From Hartford HealthCare, Heart & Vascular Institute, Hartford,
Connecticut
Funding sources: The author has no funding sources to disclose.
Conflict of Interest: The author is a consultant and a speaker for
Medtronic.
Address reprint requests and correspondence: Dr Steven Zweibel, Hartford
HealthCare Heart & Vascular Institute, 65 Memorial Road, Suite 405,
West Hartford CT 06107. E-mail address: steven.zweibel@hhchealth.org.
It is well known that patients receiving implantable cardioverter
defibrillators are at risk for developing atrial fibrillation (AF) given
their increased incidence of structural heart disease, heart failure,
and other comorbidities.1 Rates of new onset AF after
ICD implant range from 10 to 45% over 6 months to 2.5 years after
device implantation.2-7 As AF may place patients at
increased risk for inappropriate device therapy, some
electrophysiologists consider implanting a dual chamber ICD in patients
without a history of atrial arrhythmias despite the increased cost and
risk of complications.10 Beyond informing arrhythmia
discriminators, the presence of an atrial lead provides valuable
information by recording episodes of atrial arrhythmias which may
otherwise be clinically silent. As device detected AF (DDAF) lasting
between 5 minutes and 24 hours in patients with an annual rate of AF
between 1.5% and 5% is associated with an increased risk of a
thromboembolic event (HR ranging from 2.2 to 5.0)2,3,6,8,9 data about clinically silent AF is vital.
The lack of an atrial lead arguably puts clinicians at a disadvantage in
assessing the presence of silent AF in patients with single chamber
ICDs. As many of these patients have significant risk factors for stroke
- including AF - what we don’t know may harm our patients.
In this issue of the Journal of Cardiovascular Electrophysiology ,
Patel et. al. examines a new ventricular based AF detection algorithm
present in single chamber ICDs (Medtronic Visia AF devices) to quantify
the device-detected daily burden of AF and report on clinical actions
taken after DDAF was recorded.13 291 patients were
enrolled from Medtronic’s Product Surveillance Registry over a period of
about 4 years with a mean follow-up of 22.5 ± 7.9 months. 212 of these
patients had no prior history of AF at the time of device implant. Since
the device detects AF as an irregular ventricular response, atrial
flutter and atrial tachycardia that conduct irregularly to the
ventricles could also be detected. As the algorithm detects episodes
lasting 6 minutes or longer, episodes with shorter duration may be
undetected. Episodes of DDAF were adjudicated by an independent panel of
electrophysiologists on the patient level – so if a patient had one
episode that was deemed to be consistent with AF, all episodes that were
recorded as AF were also deemed to be true DDAF. Of the 212 patients
enrolled, 66% were male with a mean CHADS2-VASc score
of 3.3 ± 1.6 and a mean left ventricular ejection fraction of 33 ± 13%.
The total incidence of any duration of AF (≥ 6 minutes) in patients
without any prior history of AF was 38% with the median time to the
first episode of DDAF being 104 days. At one year follow-up after device
implantation, the Kaplan Meier rates of DDAF with daily burden ≥ 6
minutes, > 6 hours, and >23 hours were 33%,
10%, and 3% respectively. At 2-year follow-up after device
implantation, the rates of DDAF with daily burden ≥ 6 minutes,
> 6 hours, and >23 hours were 41%, 13%, and
7% respectively. After independent review of these DDAF episodes it was
determined that true AF was documented in 100% of the >23
hours, 75% of the > 6 hours, and 40% of the ≥ 6 minutes
cohorts. So all recorded episode of AF lasting more than 23 hours were
true AF. Of the 80 patients with DDAF episodes ≥ 6 minutes,
unfortunately only 23 patients were further evaluated for a clinical
diagnosis, assessment of clinical symptoms, and to record actions taken
in response to DDAF. The majority (17/23) of these patients were found
to be asymptomatic, 9 patients were newly initiated on oral
anticoagulation therapy (with all patients in the >23 hour
burden category being anticoagulated), and 2 were initiated on
antiarrhythmic drug therapy. The authors found that while clinical
action was taken across the whole spectrum of
CHADS2-VASc scores, more clinical action was taken for
those patients with higher AF burden. They conclude that continuous AF
monitoring with this new ventricular based AF detection algorithm in the
Visia AF ICDs permits early identification and actionable treatment for
patients with undiagnosed AF.
This study demonstrates that patients receiving single chamber ICDs have
a significant incidence of AF. The novel algorithm present in Visia AF
is effective at detecting these episodes. However, significant questions
remain. For example, does clinically-silent AF detected by a CIED carry
the same risk of stroke as AF that is clinically manifest? And what
percentage of AF burden recorded by a device should prompt the
initiation of anticoagulation? Kaplan et. al. studied the risk of stroke
and systemic embolism (SSE) as a function of AF duration and
CHADS2-VASc score in patients with cardiovascular
implantable electronic devices (CIEDs) using medical record data from
the Optum de-identified EHR linked to the Medtronic CareLink
database.14 They found that among 21,768
nonanticoagulated patients with CIEDs, both increasing AF duration and
increasing CHADS2-VASc score were significantly
associated with annualized risk of SSE. SSE rates were low
(<1% per year) in patients with CHADS2-VASc
scores of 0 to 1 regardless of the device-detected AF duration. However,
stroke risk exceeded a rate of 1%/year in patients with a
CHADS2-VASc score of 2 and an AF duration
>23.5 hours, those with a CHADS2-VASc score
of 3 to 4 and an AF duration >6 minutes, and in patients
with a CHADS2-VASc score of ≥5 even with no AF. This
suggests a strong association between the CHADS2-VASc
score and the future risk of stroke with some role for the duration of
AF detected by the CIED. Al-Gibbawi et. al. studied 384 patients with
CIEDs with atrial leads who were not anticoagulated and noted that the
incidence of stroke or TIA was 14.8% over 3.2 years but was not
associated with the burden of AF or with the longest episode of AF but
was strongly associated with the CHADS2-VASc
score.15 This study suggests that once AF is detected
on a device, regardless of duration, the decision to initiate
anticoagulation on a patient should be based off of the
CHADS2-VASc score.
Fortunately, on-going trials are exploring the question of when patients
with CIED detected AF should be anticoagulated. The Artesia Study
(ClinicalTrials.gov Identifier NCT01938248) is examining the potential
benefit of apixaban versus aspirin in patients with sub-clinical AF (≥
175 bpm atrial rate and ≥ 6 minutes duration) detected by their
implantable cardiac device in the prevention of stroke and systemic
embolism. The NOAH-AFNET 6 Study (ClinicalTrials.gov Identifier
NCT02618577) is examining the potential benefit of edoxaban versus
aspirin or a placebo in patients with atrial high-rate episodes (≥ 170
bpm atrial rate and ≥ 6 minutes duration) detected by their implantable
cardiac device in the prevention of stroke, systemic embolism, and
cardiovascular death. Until the results of these trials are published,
it is reasonable to utilize the patient’s risk profile for a
thromboembolic event, as measured by their CHADS2-VASc
score, to assist in the decision-making process once AF is detected by
their device. Having an algorithm in single chamber ICDs that can
reliably detect AF and allow us to have these conversations with our
patients to help make informed decisions is critically important. After
all, what we don’t know about our patients could indeed bring them harm.
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