Can brainstem problems cause tachycardia?

Possibly: The autonomic cardiovascular centers are located in the hypothalamus & brainstem. Baroreceptor signals travel through the 9th and 10th cranial nerves into the central nervous system to contact neurons in the nucleus of the solitary tract in the medulla (lower brainstem). Lesions/irritation in the medulla can result in cardiovascular changes. http://www.cvphysiology.com/Blood%20Pressure/BP008.htm