In an ICD, what type of counter is used for VT detection?

• A. Up counter
• B. Down counter
• C. Up/down counter
• D. None of the above

Answer: (C)

Ventricular tachycardia detection in an ICD relies on recognizing that fast heart activity must be sustained, not just a brief spike. An up/down counter provides this persistence and hysteresis. When the sensed beats meet the VT rate criterion, the up-counter increments toward a detection threshold. If the rhythm later slows back toward normal, the down-side of the counter decreases, allowing the device to decay the detection toward non-tachycardia. Only when the combined up/down counter reaches the programmed threshold is VT declared and therapy considered. This approach prevents brief, non-sustained fast rates from triggering therapy and helps avoid missed detections by ensuring the rhythm remains fast long enough to warrant intervention.