The goal of this study is to utilize CardioMems (measurement of pulmonary artery diastolic pressure) to assess BaroStim. At the time of CardioMems insertion, patients will be screened for candidacy to receive a BaroStim device. Patients will be followed for 3 months after the CardioMems insertion before undergoing insertion of a Barostim. Patients who have undergone a CardioMems, will be eligible for enrollment after 3 months of medication management and optimization. Patients will be followed for 1 year after insertion of Barostim.