Answer to Question 1
A
Undersensing is the inability of the pacemaker to sense spontaneous myocardial depolarizations. Undersensing results in competition between paced complexes and the heart's intrinsic rhythm. This malfunction is manifested on the electrocardiogram by pacing artifacts that occur after or are unrelated to spontaneous complexes. Oversensing occurs as a result of inappropriate sensing of extraneous electrical signals that leads to unnecessary triggering or inhibition of stimulus output, depending on the pacer mode. The source of these electrical signals can range from tall peaked T waves to external electromagnetic interference in the critical care environment. The implantable cardioverter defibrillator system consists of leads and a generator and is similar to a pacemaker but with some key differences. The leads contain not only electrodes for sensing and pacing but also integrated defibrillator coils capable of delivering a shock. If the pacing stimulus fires but fails to initiate a myocardial depolarization, a pacing artifact will be present but will not be followed by the expected P wave.
Answer to Question 2
D
To ensure accurate readings, the difference between injectate temperature and body temperature must be at least 10 C, and the injectate must be delivered within 4 seconds, with minimal handling of the syringe to prevent warming of the solution. This is particularly important when iced injectate is used.
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