This is an observational cohort study addressing the incidence of cerebral microemboli and alterations of cerebral hemodynamic physiology of the Relay®Branch thoracic stent-graft system.

This study is a prospective multi-center observational study. Eligible patients will be enrolled in RelayBranch (NCT03214601). Participating centers must have capabilities of performing intra-operative TCD monitoring and post-operative TCD monitoring. If sites have performed TCD microembolic monitoring during previous RelayBranch procedures, we will also incorporate these data in our analysis. The primary objective is to assess the number and timing of cerebral microemboli during Relay®Branch thoracic stent-graft deployment, to identify the highest risk portions of the procedure. Secondary objectives include: correlate procedural microembolic burden with neuroimaging and clinical outcome; quantify post-operative microemboli, correlating with neuroimaging and clinical outcome; and quantify the changes in cerebral blood flow and cerebral autoregulation that happens during critical procedural epochs, correlating with neuroimaging and clinical outcome.

Inclusion Criteria:

• Enrollment in NCT03214601 based on presence of a thoracic aortic aneurysm, penetrating atherosclerotic ulcer, or chronic type B dissection that would require coverage of the brachiocephalic trunk and/or left carotid if a non-branching endograft were implanted Advanced heart failure with plan to treat with LVAD
• At least 18 years of age
• Patients enrolled prospectively must sign the informed consent form
• If patients underwent TCD monitoring during a previous RelayBranch procedure as part of routine clinical care, we will also incorporate their data in our analysis

Exclusion Criteria:

• Skull defect or skull surgery that will preclude monitoring
• Known lack of TCD temporal acoustic window (if had TCD in past)
• Expected surgical position will preclude access to the patient's head for monitoring

20 subjects will be enrolled at multiple participating centers. All eligible subjects will be identified based on enrollment in RelayBranch (NCT03214601) or in their hum. We anticipate enrollment will be complete within 2 years.