Final answer:
The QRS complex on an ECG represents ventricular depolarization and contraction, while the T wave indicates ventricular repolarization and the start of relaxation. In cases where not all P waves are followed by QRS complexes and T waves, it may suggest a second-degree heart block. Each serves as a critical indicator of different cardiac functions.
Step-by-step explanation:
The T wave and QRS complex are distinct features of an ECG, representing different phases of heart function. The QRS complex is a large spike on an ECG tracing, representing the depolarization of the ventricles where they begin to contract, pumping blood to the lungs and body. The T wave, on the other hand, represents the repolarization of the ventricles, indicating the start of their relaxation phase. Notably, repolarization of the atria is masked by the QRS complex and is not visible on the ECG.
Instances where half of the P waves are not followed by the QRS complex and T waves may indicate a type of heart block, such as a second-degree block. A normal ECG would show a P wave followed by a QRS complex and T wave in a regular pattern, representing a complete and orderly heartbeat. Disturbances in this pattern can signal various cardiac conditions.