I commend the work of Ferns et al. comparing the AcuNav intracardiac echocardiographic (ICE) (Siemens Medical Solutions USA, Inc., Mountain View, CA) and microTEE (Philips Medical Systems, Andover, MA) miniaturized transducers. Support of enhancing imaging in this important population of patients is critical to the advancement of their care. However, I do not believe safety factors were given their due respect in this matter. The authors stated, “No major complications were encountered in either group. No apparent minor complications were encountered in the AcuNav ICE transducer group.” The authors then reference several small animal studies that claim safety with the use of the ICE probe in the esophagus. That in my opinion is a good start but not sufficient.
My concerns on this topic are based primarily on a series of incidents I was made aware of several years ago. These incidents occurred at a major institution and involved the use of a standard-size pediatric transesophageal echocardiographic (TEE) probe. It seems the integrity of the plastic shield on the pediatric TEE probe was compromised, and this was not recognized for some time. During the time this went unrecognized, numerous infants had undergone TEE studies using this probe. No immediate complications were noted. However, months later, these infants were noted to have significant morbidity from esophageal injuries. The injuries, I was told, were postulated to be due to esophageal electrocution or chemical damage (from residual cleaning material remaining in the probe entering and exiting through the compromised plastic TEE shield) during their TEE examinations. At least one of these infants, I was told, was so injured that an esophageal graft was required. I hope that someday this institution publishes its experience for the sake of all who undergo TEE imaging, otherwise one could argue that this is hearsay. However, until the day those data are published and open for discussion, just considering the possibility that these incidents were accurately described behooves us all to proceed with caution. The most important caution one would likely derive from these incidents, were they to be published, would be that morbidity from TEE probe injury can take time to show up, at least in infants. Thus, to be assured that no damage has resulted from using an ICE probe for transesophageal imaging, one approach could be to perform subsequent fiber optic endoscopy in a set of patients who had undergone esophageal imaging with an ICE probe to look specifically for mucosal damage and other complications. The second caution one would likely surmise from these incidents is that even though they were reportedly injuries from electrocution or chemical burns of the esophagus, one could imagine similar end points with thermal damage to the esophagus. Third, in addition to manufacturers’ recommended cleaning protocols, it is probably reasonable to check TEE probes’ structural and electrical integrity sometime before or after each use, in any patient.
Returning to Ferns et al. , they state, “The major potential safety limitation with the use of the AcuNav ICE transducer is the lack of a thermistor for temperature monitoring.” They go on to reference a study by Bruce et al. , who in addition to checking for structural and electrical integrity monitored esophageal temperatures with a thermistor during TEE examinations using ICE probes and found no complications. What Ferns et al. failed to point out is that that specific part of Bruce et al. ’s study was done in adults. With that in mind, one must question what could happen differently in a very small esophagus. Furthermore, Bruce et al. made several statements that are concerning. In the part of their study in which they monitored the temperatures of the ICE catheters in adults, they recorded maximum temperatures of 39.5 ± 1.1°C (range, 38.8°–42°C). They stated that these temperatures were below the standard TEE probe cutoff temperature of 44°C. My laboratory goes by more stringent warnings available from Philips, which state the following, raising a fair amount of concern regarding the guidelines followed in these ICE studies: “Sufficient data on thermal tolerance of the esophagus in neonate and pediatric patients does not exist, but it is likely these patients are more vulnerable than adults. Minimize the time spent imaging at distal tip temperatures in excess of 41°C (105.8°F)”.
Finally, Ferns, et al. state, “Likewise, we and other investigators…did not encounter any apparent complications related to esophageal burn or trauma. However, because of the theoretical but very unlikely possibility…of esophageal thermal injury, we limit our intracardiac transesophageal echocardiographic imaging time to not more than 15 min.” Later, they state, “The use of [transesophageal echocardiography] in critically ill postoperative infants has increased in our pediatric surgical heart unit because of the demonstrated safety and efficacy of both the AcuNav ICE and microTEE transducers.” Such a series of statements will, in my opinion, give clinicians reading this article a false sense of safety and security. The use of the phrases “theoretical but very unlikely” and “demonstrated safety,” as well as the authors’ limiting “imaging time to not more than 15 min,” is not based on conclusive scientific evidence. A more appropriate statement could have been something such as “As in previous studies, using an ICE probe in a TEE examination did not cause any untoward effects that we were able to discern, so far, in the population we studied.”