Trans-septal puncture is a key technique for the interventional electrophysiologist to allow access to the left atrium and left ventricle. In order to perform the procedure safely a detailed understanding of the technique and the anatomy of the septum is required. Techniques for trans-septal puncture vary and general principles will be covered in this section.
Indications for trans-septal puncture
• Ablation of left-sided accessory pathways.
• Ablation of atrial fibrillation and atrial tachycardias following previous ablation for atrial fibrillation.
• Ablation of focal tachycardia arising in the left atrium.
• Ablation of ventricular tachycardia – particularly where the origin is thought to be the LV free wall.
• Ablation of left-sided slow pathways in AVNRT (rarely required).
Complications of trans-septal puncture
• Aortic perforation.
• Pulmonary artery perforation.
• Pericardial tamponade.
The overall risk of significant complications is around 1%.
Tips to avoid complications with trans-septal puncture
• Never advance the trans-septal sheath over the needle unless you know where the tip of the needle is located. The trans-septal needle itself is very small and very rarely causes significant problems. Even if the needle enters the aorta, as long as the trans-septal sheath itself has not been advanced, this can usually be managed by withdrawing the needle.
• Never advance the trans-septal sheath and dilator into the SVC without a wire.
• Always confirm placement of the needle in the left atrium in at least two different ways: pressure measurement, withdrawal of oxygen-rich blood, and/or imaging.
• If in doubt, STOP and remove the trans-septal needle; replace with the guidewire and start again.
The true interatrial septum consisting of that part of the atria that is bordered by both the left and the right atrial cavities is relatively small and only makes up a minor part of the medial wall of the right atrium. It largely consists of the fossa ovale ( Fig. 2.1), which is formed from the septum secundum during embryonic life.
Anatomical relations of the interatrial septum
• Superiorly: superior vena cava.
• Antero-superiorly: aortic root.
• Postero-superiorly: pulmonary artery.
• Anteriorly: triangle of Koch and septal tricuspid annulus.
• Anteroinferiorly: coronary sinus os.
• Inferiorly: inferior vena cava.
• Posteriorly: fold of tissue between right and left atrium.
Trans-septal sheaths are pre-formed sheaths that are designed to ease access to particular parts of the LA. They come with a dilator and guidewire. Both the sheath and dilator should be flushed fully before use to avoid air bubbles.
Trans-septal needles are long, hollow needles with a pre-formed bend at the tip. Designs vary, but one of the most common is the Brockenbrough (BRK) needle. The curved end of the needle comes in various sizes, often labelled as BRK 0, 1, or 2 with increasing degrees of bend. For the majority of patients a BRK 0 needle is appropriate. Many operators feel that the BRK 0 needle does not have sufficient bend and manually increase the needle bend prior to performing a trans-septal puncture. The trans-septal needle comes with an inner guidewire designed to protect the tip of the needle as it is advanced through the dilator of the trans-septal sheath.
Pressure monitoring of the trans-septal needle is used by many operators to allow correct positioning of the needle in the LA and to allow immediate detection of inadvertent aortic or pulmonary artery puncture.
Anatomical reference markers
The most feared complication of trans-septal puncture is inadvertent aortic puncture. In order to minimize the risk of this, many operators mark the aorta so that its position can be seen fluoroscopically. This can be done in two ways:
His catheter: The bundle of His lies just adjacent to the aortic root. A catheter detecting the His signal will provide an accurate marker of the position of the aortic root.
Aortic reference: Alternatively a pigtail catheter can be placed retrogradely in the aortic root via a femoral artery puncture. However, care must be taken to ensure the catheter is advanced fully into the aortic root.
• Anatomical reference markers are placed according to the operator's preference.
• Access is gained to the right femoral vein and a wire is advanced to the SVC under fluoroscopy (Fig. 5.1).
• The trans-septal sheath with its dilator is advanced over the guidewire into the SVC. (Some operators prefer to pre-dilate the groin with a short sheath before passing the trans-septal sheath.)
• The guidewire is withdrawn from the sheath and dilator.
• The needle is advanced within the dilator under fluoroscopy to a position where the tip of the needle lies just inside the dilator. The inner guidewire is then removed and pressure monitoring attached (note: many operators remove the guidewire and attach pressure monitoring before advancing the needle into the sheath and dilator). It is often helpful to practise this outside the body so that you are aware of how far the needle needs to be inserted before its tip extends beyond the end of the sheath. As the needle is inserted into the body it should be allowed to rotate freely within the sheath, as otherwise there is often some resistance as the needle passes under the inguinal ligament.
• The entire trans-septal apparatus (needle, sheath, and dilator) is fixed together with one hand and rotated so that the curve of the needle and sheath points posteromedially to between 4 and 5 o’clock on an imaginary clockface, where the patient's chest is 12 o’clock, left arm is 3 o’clock, and back is 6 o’clock.
• The entire trans-septal apparatus is then withdrawn slowly from the SVC into the right atrium, normally during continuous fluoroscopic screening in the LAO projection (although some operators do this in the PA projection).
• As the needle enters the right atrium it will appear to jump to the left of the body (right of the screen) twice. The first (often very small) jump happens as it comes around the indentation in the SVC caused by the knuckle of the ascending aorta, and the second (usually larger) jump happens as it crosses the upper limbus of the fossa ovale and falls into the fossa itself.
• Whilst in the right atrium, a right atrial pressure trace will be recorded. The trans-septal apparatus should then be advanced slightly into the fossa ovale. At this point the fossa ovale will become tented and the pressure trace from the trans-septal needle will become ‘flat’ as the needle tip abuts against tissue. The trans-septal needle itself will usually be felt to pulsate with the cardiac motion.
• The position of the trans-septal needle should be checked in both RAO and LAO projections. It should lie behind (to the left of) the aortic markers in the RAO projection and will often pass completely behind the aortic marker in the LAO projection.
• With the left hand holding the trans-septal sheath and dilator in position tenting the fossa ovale, the operator's right hand should advance the trans-septal needle out of the end of the sheath. A pop may be felt as the needle passes through the fossa into the left atrium (Fig. 5.2).
• A left atrial pressure trace will be seen – there should be two positive deflections of the pressure trace for each heart beat (if the patient is in sinus rhythm). The pressure measurement should also be significantly lower than arterial pressure, although this can be misleading in patients with significant MR. Note: an atrial pressure trace can sometimes be seen with the needle in the pericardial space.
• It should be possible to withdraw bright red blood from the trans-septal needle. Arterial blood can also be withdrawn from the aorta but this will have a very different pressure trace. If the needle is in the pericardium no blood can be withdrawn. If it is still in the RA or in the PA, deoxygenated blood will be drawn back.
• If there is any doubt, the needle should be withdrawn and the process restarted. Otherwise the trans-septal sheath can be advanced into the left atrium. This can be done in one of two ways:
• The trans-septal needle is fixed in position with the right hand whilst the dilator is advanced a few millimetres with the left hand. The needle and dilator are then fixed in position with the right hand whilst the sheath itself is advanced into the left atrium.
• Alternatively the trans-septal needle can slowly be withdrawn completely and replaced with a guidewire, which is then advanced with fluoroscopic guidance into a pulmonary vein (usually on the left). The dilator and sheath can then be advanced over the wire into the left atrium without risk of perforating the atrial wall. This is particularly useful in patients with a tough interatrial septum, for example a patient who has previously had a trans-septal puncture performed. If the septum is really tough it is sometimes easier to advance the sheath if the wire is manipulated into a right-sided pulmonary vein.
• Dilator (and wire) are then withdrawn (Fig. 5.2). The sheath will appear to move down slightly into the LA as this happens.
• Before putting any catheters into the sheath, blood should be aspirated from it until no air is withdrawn (otherwise it is possible to get air introduced into the atrium). The line is then flushed (ideally with heparinized saline).
• The patient is then heparinized – the amount given and the desired ACT vary between operators and depend upon the case itself. Some operators will give the heparin before the puncture itself because of a fear of thrombus formation on the needle tip acutely.
• Contrast staining of the septum – small quantities of contrast are injected through the trans-septal needle when it is against the septum. If it is within the fossa ovale the dye infiltrates the septum and can be seen to ‘stain’ the tissue. The needle will tent the septum when in the correct position (Fig. 5.1) and the needle is then advanced as described previously.
• Echocardiographic guidance – the puncture may be performed whilst using intracardiac echocardiography (which requires an extra venous sheath and an intracardiac echo catheter) or using transoesophageal echocardiography (which is possible under conscious sedation but is more straightforward under general anaesthesia).
• Patent foramen ovale (PFO) – in some patients a PFO may have already been identified (on a previous echocardiographic study, for example). The trans-septal needle may not need to be advanced if the sheath can be advanced through the PFO with gentle pressure on the sheath alone. Even if a PFO is not known about already, pressure should be gently applied before the trans-septal needle is advanced out of the sheath in case a PFO is present.
• Double trans-septal puncture – with the increase in procedures to ablate atrial fibrillation, there is an increase in the number of cases where access is needed for more than one catheter in the left atrium at the same time ( Chapter 20). Various techniques exist for gaining ‘double trans-septal’ access. The most straightforward is for two separate trans-septal punctures to be performed with two sheaths. In this case it is important to ensure the second sheath is not held away from the septum by the first sheath. It is sometimes necessary to rotate the second sheath 360° clockwise or anti-clockwise to make sure the sheath falls towards the septum – this will be seen as a drop towards the septum, as with any other trans-septal puncture. Alternatively a single trans-septal puncture is performed and after the sheath is advanced into the LA a guidewire is passed through the sheath into the LA and placed in a stable position (often the left upper pulmonary vein). The sheath can then be withdrawn into the right atrium (and advanced to and fro through the septum to ensure a hole is present). With the first sheath in the RA, a catheter (usually a steerable ablation catheter) is passed through the second trans-septal sheath, used to locate the initial puncture site and hole, and advanced into the LA. Once the catheter is across the septum it is deflected maximally to ensure it will not perforate the LA and the sheath is advanced through. The first sheath can now be advanced back through the puncture using the guidewire so two sheaths are in the LA.
Where a previous trans-septal puncture has been performed and was noted to be difficult it is possible to prepare for the second time, but difficulty is encountered without any warning in some cases. Some difficulties that are encountered include:
• A more anterior fossa than usual – this is an anatomical variation and means that the sheath may only need to be in a 3 o’clock position rather than the usual 4–5 o’clock position. The concern is that there is a risk of puncturing the aorta if the needle is too anterior and so this may be best performed either with transoesophageal or intracardiac echocardiographic guidance.
• A tough septum/fossa – this may be because the muscular septum was punctured rather than the membranous part. If the whole fossa is thick then some other types of trans-septal needles may provide more support without the risk of pushing too hard, e.g. a two-part Endrys needle consisting of not only the inner sharp needle but also an outer metal dilator that goes inside both a specific trans-septal sheath and its own dilator.
• The sheath does not ‘catch’ in the fossa but slides up and down the septum freely – if the septum is entirely smooth then the sheath does not engage the fossa. Again, echocardiographic guidance can be helpful. Some operators will position the sheath just below (0.5 cm) where the fossa should be anatomically (using the standard references that they have in place, e.g. the aortic and CS catheters) and then advance the needle out of the sheath. This tends to straighten up the position slightly, lifting the needle to the correct position and the whole apparatus is then advanced. With the needle out of the sheath it now catches on the septum and punctures at this level. If it too slides freely then STOP and consider using imaging to help.
• The sheath does not seem to fall across to the fossa – particularly where there is right atrial dilatation, the standard curve on the trans-septal needle may not be enough to reach across to the fossa. There are specific needles designed with sharper curves as described previously ( p. [link]), but it is possible to simply reshape the standard needle outside of the body with a sharper curve and then re-insert it into the sheath. Care needs to be taken when doing this not to damage the inner lumen of the needle, and with the sharper curve the needle tends to catch more as it is inserted into the sheath, especially as it goes under the inguinal ligament.
• Once the trans-septal sheath is in the left atrium and has been flushed ( p. [link]) catheters can be inserted. These should be inserted and withdrawn slowly as it is possible to create a negative pressure effect at the haemostatic valve (particularly on removing the catheter) and introduce air into the sheath.
• Whenever a catheter is removed from the sheath, before another catheter is inserted the sheath should be aspirated so that blood is flowing freely with no evidence of air, and then flushed with (heparinized) saline to avoid the risk of air embolism.
• Where trans-septal sheaths are going to be in the left atrium for longer periods of time (e.g. a number of hours for AF ablation procedures), many operators will continuously infuse saline or heparinized saline through the side arm (at rates of 30 ml/hr or more).