Another type of atrial ectopic focus is a reentrant loop, which is when there's some tissue that doesn't depolarize right.

另一类房性异位起搏点是一个折返环路，主要发生在当某些组织不能正确地除极的时候。

A reentrant loop basically starts sending out depolarization waves to the rest of the heart tissue each time the wave goes around.

每沿着折返环路环绕一圈，它就开始向其余心肌组织发放除极波。

So, in short, a particularly stressed out atrial cell or a reentrant loop can send out depolarization waves that contract the atria, and result in an early, or premature, atrial contraction.

因此，简单说就是一个尤其应激的心房细胞、或者一个折返环路发放除极波导致心房收缩，造成早期或过早的心房收缩。