We use a tiny catheter through the heart to separate the pericardium with gas. We expect this to improve the safety of the Lariat procedure.

The Lariat suture device enables non-surgical exclusion of the left atrial appendage possibly to prevent thromboembolism and stroke in patients with atrial fibrillation. Subxiphoid needle access to the pericardium (a standard approach to enter the pericardial space surrounding the heart using a needle underneath the breastbone) during Lariat risks injury to the heart surface that requires surgical repair.

In this protocol the investigators propose test a new method to increase the safety of needle access to the pericardium. Before needle access, the investigators introduce a separate tiny catheter into the pericardium from inside the heart through a tiny hole. The investigators then inject gas to push the heart away from the pericardial needle. This reduces the risk of injuring the heart during the standard Lariat procedure.

Inclusion Criteria:

• Undergoing subxiphoid access to the "empty" pericardial space as part of a Lariat left atrial appendage exclusion procedure
• Age ≥ 21 years

Exclusion Criteria:

• Does not consent to participate