Under frontal fluoroscopic view, the needle-fitted transseptal catheter with its direction indicator pointing at about 4 o'clock is slowly withdrawn downwards (caudally) from the superior vena cava. In the process a sudden sharp movement towards the left may be observed when the tip of the transseptal assembly falls over the limbic ledge and enters the fossa ovalis. However, in cases of mitral stenosis, the motion is often difficult to detect because the atrial septal bulging towards the right atrium makes the fossa ovalis more shallow. In either case, a clockwise rotation is applied to the direction indicator to place the catheter/needle perpendicular to the atrial septum. As it is withdrawn caudally to the primary target site, the catheter tip is aligned with the "mid-line".

        At this point the catheter/needle direction varies according to left atrial sizes. In general, it is at 4 o'clock in a relatively small left atrium (< 4 cm), between 4 and 5 o'clock in a usual-sized left atrium, and at 6 o'clock in a large left atrium (> 5 cm). However, it should be noted that the groupings for small, usual and large left atrium by M-mode echocardiograms are arbitrary, and the needle direction may vary considerably amongst patients with a similar sized left atrium. Usually it is not difficult to engage the catheter tip at the primary target site in patients with relatively small or usual-sized left atrium. In our patient population, 10% had a relatively small left atrium, 50% had a usual-sized left atrium (4 to 5 cm) and the remaining 40% had a large left atrium (> 5 cm), including 5% with a giant left atrium (> 7 cm). The left atrial size ranged from 3.0 to 9.2 cm (unpublished observations).

       If the atrial septum bulges markedly towards the right atrium, especially in cases of a giant left atrium, it is difficult to align the catheter tip with the "mid-line" and perpendicular to the septum. The catheter tip faces a strong resistance at 4 o'clock when it touches the bulged septal surface. As the needle is being rotated clockwise, the catheter/needle will give way suddenly. In effect, the needle tip flips over the crest of the bulge and towards the right side of the patient, pointing to 9 o'clock. To prevent this, the catheter should be pressed slightly against the septum as the needle is being rotated clockwise to 6 to 7 o'clock. At the same time, a slight counterclockwise twist is applied to the catheter with the left hand to counter any excessive clockwise rotation of the needle. If the crest of the bulge happens to be at the
"mid-line", it is not possible to make a puncture on the line. In this case the puncture site is settled in the region slightly lateral to the "mid-line".

       When the septal bulge begins in the upper septum, the catheter/needle being withdrawn from the superior vena cava takes a lateral course to the "mid-line". In this case, turning the needle to the 3 o'clock direction may lead the catheter/needle to a medial position. If not, the needle alone can be withdrawn slightly, and the floppy tip of the catheter should tend to flip medially. Then the needle is advanced slowly and carefully to bring its tip back to the original position while keeping the catheter tip in the medial position. If the above means also fail to place the catheter/needle medially, the latter is withdrawn further downward and close to the lower edge of the left atrium (passing the caudal end of the bulge). With the needle pointing toward the left (about 3 o'clock), the catheter tip is allowed to shift medial to the "mid-line" and then carefully advanced cephalid. A clockwise twist is made to the needle and the catheter tip is steered to or near the target point.

       If the initial pass of the transseptal catheter/needle is not successful in engaging it at an appropriate puncture site, the needle is removed from the catheter and the second attempt is begun by repositioning the catheter in the superior vena cava over a guide wire. The alternative is to reposition the catheter/needle high in the right atrium. This is done by setting the needle in the 12 o'clock direction (ventrally) and carefully moving the catheter/needle upward (cephalid) while slightly rotating the direction indicator of the needle clockwise and counterclockwise to make certain the catheter tip is free and not caught against the right atrial appendage or its free wall.


Septal Puncture

       When the operator is satisfied with the intended puncture site, the catheter/needle is pressed firmly against the septum. Usually cardiac pulsations (so-called septal bounce) are felt by the right hand holding the catheter/needle. While keeping the catheter firmly against the septum to prevent it from slipping away from the puncture site, the operator releases the stopper-finger and forcefully advances the needle forward. The needle is aspirated and contrast medium is injected to confirm its entry into the left atrium. If no blood is aspirated, the needle either has dissected the high septum or is caught in the thickened septum. Staining of the septum with injection of a small amount of contrast medium easily distinguishes the two. When the high septum is dissected, it is stained in a more vertical fashion. In this situation the needle is withdrawn and septal puncture is made at a lower (caudal) site. When the needle is caught in the thick septum, the stain takes a more horizontal orientation. In this case the catheter/needle is carefully forced across the septum as described below or the puncture is attempted at another site. It is not possible to differentiate dissection of the high septum from entrapment of the needle in the thick septum with pressure monitoring. This is another reason why the author performs the transseptal puncture without constant pressure monitoring.


Confirmation of Left Atrial Entry

        After entry of the needle in the left atrium is confirmed, first by contrast medium injection followed by pressure recording and blood oximetry (if needed), the needle direction is set toward 3 o'clock (the left side of the patient). If there is no or little resistance, the catheter/needle is advanced forward about 2 cm into the left atrium. Then, the catheter alone is advanced another 2 cm (or until the tip of the transseptal sheath meets a resistance at the septum if the sheath is used), while the needle is being withdrawn.

       When a marked resistance is encountered, a sustained force is applied to the catheter/needle. After several cardiac beats, not infrequently a "give" is felt or seen on fluoroscopy when the catheter/needle finds its way into the left atrium. If this means fails to place the catheter/needle across the septum, a Bing stylet which has a blunt tip is inserted and extended beyond the needle. The catheter/needle is carefully forced through the tough septum by forward push with the right hand while applying counter resistance with the left hand. During the process the operator must be prepared to withdraw the needle as soon as the catheter enters the left atrium, lest the excessive forward momentum carries the needle forward and perforates the left atrial wall, causing cardiac tamponade. Upon removing the needle after the catheter is placed in the left atrium, heparin, 100 units/kg body weight, should be given immediately through the catheter. After baseline hemodynamic studies, PTMC is performed.