Which of the following are commonly sensed unwanted signals by pacing devices?

The correct choice is the one that highlights T waves and skeletal muscle contractions as commonly sensed unwanted signals by pacing devices. This is due to the fact that both T waves and skeletal muscle contractions can confuse the pacing system by mimicking the electrical activity that the device is designed to detect and respond to.

T waves represent the repolarization of the ventricles in the heart and, if sensed inaccurately by the pacemaker, could lead to inappropriate pacing or inhibition of pacing when it is actually needed. Additionally, skeletal muscle contractions can generate electrical signals that can be picked up by the pacing device, which may also interfere with the proper functioning of the device. The pacing system might erroneously interpret these signals as intrinsic cardiac activity, leading to inappropriate responses.

Other signals such as electromyographic signals relate to muscle activity overall but are not as common in the context of pacemaker interference. F waves are associated with atrial activity and ventricular arrhythmias can be more complex, generally considered pathological states rather than unwanted signals the device would typically sense in its normal operation. Thus, the focus on T waves and muscle contractions as unwanted signals emphasizes the importance of ensuring the pacing system accurately distinguishes between cardiac and non-cardiac signals to function effectively.