Atrial Transseptal Catheterization

Introduction

Access to the left heart via the atrial transseptal catheterization (TSC) was first described in 1959 by Ross and colleagues as an alternative technique to the conventional transaortic approach to obtain left-sided hemodynamic measurements. Notwithstanding subsequent technical refinements pioneered by Braunwald, Brockenbrough, and Mullins, TSC for hemodynamic studies was initially adopted only by few highly specialized institutions, because of the higher risk of potentially life-threatening complications such as cardiac perforation. The development and widespread implementation of radiofrequency (RF) catheter ablation for the treatment of cardiac arrhythmias in the 1990s renewed interest in the transseptal approach to gain access to left heart chambers for mapping and ablation. After the pivotal demonstration by that focal discharges from the pulmonary veins (PVs) are implicated in the initiation of human atrial fibrillation (AF), TSC became critical for catheter-based procedures to eliminate arrhythmogenic triggers from the PVs, and is now considered a fundamental skill for any interventional electrophysiologist. Although the general technique of TSC has not changed substantially over the years, important technologic advances have made the procedure significantly easier and safer. This chapter will review the indications, techniques, and outcomes for atrial TSC for invasive electrophysiologic procedures.

Anatomic Considerations for Transseptal Catheterization

A detailed understanding of the anatomy of the atrial septum is crucial to safely perform TSC. When the heart is viewed from an attitudinal perspective, the right atrium (RA) is rightward and anterior, whereas the left atrium (LA) is a leftward and posterior structure. As a result, the plane of the interatrial septum (IAS) is not described by the anteroposterior sagittal plane, but is instead slanted from left anterior to right posterior. Fluoroscopically, the IAS is almost perpendicular to the plane of the screen in the left anterior oblique (LAO) projection and faces the plane of the screen in the right anterior oblique (RAO) projection. Although the septal RA and LA walls are large structures, the true septum suitable for TSC is considerably smaller and coincides with the fossa ovalis and its limbus or muscular rim. In a transesophageal echocardiography (TEE) study, Schwinger et al. showed that the muscular rim around the fossa ovalis is not always a distinct and prominent structure, and a gradual thinning without a clear muscular rim can be found in up to 20% of cases ( Fig. 39.1 ). This is particularly important for the TSC technique, because most operators rely on the tactile and visual feedback of a “jump” when withdrawing the transseptal sheath and needle from the superior vena cava (SVC) to the fossa ovalis, corresponding to the passage between the limbus (superior) and the fossa ovalis (more inferior) (see Section 5.2). It is important to emphasize, to avoid complications such as intramural septal hematoma, particularly in fully anticoagulated patients. That although the muscular rim is a part of the true septum, it should not be routinely targeted for TSC ( Fig. 39.2 , Video 39.1 ). The fossa ovalis, the only structure that should be targeted for TSC, is a fibromembranous structure with a thickness ranging from 0.5 to 1.5 mm. When viewed from within the RA, the fossa ovalis appears as a crater-like translucent depression. The normal fossa ovalis is an oblong structure; its superior-inferior diameter ranges from 10 to 31 mm, whereas the anterior-posterior diameter measures 5 to 14 mm. The larger superior-inferior diameter of the fossa ovalis has relevant implications when double TSC is required. In these cases, it may be easier and safer to accommodate the transseptal sheaths obtaining accesses at different “heights” (one more superior and one more inferior), rather than at different planes in the anterior-posterior dimension (see Fig. 39.1 ).

The RA septum located anterior to the fossa ovalis (which extends to the septal leaflet of the tricuspid valve) overlies the transverse pericardial sinus and the aortic root; this invaginates the RA at the level of the noncoronary sinus of Valsalva. The RA septal wall posterior to the fossa ovalis is in continuity with the pericardial space. Therefore puncturing the RA septum outside the fossa ovalis is associated with high risk of cardiac perforation and/or puncture of the aortic root, with potential for catastrophic complications (see Fig. 39.1 ).

Indications for Atrial Transseptal Catheterization

The location of septal crossing can be optimized for the specific procedure performed ( Fig. 39.3 , Video 39.2 ). In general, a posterior crossing is optimal when targeting posterior LA structures (e.g., the PVs during AF ablation). For patients undergoing AF ablation with either magnetic navigation or balloon technologies, it may be more favorable to puncture the fossa in a more anterior and inferior location. The magnetic navigation catheter requires a greater working length within the LA to allow full deployment of the catheter-based magnets. An anterior and inferior fossa approach for balloon PV ablation greatly facilitates access to the right inferior PV. An anterior approach is also more favorable to access the left atrial appendage (LAA) (e.g., to place percutaneous LAA closure devices) or the mitral valve annulus (e.g., to gain access to the left ventricle (LV) for mapping and/or ablation, for placement of endocardial pacing leads, or to target a left-sided accessory pathway).

A transseptal approach is also recommended when there are contraindications to retrograde transaortic approach to the LV, such as the presence of severe aortic valve disease, a mechanical aortic prosthesis, significant aortic atherosclerosis, and/or an aortic aneurysm. For all the other left-sided procedures, such as mapping and ablation of accessory pathways or ventricular tachycardia (VT), TSC is alternative to the conventional retrograde transaortic approach, with different relative merits and limitations. For instance, the TSC has the advantage of avoiding arterial access, thus minimizing the time needed for complete postprocedural vascular recovery. In our experience, mapping the circumference of the mitral annulus is more easily performed via a transseptal approach; this is particularly evident during catheter mapping of left-sided accessory pathways. These two approaches were compared in a series of 106 patients undergoing catheter ablation of a left-sided accessory pathway. A transseptal approach was adopted as a first-line method in 51 (48%) subjects; the remaining patients underwent ablation with a conventional retrograde approach. The authors reported no difference in total procedure time (220 ± 12.8 min vs. 205 ± 12.5 min) or fluoroscopy time (44.1 ± 4.4 min vs. 44.7 ± 5.1 min). Of note, the retrograde approach was associated with higher incidence of periprocedural complications or crossover to the other technique (42% vs. 11%, P <.01). Similar results have also been reported in another series. Although the retrograde approach is often preferred to TSC for mapping and ablation of VT, certain structures (e.g., papillary muscles) may be more easily sampled with a TSC approach in selected patients. The presence of left atrial thrombus or mobile mass constitutes a relative contraindication to TSC. In addition, TSC should be avoided for patients in whom persistent right-to-left shunting would be unfavorable (e.g., concomitant LV assist device).

Intraprocedural Patient Management: Sedation, Anticoagulation Status

Proper procedural sedation is important to avoid unpredictable patient movements and/or respiratory excursions during the TSC, which might result in significant shifts of the transseptal sheath and needle positioning once the fossa ovalis is engaged. A recent study evaluated the impact of the phase of respiration on catheters positioned in the central venous system using computed tomography (CT). This study showed that, during inspiration, a catheter positioned in the RA might shift superiorly by an average of 9 mm. Such an inspiratory shift during TSC could result in inadvertent puncture of the muscular rim of the septum or the roof of the LA.

The practice of uninterrupted warfarin during AF ablation is commonly used. A recent metaanalysis including more than 27,000 patients undergoing catheter ablation of AF showed a significant reduction in periprocedural thromboembolism with an uninterrupted warfarin strategy compared with low-molecular-weight heparin bridging (odds ratio [OR], 0.10; 95% confidence interval [CI], 0.05 to 0.23; P <.001). Although the incidence of major bleeding complications did not differ between the two anticoagulation strategies, minor bleeding was significantly less common in patients undergoing ablation procedures during uninterrupted warfarin therapy (OR 0.38; 95% CI, 0.21–0.71; P =.002).

Before the widespread implementation of intraprocedural imaging with intracardiac echocardiography (ICE) to guide the TSC, systemic anticoagulation was typically withheld until the achievement of LA access to minimize the risk of major bleeding (e.g., in case of inadvertent puncture of the aorta or cardiac perforation). Delaying the initiation of systemic anticoagulation until after TSC may increase the risk of sheath-associated thrombus formation detected with ICE imaging; thus we routinely initiate anticoagulation before insertion of the transseptal sheaths ( Fig. 39.4 , Video 39.3 ). In a subgroup analysis of eight studies included in the metaanalysis by Santangeli et al., four prescribed heparin administration before TSC. The composite end point of major bleeding and periprocedural systemic thromboembolism occurred in 75/4257 (1.76%) patients in whom heparin was administered before left atrial access, as compared with 16/436 (3.67%) of those in whom heparin was administered immediately after the transseptal access (TSA) (OR, 0.47; 98% CI, 0.27–0.81; P = .007). These results strongly support the administration of heparin before left atrial access, particularly when ICE imaging is available to optimize the puncture site. In addition, lower levels of anticoagulation (activated clotting times 250–300 seconds) are associated with an increased incidence of both sheath-associated and in situ thrombosis in patients undergoing AF ablation; using a higher target activated clotting time (ACT; 300–350 seconds) may decrease this occurrence.

Techniques and Tools for Transseptal Catheterization