Intracardiac echocardiography: an ideal guiding tool for device closure of interatrial communications.

BACKGROUND: This study sought to evaluate safety and radiation exposure when using intracardiac echocardiography (ICE) in comparison to transesophageal echocardiography (TEE) in order to guide transcatheter closure of interatrial communications. METHODS: Eighty patients (44 males, 36 females, mean age 46, SD 13 years) undergoing device closure of atrial septal defect (n=12) or patent foramen ovale (n=68) had the procedure guided by ICE (n=50, group 1) or TEE (n=30, group 2). In group 1, all procedural stages were completely guided by ICE, including imaging of the interatrial communication during balloon sizing, device unfolding and release, and during the final check for adequate positioning. In group 2, exclusive implantation of devices was guided by use of TEE. RESULTS: Especially, the spatial relationship between device and cardiac structures (e.g. the ascending aorta, the interatrial septum and the superior vena cava) was accurately demonstrated in group 1. Image resolution provided by ICE was superior to that of TEE. No severe complications, including any related to ICE, were seen. Fluoroscopy time (FT) and procedure time (PT) were shorter in group 1 than in group 2 (FT: 5.5+/-1.5 min vs. 9.3+/-1.6 min, P<0.0001; PT: 31.9+/-4.6 min vs. 38.8+/-5.8 min, P<0.01). Neither sedation nor anesthesia was required in group 1. CONCLUSIONS: ICE is a safe tool to guide device closure of interatrial communications. For the patient, procedural stress and radiation exposure are negligible. ICE can be considered the guiding tool of choice for device closure, particularly when long or repeated echocardiographic viewing is required.     

Bounds on the number of hidden units of boltzmann machines

It is known that any given probability distribution of the states of the observable units of a Boltzmann machine can be realized if no limit is imposed on the number of hidden units. But very little is known about the number of hidden units necessary for such realization. We consider Boltzmann machines as associative memories and show that there exist vector sets whose memorization on a Boltzmann machine requires a number of hidden units which is exponential in the size of the vectors (i.e., the number of components in each vector). Additional results give tight bounds on the number of hidden units needed in terms of the vector set size (i.e., the number of vectors in the set). Furthermore, we show how to construct Boltzmann machines which realize negation, intersection, and composition of the vector sets memorized by given Boltzmann machines.