On an unstable interval with rate-only detection, the counter in newer devices decreases by how much?

• A. Minus 1
• B. Minus 20 (New devices)
• C. Sets counter to zero (Older devices)
• D. Freezes

Answer: (B)

The main idea is how newer devices manage a detection counter when the rhythm becomes unstable and the detection relies only on rate. In this scenario, the counter is decreased by twenty. That sizable decay quickly erodes any prior detection buildup, so a single short burst of high rate won’t keep the device in a detection state. A sustained, longer period of high rate would then be required to re-establish detection and potentially deliver therapy.

This approach helps prevent inappropriate therapy during irregular or transient rate spikes. By comparison, resetting the counter to zero would erase history and isn’t how newer rate-only detection behaves; freezing would keep the count unchanged and could prolong an unnecessary detection state; decreasing by only one would slow decay too much to protect against false detections.