Effects Rapid Atrial Pacing Has on the Electrocardiogram (ECG) in Patients With Dual Chamber Pacemakers

This study requires a total of two study days as well as two follow up visits. During study
day one, baseline blood will be drawn, a baseline electrocardiogram will be performed, and
continuous QT Interval monitoring will be performed. The pacemaker rate will be increased
to 90bpm at different time intervals and additional blood will be drawn to measure the
effects of these rates changes.

On study day two, baseline blood will be drawn, a urine specimen will be obtained, an
electrocardiogram will be performed, and continuous QT Interval monitoring will be
performed. Following the acquisition of this information, the pacemaker rate will be
decreased to 80bpm. We will obtain blood specimens, a urine specimen and an
electrocardiogram at 30 minutes post rate change and again at 60 minutes post rate change.

Two days following the rate decrease to 80bpm, the patient will return to clinic to have
their rate decreased to 70bpm. In two more days, the patient will return for a final rate
change to 60bpm.

Inclusion Criteria:

- Must be at least 21 years old

- Must have a dual chamber pacemaker implanted more than three months ago

- Must be followed by the Vanderbilt University Medical Center's Arrhythmia Device
Clinic

- The indication for the pacemaker must not be related to coronary artery disease (CAD)
or congestive heart failure (CHF)

Exclusion Criteria:

- Cannot be pacemaker dependent

- History of ventricular arrhythmias and/or implantable defibrillators (ICDs)

- History of paroxysmal, persistent, or permanent atrial fibrillation (AF)

- Congenital long QT syndrome

- History of coronary artery disease

- History of, or currently receiving, treatment for congestive heart failure

- Unable to tolerate dual-chamber pacing (DDD) at 90 bpm due to palpitations, chest
pain, shortness of breath, lightheadedness, dizziness, or presyncope

- Pregnant women

- Any patient without specific documentation of an echocardiogram negative for CHF
(systolic or diastolic dysfunction)within five years prior to study enrollment

- Any patient without specific documentation of an objective diagnostic test to rule
out CAD within five years prior to study enrollment