Arrhythmia
Diagnosis Following an ICD Shock: Comment
Pual A. Levine MD, FACC.
Address for correspondence: Paul
A. Levine, M.D., St. Jude Medical CRMD, 15900 Valley View Court,
Sylmar, California 91342, USA, Tel:
1-818-493-2900 Fax:
1-818-362-2242 Email: plevine@sjm.com
This case study by Dr. John1 demonstrates the care that one must take
in programming
an implantable cardioverter defibrillator, the complexity of these
patients
and the utility of the internal diagnostics in the system to facilitate
the
physician's understanding of device behavior. Even the single chamber
ICDs
have SVT discrimination algorithms that can be enabled in an effort to
differentiate
SVT from VT allowing the device to withhold ATP and shock therapy in
the
setting of an SVT. Many physicians, myself included, will initially
utilize
these discriminators in a monitoring mode preferring to deliver
unnecessary
therapy rather than inappropriately withholding needed therapy. This
also
provides an opportunity to better understand all the rhythms that may
be
occurring in a patient, many of which may not have been appreciated
prior
to the implant. After one or more SVT episodes have occurred and the
clinician
has a chance to review the stored electrograms (first introduced by
Ventritex)
along with the response of the device to any discriminators, a decision
can
be made as to how the ICD prescription might be adjusted.
My examination of the stored electrogram
documenting the initial atrial fibrillation episode suggests
significant irregularity of the ventricular response. As such, had the
stability criteria been enabled, it is likely that the system would
have appropriately recognized the rhythm as atrial fibrillation and
withheld therapy. If the stability criteria
had been programmed to the monitoring mode, the retrieved information
would
have indicated that the diagnosis was supraventricular but therapy was
delivered because the discriminator was not active. A further
refinement in single chamber and more recent dual chamber ICDs is a
feature called morphology
discrimination. This would allow the device to separate a rapid
irregular
ventricular response falling within the VT rate zone associated with
atrial
fibrillation from polymorphic ventricular tachycardia. Given the
complexity
of these patients, if atrial fibrillation was hemodynamically
compromising,
it might be appropriate to not enable any discrimination algorithms.
Dr.
John indicates that amiodarone was not tolerated and other drugs have
both
a higher incidence of side effects and lower efficacy rate. If the
episodes of atrial fibrillation were not frequent, another option would
be to allow the AF to trigger ATP therapy which was arrhythmogenic but
then take advantage of the subsequent shock to not only terminated the
induced-VT but also terminate the atrial fibrillation as occurred in
this case.
References
1. Roy
M. John. Arrhythmia Diagnosis Following an ICD Shock.. Indian Pacing
and Electrophysiology Journal; 2001;1(1):5.
