Analyze this VVI pacemaker strip. Identify any underlying rhythm and how the pacemaker is functioning. This rhythm strip shows no underlying rhythm with…
WI pacing with intermittent failure to sense
WI pacing with intermittent failure to capture
WI pacing with oversensing
Normal VI pacemaker function
WI pacing with intermittent failure to pace
The Correct Answer and Explanation is:
To accurately analyze the VVI pacemaker rhythm strip, let’s break down the terminology and expected findings for each option, and apply it to what is described:
Correct Answer: VVI pacing with intermittent failure to capture
Explanation (300+ words):
A VVI pacemaker is a single-chamber device that:
- V (ventricle): Paces the ventricle.
- V (ventricle): Senses intrinsic ventricular activity.
- I (inhibited): Inhibits pacing when intrinsic ventricular activity is detected.
In a normally functioning VVI pacemaker, we would expect to see:
- Regular pacing spikes followed by QRS complexes, if the patient has no intrinsic rhythm.
- If the patient has an intrinsic rhythm, pacing may be inhibited.
Now, analyzing the description:
- “This rhythm strip shows no underlying rhythm…”: This means the heart is not producing its own intrinsic electrical activity, so the pacemaker should be consistently pacing the ventricles.
- Therefore, every pacer spike should be followed by a QRS complex, assuming the pacemaker is functioning properly.
However, the strip shows:
- Pacing spikes are present (indicating the pacemaker is attempting to stimulate).
- But intermittently, there is no QRS complex following the pacing spikes.
This situation is termed failure to capture, meaning:
- The pacemaker is generating electrical impulses (evident from the spikes).
- But these impulses do not cause depolarization of the myocardium (i.e., no QRS complex).
- Causes may include lead displacement, battery depletion, or increased pacing threshold due to ischemia or electrolyte imbalance.
Why the other options are incorrect:
- Failure to sense: The pacemaker would fire even when intrinsic QRS complexes are present (not the issue here).
- Oversensing: The pacemaker is inhibited due to sensing non-cardiac signals—would result in absence of pacing spikes.
- Normal function: Cannot be considered normal if spikes are not followed by QRS complexes.
- Failure to pace: Would show missing pacing spikes, which is not the case.
Conclusion:
The VVI pacemaker is functioning erratically—it is firing, but not always capturing—making “VVI pacing with intermittent failure to capture” the correct interpretation.