Atrial Rhythms Flashcard

D. Rationale: Atrial P waves look different from sinus P waves because they are located outside the SA node, and the current is traveling to the leads through different pathways. Depending on when the focus fires, the P wave may get hidden or buried in the ECG’s depiction of other electrical activity occurring at the same time.

A. Rationale: Atrial tachycardia is caused by an irritable focus in the atria firing at a rate that overrides the SA node rate. Unlike a PAC, the irritable focus takes over and establishes a regular rhythm.

C. Rationale: The PAC appears earlier than the next expected P wave in the ECG strip and is often seen soon after the preceding QRS complex. The P wave may also manifest itself near to or lost entirely in the T wave.

D. Rationale: Conduction from the AV nodes to the ventricles is normal. Thus, the PR interval is usually normal (120–200 milliseconds), but at times it may be longer than normal.

A. Rationale: If a PAC succeeds in depolarizing the ventricles, ventricular depolarization occurs normally, and the QRS has a normal duration.

D. Rationale: The rate and regularity depends on the patient’s underlying rhythm. The PAC is just interrupting the existing rate and rhythm.