Bradycardia might occur secondary to unopposed vagal tone from a high sympathectomy, blockade of the cardio-accelerator fibers (T1-T4), and the Bezold-Jarisch reflex (slowing of the heart rate secondary to decreased venous return). Patients with underlying increased vagal tone (children and adults with resting heart rates < 60) are at an increased risk.
Anesthesia Secrets, 4th Edition by James Duke,
Elsevier Health Sciences, 16/03/2010 - 574 pages