How can the heart rate be determined from an ECG?

Determining the heart rate from an electrocardiogram (ECG) involves analyzing the P waves, QRS complexes, and T waves within the ECG recording. Here are the steps involved:

1. Identify the P waves: The P waves represent the electrical activity associated with the contraction of the atria. Locate the beginning of each P wave, which corresponds to the start of the electrical impulse.

2. Identify the QRS complexes: The QRS complex represents the electrical activity associated with the contraction of the ventricles. Locate the beginning of the QRS complex, which corresponds to the start of ventricular depolarization.

3. Measure the time interval: Measure the time interval between the beginning of one P wave and the beginning of the next P wave. This interval is known as the P-P interval.

4. Calculate the heart rate: The heart rate is calculated using the following formula:

$$\text{Heart rate (bpm)} = \frac{60000}{\text{P-P interval (milliseconds)}}$$

For example, if the P-P interval is 600 milliseconds, the heart rate would be:

$$\text{Heart rate (bpm)} = \frac{60000}{600 \text{ ms}} = 100 \text{ bpm}$$

5. Repeat the process: Continue measuring P-P intervals and calculating heart rates for multiple P-P intervals to get an overall understanding of the heart rate pattern.

6. Interpret the heart rate: The normal resting heart rate for adults typically ranges from 60 to 100 beats per minute (bpm). A heart rate below 60 bpm is considered bradycardia, while a heart rate above 100 bpm is considered tachycardia.

It's important to note that the ECG recording should be interpreted by a qualified healthcare professional to ensure an accurate assessment of the heart rate and other cardiac parameters.