In addition, the presence of myocardial fibers within the Eustachian ridge in some patients may allow conduction through the ridge and therefore ablation only between the tricuspid valve and the Eustachian ridge may not be adequate. It may also be helpful to alter the catheter orientation (ie, creating a loop with the ablation catheter using maximum flexion over the Eustachian ridge). Using a guiding sheath over the Eustachian ridge often overcomes the problem ( Figure 5). 2, 3 This can be detected either by identifying a paradoxical catheter response to clockwise/counterclockwise torque, or by ICE. 4 When prominent, a Eustachian ridge may act as a fulcrum that reverses the torque transmitted to the ablation catheter, making catheter manipulation along the CTI difficult. The Eustachian ridge divides the CTI into an anterior sub-Eustachian portion between the Eustachian ridge and the tricuspid annulus, and a more posterior portion leading from the ridge to the anterior border of the IVC. In our case, ICE imaging did not demonstrate a prominent sub-Eustachian pouch. When these approaches are ineffective or not feasible, electrical isolation of the pouch with an encircling ablation lesion anchored to the IVC and tricuspid annulus can be performed. Use of contact force–sensing ablation catheters may be considered. In cases where this is not possible (catheter stability, increased thickness of atrial tissue), ablation within the pouch with cautious energy titration using irrigated catheters can be attempted to prevent sudden rises in impedance, tissue vaporization, and steam pop. When the electrophysiologist is aware of the presence of a prominent sub-Eustachian pouch, the ablation approach can be modified by positioning the catheter more laterally in order to avoid the pouch ( Figure 3). Both the limited blood flow and poor catheter contact within the pouch can result in difficulty or inability to achieve bidirectional CTI block. The presence of the pouch can be recognized by the atypical movement of the catheter tip fluoroscopically and it is readily recognizable by ICE imaging, right atrial angiography, or cardiac computed tomography. 2 In addition, the pouch can generate difficulty in maintaining sufficient catheter–tissue contact while withdrawing the catheter from the tricuspid annulus to the inferior vena cava (IVC) if one assumes a planar CTI. A deep sub-Eustachian pouch may cause difficulty with CTI ablation because of poor blood flow, resulting in rapid temperature and impedance rise, possible coagulum formation, and inadequate lesion formation, while concomitantly increasing the risk of perforation. In some individuals this pouch can be prominent, particularly near the septum. The sub-Eustachian pouch (pouch of Keith) is a physiologic depression of the CTI just anterior to the Eustachian ridge and laterally to the Thebesian valve at the orifice of the coronary sinus. The tachycardia terminated with ablation, but achievement of bidirectional block across the CTI ablation line was challenging. We used a power-controlled setting with a maximum temperature setting of 40☌ and a flow rate of 17 mL/min. Using an open-irrigated 3.5-mm-tip RF ablation catheter (THERMOCOOL, Biosense Webster) through a Swartz Braided SL1 guiding introducer sheath (St Jude Medical, Saint Paul, MN), ablation along the CTI was performed at a power of 30 W with titration guided by impedance and temperature monitoring. Entrainment maneuvers confirmed the atrial flutter to be CTI-dependent. The right atrial electrograms demonstrated high-to-low activation, and the coronary sinus electrograms demonstrated proximal-to-distal activation. An intracardiac echocardiography catheter (ICE ACUNAV, Siemens, Mountain View, CA) was inserted through the right femoral vein ( Figure 2). Diagnostic catheters were positioned in the high right atrium, annular right atrium across the CTI, coronary sinus, and right ventricle. The patient was brought to the electrophysiology laboratory in atrial flutter. Patient’s electrocardiogram revealing typical atrial flutter.Ī repeat electrophysiologic study was performed.
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