2D and 4D Image Quality
Ultrasound has been used for many years to guide cardiac interventions. Phased-array ICE has been used to guide transseptal catheterization for over twenty years and is routinely used in many countries, including the United States, in the EP lab during complex ablation procedures. Transesophageal echocardiography can also be used to guide cardiac procedures and is commonly used during structural heart procedures, including LAAC, because it has the advantage of accurate imaging from the esophagus with the ability to generate 3D images. The disadvantage of using TEE to guide procedures in the EP lab is the need for general anesthesia and a dedicated imaging specialist to manipulate the TEE probe to assist the physician performing the procedure. There is already experience using 2D ICE to guide LAAC with the catheter in the LA. A 4D ICE catheter could have even more potential to act as a substitute for a TEE.
There are usually tradeoffs with imaging innovation. Fortunately, this novel 4D ICE catheter also performed well as a basic 2D ICE catheter. The handle is intuitive, the catheter was stable and highly responsive to manipulation, and the catheter tip was flexible enough to provide reassurance to the operator that the risk of cardiac injury during catheter manipulation would be very low. The 2D images from this imaging system were as good or better than the images obtained from the two major commercially available ICE imaging systems. The advantages of the 4D ICE catheter used in this case series are not only the ability to create high quality 3D images in real-time, but the ability to also use digital steering to optimize a view without having to mechanically manipulate the catheter, and the ability to obtain orthogonal X-plane views. For example, with the ICE catheter in one position in the RA, both a short and long axis view of the aortic root could be obtained. This would be very helpful during ablation of ventricular arrhythmias arising from the aortic cusps.
For those accustomed to using 2D ICE, there are certain fluoroscopic positions of the catheter that usually predict views of specific structures. Two-dimensional ICE uses an imaging angle of zero degrees. Because the image quality of the 4D ICE catheter degrades with digital steering as the imaging angle increases beyond approximately +60 degrees, orthogonal views are usually made at -45 and +45 degrees. This requires finding an initial view at -45 degrees rather than at 0 degrees which may not be intuitive for those already comfortable with 2D ICE.
During most EP procedures, the electrophysiologist can use ICE independently and make minor adjustments to the imaging depth, gain, and color Doppler settings. A downside of this 4D system is the need for an additional person to be at the ultrasound console to acquire, process, optimize, crop, and manipulate the images. While electrophysiologists may be accustomed to basic adjustments on the 2D console, few have enough experience with 3D imaging acquisition to take advantage of most of the features of the 4D ICE catheter. Such cases will require either intensive on-site support from manufacturer, or collaboration with cardiologists with advanced imaging expertise.