The physics of ICE are the same that are used for all applications of ultrasound. These include: 1) Mechanical waves with frequencies greater than 20,000 Hz; 2) Laws of sound wave reflection and refraction while crossing borders between materials of different densities; and 3) The application of miniaturized transducers and techniques that create images.

These images can then be displayed as M and B modes, with Doppler Effect (pulsed wave, continuous wave, or color flow imaging), and as three-dimensional reconstruction.

Two-dimensional ICE is the primary echo modality used in today s electrophysiology laboratory because it provides meaningful, real-time anatomic information occurring within the structures of the heart. The catheter-tipped miniaturized echo transducer uses either a series of crystals (phased arrays: EPMedSystems, Siemens, JoMed), or a single crystal in which the beam is moved by mechanical means around a circle (Boston Scientific). The phased array systems consist of either linear phased arrays (sector shaped images with side-firing arrays: EPMedSystems and Siemens), or circular phased arrays (radially arranged crystals around the tip of the catheter with a circular image format: JoMed).

Applications for ICE in EP Diagnosis and Intervention

Applications for ICE utilization in the EP laboratory environment are as varied as the procedures performed within those labs. With ablation procedures for atrial fibrillation, ICE imaging allows for the direct visualization of the pulmonary veins, location of the atrial-venal junction and assurance of the ablation catheter tip location within the pulmonary vein antrum. ICE also permits continuous monitoring for radiofrequency (RF) energy delivery during ablation, hemodynamic performance of the myocardium and pericardial space monitoring. For transseptal puncture procedures, right atrial ICE catheter positioning provides clear visualization of the fossa ovalis, tenting by the transseptal catheter and presence of saline bubbles in the left atrium once penetrated by the Brockenbrough needle. ICE has also recently contributed to the understanding of AVNRT mechanisms by confirming the association of a dilated coronary sinus ostium with the slow pathway.³

Phased array ICE catheters have been placed into the right ventricle to assess left ventricular septal/left free-wall strain rates and aortic flow/velocity for the evaluation of dyssynchrony and optimizing cardiac resynchronization therapy. ICE can therefore be utilized during the implant of coronary sinus placed, left ventricular pacing leads to assess the effects of pacing on ventricular wall motion and resynchrony efforts.⁴ ICE can also be used to accurately place a right atrial pacing lead above the fossa ovalis to shorten the p-wave duration. This cannot reliably be accomplished using fluoroscopy alone.⁵

Basic ICE Catheter Insertion Techniques