To the Editor:—
With interest, we read the recent review articles “Cardiac Rhythm Management Devices, Parts 1 and 2” by Atlee and Bernstein. 1,2We fully agree with the authors that in a pacemaker-dependent patient the device should be reprogrammed to an asynchronous mode, as stated in the text (page 1503) and in table 8 (page 1504) of the article. 2However, the paper does not contain a clear statement as to what to do with patients who are not fully pacemaker-dependent, i.e. , patients with an intrinsic rhythm who have occasional episodes of bradycardia. In these patients, reprogramming the device in an asynchronous mode can provoke harmful interactions with the patient's intrinsic rhythm, resulting in R-on-T-phenomenon causing possible ventricular fibrillation. This phenomenon is demonstrated in two examples (fig. 1) of intraoperative Holter recordings in patients with intrinsic rhythm in whom the pacemaker was reprogrammed to an asynchronous mode.
Therefore, we strongly recommend that a pacemaker should not be reprogrammed to an asynchronous mode in patients who have an intrinsic cardiac rhythm with only occasional episodes of bradycardia. To protect the battery, the atrial and ventricular sensing should be programmed, if possible, to a bipolar mode. If an episode of bradycardia occurs in the operating room and the pacemaker does not detect it correctly because of an electromagnetic interference, the pacemaker can easily be switched on by placing a magnet over the pacemaker, and if possible, by interrupting the source of electromagnetic interference. This strategy results in a short episode of bradycardia, but it is a situation much less harmful than an episode of ventricular fibrillation.