CLINICAL RESEARCH
Europace (2012) 14, 968–974
doi:10.1093/europace/eus028
Sudden Death and ICDs
Long-term follow-up on high-rate cut-off
programming for implantable cardioverter
defibrillators in primary prevention patients with
left ventricular systolic dysfunction
Nicolas Clementy 1*, Bertrand Pierre 1, Bénédicte Lallemand 1, Olivier Marie 1,
Eric Lemoine 2, Pierre Cosnay1, Laurent Fauchier 1, and Dominique Babuty 1
1
Cardiology B Department, Service de Cardiologie B, Trousseau Hospital, François Rabelais University, 37044 Tours, France; and 2Cardiovascular Surgery Anaesthesiology
Department, Trousseau Hospital, François Rabelais University, Tours, France
Received 13 December 2011; accepted after revision 31 January 2012; online publish-ahead-of-print 1 March 2012
Aims
Implantable cardioverter defibrillators (ICDs) are efficient in reducing mortality in patients with left ventricular systolic dysfunction. High-rate cut-off programming may be effective in reducing appropriate and inappropriate therapies, but as the long-term consequences on morbidity and mortality remain unclear, it is
underutilized.
.....................................................................................................................................................................................
Methods
We prospectively studied 365 consecutive patients (mean age 60 + 10 years), with ischaemic (63%) or non-ischaemic
and results
cardiomyopathy and left ventricular dysfunction (mean ejection fraction 25 + 7%), who were implanted with an ICD
in primary prevention of sudden cardiac death (41% single chamber, 31% dual chamber, and 28% biventricular). All
devices were programmed with a shock-only zone over 220 beats per minute (b.p.m.) and a monitoring zone
between 170 and 220 b.p.m. During a median follow-up of 40 months, 41 patients received appropriate shocks
(11.2%) and 24 inappropriate shocks (6.6%). Then, 306 patients never experienced any ICD shock (84%). Inappropriate discharges were related to supraventricular tachyarrhythmia in 10 patients, and noise/oversensing in 14
patients. Ventricular tachycardia episodes, sustained or not, were recorded in the monitoring zone in 43 patients
(11.8%). Seven of these patients were symptomatic (1.9%), without lethal consequence. Sixty-two patients (17%)
died: 35 from end-stage heart failure, 1 from unexplained sudden death, and 26 from a documented non-cardiac
cause.
.....................................................................................................................................................................................
Conclusion
High-rate cut-off (220 b.p.m.) shock-only ICD programming, in primary prevention patients with reduced left ventricular ejection fraction, appeared to be safe during a long-term follow-up. It also resulted in a very low rate of discharges, which are known to be deleterious in this population.
----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords
Implantable cardioverter defibrillator † Primary prevention † Sudden cardiac death † High-rate cut-off †
Programming † Shock
Introduction
Implantable cardioverter defibrillators (ICDs) reduce all-cause
mortality in primary prevention of sudden cardiac death in
certain groups at increased risk. Systematic implantation is then
recommended for patients with or without ischaemic
cardiomyopathy presenting with reduced left ventricular ejection
fraction (LVEF), associated or not with cardiac resynchronization
therapy.1 These indisputable benefits are, however, spoiled by a
significant morbidity, including appropriate shocks in about one
patient out of five, and worse inappropriate shocks in about one
patient out of seven.2,3
* Corresponding author. Tel: +33 247474687; fax: +33 247475919, Email: [email protected]
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2012. For permissions please email: [email protected].
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High-rate cut-off ICD programming
Internal electrical shocks decrease quality of life,4 may be involved
in depression and anxiety,5 are known to be proarrhythmic,6,7 and
may finally be associated with an increased mortality.2,3
It is thus a major challenge for physicians to reduce the rate of
shock therapies. This could be achieved with new algorithms and
improved discrimination, additional atrial lead, and more aggressive
antitachycardia pacing (ATP) before shock. A strategy of programming longer detection intervals has also proven to be safe and
effective.8 – 10
High-rate cut-off programming may be another promising way
to decrease the rate of both appropriate and inappropriate therapies, but as the consequences of such programming on morbidity
and mortality remain unclear,11 it is underutilized.
Patients and methods
Population
Our study’s population consisted of all consecutive patients with
left ventricular systolic dysfunction who underwent implantation
of an ICD in primary prevention of sudden cardiac death in our department between 1 January 2001 and 31 December 2009. Cardiomyopathy aetiology, both ischaemic (with or without
myocardial infarction) and non-ischaemic (idiopathic or valvular),
with an LVEF of 40% or less, with or without syncope and inducible
ventricular arrhythmia at electrophysiological study, but without
spontaneous documented sustained ventricular arrhythmia, indicated prophylactic implantation of a single-chamber, dual –
chamber, or biventricular ICD, according to the guidelines.
Exclusion criteria were an age ,18 years, a previous documented spontaneous sustained ventricular arrhythmic event, and previous implantation of an ICD.
Implantation
All patients were implanted under general anaesthesia, in a pre- or
retro-pectoral position. The defibrillator lead was preferentially
introduced through a cephalic vein if available. The final position
of the leads was left to the discretion of each physician. Adequate
pacing threshold and signal amplitude detection were mandatory.
The defibrillation threshold was then tested, the first attempt
at 20 J, and at the maximum energy available for the second
attempt. If the second shock was ineffective, the lead was repositioned or replaced by a dual-coil lead, and/or the shock vector
was changed, until defibrillation was operational.
Device programming
At discharge, all devices were programmed the same way we do in
our centre with patients with a prophylactic indication of an ICD
for Brugada syndrome,12 or hypertrophic cardiomyopathy, for
example. Tachycardia settings then consisted of two detection
zones: a monitoring zone starting at a frequency of 170 beats
per minute (b.p.m.) or above, and a ventricular fibrillation (VF)
zone at 220 b.p.m. or above (Figure 1). All therapy timers were
set off.
Discrimination algorithms in the monitoring zone were programmed, unless unnecessary such as in patients with complete
atrioventricular block. Standard nominal settings for the number
Figure 1 Defibrillators tachycardia settings at baseline. NID,
number of intervals for initial detection; SVT, supraventricular
tachycardia; VF zone, ventricular fibrillation zone without discrimination algorithms.
of detection intervals were programmed in the Holter zone: 26
intervals with Biotronik (Berlin, Germany) devices (except 16 for
Cardiac Airbag models), 18 intervals with Ela Medical/Sorin
Group (Milan, Italy), 12 intervals with Saint Jude Medical (St Paul,
MN, USA); 16 intervals with Medtronic Inc. (Minneapolis, MN,
USA), and 18 intervals with Guidant/Boston Scientific Corp.
(St Paul, MN, USA) devices.
Shock therapies in the VF zone were at maximum output from
the first shock with nominal settings for detection: after 8 (Biotronik), 12 (St Jude Medical and Ela/Sorin) or 18 (Medtronic) detected
intervals, or 8 of 10 intervals for initial detection and 6 of 10 intervals during a 1 s duration window for therapy delivery (Guidant/
Boston). When available, ATP during charging was programmed.
Bradycardia settings were programmed according to each
patient’s clinical status, in order to limit pacing in single- and dualchamber device patients, and to achieve permanent biventricular
pacing in cardiac resynchronization therapy device recipients.
The local ethics committee approved the programming strategy,
as there is no official guideline or expert consensus on how to programme ICDs tachycardia settings in primary prevention patients.
Additionally, programming in these patients obviously cannot be
based on previous documented spontaneous arrhythmias. Signed
informed consent of all implanted patients was obtained.
Follow-up
All patients underwent a clinical examination, an electrocardiogram, and an interrogation of their device usually 3 months after
discharge, and then at least twice a year. Data were collected
during interrogation consultation, through the computerized
patient file, or by telephone, fax or mail whenever an event occurred in another hospital. All cardiovascular events were then collected. All detected true ventricular episodes in the monitoring
zone were collected. All detected episodes in the VF zone were
collected. Episodes were classified as ventricular, supraventricular,
or noise/oversensing-related events by two electrophysiologists
working blind. Discrepancies between the two interpretations
were found in three episodes in two patients and were discussed
during an additional review so as to reach a final diagnosis [nonsustained ventricular tachycardia (VT) in all cases].
When a ventricular episode was detected in the monitoring
zone, baseline programming was only modified in case of concomitant symptoms, whether the episode was sustained or not. Modification then usually consisted of three bursts of ATP followed by
defibrillation shocks (at 20 J for the first attempt, then at maximum
output) between 170 and 220 b.p.m., with same standard nominal
970
settings for the number of detection intervals. Same modification
was implemented in patients with documented symptomatic
slow VT episodes below the monitoring zone, the VT zone in
that case obviously beginning below the rate of documented VT.
Follow-up ended when death, heart transplantation or definitive
ICD explantation occurred, or at the last consultation dating from
6 months or less on 30 November 2011 for the remaining patients.
Patients were lost to follow-up if the last consultation dated from
.6 months on 30 November 2011.
Outcomes
The key outcome in this study was the presence or absence of any
adverse event related to specific programming, including death,
heart failure, hospitalization, and symptoms (syncope and
pre-syncope).
Freedom from appropriate or inappropriate therapy was also
assessed. All-cause mortality, cardiovascular mortality, sudden
cardiac death, early and late operative morbidity, and ventricular
events in the monitor zone were also assessed.
Statistical analysis
All statistical analyses were performed using JMP (version 8.0, SAS
Institute Inc., Cary, NC, USA).
Descriptive statistics were reported as mean and standard deviation for normally distributed continuous variables. Median was
also reported, when relevant, as the numerical value separating
the higher half of the population from the lower half.
The Kaplan –Meier method was used to analyse survival from
all-cause mortality, and from appropriate or inappropriate
therapies.
Results
Demographics and follow-up
A total of 365 patients were enrolled. Patients’ characteristics at
implantation are reported in Table 1.
Biotronik manufactured the primo-implanted devices in 70
patients (models: 7 Belos, 2 Cardiac Airbag, 11 Lexos, 33 Lumax,
17 Lumos), Sorin Group/Ela Medical in 58 (models: 11 Alto, 42
Ovatio, 5 Paradym), Saint Jude Medical in 78 (models: 47 Atlas, 6
Current, 14 Epic, 2 Photon, 9 Promote), Medtronic in 66
(models: 7 Concerto, 15 Entrust, 9 Insync, 11 Marquis, 4
Maximo, 20 Virtuoso), and Boston Scientific/Guidant in 93 patients
(models: 17 Cognis, 57 Renewal, 5 Teligen, 14 Vitality).
Mean follow-up was 42 + 23 months (median 40 months), i.e.
1278 patient-years. One patient (0.3%) was lost during follow-up
(7 months) because of location change, but was still alive on 30 November 2011 (no death certificate recorded in the city of birth).
Clinical and ICD data dating from 6 months or less were available
for all the remaining (implanted and alive) patients at the end of
follow-up.
Late operative morbidity
During follow-up, ICD device was replaced twice in 2 patients,
once in 66 patients. Replacement cause was battery depletion in
N. Clementy et al.
Table 1 Population baseline characteristics (n5365)
Age (years), mean + SD
Male gender (%)
60 + 10
89
NYHA functional class I/II/III/IV (%)
15/48/36/1
LVEF (%), mean + SD
LVEDD (mm), mean + SD
25 + 7
65 + 8
Ischaemic cardiomyopathy (%)
63
Myocardial infarction (%)
Valvular heart disease (%)
54
3
Matching MADIT II/SCD-HeFT criteria (%)
36/61
PTCA/CABG (%)
Atrial arrhythmia/AV block history (%)
27/10
27/15
Preoperative documented spontaneous
non-sustained VT episode (%)
49
Syncope (%)
17
Single chamber/dual chamber/biventricular devices (%)
Beta-blocker/amiodarone (%)
41/31/28
98/6
AV, atrioventricular; CABG, coronary artery bypass graft; LVEDD, left ventricular
end-diastolic diameter; LVEF, left ventricular ejection fraction; MADIT II,
Multicenter Automatic Defibrillator Implantation Trial II; NYHA, New York Heart
Association; PTCA, percutaneous transluminal coronary angioplasty; SCD-HeFT,
Sudden Cardiac Death in Heart Failure Trial; SD, standard deviation; VT,
ventricular tachycardia.
46 patients, upgrading to a biventricular device in 9 patients, and
during necessary delayed surgical revision in 13 patients. Mean longevity for the devices with a depleted battery was 64 + 12 months,
comparable with the available data.13
Perioperative complications necessitating surgical revision were:
lead dislodgement in 3 patients, pocket infection in 1 patient, and
pocket haematoma in 21 patients.
Delayed complications necessitating surgical revision were: lead
dislodgement in 12 patients, pocket or leads infection in 7
patients, and defibrillation lead fracture in 9 patients. One
patient who had undergone a complete removal of the implanted
material following pocket infection was not reimplanted (followup 15 months).
Appropriate therapies
Mean minimum number of intervals detected in VF zone in
order to treat a ventricular episode (nominal settings) was
12 + 4.
Forty-one patients (11.2%) experienced at least one appropriate
shock during follow-up, 19 for fast VT, 18 for VF or polymorphic
VT, and 4 for both VT and VF episodes (Figure 2). Five patients
out of 48 programmed with this feature experienced successful
ATP during charging on fast VT episodes in the VF zone. Three
patients experienced successful ATP in the VT zone after reprogramming for symptomatic ventricular episodes in the monitoring
zone, or documented slower symptomatic ventricular episodes
,170 b.p.m.
Median time between implantation and first appropriate therapy
was 12 months. Ninety-three per cent of the patients were free of
any appropriate therapy at 2 years (Figure 3).
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High-rate cut-off ICD programming
Figure 2 Distribution of patients according to symptoms and/or episodes detected in the monitoring and/or ventricular fibrillation zones.
*Patient lost during follow-up because of location change, still alive at the end of follow-up. †Patient deceased from unexplained sudden
death, without post-mortem device interrogation and necropsy, and with a previous history of appropriate shocks on ventricular fibrillation
episodes.
No inappropriate shock was related to the potential mechanisms of combined, cumulative, or shared counters within the monitoring zone.14
Median time between implantation and first inappropriate discharge was 22 months. Ninety-six per cent of the patients were
free of any inappropriate shock at 2 years (Figure 3).
Monitored ventricular arrhythmias
Figure 3 Kaplan– Meier analysis of event-free survival for appropriate and inappropriate shocks (mean follow-up 42 + 23
months, median 40 months).
Inappropriate therapies
Twenty-four patients (6.6%) experienced inappropriate shocks, 9
being related to atrial fibrillation, 1 to sinus tachycardia, 2 to
T-wave oversensing, and 12 to noise oversensing (including 7
patients with a defibrillation lead fracture).
Mean minimum number of intervals detected in monitoring zone in
order to record a VT episode (nominal settings) was 18 + 5.
True ventricular episodes long enough to be detected in the
monitoring zone were recorded in 44 patients (12%). Thirty-seven
patients (84%) remained strictly asymptomatic, so device programming was not altered. Among asymptomatic VT episodes, mean
heart rate was 185 + 12 b.p.m. (range 170– 210 b.p.m.) and
mean duration 9 + 3 s (range 6–14 s) (Figure 4).
Only seven patients experienced symptoms (1.9%): six presenting with pre-syncope and one with syncope (Table 2). Three
patients had to be hospitalized. One patient was already hospitalized for decompensate heart failure when the event occurred.
No significant traumatic injury was related to syncope or presyncope, and no patient died. Multiple ATP therapies followed
by shocks were then constantly programmed in the VT zone in
these patients (170–220 b.p.m.). One patient suffered the recurrence of one VT episode and was successfully treated by ATP.
Four patients were hospitalized during follow-up for symptomatic prolonged slow VT episodes below the monitoring zone
(,170 b.p.m.). A slow VT zone with multiple ATP therapies was
added for these patients.
972
N. Clementy et al.
Figure 4 Example of an asymptomatic untreated ventricular tachycardia episode recorded in the monitoring zone. Electrograms at a sweep
speed of 25 mm/s (single-chamber device Lexos VR-T, Biotronik, Berlin, Germany). Average rate is 185 b.p.m., and ventricular tachycardia is
appropriately detected (1) (ventricular tachycardia zone settings: 171 b.p.m., 16 detection intervals + 10 intervals for confirmation, sudden
onset 20%, stability + 24 ms). As the event is detected in the monitoring zone, no therapy is delivered and ventricular tachycardia eventually
terminates spontaneously after 13 s (2).
Table 2 Symptomatic ventricular tachycardia episodes recorded in the monitoring zone (170–220 b.p.m.)
No.
CM/LVEF (%)
Symptoms
Rate (b.p.m.)
Duration (s)
Outcome
Hospitalization
1
2
I/23
I/27
Pre-syncope
Pre-syncope
180
210
12
50
ST
Shocka
No
Yes
3
NI/27
Pre-syncope
195
320
ST
Yesb
4
5
NI/20
NI/30
Pre-syncope
Syncope
172
180
25
30
ST
ST
Yes
Yes
6
NI/23
Pre-syncope
7
NI/25
Pre-syncope
205
8
ST
No
202
10
ST
No
...............................................................................................................................................................................
CM, cardiomyopathy; I, ischaemic; LVEF, left ventricular ejection fraction; NI, non-ischaemic; ST, spontaneous termination.
a
Shock was delivered after progressive spontaneous acceleration of VT into VF zone.
b
The patient was already hospitalized for decompensate heart failure.
Mortality
Sixty-two patients (17%) died during follow-up: 35 from refractory
end-stage heart failure, 1 with previous successfully treated VF episodes from unexplained sudden death (no necropsy or device interrogation), and 26 from documented non-cardiac cause.
Survival of death by any cause was 97% at 1 year, 91% at 2 years,
and 80% at 5 years.
Thirty-two patients (8.8%) underwent successful heart transplantation during follow-up.
Discussion
This is the first long-term study of high-rate cut-off programming in
patients implanted with an ICD in primary prevention for left
ventricular systolic dysfunction. This is also the first large cohort
study with a high-rate cut-off programming over 220 b.p.m.
The main findings of the present study are:
-
A safe programming during a long-term follow-up (median 40
months);
- A rather low rate of both appropriate shocks (11.2%) and
inappropriate shocks (6.6%).
Safety
It had been suggested that high-rate cut-off programming was
potentially dangerous, as it might fail to treat sustained prolonged
VT episodes, with potential lethal consequences.
In our study, during a median follow-up of 40 months, no patient
seemed to experience any fatal consequence from this specific
973
High-rate cut-off ICD programming
programming, although one patient died from unexplained sudden
death. Moreover, most of the significant VT episodes detected in
the monitoring zone were asymptomatic (in 37 out of 44 patients,
i.e. 84%), with spontaneous termination, suggesting that these episodes might not need to be treated. Only a minority of VT episodes in our population were poorly tolerated. Seven patients
(1.9%) experienced such episodes, with syncope or pre-syncope,
and no fatal consequence. It is interesting to note that poor
haemodynamic tolerance was not directly related to duration or
heart rate during the VT episode. Thus, among symptomatic episodes, the lowest VT rate was 172 b.p.m. and the shortest duration
was 8 s, whereas among asymptomatic episodes, the highest VT
rate was 210 b.p.m. and the longest duration was 13 s. These
data confirm that no strategy of programming could anyway
prevent all symptomatic events such as syncope or pre-syncope
in patients with systolic dysfunction. Syncopes are indeed related
in all major ICD trials.
Above 220 b.p.m., haemodynamic tolerance of a high ventricular
rate is usually poor, especially in patients with left systolic dysfunction, and shock therapy should be rapidly delivered. Then, ‘shockbox’ programming, with the absence of discrimination in the VF
zone, and short detection periods, reducing the time from tachycardia onset to treatment delivery, may be then beneficial in
case of rapid ventricular arrhythmias.
The main limitation of assessing safety of such programming is
that one patient died from unexplained sudden death during
follow-up. High-rate cut-off programming might have been
involved in this fatal event if a prolonged ventricular arrhythmia occurred in the monitoring zone, as it may have been the case for
one patient in the PREPARE study.9
Higher or lower?
The incidence of appropriate shocks in our study (11.2% overall,
mean follow-up 42 months) is much lower than in the
SCD-HeFT trial (22.4%, 45 months).15 Despite the obvious differences between our population and those of large trials, the lower
rate of appropriate shocks may be explained by the difference in
programming. In the SCD-HeFT trial, a single VF zone at
188 b.p.m. was programmed (18 of 24 beats), leading to a high incidence of shocks for VT episodes that may have been asymptomatic and non-sustained. Some of these appropriate shocks may
then have been unnecessary therapies on appropriately detected
episodes. Indeed, the PainFREE Rx II trial found that 34% of
the fast VT episodes terminated spontaneously during capacitor
charging.16
Inappropriate shocks are also very frequent with a low-rate
single zone (17.4% in SCD-HeFT), as supraventricular tachycardia
(SVT) episodes are not discriminated. It is now well admitted by
experts that programming a single therapy zone without discrimination (VF zone) below 200 b.p.m. should not be performed in
primary prevention patients, as this strategy is related to a high
rate of both appropriate and inappropriate shocks.17
Monitoring or treating?
A two-zone programming with ATP may not necessarily be more
efficient than single VF zone programming. Duncan et al.,18 in a
retrospective study, compared patients programmed for a single
VF zone (mean . 193 b.p.m.) with patients programmed for two
zones (mean VT zone .171 b.p.m., mean VF zone
.205 b.p.m.). The two-zone group actually received more appropriate shocks than the group with a single VF zone (22 vs. 12%). A
much larger but non-controlled trial, the PROVE Trial, showed a
beneficial effect of ATP in VT zone (182– 222 b.p.m.) with 92%
of true VT episodes successfully terminated. But the price to pay
was a rather high rate of inappropriate shocks at 12 months compared with our study (in 2.5 and 1.9% of the patients,
respectively).19
Finally, ATP programming may not always prevent symptoms, as
it may only delay the occurrence of an efficient therapy.20 It may
also accelerate a non-sustained VT and provoke unnecessary
shock. In a prospective study by Grimm et al.,21 this was the
case in up to 14% of VT episodes and 48% of patients.
Same concerns to inappropriate therapies can be applied. In
MADIT II, the incidence of inappropriate shocks was 11.5%.22 Similarly, in the PainFREE Rx II trial, 15% of the primary prevention
patients had inappropriate therapies, despite the systematic use
of ATP for fast VT episodes (over 188 b.p.m.).16 In the Detect
Supraventricular Tachycardia Study, despite a dual-chamber algorithm, inappropriate therapies remained very frequent, and 31%
of SVTs were inappropriately detected.23 In a recently published
‘real life’ prospective study of 1544 patients (mean follow-up 41
months), ≥1 inappropriate shock occurred in 13% of ICD recipients, which is twice as high as in our study.24 Devices were programmed with a monitoring zone between 150 and 188 b.p.m., a
VT zone with two bursts of ATP between 188 and 210 b.p.m.,
and a shock-only zone above. Inappropriate shocks were related
to SVT or sinus tachycardia episodes in 76% of cases (11.5% of
patients). In the study by Duncan et al.,18 inappropriate shocks
were also more frequent in the two-zone programming group
(10 vs. 2%).
Supraventricular tachyarrhythmia-related inappropriate shocks
were only present in 2.7% of the patients at the end of the
study, which is a very low rate. High-rate cut-off programming is
an expedient programming strategy in this case, as the maximum
ventricular rate during SVT should rarely exceed 220 b.p.m.
Indeed, the majority of inappropriate shocks were related to oversensing (58%). These data are confirmed by the results of the Altitude Reduces Study, which showed a majority of inappropriate
shocks for event rate ,200 b.p.m., and a majority of appropriate
shocks above.25 The authors concluded that increasing rate detection to ≥200 b.p.m. resulted in a four-fold reduction in overall
shock risk of both appropriate and inappropriate therapies, and
was not associated with excess mortality.
Limitations
As this is a registry-based study, it is non-controlled. Therefore, the
benefits of high-rate cut-off programming in reducing the rate of
appropriate or inappropriate therapies cannot be established at
all. The primary objective was actually to assess the safety of
such programming. Further controlled randomized studies will be
necessary to assess the potential beneficial effects.
Patients with shorter intervals of detection in VF zone may then
have experienced more appropriate therapies, although this was
974
not significant in the subgroups analysis (no significant difference
between the 8, 12, and 18 intervals groups).
The low number of patients with true detected VT episodes
may be explained by a high proportion of non-sustained VT episodes lasting less than the number of programmed detection intervals (mean 18 + 4 intervals), which were not recorded in the
devices memories. The high incidence of well-treated patients
(98% under beta-blocking therapy) may also have played a role.
One patient died from sudden death, and as post-mortem interrogation of the device was not performed, although highly unlikely,
a fatal event due to high-rate cut-off programming cannot be ruled
out.
Finally, one patient was lost during follow-up, and adverse events
due to high-rate cut-off programming in this patient cannot be
ruled out, although no fatal event occurred.
Conclusion
High-rate cut-off ICD programming, with a VF zone over
220 b.p.m. and a monitoring zone over 170 b.p.m., in primary prevention patients with reduced LVEF, remained safe during a longterm follow-up. It also resulted in a low rate of both appropriate
and inappropriate shocks, which are known to be deleterious in
these patients and could also be associated with a higher mortality.
Conflict of interest: N.C. received a one-year fellowship (2012)
research grant from St. Jude Medical. The other authors declare no
conflicts of interest.
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