in an effort to determine
which factors may have contributed to the more favorable outcome in our patients. One of the most important
differences is that immediately post-ICD implant, 80%
of our patients were on antiarrhythmics, primarily
-blockers including sotalol (74% of patients). This is a
higher percentage of patients than all other studies
reviewed[13–17].
It is generally accepted that a lower ejection fraction
(EF) is associated with the ICD being more likely to be
required to deliver therapy during follow-up[17,18], and
that overall mortality is higher in the low EF group.
Villecastin et al.[2] found that patients experiencing multiple consecutive appropriate discharges had a worse
prognosis than patients with single appropriate discharges and that a lower EF was an independent predictor of multiple consecutive discharges. Khono et al.[12]
and Kluger et al.[13] both found that cluster shocks due
to ventricular arrhythmias were associated with a lower
EF and higher mortality. In our study, however, no
significant differences were found in EF or overall
mortality between the group who had only isolated
appropriate ICD therapy versus those who had experienced one or more stors. Villacastin et al.[2] found that
multiple consecutive appropriate discharges in ICD
patients not only was a marker for a bad prognosis, but
that they predicted the approach of death. Our results
indicate that storm patients do not necessarily have a
Europace, Vol. 2, July 2000
268
M. Greene et al.
shorter survival time than patients who have received
isolated appropriate ICD therapies.
Prediction of electrical storm
The time to first therapy was not found to be a predictor
of electrical storm onset as there was no difference in
time to first appropriate ICD therapy between those
patients who had a storm event and those that had only
experienced single isolated episodes requiring ICD
therapy. Our results differ from those of Villecastin et
al.[2], who found that those individuals who had experienced multiple consecutive ICD discharges had received
their first appropriate ICD therapy earlier than those
who had only had isolated appropriate ICD therapy.
We were unable to determine whether a pattern of
increasing frequency of tachyarrhythmic events was evident in the days leading up to storm onset. Some
patients may have had an increased frequency of nonsustained runs of VT prior to the onset of storm that
were either not detected by the ICD or where information was not stored in the datalogs of the device. Despite
this fact, 35% of the storm patients had the onset of
storm as their first event. More detailed datalogging
available with current devices may allow the rhythm
history prior to storm to be examined in greater detail.
A majority of VT electrical storms occurred during
the winter and summer months (P=0·006). These
findings are supported by others who have shown that
there is seasonal variation in death due to cardiac
diseases[19–22], and mortality due to myocardial infarction occurred more often in winter[23]. Stress has also
been shown to play a very important role in sudden
death occurrence. Increased mortality as well as an
increase in frequency of VT in the days following the
Northridge earthquake was observed, suggesting a relationship between emotional stress and sudden
death[24,25]. The effects of mental stress as a trigger for
sudden death was exemplified by the missile attack on
Israel during initial days of the 1991 Gulf War[26].
Mittleman et al.[27], interviewed 1623 patients within 4
days post MI and found that anger was a trigger for the
onset of acute MI more than expected by chance.
In 43 of the 61 episodes of electrical storm, we
observed a temporal association between storm occurrence and some physical or emotional stress (i.e. worsening heart failure, ethanol use, unusual psychological
stress, and concurrent illness). The remainder had either
no identifiable trigger, or storm occurred as a result of
non-compliance or a change in pharmacotherapy. Our
results support the hypothesis that triggering of cardiovascular events is a real and important but poorly
understood phenomenon.
established[4–6], although some controversy exists
around its use in patients with ICDs because of concerns
over a drug related increase in defibrillation threshold
(DFT)[7–9]. Intravenous amiodarone has also been
shown to decrease the frequency of haemodynamically
unstable VT/VF[30–33]. Levine et al.[4] prospectively randomized 273 patients with recurrent hypotensive VT
refractory to other antiarrhythmic agents to receive one
of three doses of i.v. amiodarone and found that 40%
patients responded to this therapy.
Sotalol, on the other hand has been shown to lower
DFT[28]. These drugs as well as class I agents may slow
tachycardia rates, making VT and SVT rates overlap, or
they may make some ventricular arrhythmias no longer
pace terminable[10].
Seventy seven percent of the storms in our study were
treated with shock therapy, either as the initial programmed therapy, or after failed ATP. Of the 23% of
storms (14 storms occurring in eight patients) where all
episodes within the storm were treated with ATP, 10
storms occurred while the patient was on sotalol and
four storms occurred while the patients were taking
amiodarone. When we compared the survival of those
patients who had storms where ATP was the only ICD
therapy with the rest of the storm group, no difference
was observed in overall mortality (25% overall mortality
in both groups).
Most patients in our study who were symptomatic
with storm (23 at the time of first storm and 28/40 (70%)
of patients overall) were treated with amiodarone (either
new or increased oral or intravenous followed by oral
dosing) except for one patient who had experienced
amiodarone-induced torsades de pointes prior to ICD
implant. Although our study was not controlled and
almost all patients received some additional therapy at
the time of storm, we have found amiodarone highly
effective in terminating electrical storm due to VT.
Only one patient went on to have a radio frequency
ablation of his VT focus, and following this procedure
he has had no further tachyarrhythmia episodes.
Limitations of the study
This study is limited by the relatively small numbers of
patients included as well as our arbitrary definition of
electrical storm. Since the study was retrospective and
uncontrolled, the contribution of post-storm therapy to
outcome as opposed to the natural history is not known.
Future investigation should attempt to determine which
factors affect the onset of storm and what modifications
should be made in the therapeutic management of the
patient.
Therapy for electrical storm
Conclusions
The antiarrhythmic efficacy of amiodarone as treatment
for acute, severe, ventricular arrhythmias is well
Electrical storm is an unpredictable phenomenon that
may occur at any time in ICD patients. The presence of
Europace, Vol. 2, July 2000
Outcome of ICD patients with electrical storm
electrical storm in ICD patients does not confer an
increased mortality compared with patients who have
received appropriate ICD therapy but no storm. With
prompt intervention many of these patients have no
further device activity after storm cessation.
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