A system for monitoring blood pressure includes an implantable medical device (IMD) and an external device (ED). The IMD senses an electrogram (EGM) signal, identifies a feature thereof indicative of a ventricular depolarization, and transmits a conductive communication signal through patient tissue indicating when the ventricular depolarization occurred. The ED is worn against skin and configured to receive the conductive communication signal. The ED is also configured to sense a plethysmography (PG) signal and identify a feature thereof indicative of when a pulse wave responsive to the ventricular depolarization reaches a region of the patient adjacent the ED, and determine a delay time (TD) indicative of how long it takes the pulse wave to travel from the patient's heart to the region of the patient adjacent to the ED. The TD is a surrogate of the patient's blood pressure and useful for monitoring the patient's blood pressure and/or changes therein.