A VVI pacemaker is programmed to 70 beats per minute but shows a preoperative rate of 61 bpm. The most likely reason is:

A VVI pacemaker is programmed to 70 beats per minute but shows a preoperative rate of 61 bpm. The most likely reason is:

• A. Decreased atrial rate
• B. Third-degree heart block
• C. Trifascicular block
• D. Battery failure

Answer: (D)

In a ventricular-inhibited (VVI) pacemaker, pacing occurs only if the intrinsic ventricular rate falls below the programmed lower rate. If you see the heart rate sitting at 61 bpm while the device is programmed to pace at 70 bpm, it means the pacemaker is not delivering pacing at all—the heart is running on its own intrinsic rate. Battery failure or generator malfunction is the most likely reason for the loss of pacing output. When the battery is depleted or the device malfunctions, the pacemaker can stop delivering stimuli, so the observed rate reflects the patient’s native rhythm (about 61 bpm in this case) rather than the programmed 70 bpm. Why the other reasons don’t fit as well: in a VVI system there’s no atrial pacing, so a decreased atrial rate wouldn’t account for a lack of ventricular pacing. A complete heart block or trifascicular disease would still typically trigger the pacemaker to pace the ventricle at the set rate if the generator is functioning; a functioning device would enforce the programmed lower rate. Thus, restoration of pacing output is unlikely unless the device is failing. In practice, preoperative device interrogation would confirm battery status; if depleted, external pacing readiness and generator replacement would be planned.

In a ventricular-inhibited (VVI) pacemaker, pacing occurs only if the intrinsic ventricular rate falls below the programmed lower rate. If you see the heart rate sitting at 61 bpm while the device is programmed to pace at 70 bpm, it means the pacemaker is not delivering pacing at all—the heart is running on its own intrinsic rate.

Battery failure or generator malfunction is the most likely reason for the loss of pacing output. When the battery is depleted or the device malfunctions, the pacemaker can stop delivering stimuli, so the observed rate reflects the patient’s native rhythm (about 61 bpm in this case) rather than the programmed 70 bpm.

Why the other reasons don’t fit as well: in a VVI system there’s no atrial pacing, so a decreased atrial rate wouldn’t account for a lack of ventricular pacing. A complete heart block or trifascicular disease would still typically trigger the pacemaker to pace the ventricle at the set rate if the generator is functioning; a functioning device would enforce the programmed lower rate. Thus, restoration of pacing output is unlikely unless the device is failing.

In practice, preoperative device interrogation would confirm battery status; if depleted, external pacing readiness and generator replacement would be planned.