ABSTRACT

Introduction – an overview of intravascular and intracardiac imaging Ultrasonography, with a probe placed directly in the vascular system, has been in existence for over two decades. Initial probes, mounted on intravascular catheters/sheaths, produced radial or 360° axial imaging.1,2 In addition, relatively high frequencies were used such that images demonstrated excellent resolution of the vessels in which the ultrasound catheters were placed (e.g. coronary arteries); however, other portions of the cardiac anatomy were not well seen.3-6 With the development of lower frequency transducers, greater depth penetration was possible allowing improved imaging of other parts of the cardiac anatomy;7 hence the term ‘intracardiac (ICE)’ rather than ‘intravascular (IVUS)’ echocardiography to denote the location of the catheter. Axial or radial intracardiac imaging has been used to determine chamber and valve sizes, thicknesses, and function.8-13 In addition, this type of imaging was also used for guidance of cardiac interventions such as endomyocardial biopsy,14 trans-septal puncture,15 and electrophysiologic studies.16 During the latter, ICE has been used to guide the placement of electrophysiologic pacing catheters and trans-septal puncture, as well as to evaluate lesion size, anatomy, and post-procedure complications.17-19 Since initial intracardiac imaging used an axial plane only, only portions of the two-dimensional (2D) anatomy were visualized at a time, and only a poor mental sense of the underlying 3D anatomy was possible. In addition, initial ICE catheters lacked pulse Doppler capabilities. Linear array transducers20 and steerable catheters20,21 were developed to enhance 2D visualization. Over the last 5 years, phased-array intracardiac transducers22-24 have been introduced and essentially replaced other intracardiac imaging catheters. These ultrasound catheters

have lower frequency as well as Doppler imaging capability. They have been used for guidance in numerous invasive cardiac procedures and interventions, including electrophysiologic studies,25-28 balloon atrial septostomy,29 gene insertion,30 and closure of atrial level defects.31-34 ICE has been shown to have imaging comparable to prior imaging modalities used during cardiac interventions,34,35 and is perhaps a superior imaging method.36-38 The cost of ICE had been deemed prohibitive, but investigators have shown that the costs may be equal to or less than prior imaging modalities.39