What could cause poor circulation and tachycardia?

Chicken or egg?: Depends on what you mean by "poor circulation. Rapidly beating hearts may pump blood inefficiently, reducing circulation in limbs & organs thus causing symptoms & complications. Or, clogging and hardening of the arteries may reduce blood flow to the heart, causing irregular rhythms like tachycardia. There are other more complex diseases that can also cause both.

Multiple: Poor arterial circulation from smoking and atherosclerosis. Poor venous circulation from deep vein clots tachycardia is secondary to a huge list anemia emphysema cardiac etc.