Inappropriate implantable cardioverter defibrillator shocks—incidence, effect, and implications for driver licensing
Inappropriate implantable cardioverter def ibrillator shocks-incidence, effect, and implications for driver licensing
Eiichi Watanabe 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Katsunori Okajima 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Akira Shimane 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Tomoya Ozawa 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Tetsuyuki Manaka 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Itsuro Morishima 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Toru Asai 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Masahiko Takagi 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Toshihiro Honda 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Atsunobu Kasai 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Eitaro Fujii 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Kohei Yamashiro 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Ritsuko Kohno 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Haruhiko Abe 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Takashi Noda 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Takashi Kurita 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Shigeyuki Watanabe 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Hiroya Ohmori 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Takashi Nitta 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Yoshifusa Aizawa 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Ken Kiyono 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
Ken Okumura 0 1 2 3 4 5 6 8 9 10 11 12 13 14 15 16 17 18
0 Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center , Suita , Japan
1 Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science , Otsu , Japan
2 Department of Cardiology, Himeji Cardiovascular Center , Himeji , Japan
3 Department of Heart Rhythm Management, University of Occupational and Environmental Health , Kitakyushu , Japan
4 Department of Cardiology, Tsukuba University Hospital Mito Education and Training Center , Mito , Japan
5 Department of Cardiology, Fujita Health University School of Medicine , Dengakugakubo 1-98, Kutsukake-cho, Toyoake, Aichi 470-1192 , Japan
6 Department of Medicine, Faculty of Medicine, Division of Cardiovascular Center, Kinki University School of Medicine , Osaka-Sayama, Osaka , Japan
7 Eiichi Watanabe
8 Cardiovascular Medicine, Toyohashi Heart Center , Toyohashi , Japan
9 Department of Cardiology, Ise Red Cross Hospital , Ise , Japan
10 Division of Cardiology, Saiseikai Kumamoto Hospital Cardiovascular Center , Kumamoto , Japan
11 Department of Research and Development, Tachikawa Medical Center , Nagaoka , Japan
12 Department of Cardiovascular Medicine, Osaka City University Graduate School of Medicine , Osaka , Japan
13 Department of Cardiovascular Surgery, Nippon Medical School , Tokyo , Japan
14 Department of Cardiology, Ichinomiya Municipal Hospital , Ichinomiya , Japan
15 Department of Cardiology, Hirosaki University Graduate School of Medicine , Hirosaki , Japan
16 Department of Cardiology, Ogaki Municipal Hospital , Ogaki , Japan
17 Division of Bioengineering, Graduate School of Engineering Science, Osaka University , Toyonaka , Japan
18 Department of Cardiology, Tokyo Women's Medical University , Tokyo , Japan
Purpose Patients with implantable cardioverter defibrillators (ICDs) have an ongoing risk of sudden incapacitation that may cause traffic accidents. However, there are limited data therapies. We studied the rate of syncope associated with inappropriate ICD therapies to provide a scientific basis for formulating driving restrictions. Methods Inappropriate ICD therapy event data between 1997 on the magnitude of this risk after inappropriate ICD and 2014 from 50 Japanese institutions were analyzed This study was registered in the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) 000025995.
Department of Cardiology and Nephrology, Mie University Graduate
School of Medicine, Tsu, Japan
retrospectively. The annual risk of harm (RH) to others posed
by a driver with an ICD was calculated for private driving
habits. We used a commonly employed annual RH to others
of 5 in 100,000 (0.005%) as an acceptable risk threshold.
Results Of the 4089 patients, 772 inappropriate ICD therapies
occurred in 417 patients (age 61 ± 15 years, 74% male, and
65% secondary prevention). Patients experiencing
inappropriate therapies had a mean number of 1.8 ± 1.5 therapy episodes
during a median follow-up period of 3.9 years. No significant
differences were found in the age, sex, or number of
inappropriate therapies between patients receiving ICDs for primary
or secondary prevention. Only three patients (0.7%)
experienced syncope associated with inappropriate therapies. The
maximum annual RH to others after the first therapy in
primary and secondary prevention patients was calculated to be
0.11 in 100,000 and 0.12 in 100,000, respectively.
Conclusions We found that the annual RH from driving was
far below the commonly cited acceptable risk threshold. Our
data provide useful information to supplement current
recommendations on driving restrictions in ICD patients with private
Implantable cardioverter defibrillators (ICDs) improve
survival in patients at risk of sudden cardiac death [
these patients have an ongoing risk of sudden incapacitation
that may cause harm to themselves and others when driving
]. An obvious concern is the effect of arrhythmias and/or
discharges of devices on a patient’s level of consciousness and
ability to drive. According to the literature, the rate of syncope
or loss of consciousness associated with appropriate ICD
therapy varies from 2 to 15% [
]. Approximately 10–
20% of ICD patients experience inappropriate ICD therapies
(therapies delivered for non-ventricular arrhythmias)
according to the previous reports [
]; however, few studies
have studied the rate of syncope or loss of consciousness as a
result of inappropriate therapy. Thus, a large variation exists
among countries concerning driving restrictions following
inappropriate ICD therapies [
Currently, inappropriate therapy reduction programming,
including higher detection rates, longer detection intervals,
and optimized supraventricular tachycardia discriminators,
have been reported to reduce ICD shocks without increasing
the arrhythmic syncope among ICD patients for primary
]. Although such shock reduction
programming is beneficial, it may take time for this programming to
spread to the actual clinical setting.
It is critical to collect data regarding the rate of the
incidence that lead to impaired driving after inappropriate ICD
therapy to prevent serious driving accidents, while at the same
time avoiding unnecessary driving restrictions on patients
with ICDs for both primary prevention and secondary
prevention. We set two objectives: (1) to identify the rate and causes
of syncopal episodes associated with inappropriate ICD
therapy and (2) to calculate the risk of harm to other road users in
order to provide a scientific basis for driving restrictions in
We analyzed the inappropriate ICD therapy event data
between 1997 and 2014. This retrospective, observational,
non-randomized study was conducted at 50 institutions
participating in prospective ICD studies [
] and Japanese
Heart Rhythm Society board-certified institutions
(participants’ list in Supplementary File). The ethics committee of
each institution approved the study protocol, and all patients
gave their written informed consent. The study complied with
the Declaration of Helsinki and its later amendments or
comparable ethical standards.
2.1 Database and ICD therapy event analysis
The Japanese Heart Rhythm Society board-certified
electrophysiologists at the 50 institutions were asked to submit a total
number of ICD implantation and case report form for the
patients who had inappropriate therapies after the initial
implantation. It included the patient demographics, underlying
disease, comorbidities, ventricular function, and medications.
The data regarding the ICD included the date and indication
for the implantation, date and time of the onset of any
appropriate or inappropriate therapies, cause, and type of
inappropriate therapy, in addition to the activity associated with the
inappropriate therapy. Finally, we asked them whether or not
each inappropriate ICD therapy was associated with syncope.
The implanted system manufacturers were Biotronik (Berlin,
Germany), Boston Scientific (St. Paul, MN, USA), Medtronic
(Minneapolis, MN, USA), and St. Jude Medical (St. Paul,
MN, USA). All ICDs in this study were equipped with
intracardiac electrogram (EGM) storage. The ICDs were
interrogated every 3 months and when clinically appropriate, such as
after a delivered therapy. ICD therapies were defined as either
antitachycardia pacing (ATP) or shock therapy, including
cardioversion and defibrillation. Therapies were categorized as
appropriate when they occurred in response to ventricular
tachycardia (VT) or ventricular fibrillation (VF) and as
inappropriate. An inappropriate therapy included therapy for atrial
fibrillation (AF), supraventricular tachycardias (SVTs),
including sinus tachycardia, abnormal sensing (T wave
oversensing, myopotential, and electromagnetic interference,
other than oversensing of short VV intervals related to lead
fractures), and lead failures [
]. The determination of an
inappropriate or appropriate ICD therapy was made by the
electrophysiologists at the participating institutions and
was not adjudicated by independent electrophysiologists.
The ICD programming was left to the discretion of each
investigator. We did not exclude patients in whom the
generator or leads were replaced. A syncopal event associated
with inappropriate therapies was the primary endpoint and
was defined as a total loss of consciousness with
spontaneous recovery. These events were identified through
reviewing the medical charts. We excluded syncopal
episodes not related to inappropriate therapies. The time to the
first inappropriate therapy was measured from the date of
the ICD implant to the date of an inappropriate ICD
therapy. The time to the second therapy was measured from the
date of the first inappropriate ICD therapy to the date of the
second inappropriate therapy. Regarding the second
therapy analysis, only subsequent inappropriate therapies
occurring >24 h after the first inappropriate therapy were
considered to be second therapies.
2.2 Risk assessment
The Canadian Cardiovascular Society Consensus Conference
published a Brisk of harm^ (RH) formula to quantify the level
of risk to drivers with ICDs according to the Ontario Road
Safety Annual Report [
]. It has been used in several other
5, 9, 16, 19, 22, 30
]. The following equation is the risk
of harm formula: RH = TD × V × SCI × Ac, which calculates
the yearly RH to other road users posed by a driver with heart
disease; TD equals the proportion of time the patient spends
driving during the year (0.04 for private drivers, 0.25 for
commercial drivers); V is a vehicle-specific constant based on the
type of vehicle driven (1.0 for a commercial heavy truck and
0.28 for a standard-size passenger car); SCI is the annual
probability of sudden incapacitation, and Ac is the probability
of injury or an accident after the SCI. We used an Ac of 0.02
according to the previous studies [
]. In this study, the
yearly risk of SCI was calculated to be 0.13 for primary
prevention and 0.14 for secondary prevention, respectively, based
on the incidence of syncope associated with inappropriate
ICD therapies (i.e., 1 out of 144 patients for primary
prevention and 2 out of 273 patients for secondary prevention)
divided by the mean follow-up period of 5.3 years. Standard
errors were derived from the binomial distribution, and the
95% confidence interval was constructed with the normal
approximation according to the previous study . We
calculated the RH after the first and second shocks, respectively, along
with the previous study [
]. An acceptable RH was defined to
be 5/100,000 or 0.005% [
8, 9, 16
2.3 Statistical analysis
The χ2 test or Fisher exact test was used for categorical data,
and a Student’s t test or Mann–Whitney test was used for
continuous variables. Comparisons of the time to therapy were
made using the Kaplan–Meier method and compared with the
log-rank test. Quantitative data are expressed as the
mean ± standard deviation (SD) values or median with an
inter-quartile range. A two-tailed p value of <0.05 was
considered significant. Statistical analyses were performed using
JMP 10.0.2 software (SAS Institute, USA) and R Project for
Statistical Computing 3.2.2.
3.1 Clinical characteristics of the patients
The baseline characteristics of the patients are summarized in
Table 1. Of the 4089 patients, 772 inappropriate ICD therapies
occurred in 417 patients (age 61 ± 15 years, 74% male, and the
reason for the implantation was secondary prevention in
65%). No significant differences were noted in the age, sex,
and baseline cardiac rhythms between the primary and
secondary prevention patients. There was a significant difference
in the prevalence of single-chamber or dual-chamber ICDs
and cardiac resynchronization therapy with defibrillators
(CRT-Ds) between the primary and secondary prevention
patients. Coronary artery disease was observed in 20% of
patients, and the mean left ventricular ejection fraction was 45%.
The median date of the implantation was November 2010, and
approximately 90% of the patients received ICDs after 2005
3.2 Inappropriate ICD therapies
Patients experiencing inappropriate therapies had a mean
number of 1.8 ± 1.5 inappropriate therapy episodes during a
median follow-up period of 3.9 [inter-quartile range, 3.1 to
6.8] years (Table 2). A total of 169 patients (41%) had more
than 1 inappropriate therapy, with a maximum of 15
inappropriate therapies. There were no significant differences in the
number of inappropriate therapies between the primary
prevention and secondary prevention patients (1.7 ± 1.7 vs.
1.9 ± 1.6, p = 0.13). The first inappropriate therapy occurred
a median of 382 days after the implantation (inter-quartile
range, 85 to 841 days). The median time between the first
and second inappropriate therapies was 117 days
(inter-quartile range, 25 to 408 days). There was a significant difference
in the time to the first inappropriate therapy between the
primary prevention and secondary prevention patients (median
314 vs. 401 days, p < 0.01). The time-dependent occurrence of
Data represent the number, frequency, or means ± SD. Chronic kidney disease = estimated glomerular filtration rate <60 mL/min/1.73 m2
ICD implantable cardioverter defibrillator, CRT-D cardiac resynchronization therapy with defibrillator, ARVC arrhythmogenic right ventricular
cardiomyopathy, VHD valvular heart disease, ACE-I angiotensin-converting enzyme inhibitor, ARB angiotensin II type 1 receptor blocker
the first and second inappropriate therapies for primary and
secondary prevention is shown in Fig. 1.
The total number of inappropriate therapies by the
mechanism rather than by the patient and the subclassifications of
inappropriate therapies are shown in Table 3. SVT was the
most common mechanism for an inappropriate therapy
(63%), followed by AF (27%) and abnormal sensing (7%).
A small percentage of rhythms triggering ICD therapies (2%)
were unclassified. There was no significant difference in the
type of inappropriate therapies between the primary and
secondary prevention patients. In this study, 373 patients
(89%) had one mechanism of inappropriate therapy, 38 (9%)
had two mechanisms, and 6 (1%) experienced all three
3.3 Rate of syncope and risk of harm
Three patients (0.7%) experienced syncope associated with
inappropriate therapies. Two of these patients had syncope,
one during an SVT and the other during sinus rhythm and
oversensing, both of which degenerated to VF, as a result of
the inappropriate therapies. The latter case is presented in Fig.
2. The remaining patient who was implanted with a
dualchamber ICD for primary prevention had syncope due to AF
with a rapid ventricular response, which was terminated by
shock therapy. These three syncope patients did not have any
further episodes of syncope with ICD therapies. In this study,
only one patient experienced a shock for SVT while driving a
motor vehicle, but did not experience any syncope nor cause
an accident on the road. Further, no patients had any syncope
or deaths related to motor vehicle accidents. For private
driving habits, the maximum annual RH of the first and second
inappropriate therapies in the primary prevention patients was
calculated as 0.12 in 100,000 and 0.15 in 100,000,
respectively. Also, that in the secondary prevention patients was
calculated as 0.12 in 100,000 and 0.16 in 100,000, respectively.
These RH values were found to be far below the acceptable
level of 5 in 100,000 (Fig. 3).
In this study, we presented data on the RH posed by
individuals with ICDs toward other users of the road based on the rate
of syncope associated with an inappropriate ICD therapy. We
showed that the annual RH from driving was far below the
commonly cited acceptable risk threshold. Our data may
provide useful information to supplement the current
recommendations on driving restrictions in ICD patients with private
The mean age of the study patients was 61 years, which
was comparable to a previous observational study by van Ree
et al. [
] (mean age, 61 years) that characterized
inappropriate ICD therapies and a recent randomized study of the
MADIT-RIT trial [
] (mean age of the conventional group,
63 years), but somewhat older than that in the subgroup
analysis of the SCD-HeFT trial [
] (median age, 57 years).
Further, in this study, the rate of single-chamber ICDs in
Fig. 1 The time-dependent occurrence of an inappropriate therapy. a
Primary prevention. The first inappropriate therapy occurred at a
median time of 314 days (inter-quartile range, 64 to 697 days) after the
implantation. The median time between the first and second inappropriate
therapies was 85 days. b Secondary prevention. The first inappropriate
therapy occurred at a median time of 401 days (inter-quartile range 97 to
1040 days) after the implantation. The median time between the first and
second inappropriate therapies was 123 days
Data represent the number and frequency
SVT supraventricular tachycardia, AF atrial fibrillation, ATP antitachycardia pacing, VT ventricular tachycardia, VF ventricular fibrillation
primary prevention was 12%, which was lower than that in the
recent ICD registries ranging from 23 to 39% [
potential explanation for the differences in the age and lower
use of single-chamber ICDs for primary prevention may be
found within the evolving and expanding guidelines for the
implantation of ICDs over a 17-year period, device
programming, and (non-) pharmacological treatment of arrhythmias or
other unknown confounders. Our data indicated that the
most common cause of inappropriate therapy was SVT,
which included sinus tachycardia, followed by AF. We
made every effort to identify the mechanism of the SVT,
but missing or incomplete data hampered the complete
clarification of the SVT.
There is a wide variation in the driving restrictions after
inappropriate ICD therapies among countries. In the USA,
scientific statements showed that a private driver must refrain
from driving for 6 months after receiving any ICD therapy,
regardless of whether the therapy is appropriate or
]. In the UK, a patient must cease from driving for
1 month after the cause of inappropriate therapy has been
corrected . In Europe, no time frame is set; however, the
patient is not allowed to drive until the cause of the
inappropriate therapy is resolved [
]. According to the previous
Japanese driving restrictions, ICD patients were advised
not to drive for 12 months after receiving either appropriate
or inappropriate therapies [
], but from 2017, ICD
patients do not have to refrain from driving after receiving
an inappropriate ICD therapy if it is not associated with a
loss of consciousness [
Two recent studies calculated the RH using the data on the
incidence of syncope associated with appropriate therapy [
]. Merchant et al. showed that if they used a contemporary
estimate for syncope associated with an appropriate ICD
shock of 14%, the RH fell below the threshold at 1 month
after an initial shock . Few reports, however, have
calculated the RH because the data on the rate of inappropriate ICD
therapy-related syncope are scarce. To the best of our
knowledge, for the first time, we have provided data demonstrating
that the maximum annual RH posed by ICD drivers to other
users of the road after a first therapy for primary and second
prevention was far below the cutoff level proposed by the
Canadian consensus [
]. The RH formula was developed in
Fig. 2 An ICD-stored intracardiac electrogram. A 61-year-old man that
had dilated cardiomyopathy and chronic hemodialysis received an ICD
(Secura DR, Medtronic) for secondary prevention in 2009. In 2011, he
had chest discomfort and unconsciousness, followed by a shock delivery
at work. A stored electrogram shows that the sinus tachycardia with T
wave oversensing with a cycle length of 330 ms triggers a burst of ATP
(① VT Rx 1 Burst, cycle length of 280 ms). This results in an acceleration
to a tachycardia with a 250 to 320-ms cycle length, with a subsequent
burst of ATP (② VF Rx 1 Burst During Charging, cycle length of
250 ms). This therapy degenerated the VT into VF, which required
shock therapy for termination (③ 35.3 J). His creatinine was 12.1 mg/
dL, and serum potassium was 7.0 mmol/L at admission. The upper and
lower electrograms are continuous recordings. ATP antitachycardia
pacing, VT ventricular tachycardia, VF ventricular fibrillation
order to quantify the level of risk for drivers with cardiac
disorders and to provide an objective and theoretical method
for assigning risk to a driver [
]. The RH analysis was
performed based upon the data from the early Ontario Road
Safety Annual Report [
]; it is important to understand that
there may be some differences among geographic areas due to
the variation in the population density, driving habits, and type
of vehicles. Although we have no data on the driving
parameters (i.e., TD, V, or Ac) in Japan, it is feasible to implement
contemporary area-specific driving parameters to calculate the
RH to other users of the road. Driving restrictions are useful to
protect the society from harm, but they should be balanced
against the QOL of the ICD patients, which may be reduced
by unnecessary driving restrictions. To accomplish this, up to
date clinical evidence is required.
In this study, there were 5 episodes of VT and 12 episodes
of VF as a result of inappropriate ICD therapies. Of those, two
patients lost consciousness due to inappropriate ICD therapies
for SVTs or abnormal sensing degenerating into VF. While
ATP is highly effective in terminating VT and lowers the use
of high-energy shocks, ATP may degenerate stable
arrhythmias into VF and hence result in incapacity prior to the
delivery of the shock [
11, 34, 35
]. A prospective study of 770
primary and secondary prevention ICD patients revealed that
Fig. 3 The annual risk of harm from an inappropriate ICD therapy. The
risk of harm (solid lines) is calculated in years following the implantation
or following the first inappropriate shock. The dotted lines represent the
95% confidence interval. a Primary prevention. Driving is acceptable
directly following an implantation (blue line) (0.11/100,000) or
following the first inappropriate shock (red line) (0.15/100,000). b
Secondary prevention. Driving is acceptable directly following an
implantation (blue line) (0.12/100,000) or following the first
inappropriate shock (red line) (0.16/100,000)
in patients receiving ATP for termination of a fast VT, syncope
occurred in 0.2% of cases [
]. In the PITAGORA ICD trial,
the incidence of a fast VT-related syncope following ATP was
]. These observations were similar to the rates
observed in our study.
In this study, one patient experienced a shock while driving
a motor vehicle, but did not report any syncope nor cause a
traffic accident. An observational study of 241 ICD patients
followed for 36 months found that 5% of secondary
prevention patients had ICD shocks while driving but did not report
any syncope during these shocks [
]. Data from the
Antiarrhythmics Versus Implantable Defibrillators trial
showed that 8% of drivers experienced ICD shocks while
driving without leading to an accident on the road [
According to an early survey of ICD implanting physicians
in the USA, there were a total of 30 motor vehicle accidents
related to shocks from ICDs over a 12-year period [
those, nine were fatal accidents (eight patients with ICDs
died); further, the estimated motor vehicle fatality rate for
patients with ICDs of 7.5/100,000 patient-years was
significantly lower than that for the general population (18.4/
100,000 patient-years). From these results, we can conclude
that ICD patients with secondary prevention may
experience vehicle accidents due to arrhythmias or ICD
discharges, but the occurrence rate is quite small, and the
relative safety of driving with ICDs is supported [
Few studies, however, have specifically examined the rate
of syncope or ICD discharges while driving in patients
receiving ICDs for primary prevention.
4.1 Study limitations
This study was a retrospective observation, and there are
confounders associated with such a study method. Underreporting
is another limitation since the occurrence of syncope was
determined by only a chart review. It has been well documented
that patients often drive despite instructions not to do so, and it
can be anticipated that they do not tell doctors about
symptoms if they think reporting would lead to curtailment of their
driving. Because of the long time span, going back to 1997,
there is a heterogeneous patient population with regard to
programming, but it is certainly encouraging to see a low
event rate given the change in the detection algorithms and
recommendations for programming for a shock reduction that
has occurred in the more recent years. Data regarding the
device therapies have been reported by the participating
electrophysiologists and were not adjudicated by an independent
committee. ICD programming was left to the discretion of
each investigator. We could not assess the drivers’ licensing,
driving habits, and driving times. A near syncopal event while
driving may result in a motor vehicle accident, but we did not
collect data on near syncope. We do not have data on the rate
of post mortem interrogations. Earlier ICDs were not
equipped with EGM storage, and the programming options
were limited. We collected data back to 1997 and ascertained
that all ICDs in this study were equipped with EGMs.
However, a more contemporary cohort would provide a more
accurate estimation of the current risks. It is important to
compare the rate of syncope between inappropriate and
appropriate therapies, and the risk of harm. In the present study,
however, we focused on the rate of syncope associated with
inappropriate ICD therapy. Actually, we examined the number of
appropriate therapies in this population, but we did not try
to determine the rate or cause of syncope associated with
appropriate ICD therapies. We will examine the rate of
syncopal events associated with appropriate ICD therapy
in the near future.
We demonstrated that a small number of patients (0.7%)
experienced syncope associated with inappropriate ICD
therapies, with an estimated maximum annual risk of harm that was
far below the commonly cited acceptable risk threshold of 5 in
100,000. This observation suggests that in the case of private
driving habits, there may be no need for driving restrictions
following inappropriate ICD therapies, if it is not associated
with a loss of consciousness.
Acknowledgements The authors thank Ms. Yoko Sato at the JHRS and
Mr. Masaru Yamamoto and Dr. Yoshihiro Sobue for the data
management. This work was supported by JSPS KAKENHI Grant Number
Compliance with ethical standards
Conflict of interest Dr. Kurita discloses being on the speakers’ bureaus
for Daiichi-Sankyo, Bayer Schering Pharma, Bristol Myers, Boehringer
Ingelheim, Medtronic Japan, St. Jude Medical Japan, and Biotronik
Japan. All other authors have no disclosures for this work.
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