Intracardiac echocardiography (ICE) allows not only real-time visualization of intracardiac structures during invasive cardiac electrophysiological procedures, but also assessment of vascular and valvular flow parameters, using pulsed wave and color flow Doppler.1-5 The use of ICE can decrease radiation exposure to the patient, operator and staff by guiding catheter placement and localizing the tip of certain ablation catheters in real time. When combined with electroanatomic mapping systems, fluoroscopy can be significantly reduced for catheter movement, placement and ablation. Recent reports have demonstrated a significant reduction in radiation dose used for atrial fibrillation ablation procedures using this approach.6-9 These features of ICE have made the technology invaluable to perform cardiac ablation procedures.
The Medtronic Arctic Front® system was recently introduced to perform balloon cryoablation of the pulmonary veins. This procedure is primarily done with fluoroscopy and the use of intravenous contrast to guide balloon position and confirm pulmonary venous occlusion, although one group has published data demonstrating a significant reduction in both fluoroscopy and contrast use when cryoablation is performed with ICE.10 One potential complication of balloon cryoablation during right pulmonary vein ablation includes right phrenic nerve palsy leading to transient or long-term loss of right hemidiaphragm contraction with a reported incidence as high as 11%. Various techniques have been described to minimize this complication, all of which involve pacing the superior vena cava above the region of the sinus node in order to stimulate the right phrenic nerve, eliciting right hemidiaphragm stimulation and contraction. This can then be monitored visually, electrically or mechanically by the use of fluoroscopy, recording of compound motor action potentials, manual palpation, abdominal contraction assessment with a fetal monitor (M. Kowalski MD, personal communication), or even visual assessment of diaphragm movement by ICE. Pulsed wave Doppler through the ICE catheter with audio output can also be used to assess diaphragm contraction, as will be shown.
This article will illustrate some of the above-mentioned uses of ICE during balloon cryoablation for atrial fibrillation using the Arctic Front® system. Fluoroscopic runs with contrast injection will be compared to ICE images to better compare the two techniques. Finally, the use of CT registration with real-time fluoroscopy to show balloon position within the left atrium will be shown. The videos and figures are as follows:
Video series #1: ICE guiding transseptal puncture more anteriorly and inferiorly, which may facilitate balloon approach to pulmonary veins.
- Video 1.1 illustrates tenting of the fossa ovalis low and anteriorly. Note that the MV can be seen intermittently indicating more anterior approach.
- Video 1.2 shows the transseptal needle crossing the fossa.
- Video 1.3 shows a guidewire crossing the septum and directed into the left superior vein.
- Video 1.4 shows the FlexCath™ 14F sheath across the septum. Notice that the aortic and mitral valves can be seen intermittently, indicating a low anterior fossa puncture.
Video series #2: Assessment of pulmonary vein ostial diameter as well as pulmonary vein flow by color flow and pulsed wave Doppler, which if done pre and post procedure, can help to assess for PV narrowing or stenosis.
- Video 2.1 shows color flow and Doppler flow from the left superior and left inferior veins with turbulence as the flow from the left superior vein encounters the deflated balloon and Achieve catheter (blue).
- Videos 2.2 and 2.3 show pulsed wave Doppler flow from the left superior and left inferior veins, respectively. Note that the carina between the two veins is clearly visible.
Video series #3: Real-time visualization of circular mapping catheter in the targeted vein.
- Video 3.1 shows the Achieve circular mapping catheter being pushed into and pulled out of the left inferior vein.
- Video 3.2 shows the Achieve in the right inferior pulmonary vein.
Video series #4: Balloon visualization in left atrium to occlude vein compared to fluoroscopy for the left pulmonary veins.
- Video 4.1 shows the left atrium prior to balloon inflation. The Achieve™ spiral catheter is seen in the LIPV.
- The balloon is inflated in Video 4.2, and advanced toward the left inferior vein in Videos 4.3 through 4.6. Note that flow from the left superior vein can be seen to the right side of the balloon in the video clips.
- An inferior leak from the left inferior vein is seen until Video 4.6, which shows no flow from the left inferior vein.
- Videos 4.7a and 4.7b show the corresponding fluoroscopic images with contrast injection. Notice incomplete occlusion in Video 4.7a with extensive contrast leak into the left atrium with only a trace of inferior leak in Video 4.7b.
- Videos 4.8, 4.9, and 4.10 show the inflated balloon being advanced toward the left superior vein with no leak seen.
- Video 4.11 shows the corresponding fluoroscopic contrast injection into the left superior vein with complete occlusion. Note the position of the ICE catheter in the right atrium to visualize the left veins.
Video series #5:
- Video 5.1 shows the balloon advanced too distally into the left inferior vein.
- Video 5.2 shows it pulled back, revealing more of the posterior curve of the balloon. Note that even after pull back, there is no leak around the left inferior vein. The linear colored line to the left of the balloon is noise artifact.
Video series #6:
- Video 6.1 shows the fluoroscopic position of the ICE catheter to best visualize the right superior vein. Note the decapolar catheter in the SVC to pace the phrenic nerve. The ICE catheter is in the low medial right atrium pointed toward the balloon inflated in the right superior vein and the Achieve catheter is advanced in the right superior vein.
- Video 6.2 shows the flow from the right superior vein with the balloon deflated.
- Video 6.3 shows the balloon inflated and advancing toward the right superior vein with extensive leak on both sides of the balloon.
- Video 6.4 shows a better seal; however, a small inferior leak remains.
- Video 6.5 shows a fluoroscopic image for ICE placement to view the right inferior vein.
- Video 6.6 shows the balloon inflated with extensive leak superiorly and inferiorly from the right inferior vein.
Video series #7: Visualization and audiographic monitoring of diaphragmatic movement with phrenic nerve pacing.
- Video 7.1 shows the fluoroscopic position of the ICE catheter in the low right atrium pointed toward the right hemidiaphragm.
- Video 7.2 shows pulse and audio Doppler during phrenic nerve pacing. The spectral and audio Doppler correlate in intensity during phrenic nerve pacing.
Figures 1 and 2 show the use of digital CT-fluoroscopic registration to overlay a CT image with real-time fluoroscopy.
As shown, ICE is a very useful tool to decrease fluoroscopy and contrast use during balloon cryoablation. The left pulmonary veins are usually visualized more easily than the right, and the right superior vein is the most difficult to visualize from the standpoint of balloon occlusion, when the ICE catheter is in the right atrium. The right pulmonary veins are best visualized from an ICE catheter placed in the inferior right atrium or within the coronary sinus. The ability to visualize the guidewire or Achieve™ spiral catheter in the pulmonary veins is helpful to assure that the balloon is being inflated at the appropriate site without having to rely on fluoroscopy, which can sometimes be equivocal with respect to distinguishing between the left pulmonary veins and the left atrial appendage, particularly in the absence of an electroanatomic mapping system. Monitoring the audio output from pulsed wave Doppler of the right hemidiaphragm is a useful way to monitor its contraction during freezing of the right pulmonary veins. Limitations of ICE are mainly related to poor acoustic windows due to interference or ultrasound scattering from other catheters or noise artifact, which may preclude identification of key structures, thereby reducing endocardial and catheter resolution. In most procedures, however, ICE is of significant benefit in terms of added safety (transseptal puncture, esophageal localization, early pericardial effusion detection) as well as providing imaging data to reduce fluoroscopy and contrast use. While it does add an expense to the procedure, many labs routinely use ICE to perform transseptal puncture safely. If this is the case, its other advantages in facilitating the cryoablation should be fully utilized. Additional techniques such as CT overlay and registration with fluoroscopy can also be used to confirm balloon position during cryoablation.
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