Making it easier to see exactly how the wave of depolarization moves through the heart.

让我们更清楚地看到，极波是怎样流过心脏的。

Normally, the resting state of sodium channels is stabilized by calcium ions, which prevents them from spontaneously opening and potentially causing depolarization.

正常情况下，钙离用来稳定钠离的静息状态，这可以防止钠离自发打开，从而导致去极化。

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极，这个心房细胞被称为房性异位起搏点。

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

每沿着折返路绕一圈，它就开始向其余心肌组织发放极波。

The P wave represents the spread of the electrical impulse through the atria, and this is referred to as atrial depolarization.

P波代表电脉冲过心房的传播，这被称为心房去极化。

Similarly, each of the limb leads produces its own viewpoint of the depolarization wave as well.

同样地，每一个肢体导联也在用不同的角度去记录极波。

For example let’s say that the depolarization happened this way - at an angle, then we’d break the vector into two parts.

比如，极波是沿着如图方向进行的，成一个角度，那么我们把向量分成两个部分。

An ECG tracing specifically shows how the depolarization wave during each heartbeat - which is a wave of positive charge.

心电图描记明确显示了极波在每次心跳中是怎样运动的；极波是一种正电荷的波。

Now, lead V1 on an ECG measures a depolarization wave that moves towards the right ventricle.

好，心电图的导联V1测量向右心室传导的极波。

The QRS wave, which is sometimes called the QRS complex, represents the spread of the electrical impulse through the ventricles, or ventricular depolarization.

QRS波，有时被称为QRS波群，代表电脉冲过心室的传播，或心室去极化。

As an example, consider how the 6 chest leads - V1 through V6 - register this depolarization wave form called the QRS complex.

作为例，我们来看一下这6个胸导联，V1-V6是怎样来记录被称为“QRS波群”的极波形的。

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极化而过早地收缩。

This could be like scar tissue after a heart attack - and as a result the wave of depolarization ends up circling around and around that tissue.

就比如心梗后生成的瘢痕组织，极波由此可以围绕着这些组织不停的循。

In this situation, the depolarization wave conducts down the left bundle branch and then through the ventricles aberrantly, resulting in an abnormally wide QRS complex.

在这种情况下，极波向下传导到左束支，然后异常地穿过心室，导致一个异常增宽的QRS波群。

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.

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

And this one is called the ST segment, and it corresponds to the interval between ventricular depolarization and repolarization.

这个叫做ST段，它相当于心室去极化和复极化的间隔。

These can appear lots of different ways depending on where the two depolarization waves meet each other.

这会以许多不同方式出现，取决于两个极波相遇的地点。

In fact, if there’s a depolarization wave that goes straight up, which is perpendicular to the positive and negative electrodes, then there’d be no deflection at all!

事实上，如果有一个极波是竖直向上的，即完全垂直于正、负电极的话，那么心电图上就不会显示任何波形。

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、或者一个折返路发放极波导致心房收缩，造成早期或过早的心房收缩。

So let’s say that when this set of cells is at rest they’re red and then they turn green as the wave of depolarization moves through them.

我们，这些细胞处于静息状态时是红色的，而当极波流过这些细胞时，它们变成绿色。