Release of Acetylcholine From the Ganglionated Plexus During the Thaw Phase of Cryoballon Pulmonary Vein Ablation (GP RESPONSE Study)

This will be a two-phase (feasibility and primary study phases), prospective observational
study with pulmonary vein ablation applications during which a hypotensive response is not
observed serving as within-subject controls. A total of 14 patients age 18-80 with atrial
fibrillation undergoing first time cryoballoon ablation will be enrolled. Exclusion criteria
are any prior left atrial ablation or cardiac surgery, a hemoglobin level of < 12.0 g/dL, or
refusal or inability to provide informed consent.

The ablation procedure will be carried out per routine clinical practice by one operator. Two
cryoballoon applications targeting 180 seconds per application will be performed per vein.
Applications may be abbreviated at the discretion of the operator for indications such as
balloon temperatures reaching the mid -50s C, esophageal temperatures approaching 20 C, or a
decrease in diaphragmatic movement during phrenic nerve pacing. Application times may be
extended to 200 to 240 seconds, also at the discretion of the operator, if within-freeze
target temperatures (such as -30 C by 30 seconds or -40 C by 60 seconds) are not met.

A hypotensive response will be defined as a transient ≥ 20% decrease in systolic blood
pressure from baseline (start of thaw) during the thaw phase and up to 60 seconds post-end of
thaw (balloon deflation). A partial hypotensive response will be defined as a transient
10-19% decrease in systolic blood pressure. For all patients, the time from the end of the
cryoballoon freeze to the end of the thaw, to the onset of the hypotensive response, and to
blood pressure recovery within 10% of baseline will be recorded. Blood pressure and heart
rate will be recorded at each time point. For the first 4 patients (phase I), blood samples
of 2-3mL each will be drawn from the mid-right atrium at baseline and then at 30, 60 and 90
seconds after the end of each cryoballoon freeze application. Samples will also be drawn at
onset of hypotension and 30 seconds later (superseding the drawing of other samples in the
first 90 seconds post-end of freeze), and at blood pressure recovery. Samples will be drawn
within 10 seconds of each specified time point; or will not be obtained and will be marked as
a missing data point. If more than 20% of the specified data are missing for a given subject,
that subject will be excluded from analysis. The samples will then be run on a commercially
available 96-well colorimetric assay kit by Cell Biolabs Inc (catalog number STA-603) to
assay for acetylcholine.

If the first phase of the study demonstrates the presence of acetylcholine at one or more
time points during the thaw phase of 20% or more of cryoballoon applications during which a
hypotensive response is observed, the study will proceed to phase 2. The results will be used
to determine the optimal time point(s) at which to obtain samples during the second phase of
the study (remaining 10 patients), with an anticipated need for 2-4 samples per cryoballoon
application, one at start of thaw, another at a determined time point, and when there is a
hypotensive response at the onset of hypotension and at blood pressure recovery. An interim
report will be produced detailing the observations of phase 1 and specifying the plan for
obtaining samples in phase 2.

Inclusion Criteria:

- patients with atrial fibrillation undergoing first time cryoballoon ablation

- age 18-80

Exclusion Criteria:

- any prior left atrial ablation or cardiac surgery

- hemoglobin level of <12.0 g/dL

- refusal or inability to provide informed consent