HRV as a Marker of Treatment Response in PAH Arterial Hypertension

Inclusion Criteria: * All adult patients (ages 18-70) of any functional class with a new diagnosis of PAH (World health Organization Group 1) placed on targeted therapy * Eligible PAH etiologies include idiopathic PAH, associated with connective tissue disease, human immunodeficiency virus, hereditary, or portopulmonary hypertension * Right heart catheterization (RHC) hemodynamics with a mean pulmonary arterial pressure \>=20 millimetres of mercury at rest, a pulmonary capillary wedge pressure \<= 15 millimetres of mercury, and a pulmonary vascular resistance \>= 3 woods units Exclusion Criteria: * Inability to undergo (non-contrast) Magnetic Resonance Imaging (MRI) testing * On chronotropic agents (Beta-Blockers, anti-arrhythmic medications, etc.) that could affect the calculation and interpretation of HRV measures * Conditions that could affect the accuracy of MRI imaging, including a history previously repaired or unrepaired congenital heart defects, ventricular or atrial septal defects, or other anatomic cardiac abnormalities) * Inability to complete a six-minute walk test * Currently being on targeted PAH therapy at the time of consent and enrollment * Thyroid disease, known arrhythmias in the past six months, uncontrolled anemia with a hemoglobin less than 7 grams per deciliter, untreated coronary artery disease or a diagnosis of myocardial infarction in the past 6 months, the presence of a cardiac pacemaker * Clinically significant lung disease (including pulmonary function testing forced vital capacity \< 60%), a positive ventilation/perfusion scan, uncontrolled sleep apnea not adherent with noninvasive positive pressure ventilation * Unable to consent, pregnant women, and prisoners.