What do P-wave and QRS-complex represent and what they initiate/lead to?

Explanation

To answer the question regarding what the P-wave and QRS complex represent and what they initiate or lead to, we can break it down into the following steps:

### Step 1: Understanding the P-wave
- The P-wave is the first wave in the electrocardiogram (ECG) and represents the depolarization of the atria.
- This depolarization is initiated by the sinoatrial (SA) node, which is located in the wall of the right atrium.
- When the SA node is activated, it generates electrical impulses that spread through the atria, leading to their contraction.

### Step 2: Understanding the QRS Complex
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