In the past two decades, the association between the cardiovascular autonomic dysfunction and the cardiovascular mortality has been well documented. This association indicates that individuals with abnormal autonomic function tests are candidates for close surveillance. In type 2 diabetes it is recommended that a baseline determination of cardiovascular autonomic function be performed upon diagnosis and within 5 years of diagnosis for those with type 1 diabetes, followed by a yearly repeat test.
Out of the markers that objectify this relationship, heart rate variability (HRV) has proven to be the most reliable and the easiest to quantify. Although HRV has been the subject of numerous clinical studies whose purpose was linking heart rate changes to the gravity and the evolution of the disease, only in two clinical settings a consensus was reached. The drop in HRV can be used as a risk factor in the period following an acute myocardial infarction (AMI) and as a warning sign for cardiac autonomic neuropathy (CAN) in diabetic patients. HRV parameters and their possible prognostic significance have not been thoroughly evaluated in patients presenting pulmonary arterial hypertension.