The Acuson AcuNav™, part of the Siemens Corporation, is a catheter that brings ultrasound technology inside the heart. This technology allows physicians to have clear intracardiac details of the hearts structure during complex procedures. This device provides images that are unparalleled in detail resolution and penetration, down to 15 cm in the heart utilizing high resolution 2-dimensional and color doppler images of intracardiac anatomy. This new device enables physicians to see areas of the anatomy that were not previously seen with other technologies.

T

wo Mayo Clinic physicians, Dr. James Seward and Dr. A. Jamil Tajik originally conceived the idea for such a device. A separate team led by Dr. Douglas Packer, a Mayo Clinic Electrophysiologist, tested the tool’s effectiveness at imaging cardiac anatomy and physiology, and other devices within the heart. Due to collaboration between Acuson and these Mayo Clinic cardiologists, this product received 510(k) clearance on December 21st, 1999, allowing Acuson to market the AcuNav™ diagnostic ultrasound catheter in the United States.

The AcuNav™ has many useful indications. Many electrophysiologists rely on this technology to provide the critical visualization necessary to perform complex ablations for the treatment of atrial fibrillation, ventricular tachycardia, congenital heart disease, and other complex arrhythmias. It is a useful tool for precise localization of the membranous fossa during transseptal punctures. This has been extremely advantageous involving cases that have fossa scarring related to previous procedures (Figure 1). Interventional cardiologists find this technology especially helpful during closure of atrial or ventricular septal defects. A septal closure device in conjunction with the AcuNav has allowed interventional cardiologist to replace open chest procedures with transcatheter techniques.

Case Discussion

Figure 2

Anatomic location and dimensions via two-dimensional imaging of the LI/LS antrum = 31.8 mm, LIPV = 17mm, LSPV = 18mm.

Figure 1

Visualization of septal membrane tenting at the time of transseptal crossing via two-dimensional imaging.

In this case, a 61-year-old was referred for further treatment of atrial fibrillation. This patient has a long-standing history of hypertension, but no history of TIA, CVA, diabetes, CAD, hyperlipidemia, or family history of atrial fibrillation. He previously presented to his community based physician with prolonged flu-like symptoms, and during this encounter he was found to be in atrial fibrillation with a fast ventricular response. He was previously treated with Betapace and amiodarone, neither were effective with maintaining normal sinus rhythm after *electrical cardioversion. Despite rate control drug therapy, this patient still experienced rapid ventricular rates with minimal physical activity. This resulted in decreased stamina, increased fatiguability, and a decrease in overall exercise tolerance. At the time of referral, he had been in incessant atrial fibrillation for over six months.

Treatment options were presented to him. The first option was for more aggressive medication treatment to control his fast ventricular rates during activity. Despite aggressive treatment in the past, this goal was never achieved. The second option was to perform an AV node ablation and placement of a permanent pacemaker which he declined. When looking at patients that present with focal atrial fibrillation, 90% of these are found to have atrial fibrillation originating in one or more of the pulmonary veins. Therefore, a third option of pulmonary vein isolation, atrial flutter ablation, and assessment for a non-pulmonary vein trigger was offered. If non-pulmonary vein triggers were present, linear ablation lines would be considered if clinically indicated. After discussing the risks and benefits of the procedure he elected for a curative treatment approach for his atrial fibrillation.

Figure 4

Normal Doppler velocities within the right middle pulmonary vein prior to RF ablation for atrial fibrillation.

Figure 3

Right middle pulmonary vein (RM) measuring 10 mm prior to isolation with RF ablation.

The patient was brought to the electrophysiology lab. Catheters were placed in the right ventricle, HIS region, right atrium, and coronary sinus. The AcuNav catheter was placed in the right atrium. Accurate pulmonary vein dimensions and anatomy were assessed by two-dimensional imaging, color flow Doppler and pulsed wave Doppler (Figures 2–6). Two transseptals were performed utilizing the visualization provided by the AcuNav catheter. This access to the left atrium lends itself well to accurate mapping and ablation of the pulmonary veins. One of the transseptals provided access for Lasso™ catheter (Biosense Webster, Diamond Bar, California) and the second for the ablation catheter or 20 pole diagnostic mapping catheter (Figure 7). The pulmonary veins were isolated utilizing radiofrequency energy under the guidance of intracardiac ultrasound, fluoroscopy, and intracardiac electrograms (Figure 8). After successful isolation of the pulmonary veins, a right atrial isthmus flutter line was placed which showed bi-directional block during pacing maneuvers. The patient left the laboratory in normal sinus rhythm.

Figure 5

Color flow Doppler demonstrating normal flow patterns within the RSPV branches.

Figure 6

Two-dimensional images confirm/assist the proper positioning of the LASSO catheter in the antrum to the LI and LS pulmonary veins as well as the ablation catheter at the ostium of the LSPV.

Figure 7

Determination of adequate catheter tip temperature and contact visualized by two-dimensional images demonstrating the development of micro bubbles.

Conclusion
The AcuNav intracardiac ultrasound catheter provides superior images of the cardiac structure for complex electrophysiology procedures and for complex interventional cardiology cases. This product demonstrates clear advantages for curative ablation of atrial fibrillation as well. The AcuNav allows for improved efficiency and safety during transseptal puncture, proper sizing of pulmonary veins, accurate pulmonary vein sizing comparisons before and after ablation, and visualization of proper catheter placement assuring that the ablation catheter is at the pulmonary vein ostium. Post ablation imaging, color flow and pulsed wave Doppler assessments allow for immediate detection of complications involving pulmonary vein stenosis. This breakthrough ultrasound technology has proven to be an essential tool during ablation procedures for the treatment of atrial fibrillation and other complex arrhythmias.