TSP was developed in the 1950s for left atrial catheterization, and evaluation of valvular heart disease (1). It was developed by Ross, Morrow and Braunwald1. Further improvements were made by Brockenbrough with the development of a special needle and catheter (2) and Mullins (3) contributing with a designated dilatator and sheath. Although there are many products by different manufacturers available today, the system and the technique remain essentially the same. Nowadays, TSP is mainly being used by electrophysiologists for left atrial ablation procedures and access to the left ventricle (4). Indications and contraindications for TSP today are shown in Table 1.

The goal of transseptal puncture is to access the left atrium through the thinnest part of the interatrial septum, the fossa ovalis. Fossa ovalis is limited by the tricuspid valve anteriorly, the aortic root antero-superiorly, right and left atrial free wall with pericardial duplicature posteriorly, while inferior border is thr lower right atrium and inferior vena cava and superior border is limbus fossae ovalis and above it superior vena cava. The fossa takes up 25% of the septal area and has a diameter of 10-25mm (average 16mm) (5). It is of utmost importance to avoid aortic root puncture anterosuperiorly and right and left atrial free wall puncture posteriorly. All critical structures can be visualized during the procedure by using transesophageal (TOE) or intracardiac echocardiography (ICE). Since the use of these modalities adds cost and complexity to the procedure and they may not always be available, several methods have been developed to delineate the boundaries of the fossa ovalis using fluoroscopy.

One of the methods includes directly marking the aortic root by positioning a long J-tip guidewire or pigtail catheter in the aortic root. However, this technique requires arterial access and increases bleeding complications. Another method is to position a diagnostic EP- catheter in the His-bundle position, which is in close proximity to the right coronary cusp. The most frequently used method is to simply position an EPcatheter in the coronary sinus (CS). The CS runs along the posterior aspect of the atrioventricular groove and delineates the level of the annulus of the atrioventricular valves, the anterior boundary of the interatrial septum. While this does not directly visualize the aortic root, it allows for proper anatomical orientation and direction of TSP, particularly in conjunction with catheter in his-position (Figure 1).

TSP is performed by using specially designed and preformed needles, sheaths and dilatators. Although there are many forms, designs and sizes in use, still the most frequently used are Brockenbrough needle and Mullins sheaths (Figure 2). The procedure typically starts with access to the femoral vein using a Seldinger technique. One short sheath is placed for a coronary sinus catheter and as a vascular access for drug and fluid administration. Two long sheaths together with dilators are placed in the SVC over a long 0.032 inch J tip wire. The wire is then removed, blood aspirated and the transseptal needle is positioned just at the tip of the system. It is important to forward the needle in the sheath with a stylet in place in order to avoid inadvertent avulsion of the lining of the dilator by the sharp needle tip.

Further orientation and procedure depends on the technique used. We will describe TSP with the use of fluoroscopy with contrast injection and pressure measurement from the tip of the needle. In the LAO 45 projection, the whole system (needle, dilator and sheath) is slowly pulled back from the SVC to the RA. Orientation of the system is important, and it is held so the dilatator handle points to the 4-5 o’clock (needle and sheath should be pointing in the same direction). While pulling the system down, two ‘’jumps’’ can be seen on the fluoroscopy image. The first jump occurs, when the system enters the RA from the SVC, and the other when system jumps from muscular part of the septum, over the limbus fossae ovalis into the fossa. At this point the tip of the dilator should be above the CS catheter in the LAO projection and behind and parallel to it in the RAO projection (Figure 1). The direction of the system (projected from the tip) should not cross the line of CS catheter as it increases the risk of an anterior puncture (aortic root puncture).

When the operator is satisfied with catheter position, the needle is advanced. At the same time, the contrast is applied through the needle which opacifies the left atrium. Additionally, the position is verified by removing the syringe and performing a pressure measurement from the needle tip.

In case of a difficult puncture or a rigid interatrial septum, staining of the septum may prove very helpful. As depicted in Figure 3, the operator can then observe a “tenting” of the stained septum into the left atrial cavity when advancing the needle.

In case of uncertainty or inadequate position of the system for TSP as well as in case of staining of other structures apart from the fossa ovalis after needle advancement, the needle and the system should be withdrawn and the whole system repositioned again. As long as other structures have only been punctured with the needle, (Figure 4) the latter can be withdrawn and the risk of complications is minimal. In case of dilator and sheath advancement (8.5 Fr) into the aorta or through the atrial free wall, the complications beome potentially fatal. In case of staining of the aortic root or atrial free wall/pericardium we advise early use of echocardiography to exclude serious complications.

After the needle has crossed the septum, the whole system is slightly advanced, ensuring positioning of the dilator tip in the left atrial cavity and then removed. After aspiration of oxygenated blood (at this point O2 saturation can be measured to prove the correct position), the J tip wire should be positioned in the left superior or left inferior pulmonary vein (Figure 5). The whole system is then advanced across the septum over the wire. The wire positioned in a pulmonary vein minimizes the risk of an inadvertent injury to the left atrial wall or appendage when forcing the sheath into the left atrium. After successful TSP, the needle and the dilator are removed. The sheath is aspirated and continuously flushed with heparinized saline. At this point the further management is dependent on the procedure being performed. A second transseptal puncture is to be performed for left atrial ablation procedures, typically, using the first as a “roadmap”. In cases of a very difficult TSP, left atrial access of two long sheaths can be achieved by trying to pass the first puncture site along the guidewire with a second guidewire or a steerable EP catheter.

Some labs use additional methods for TSP like the use of transesophageal (6) and intracardiac (7) echocardiography or right atrial angiography (8). While the use of echocardiography potentially reduces the risk of complications, ICE significantly increases the costs of the procedure, while TOE increases the patient’s discomfort. Angiography of the right atrium can be used in patients with unusual anatomy. Specially designed ‘’sharp’’ J tip wires can be used (9) or radiofrequency energy over the tip of the needle can be applied (10) in difficult TSP. Recently, fluoroscopy free transseptal punctures have been described by using echocardiography and 3D navigation systems (11).

As in any other invasive procedure, a thorough preparation is important to minimize the risk for complications. Before performing TSP in patients with AF, transesophageal echocardiography should be performed to exclude a left atrial thrombus. During the TOE, anatomy of the interatrial septum, presence of PFO, ASD or septal hypertrophy can be defined and assist the operator in the procedure. TOE should also be performed in other patients who are at risk for the left atrial thrombus. During the procedure, we only use TOE in some patients who have a PFO occluder in place and TSP could not be performed using fluoroscopy only (Figure 6).

Since TSP is an invasive procedure which also requires systemic heparinization, complete blood count and coagulogram (thrombocytes, INR) should be obtained in all patients. For prevention of thromboembolic incidents, after successful TSP, patients receive 100 IU/kg of heparin. After that, ACT is measured every 20-30 minutes and should be kept >300 s (12). Although increased INR (>2.5) was considered a contraindication for TSP (4, 13), the COMPARE trial (NCT01006876) showed a decreased risk for thromboembolic incidents and major bleeding in patients who continued warfarin therapy. Today, an increasing number of centers perform TSP and PVIs without discontinuation of warfarin therapy and with INRs in the therapeutic range.

After TSP and the procedure, sheaths are removed and manual compression applied to stop the bleeding. A patient should rest 6-8 hours, and if there are no complications, he can be released home next day. A pericardial effusion should be excluded by transthoracic echocardiography. In patients after PVI, anticoagulation therapy is continued for at least three months and further management depends on thromboembolic risk (CHADS2VASc score). Patients who were ablated for left sided accessory pathways receive aspirin for 4 weeks.

Complications have been described to occur in around 1% of TSP (14, 15). Complications include pericardial effusion and tamponade, aortic root puncture, stroke, TIA, ST segment elevation, chest pain, persistence of ASD and death. In early days of TSP, first reports described an incidence of tamponade in 1.2% (16) patients. In the largest survey of TSPs which included 5,520 TSPs, the incidence of tamponade was 0.74% (14) with one death (0.018%). The incidence of tamponade also differs depending on the procedure. Tamponade is described in 1.2-6% of patients undergoing PVI which is much higher than in patients undergoing left sided accessory pathway ablation. The higher risk is probably attributable to double TSP, need for systemic anticoagulation, treatment of patients with structural heart disease (dilated chambers) and more extensive ablation in the left atrium. A part of the risk is related to ablation duration and catheter manipulation in the left atrium rather than TSP itself.

The incidence of tamponade and other complications can potentially be reduced with the use of ICE during the puncture (17). However, TSP with the use of fluoroscopy and ICE versus fluoroscopy only has never been compared in a randomized manner. It must be training, volume and experience of the operator that is more important for the reduction of complications. According to several published papers, the steepest part of the learning curve includes 25-50 TSPs after which complication rates significantly decrease (17, 18).

Thromboembolic risk during TSP exists, although it is more related to the procedure which is performed after the TSP. An adequate anticoagulation during the procedure and careful aspiration/flushing of the whole system is required for the reduction of the risk of stroke/TIA. Additional reduction in thromboembolic incidents is achieved by performing the procedures with therapeutic INR and additional heparinization during the procedure.

Transseptal puncture has become an indispensable technique for interventional electrophysiologists. The technique has become even more widely used with an increase in valvular interventions (mitral valvuloplasty and MitraClip) and the advent of left atrial appendage occlusion devices. When used by experienced hands, transseptal puncture can be performed safely and reliably when using fluoroscopy only.