Tachycardia-induced S1 is characterized by which finding?

Tachycardia-induced S1 is characterized by which finding?

• A. Short PR interval with increased cardiac output
• B. Prolonged PR interval with decreased cardiac output
• C. No change in PR interval
• D. Delayed S1 onset with slow heart rate

Answer: (A)

In tachycardia, the rapid heart rate shortens the time between atrial and ventricular activation, so the AV node conduction tends to be faster, producing a short PR interval. At the same time, the overall rate is higher, which tends to increase cardiac output despite the reduced filling time. So tachycardia-induced S1 aligns with a short PR interval and increased cardiac output. Longer PR intervals imply slower AV conduction and often lower output, no change in PR interval wouldn’t reflect tachycardia, and a delayed S1 with a slow rate fits bradycardia, not tachycardia.

In tachycardia, the rapid heart rate shortens the time between atrial and ventricular activation, so the AV node conduction tends to be faster, producing a short PR interval. At the same time, the overall rate is higher, which tends to increase cardiac output despite the reduced filling time. So tachycardia-induced S1 aligns with a short PR interval and increased cardiac output. Longer PR intervals imply slower AV conduction and often lower output, no change in PR interval wouldn’t reflect tachycardia, and a delayed S1 with a slow rate fits bradycardia, not tachycardia.