The P wave and the QRS complex represent depolarization of the atrial and ventri

Question

The P wave and the QRS complex represent depolarization of the atrial and ventricular muscle respectively. What causes the QRS complex to have the largest amplitude? What is the specific aspect of ventricular depolarization that produces the S wave? What does the PR interval represent? What happens to the PR interval with a first-degree block? What does the QT interval represent? The range for a normal resting heart rate is 60 to 90 BPM. A trained athlete could have a resting heart rate of 45 to 60 BPM. What could cause a very fit person to have a slower heart rate than someone of average fitness?

Explanation / Answer

Answer:

1) What causes the QRS complex to have the largest amplitude?

Answer: A QRS Complex represents depolarization of the right and left ventricles.The QRS complex has the highest amplitude because a higher pressure is required to push blood back and away from the heart and a considerably larger muscle mass is involved in process of ventricular depolarization as compared to atrial depolarization.

2) What is the specific aspect of ventricular depolarization that produces the S wave?

Answer: The specific aspect of ventricular depolaziation that produces the S wave is Pukinjie fibers and left ventricles enlargment or hypertropy. Therefore S wave represents depolarisation in the Purkinje fibres

3) What does PR interval represent?

Answer: PR interval represents the AV conduction time - time taken by electrical impulses to travel from the begining of atrial depolarization to the beginning of ventricular depolarization ( SA node --> atria --> AV node --> ventricles)

4) What happens to the PR interval with a first degree block?

Answer: A first degree block causes prolongation of the PR interval. As a result, it appears as a longer PR interval (>200msec) on the electrocardiogram because the electrical impulses takes more time to spread from the begining atrial.

5) What does the QT interval represent?

Answer: The QT interval represents the total time required for ventricular activity including both start of ventricular depolarization and end of ventricular repolarization and it ranges from 0.35-0.44 seconds

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