The REACT-ICD Trial

Atrial tachyarrhythmias (ATA) and heart failure (HF), which are well-recognized causes of
morbidity and mortality, are growing and concerning issues in our patient population. In
patients implanted with a dual-chamber implantable cardioverter defibrillator (ICD),
progression of paroxysmal to persistent or permanent atrial fibrillation (AF) has been
documented. Because of the untoward consequences of AF, such as development/worsening of HF
or thromboembolic events (stroke and myocardial infarction [MI]), prevention of permanent AF
has the potential to improve quality of life, reduce hospitalizations, and decrease the
complications associated with AF.

Recent advancements with implantable cardiac device technology include extensive diagnostic
and therapeutic algorithms for prevention as well as termination of ATA. Preventive atrial
pacing (PAP) and a novel atrial antitachycardia pacing algorithm (Reactive ATP™) in
conjunction with managed ventricular pacing (MVP) recently has been shown to reduce
progression to permanent AF in pacemaker patients with intact atriovenous (AV) conduction
and a history of ATA. Results of that study suggested that Reactive ATP™ specifically was
responsible for this effect. Whether the use of Reactive ATP™ for reducing AF burden extends
to patients with an implantable cardioverter defibrillator (ICD), who typically have
structural heart disease and HF, is unknown.

The aim of this study is to evaluate the effectiveness of atrial antitachycardia pacing
(Reactive ATP) in patients implanted with either a dual-chamber or cardiac resynchronization
therapy (CRT) ICD who have a history of ATA.

Inclusion Criteria:

- male and female patients

- ≥18 years old (no upper age limit)

- previously implanted with a Medtronic dual-chamber or CRT ICD with capability of
atrial antitachycardia pacing; specifically, Reactive ATP™ at least 9 months
previously (six months data collection and implant occurring at least 3 months
previously to allow healing and establishment of stable sensing)

- measured P wave in sinus rhythm of at least 0.8 mV

- >=6 months AT/AF burden data available, either from CareLink® or in-office
interrogation

- >=1.0% AT/AF burden (hours in atrial fibrillation/total hours monitored) in the last
6 months

- No change in antiarrhythmic drug therapy (Vaughan-Williams class I or III) in the
last 6 months

Exclusion Criteria:

- Persistent or permanent AT/AF (AF burden >95%)

- Cardioversion for atrial fibrillation or atrial flutter within the last 6 months,
either intentional or as a result of a tachyarrhythmia therapy

- Ablation for atrial fibrillation or atrial flutter within the last 9 months (6 months
data collection following a 3 month blanking period post procedure)

- Reactive ATP™ previously programmed on

- Measured P waves in sinus rhythm consistently <0.8 mV on repeat measurements.

- Unresolved artifactual AT/AF detection due to far-field R wave or other oversensing

- Expected generator change or other device surgery within six months