Final answer:
On an ECG, atrial flutter and atrial fibrillation typically result in the absence or abnormality of the P wave, which represents atrial depolarization. The QRS complex and T wave, representing ventricular depolarization and repolarization, usually remain visible.
Step-by-step explanation:
On an ECG, both atrial flutter and atrial fibrillation are characterized by the absence or abnormal presentation of the P wave. The P wave represents the depolarization of the atria, which is the electrical activity that precedes atrial contraction. In atrial fibrillation, the electrical pattern before the QRS complex is irregular and disorganized, leading to the absence of consistent P waves. Instead, there are rapid oscillations known as fibrillatory waves. Similarly, in atrial flutter, the P wave is replaced by a sawtooth pattern of regular atrial depolarization called flutter waves.
The QRS complex represents the depolarization of the ventricles and is typically present and unchanged in these conditions, whereas the T wave represents the repolarization of the ventricles and is also usually visible on the ECG. Atrial repolarization occurs during the QRS complex and is masked by the electrical activity of the ventricles.