Intracardiac echocardiography (ICE) is an intravascular ultrasound (IVUS) modality that provides diagnostic imaging of cardiac structures from within the heart and has become widely used for guiding noncoronary interventions in the catheterization and electrophysiology laboratories. The first IVUS catheters used high-frequency transducers (20-40 MHz) containing a single ultrasound crystal that rapidly rotated at the end of the catheter, producing a radial 2-dimensional image.1 This type of high-frequency IVUS transducer provides excellent spatial resolution in the near field, making it uniquely suited for imaging the coronary arteries and other small vessels. The main limitation of IVUS in this frequency domain, however, is the short imaging depth (several millimeters).1,2 To accomplish ICE imaging from atria to apex, lower frequency transducers (5-12 MHz) have been miniaturized and mounted onto catheters capable of percutaneous insertion and manipulation within the heart.1,3-7 These lower frequency transducers are capable of greater tissue penetration and imaging depth, permitting high-resolution two-dimensional imaging of the whole heart.2,8-11 The earliest experiences with such low-frequency ICE catheters were described in the late 1970s and early 1980s.3,4 More recently, with the introduction of the newest phased array transducers, full Doppler flow data can be obtained.
Two different types of ICE catheters are currently available for clinical use. A mechanical transducer, similar to that used with IVUS, has a rotating ultrasound transducer driven by a motor unit at the opposite end of the drive shaft, which results in a 360° “radial” view perpendicular to the axis of the catheter. The second type is a fixed or phased array catheter-mounted transducer that uses electronically controlled transducers mounted on one side of the catheter shaft, which results in a wedge-shaped 90° image sector similar to that of transthoracic or transesophageal echo probes.
Both types of catheters provide high-resolution, real-time images of cardiac morphology and devices or catheters in the heart. Current ultrasound catheters, with a diameter size between 6- and 10- Fr, are typically introduced via a sheath in the femoral vein. Phased array catheters offer a large depth of field and add Doppler imaging capabilities, whereas mechanical catheters offer superior near-field resolution.
BENEFITS OF INTRACARDIAC ECHOCARDIOGRAPHY
ICE offers imaging that is comparable or, in some cases, superior in quality to transesophageal echocardiography (TEE). ICE adds substantial anatomic information to x-ray fluoroscopy for electrophysiologic ablation procedures and transcatheter atrial septal defect closure. ICE has been shown to provide procedural benefits in the context of radiofrequency ablation procedures for atrial fibrillation and transcatheter atrial septal closure procedures,12-26 and as such, ICE has become the “reference standard” for imaging during these procedures. The major advantage over TEE is that no general anesthesia is needed for ICE. Patients who have contraindications to TEE, eg, those with significant esophageal disease, can also avoid TEE while maintaining adequate imaging using ICE. In addition, if sufficiently skilled ...