What is the 300 rule for ECG?

As a domain expert in cardiology, I can explain the "300 Rule" for ECG interpretation, which is a simplified method to help determine the rate of atrial activity when analyzing an electrocardiogram (ECG). In an ECG, the P wave represents atrial depolarization, and the QRS complex represents ventricular depolarization. The "300 Rule" is a way to estimate the atrial rate when the P waves are not clearly visible or when they are superimposed on the T waves or QRS complexes. Here's how the rule works: 1. **Count the number of large blocks (also known as "R-R intervals") between P waves**. A large block typically represents a complete QRS complex and a T wave. 2. Divide the number of large blocks by 300 to get the atrial rate per minute. For example, if you count 3 large blocks between P waves, the atrial rate would be 300 / 3 = 100 beats per minute. This rule is a quick way to estimate the atrial rate but is not always accurate, especially in cases of irregular rhythms or when the P waves are not clearly discernible. It's always best to use a more precise method if possible. Now, let's translate that into Chinese:

The square counting method is ideal for regular heart rates. Use the sequence 300-150-100-75-60-50-43-37. Count from the first QRS complex, the first thick line is 300, the next thick line 150 etc. ... Count the number of QRS complexes that fit into 3 seconds (some ECG writers print this period on the ECG paper).