If an atrial cell outside of the SA node initiates a depolarization, it's called an atrial ectopic focus.

如果一个窦房结以外的心房细胞引发了一个除极，这个心房细胞被称为房性异位起搏点。

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。

When that depolarization wave from an atrial ectopic focus gets to the AV node, there are a couple options.

当除极波从房性异位起搏点到达房室结，它有许多选择可做。

In rare situations, an ectopic focus can trigger atrial fibrillation, which is a more serious arrhythmia where the atria essentially just quiver.

罕见情况下，异位起搏点会引发心房颤动，这是更为严重的心律失常，心房基本上只能颤动（不能正常收缩）。

Alright, so also the location of the ectopic focus in the atria determines how the heart contracts and therefore what the ECG looks like.

并且心房异位起搏点的位置决定了心脏如何收缩以及因此产生的心电图形状。

So let's say the SA node is firing along as usual, but all the sudden an ectopic focus fires one off early.

比方说窦房结和往常一样发放冲动，但是一个异位起搏点提前发放冲动阻断了这些冲动的传播。

Alright, as a quick recap - A premature atrial contraction is when the atria contract too early because of a depolarization from an ectopic focus.

好，快速总结一下：房性期前收缩是指心房因为来自异位起搏点的除极化而过早地收缩。

A ventricular ectopic focus can fire at different points in the cardiac cycle, which we can look at using the ECG.

室性异位起搏点会在心动周期的不同时间点放电，我们可以用心电图监测到。

One important effect of the premature depolarization is that the ectopic focus will depolarize the cells of the SA node, causing the SA node to skip a cycle.

过早除极的一个重要影响就是异位起搏点将会使窦房结细胞除极，导致窦房结跳过一个心动周期。

This so-called " group beating" can be differentiated from a type 1 second-degree atrioventricular heart block by identifying the abnormally shaped p-waves that are characteristic of an atrial ectopic focus.

所谓的“成组搏动”可以通过辨认房性异位起搏点产生的异常形状的P波与二度I型房室传导阻滞相鉴别。

Also, the closer the ectopic focus is to the AV node, the shorter the PR interval, which is the time from the P wave to the QRS complex.

并且，异位起搏点越靠近房室结，PR间期就越短，也就是P波到QRS复合波群的时间。

If an ectopic focus is triggering atrial fibrillation, radiofrequency ablation can be done, which is where radiofrequency waves are used to destroy the tissue that's causing the ectopic heartbeat.

如果异位起搏点引发了心房颤动，就需要做射频消融了，即利用射频波破坏导致异位心搏的组织。

Now, if we measure out the interval between each SA node fire, we see that it should have fired here, but it doesn't because it was depolarized by the ectopic focus.

这时，如果我们测量每一个窦房结冲动的间隔，我们可以看到它本应在此处发放，但并没有，因为它被异位起搏点除极化了。

So, when an ectopic focus originates in the left ventricle, and moves towards the right ventricle, the V1 lead shows a large positive complex, with a dominating R wave.

所以，当异位起搏点起源于左心室，并向右心室传导，V1导联出现一个有主导地位R波的大型正相复合波。

When an ectopic focus originates in the right ventricle, and then moves towards the left ventricle, the V1 lead shows a large negative complex, with a dominating S wave.

当异位起搏点起源于右心室，并向左心室传导，V1导联出现一个带主导地位S波的大型负相复合波。

If an ectopic focus is triggering ventricular arrhythmias, radiofrequency ablation can be done, which is where radiofrequency waves are used to destroy the tissue that's causing the ectopic heartbeat.

如果异位起搏点引发了室性心律失常，可以做射频消融，就是射频波被用于摧毁导致异位心搏的组织。

Another scenario, though, is if a depolarization wave from an atrial ectopic focus gets through the AV node but get sent through the ventricles abnormally like when a bundle branch is in refractory.

另一种情况，如果从房性异位起搏点来的除极波通过了房室结，但却在一个异常的时间到达心室，比如当一个束支处于不应期。

If the ectopic focus originates in the left ventricle, the wave will depolarizing the left ventricle first and then the right ventricle, which produces a QRS complex that looks like a right bundle branch block.

如果异位起搏点源于左心室，这个波将会首先除极左心室，然后是右心室，这会产生类似于右束支阻滞的一个QRS波群。

If the ectopic focus originates in the right ventricle, the wave will depolarize the right ventricle first and then the left ventricle, and this produces a QRS complex that looks like a left bundle branch block.

如果异位起搏点源于右心室，这个波将会首先除极右心室，然后是左心室，这会产生类似于左束支阻滞的一个QRS波群。

In rare situations, an ectopic focus can trigger ventricular tachycardia or even ventricular fibrillation, which are more serious arrhythmias where the ventricles beat too quickly to fill up with an adequate amount of blood.

罕见情况下，异位起搏点会引发室性心动过速，甚至是心室纤颤，都是更为严重的心律失常，即心室搏动太快，以至于不能填充足量的血液。