What does a negative deflection in the P wave signify?

A negative deflection in the P wave on an ECG typically indicates that the electrical impulse is originating from a site other than the sinoatrial (SA) node, which is the natural pacemaker of the heart. When the conduction starts from the junctional area, the P wave may be inverted or may not be present at all, leading to the conclusion that a junctional dysrhythmia is likely present. This dysrhythmia occurs because the impulse is generated below the SA node, often due to a failure of the SA node to initiate the heartbeat.

In contrast, the other choices do not accurately describe a negative deflection in the P wave. For example, normal conduction from the SA node to the AV node would typically result in a positive deflection in the P wave, indicating a standard electrical activity pattern. Similarly, a normal ventricular contraction would not be associated with a negative P wave; it would display a normal morphology. Lastly, atrial fibrillation is characterized by an irregular rhythm and absent P waves rather than negative deflections. Thus, the presence of a negative P wave is more closely tied to the electrical activity seen in junctional dysrhythmias.