Multiple Choice
When a premature ventricular contraction (PVC) appears on the ECG, which of the following is most characteristic?
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18. The Heart
Electrocardiogram (ECG)
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Which region of the ECG corresponds to the electrical changes associated with atrial repolarization?
A
P wave
B
T wave
C
It is masked by the QRS complex
D
QRS complex
Verified step by step guidance1
Step 1: Begin by understanding the components of an ECG (Electrocardiogram). The ECG is a graphical representation of the electrical activity of the heart. It consists of several waves: the P wave, QRS complex, and T wave, each corresponding to specific electrical events in the heart.
Step 2: Recall the physiological events associated with each wave. The P wave represents atrial depolarization (the electrical activity that triggers atrial contraction). The QRS complex represents ventricular depolarization (the electrical activity that triggers ventricular contraction). The T wave represents ventricular repolarization (the recovery phase of the ventricles).
Step 3: Consider atrial repolarization. Atrial repolarization is the recovery phase of the atria after depolarization. However, this electrical activity is relatively small and occurs simultaneously with the QRS complex.
Step 4: Understand why atrial repolarization is not visible on the ECG. The electrical signal of atrial repolarization is masked by the much larger electrical activity of the QRS complex, which represents ventricular depolarization.
Step 5: Conclude that the region of the ECG corresponding to atrial repolarization is not directly visible because it is obscured by the QRS complex.
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