Sinus node dysfunction: sick sinus syndrome, tachy-brady syndrome
Second or third degree AV block, bundle of HIS dysfxn
Meds: beta blockers, non-dihydropyridine calcium channel blockers, clonidine, other
Acute ischemia/MI involving SA, AV node (e.g. RV infarct), post-cardiac surgery (in particular, AVR)
Non-cardiac: hypoxemia, hypothermia, hypothyroidism, increased vagal tone, increased ICP
Physiologic--> patients with excellent cardiovascular fitness (e.g. distance runners)--> no symptoms or activity limitation

Bradycardia