When does ventricular contraction (systole) start and end?

When does ventricular contraction (systole) start and end?

• A. From the P wave to the T wave
• B. From the QRS complex to the T wave
• C. From the PR interval to the QRS complex
• D. From the T wave to the P wave

Answer: (B)

Ventricular contraction, or systole, begins at the onset of the QRS complex and ends at the completion of the T wave. This is because the QRS complex represents the depolarization of the ventricles, which triggers the contraction of the ventricular myocardium. The contraction continues through the majority of the T wave, which represents repolarization of the ventricles. Thus, the correct answer highlights the period during which the ventricles are electrically activated, leading to contraction, and then the subsequent repolarization before the next cycle begins. Understanding the relationship between these waves in the EKG is crucial for interpreting cardiac activity and understanding the mechanical events of the heart.