CARDIAC ELECTRICAL ACTIVITY-INTERVALS

SUMMARY

1. PR interval: defined from beginning of P wave to the beginning of the QRS complex. Corresponds to the time taken for the impulse to travel from the SA node to the ventricles. Normal: 0.12-0.20 sec.

2. QRS complex: represents ventricular depolarization. Upper limit: 0.12 sec.

3. QT interval: defined from the start of the QRS complex to the end of the T wave. Represents the time from the onset of ventricular depolarization to full repolarization. HR dependent.

4. QTc interval: QT interval that has been corrected for variations in HR (standardised to 60 beats/min) & and permits comparison between and within individuals. Normal: 0.35-0.43 sec.



Image: Dr. Appukutty Manickam.

Reference(s)

Barrett, K.E., Barman, S.M., Boitano, S., Brooks, H.L., Weitz, M., Brian Patrick Kearns, Ganong, W.F. and Mcgraw-Hill Education (Firm (2016). Ganong’s review of medical physiology. 25th ed. New York: Mcgraw Hill Education.
Hall, J.E. and Hall, M.E. (2020). Guyton And Hall Textbook Of Medical Physiology. 14th ed. S.L.: Elsevier - Health Science.
West, J.B. and Luks, A.M. (2021). West’s Pulmonary Pathophysiology. Lippincott Williams & Wilkins.