Definition Defined as imaging from within the cardiac chambers and the major blood vessels. It differs from intravascular ultrasonographic imaging that refers to ultrasonographic navigation and visualization in small blood vessels (usually coronary arteries).
History In the 1960s and 1970s, the use of ultrasound- tipped catheters marked the advent of intracardiac ultrasonography. The introduction of the intracoronary ultrasound- tipped catheter in the 1980s made clinical intracardiac ultrasonography feasible. This initial use of intracardiac ultrasound in human beings was limited to imaging of a single piezoelectric crystal on the tip of a 6F or 10F catheter.
Instrumentation 9F, 9-MHz, rotating element mechanical catheter (Boston Scientific) –360-degree 2-dimensional imaging on a transverse plane perpendicular to the transducer; –radial field of view of approximately 5 cm in depth producing high-resolution near-field images in cross section; –limitations: it must be guided by a wire, and it lacks Doppler capabilities.
Instrumentation Steerable and deflectable ICE 8F and 10F diagnostic ultrasound catheter (Siemens) –64-element vector phased-array transducer ( MHz) with full Doppler capabilities including color Doppler, tissue Doppler, and spectral Doppler; –better depth penetration up to 12 cm for the 10F catheter and 16 cm for the 8F catheter; –Biplane fluoroscopy is recommended to safely advance the catheter to the desired position without a guidewire
Technique The catheter is interfaced to a standard ultrasound platform. It is introduced by either a femoral or internal jugular approach. An 11F sheath is recommended to introduce the 10F catheter, which is 90 cm long. The 8F catheter can be introduced through an 8F sheath and has a 110-cm insertable length.
Technique The transducer can be positioned in three locations: –Inferior vena cava –Right atrium –Right ventricle The RA location is most useful for monitoring invasive procedures as it visualizes the short axis aortic valve, tricuspid valve, mitral valve, RV, LV, interatrial septum, LA and left pulmonary veins.
ICE at junction of inferior vena cava and right atrium
Comparison with other imaging modalities In comparison to fluoroscopy, ICE provides direct visualization of anatomical structures as well as physiologic information. In the event of procedural complications, such as perforation and pericardial tamponade, those can be immediately identified with ICE.
Pericardial effusion (PE) adjacent to free wall of left ventricle (LV)
Comparison with other imaging modalities When compared to TEE, several studies have demonstrated that the images obtained by ICE were comparable. The near-field images obtained by ICE during PFO and ASD closure were reported by one group to be superior to those obtained by TEE. Does not require prolonged sedation or general anesthesia. Other potential complications of TEE such as esophageal trauma are also avoided.
Trans-septal puncture Transseptal puncture is often performed as part of various percutaneous procedures. The area of the fossa ovalis can be clearly visualized by using ICE. Orient the image so that the long axis of the IAS is perpendicular to the ultrasound beam. Opposition of the needle against the IAS, with resultant tenting of the septum, should be visualized before puncture is attempted.
Percutaneous PFO closure Direct visualization of the IAS by ICE can accurately define the morphology of the septum and help to exclude morphologic variations such as a long PFO tunnel, convex IAS, and hypertrophic superior limbus, as well as the presence of other potential interatrial communications. During deployment of the closure device, ICE can be used to ensure that the IAS is completely between the left and right arms of the device, and that no residual shunt is present.
Percutaneous PFO closure
Percutaneous ASD closure The size of the ASD can be determined using ICE. ICE can also be used to inspect the septum before the closure, guide crossing the septum, ensure optimal position of the device, and exclude residual shunt and possible complications.
Percutaneous ASD closure
Percutaneous balloon valvuloplasty ICE can be used to guide proper positioning of the balloon apparatus within the leaflets. It can also be used to measure the gradients across the valve as a measure of success, to grade the degree of insufficiency across the valve to determine when to stop balloon inflations, and to exclude potential complications.
Percutaneous balloon valvuloplasty
Cardiac biopsy Cardiac tumors can be well visualized using ICE, allowing for accurate tissue sampling. In addition, potential complications can be identified immediately.
Radiofrequency Ablation of A Fib ICE guides trans-septal puncture. It also delineates abnormal anatomy. It has been demonstrated that both catheter position and stability can be evaluated more accurately by ICE when compared with traditional methods. It also allows sizing and positioning of PV mapping catheters, measurement of PV ostial diameters, and continuous monitoring of PV Doppler flow velocities.
Radiofrequency Ablation of A Fib Other complications related to ablation, such as pericardial effusion, perforation of the aorta, and thrombus formation, can be recognized early and prevented by use of ICE. An additional potential complication of ablation in the LA is the development of a fistula between the LA and the esophagus which can also be detected by ICE.
Radiofrequency Ablation of A Fib
Catheter Ablation of Atrial Flutter The anatomic thickness of the RA isthmus, the diameter of the RA, and thickness of the RA free wall can all be measured by using ICE. These measurements are critical for constructions of complete bidirectional block by radiofrequency energy in the isthmus between the tricuspid annulus and inferior vena cava.
Placement of a Pacing Catheter in the Coronary Sinus ICE can be used during this procedure for visualization of the coronary sinus anatomy. This has the potential of facilitating coronary sinus lead placement, while reducing fluoroscopy time and rate of possible complications.
Placement of a Pacing Catheter in the Coronary Sinus
Limitations The echo probe is single use only and therefore considered an expensive addition to a procedure. Another limitation is the size of the original 10F catheter, which limits its use in small adults and children. Furthermore, a monoplane imaging catheter does not provide a wide field of view in multiple planes, and therefore requiring manipulation of the catheter to obtain additional views.
Future Advances in ICE Technology Newer imaging modalities, including Doppler tissue imaging and velocity vector imaging, are now being investigated for use in combination with ICE. Another future area of development is combining the ICE catheter with an EP mapping catheter. Finally, efforts are being applied to the development of ICE catheters with the ability to generate 3-dimensional volumes that could be reconstructed for improved visualization of intracardiac structures.