'Effect of CRT on Defibrillation Threshold Estimates' Study

Cardiac Resynchronization Therapy (CRT) has emerged as a promising therapeutic addition in
patients with drug refractory heart failure (HF). Along with providing relief of symptoms of
HF, cardiac resynchronization therapy defibrillators (CRT-D) are used for the prevention of
sudden cardiac death (SCD). Although there are concerns that the defibrillation threshold
(DFT) estimates are elevated in the heart failure (HF) patient population due to lower LV
ejection fraction (EF) and left ventricular (LV) dysfunction, there is paucity of data
available to evaluate this theory.

Recently, two different studies in a retrospective manner evaluated the energy requirements
in patients receiving cardiac resynchronization therapy defibrillators (CRT-D). Burke et al
analyzed DFTs in 50 patients each implanted with a cardiac resynchronization therapy
defibrillators (CRT-D) device and an implantable cardioverter defibrillator (ICD). Although
the ejection fraction (EF) in cardiac resynchronization therapy defibrillators (CRT- D) group
was lower than the implantable cardioverter defibrillator (ICD) group, the mean
defibrillation thresholds (DFTs) between the two groups were not significantly different
(10.2 ± 6.1 J for the cardiac resynchronization therapy (CRT) group vs. 9.5 ± 5.0 J for the
control group)14. In the ASSURE study, Doshi et al. showed that patients receiving cardiac
resynchronization therapy defibrillators (CRT-D) devices do not have higher energy
requirements when compared to patients receiving modern single or dual chamber implantable
cardioverter defibrillators (ICDs). Although, there was a trend toward higher energy
requirements found among patients with higher degrees of heart failure.

Major cardiac resynchronization therapy (CRT) trials have showed that cardiac
resynchronization therapy (CRT) therapy has positive effects on ejection fraction (EF) and
the heart failure (HF) condition of the patient over time. But, there is no study that has
evaluated the defibrillation thresholds (DFTs) in the heart failure (HF) patients over time
of receiving cardiac resynchronization therapy (CRT). This information will help the
clinicians decide if they need to perform more invasive procedures during device implant to
lower DFTs in patients who do not meet the defibrillation safety margin or they should just
wait over time for the CRT to reduce the defibrillation threshold (DFT). Also, there is no
published data about the stability of defibrillation thresholds (DFTs) in heart failure (HF)
patients over time. The results from this study will also help to clarify whether it is safe
to never test the defibrillation thresholds (DFTs) post-implant in this patient population.

Inclusion Criteria:

- Patient meets standard indications for a Cardiac Resynchronization Therapy -
Defibrillator (CRT-D).

- Patient will be implanted with an FDA approved St Jude Medical (SJM) Cardiac
Resynchronization Therapy - Defibrillator (CRT-D) and compatible defibrillation lead
system.

- Patient is able to tolerate defibrillation threshold (DFT) testing.

- Patient is geographically stable and willing to comply with the required follow-up
schedule.

- Patient has a life expectancy of greater than 6 months from the time of implant.

- Patient has stable heart failure (HF) medications at least one month prior to
enrollment.

Exclusion Criteria:

- Inability to successfully implant an intravascular lead Cardiac Resynchronization
Therapy - Defibrillator (CRT-D) device. (i.e. exclude epicardial leads).

- Patient is getting his Cardiac Resynchronization Therapy - Defibrillator (CRT-D)
device replaced.

- Inability to successfully obtain the defibrillation threshold (DFT) at implant.

- Currently participating in a clinical trial that includes an active treatment arm or
another data collection registry.

- Recent (within 24 hours) administration of Nesiritide™.

- Patient is on amiodarone (other antiarrhythmic agents known to affect defibrillation
thresholds - DFTs) at the time of enrollment.

- Patient is pregnant.

- Patient is less than 18 years old.