Final answer:
Junctional rhythms, associated with the AV node acting as the pacemaker, can lead to various ECG changes such as no P wave, an inverted P wave, a shortened PR interval, and a P wave after the QRS complex. A normal P wave and PR interval are rare in junctional rhythms.
Step-by-step explanation:
The AV node is responsible for the delay and conduction of electrical impulses from the atria to the ventricles. In junctional rhythms, where the AV node may take over as the pacemaker of the heart, the typical P wave and PR interval patterns seen on an electrocardiogram (ECG) can be altered. The potential changes in P waveforms in junctional rhythms include:
- No P wave: Occurs when the AV node generates the impulse and effectively bypasses atrial activation.
- Inverted P wave: May be seen when the impulse moves in a retrograde manner from the AV node to the atria.
- Shortened PR interval: If the impulse originating from the AV node conducts to the atria and ventricles nearly simultaneously, the PR interval may appear shortened.
- P wave after the QRS complex: This can occur when the atria are activated after the ventricles due to retrograde conduction.
- Normal P wave and PR interval: Rarely observed in junctional rhythms, as this usually indicates a normal conduction pathway starting from the SA node.
Junctional rhythms can thus exhibit a variety of P wave and PR interval abnormalities on the ECG due to the altered sequence of electrical activation in the heart.