Many multipolar electrode catheters have been developed to facilitate placement of the catheter in the desired place and to fulfill various recording requirements. Bipolar or quadripolar electrode catheters are used to record and pace from specific sites of interest within the atria or ventricles. These catheters come with a variety of preformed distal curve shapes and sizes (Fig. 4-1). Multipolar recording electrode catheters are placed within the coronary sinus (CS) or along the crista terminalis in the right atrium (RA). The Halo catheter is a multipolar catheter used to map atrial electrical activity around the tricuspid annulus during atrial tachycardias, as well as for locating right-sided bypass tracts (BTs) (Fig. 4-2). A decapolar catheter with a distal ring configuration (Lasso catheter) is used to record electrical activity from the pulmonary vein (PV; Fig. 4-3). Basket catheters capable of conforming to the chamber size and shape have also been used for mapping atrial and ventricular arrhythmias (Fig. 4-4). Special catheters are also used to record LA and left ventricular (LV) epicardial activity from the CS branches.⁵

FIGURE 4-1 Multipolar electrode catheters with different preformed curve shapes.

(Courtesy of Boston Scientific, Boston.)

FIGURE 4-2 Multipolar electrode catheters with different electrode numbers and curve shape. Left to right, Duodecapolar catheter, quadripolar catheter, and Halo catheter.

(Courtesy of Boston Scientific, Boston.)

FIGURE 4-3 Lasso catheter with two different loop sizes.

(Courtesy of Biosense Webster, Inc., Diamond Bar, Calif.; www.BiosenseWebster.com.)

FIGURE 4-4 Basket catheter (Constellation).

(Courtesy of Boston Scientific, Boston.)

Catheters can have a fixed or deflectable tip. Steerable catheters allow deflection of the tip of the catheter in one or two directions in a single plane; some of these catheters have asymmetrical bidirectional deflectable curves (Fig. 4-5).

FIGURE 4-5 Deflectable multipolar electrode catheters with different curve sizes and shapes.

(Courtesy of Boston Scientific, Boston.)

Ablation catheters have tip electrodes that are conventionally 4 mm long and are available in sizes up to 10 mm in length (Fig. 4-6). The larger tip electrodes on ablation catheters reduce the resolution of a map obtained using recordings from the distal pair of electrodes.

FIGURE 4-6 Ablation catheters with different tip electrode sizes and shapes. Left to right, Peanut 8-mm, 2-mm, 4-mm, and 8-mm tip electrodes.

(Courtesy of Boston Scientific, Boston.)

Catheter Positioning

The percutaneous technique is used almost exclusively. RA, His bundle (HB), and right ventricular (RV) electrograms are most commonly recorded using catheters inserted via a femoral vein. Some other areas (e.g., the CS) are more easily reached through the superior vena cava (SVC), although the femoral approach can be adequate in most cases. Insertion sites can also include the antecubital, jugular, and subclavian veins. Femoral arterial access can be required for mapping of the LV or mitral annulus or for invasive blood pressure monitoring. Occasionally, an epicardial approach is required to map and ablate certain VTs and BTs as well as the sinus node. For this purpose, the epicardial surface is accessed via the CS and its branches or percutaneously (subxiphoid puncture).⁶

Fluoroscopy is conventionally used to guide intracardiac positioning of the catheters. It is important to remember that catheters can be withdrawn without fluoroscopy, but they should always be advanced under fluoroscopy guidance. More recently, newer navigation systems have been tested to guide catheter positioning in an effort to limit radiation exposure (see Chap. 6).

Transcaval Approach

The modified Seldinger technique is used to obtain multiple venous accesses. The femoral approach is most common, but the subclavian, internal jugular, or brachial approaches may be used, most often for the placement of a catheter in the CS.⁶

The femoral access should be avoided in patients with any of the following: known or suspected femoral vein or inferior vena cava (IVC) thrombosis, active lower extremity thrombophlebitis or postphlebitic syndrome, groin infection, bilateral leg amputation, extreme obesity, or severe peripheral vascular disease resulting in nonpalpable femoral arterial pulse. IVC umbrella filters are not necessarily a contraindication to the femoral approach.

Typically, the RA, HB, and RV catheters are introduced via the femoral veins. It is advisable to use the left femoral vein for diagnostic EP catheters and to save the right femoral vein for potential ablation or mapping catheter placement, which then would be easier to manipulate because it would be on the side closer to the operator. Multiple venous punctures and single vascular sheaths may be used for the different catheters. Alternatively, a single triport 12 Fr sheath can be used to introduce up to three EP catheters (usually the RA, HB, and RV catheters). The CS catheter is frequently introduced via the right internal jugular or subclavian vein, but also via the femoral approach.

Right AtriAL Catheter

A fixed-tip, 5 or 6 Fr quadripolar electrode catheter is typically used. The RA may be entered from the IVC or SVC. The femoral veins are the usual entry sites. Most commonly, stimulation and recording from the RA is performed by placing the RA catheter tip at the high posterolateral wall at the SVC-RA junction in the region of the sinus node or in the RA appendage (Fig. 4-7).

FIGURE 4-7 Fluoroscopic views of catheters in study for supraventricular tachycardia (superoparaseptal bypass tract ablation). Catheters are labeled HRA (high right atrium), right ventricle (RV), and coronary sinus (CS); the CS catheter was inserted from a jugular venous approach.

Right VentricULAR Catheter

A fixed-tip, 5 or 6 Fr quadripolar electrode catheter is typically used. All sites in the RV are accessible from any venous approach. The RV apex is most commonly chosen for stimulation and recording because of stability and reproducibility (see Fig. 4-7).

A fixed- or deflectable-tip, 6 Fr quadripolar electrode catheter is typically used. The catheter is passed via the femoral vein into the RA and across the tricuspid annulus until it is clearly in the RV (under fluoroscopic monitoring, using the right anterior oblique [RAO] view; see Fig. 4-7). It is then withdrawn across the tricuspid orifice while maintaining a slight clockwise torque for good contact with the septum until a His potential is recorded. Initially, a large ventricular electrogram can be observed, then, as the catheter is withdrawn, the right bundle branch (RB) potential can appear (manifesting as a narrow spike less than 30 milliseconds before the ventricular electrogram). When the catheter is further withdrawn, the atrial electrogram appears and grows larger. The His potential usually appears once the atrial and ventricular electrograms are approximately equal in size and is manifest as a biphasic or triphasic deflection interposed between the local atrial and ventricular electrograms. If the first pass was unsuccessful, the catheter should be passed again into the RV and withdrawn with a slightly different rotation. If, after several attempts, a His potential cannot be recorded using a fixed-tip catheter, the catheter should be withdrawn and reshaped, or it may be exchanged with a deflectable-tip catheter. Once the catheter is in place, a stable recording can usually be obtained. Occasionally, continued clockwise torque on the catheter shaft is required to obtain a stable HB recording, which can be accomplished by looping the catheter shaft remaining outside the body and fixing the loop by placing a couple of towels on it, or by twisting the connection cable in the opposite direction so that it maintains a gentle torque on the catheter.

When the access is from the SVC, it is more difficult to record the His potential because the catheter does not lie across the superior margin of the tricuspid annulus. In this case, a deflectable-tip catheter is typically used, advanced into the RV, positioned near the HB region by deflecting the tip superiorly to form a J shape, and then withdrawing the catheter so that it lies across the superior margin of the tricuspid annulus. Alternatively, the catheter can be looped in the RA (“figure-of-6” position); then the body of the loop is advanced into the RV so that the tip of the catheter is pointing toward the RA and lying on the septal aspect of the RA. Gently withdrawing the catheter can increase the size of the loop and allow the catheter tip to rest on the HB location.

Recording of the HB electrogram can also be obtained via the retrograde arterial approach. Using this approach, the catheter tip is positioned in the noncoronary sinus of Valsalva (just above the aortic valve) or in the LV outflow tract (LVOT), along the interventricular septum (just below the aortic valve).

Coronary Sinus Catheter

A femoral, internal jugular, or subclavian vein may be used. It is easier to cannulate the CS using the right internal jugular or left subclavian vein versus the femoral vein because the CS valve is oriented anterosuperiorly and, when prominent, can prevent easy access to the CS from the femoral venous approach. A fixed-tip, 6 Fr decapolar electrode catheter is typically used for access from the SVC, whereas a deflectable-tip catheter is preferred for CS access from the femoral veins.

The standardized RAO and left anterior oblique (LAO) fluoroscopic views are used to guide placement of catheters in the CS. Although the CS cannot be directly visualized with standard fluoroscopy, the epicardial fat found in the posteroseptal space just posterior to the CS os can be visualized as a characteristic radiolucency on cine fluoroscopy in the RAO projection, where the cardiac and diaphragmatic silhouettes meet.⁷

When cannulating the CS from the SVC approach, the LAO view is used, the catheter tip is directed to the left of the patient, and the catheter is advanced with some clockwise torque to engage the CS os; electrodes should resemble rectangles rather than ovals when the catheter tip is properly oriented to advance into the CS. Once the CS os is engaged, the catheter is further advanced gently into the CS, so that the most proximal electrodes lie at the CS os (see Fig. 4-7).

During cannulation of the CS from the IVC approach, the tip of the catheter is first placed into the RV, in the RAO fluoroscopy view, and flexed downward toward the RV inferior wall (Video 2 ). Subsequently, the catheter is withdrawn until it lies at the inferoseptal aspect of the tricuspid annulus. In the LAO or RAO view, the catheter is then withdrawn gently with clockwise rotation until the tip of the catheter drops into the CS os. Afterward, the catheter is advanced into the CS concomitantly with gradual release of the catheter curve (Fig. 4-8). Alternatively, the tip of the catheter is directed toward the posterolateral RA wall and advanced with a tight curve to form a loop in the RA, in the LAO view, with the tip directed toward the inferomedial RA. The tip is then advanced with gentle up-down, right-left manipulation using the LAO and RAO views to cannulate the CS. In the RAO view, the atrioventricular (AV) fat pad (containing the CS) appears as more radiolucent than surrounding heart tissue.

FIGURE 4-8 Right anterior oblique (RAO) and left anterior oblique (LAO) fluoroscopic views of catheters in a study of typical atrial flutter. A 20-pole Halo catheter is positioned along the tricuspid annulus. The coronary sinus (CS) catheter was introduced from a femoral venous approach. The ablation catheter (Abl) is at the cavotricuspid isthmus.

When attempting CS cannulation, the catheter can enter the RV, and premature ventricular complexes (PVCs) or VT can be observed. Catheter position in the RV outflow tract (RVOT) can be misleading and simulate a CS position. Confirming appropriate catheter positioning in the CS can be achieved by fluoroscopy and recorded electrograms. In the LAO view, further advancement in the CS directs the catheter toward the left heart border, where it curves toward the left shoulder. Conversely, advancement of a catheter lying in the RVOT leads to an upward direction of the catheter toward the pulmonary artery. In the RAO view, the CS catheter is directed posteriorly, posterior to the AV sulcus, whereas the RVOT position is directed anteriorly. Recording from the CS catheter shows simultaneous atrial and ventricular electrograms, with the atrial electrogram falling in the later part of the P wave, whereas a catheter lying in the RVOT records only a ventricular electrogram. The catheter can also pass into the LA via a patent foramen ovale, in which case it takes a straight course toward the left shoulder, and all recordings are atrial.

If used, the CS catheter should be placed first, because its positioning can be impeded by the presence of other catheters. It is also recommended that the CS catheter sheath be sutured to the skin to prevent displacement of the catheter during the course of the EP study.

Transaortic Approach

This approach is generally used for mapping the LV and mitral annulus (for VT and left-sided BTs). The right femoral artery is most commonly used. The mapping-ablation catheter is passed to the descending aorta, and, in this position, a tight J curve is formed with the catheter tip before passage to the aortic root to minimize catheter manipulation in the arch. In a 30-degree RAO view, the curved catheter is advanced through the aortic valve with the J curve opening to the right, so the catheter passes into the LV oriented anterolaterally (Fig. 4-9; Video 3 ). The straight catheter tip must never be used to cross the aortic valve because of the risk of leaflet damage or perforation and also because the catheter tip can slip into the left or right coronary artery or a coronary bypass graft, thus mimicking entry to the LV and causing damage to these structures.

FIGURE 4-9 Right anterior oblique (RAO) fluoroscopic views of a mapping-ablation catheter introduced into the left ventricle (LV) via the retrograde transaortic approach. In a 30-degree RAO view, the curved catheter (A) is prolapsed across the aortic valve into the LV (B).

A long vascular sheath can provide added catheter stability. Anticoagulation should be started once the LV is accessed or before (intravenous heparin, a 5000-unit bolus followed by a 1000-unit infusion is usually used), to maintain the activated clotting time (ACT) between 250 and 300 seconds.

Transseptal Approach

Mapping and ablation in the LA are performed through a transseptal approach. Knowledge of septal anatomy and its relationship with adjacent structures is essential to ensure safe and effective access to the LA. Many apparent septal structures are not truly septal. The true interatrial septum is limited to the floor of the fossa ovalis, the flap valve, and the anteroinferior rim of the fossa. Therefore, the floor of the fossa (with an average diameter of 18.5 ± 6.9 mm [vertically] and 10.0 ± 2.4 mm [horizontally] and 2 mm thickness) is the target for atrial septal crossing. The area between the superior border of the fossa and the mouth of the SVC is an infolding of the atrial wall filled with adipose tissue. Although this area is often referred to as the septum secundum, it is not really a true septum, and puncture in this region would lead to exiting of the heart. The infolded groove ends at the superior margin (superior rim) of the fossa ovalis. Anterior and superior to the fossa ovalis, the RA wall overlies the aortic root. Advancing the transseptal needle in this area can puncture the aorta.

A search for a patent foramen ovale, which is present in 15% to 20% of normal subjects, is initially performed. If one is absent, atrial septal puncture is performed. The challenge for a successful atrial septal puncture is positioning the Brockenbrough needle at the thinnest aspect of the atrial septum, the membranous fossa ovalis, guided by fluoroscopy or intracardiac echocardiography (ICE; Videos 4, 5, and 6 ).

Although fluoroscopy provides sufficient information to allow safe transseptal puncture in most cases, variations in septal anatomy, atrial or aortic root dilation, the need for multiple punctures, and the desired ability to direct the catheter to specific locations within the LA can make fluoroscopy an inadequate tool for complex LA ablation procedures. Intraoperative transesophageal echocardiography allows identification of the fossa ovalis and its relation to surrounding structures and provides real-time evaluation of the atrial septal puncture procedure, with demonstration of tenting of the fossa prior to entry into the LA and visualization of the sheath advancing across the septum (Video 7 ). However, the usefulness of transesophageal echocardiography is limited by the fact that the probe obstructs the fluoroscopic field, and it is impractical in the nonanesthetized patient. ICE, which provides similar information on septal anatomy, can be used for the conscious patient and does not impede fluoroscopy.

Fluoroscopy-Guided Transseptal Catheterization

Equipment required for atrial septal puncture includes the following: a 62-cm, 8 Fr transseptal sheath for LA cannulation (e.g., SR0, SL1, Mullins, or Agilis NxT Steerable sheath, St. Jude Medical, Minnetonka, Minn.), a 0.035-inch J guidewire, a 71-cm Brockenbrough needle (e.g., BRK, St. Jude Medical, Minnetonka, Minn.), and a 190-cm, 0.014-inch guidewire.

Venous access is obtained via the femoral vein, preferably the right femoral vein because it is closer to the operator. The sheath, dilator, and guidewires are flushed with heparinized saline. The transseptal sheath and dilator are advanced over a 0.035-inch J guidewire under fluoroscopy guidance into the SVC. The guidewire is then withdrawn, thus leaving the sheath and its dilator locked in place. The dilator within the sheath is flushed and attached to a syringe to avoid introduction of air into the RA.

Attention is then directed to preparing the transseptal needle. The Brockenbrough needle comes prepackaged with an inner stylet, which may be left in place to protect it as it is advanced within the sheath. Alternatively, the inner stylet may be removed and the needle connected to a pressure transducer line (pressure monitoring through the Brockenbrough needle will be required during the transseptal puncture); continuous flushing through the Brockenbrough needle is used while advancing the needle into the dilator. A third approach, when the use of contrast injection is planned, is to attach the Brockenbrough needle to a standard three-way stopcock via a freely rotating adapter. A 10-mL syringe filled with radiopaque contrast is attached to the other end of the stopcock while a pressure transducer line is attached to the third stopcock valve for continuous pressure monitoring. The entire apparatus should be vigorously flushed to ensure that no air bubbles are present within the circuit.

The Brockenbrough needle is advanced into the dilator until the needle tip is within 1 to 2 cm of the dilator tip. The needle tip must be kept within the dilator at all times, except during actual septal puncture. The curves of the dilator, sheath, and needle should be aligned so that they are all in agreement and not contradicting each other. The sheath, dilator, and needle assembly is then rotated leftward and posteriorly (usually with the Brockenbrough needle arrow pointing at the 3 to 6 o’clock position relative to its shaft) and retracted caudally as a single unit (while maintaining the relative positions of its components) to engage the tip of the dilator into the fossa ovalis. Under fluoroscopy monitoring (30-degree LAO view), the dilator tip moves slightly leftward on entering the RA and then leftward again while descending below the aortic root. A third abrupt leftward movement (“jump”) below the aortic root indicates passage over the limbus into the fossa ovalis (Fig. 4-10). This jump generally occurs at the level of the HB region (marked by an EP catheter recording the HB potential). If the sheath and dilator assembly is pulled back farther than intended (i.e., below the level of the fossa and HB region), the needle should be withdrawn and the guidewire placed through the dilator into the SVC. The sheath and dilator assembly is then advanced over the guidewire into the SVC and repositioning attempted, as described earlier. The sheath and dilator assembly should never be advanced without the guidewire at any point during the procedure.

FIGURE 4-10 Right anterior oblique (RAO; left) and left anterior oblique (LAO; right) fluoroscopic views during transseptal catheterization. A, Initially, the transseptal sheath-dilator assembly is advanced into the superior vena cava. B, The transseptal assembly is withdrawn into the high right atrium. C, With further withdrawal, the dilator tip abruptly moves leftward, indicating passage over the limbus into the fossa ovalis at the level of the His bundle catheter. At the fossa ovalis, the dilator tip has an anteroposterior orientation in the RAO view and a leftward orientation in the LAO view. D, The transseptal assembly is advanced across the atrial septum. CS = coronary sinus.

Several fluoroscopic markers are used to confirm the position of the dilator tip at the fossa ovalis. As noted, an abrupt leftward movement (jump) of the dilator tip below the aortic knob is observed as the tip passes under the muscular atrial septum onto the fossa ovalis (see Video 4 ). In addition, the posterior extent of the aortic root can be marked by a pigtail catheter positioned through the femoral artery in the noncoronary cusp or by the HB catheter (recording a stable proximal HB potential), which lies at the level of the fibrous trigone opposite and caudal to the noncoronary aortic cusp. When the dilator tip lies against the fossa ovalis, it is directed posteroinferiorly to the proximal HB electrode (or pigtail catheter) in the RAO view and to the left of the proximal HB electrode (or pigtail catheter) in the LAO view (see Fig. 4-10). Another method that can be used to ensure that the tip is against the fossa ovalis is injection of 3 to 5 mL of radiopaque contrast through the Brockenbrough needle to visualize the interatrial septum. The needle tip then can be seen tenting the fossa ovalis membrane with small movements of the entire transseptal apparatus. Typically, septal staining remains visible after contrast injection, which allows for real-time septal visualization while monitoring the pressure during transseptal puncture.

Once the position of the dilator tip is confirmed at the fossa ovalis, the needle, dilator, and sheath assembly is pushed slightly against the interatrial septum, and the needle is then briskly advanced to protrude outside the dilator in the LAO view during continuous pressure monitoring. If excessive force is applied without a palpable “pop” to the fossa, then the Brockenbrough needle likely is not in proper position. After passage through the fossa ovale and before advancing the dilator and sheath, an intraatrial position of the needle tip within the LA, rather than the ascending aorta or posteriorly into the pericardial space, needs to be confirmed. Recording an LA pressure waveform from the needle tip confirms an intraatrial location (Fig. 4-11). An arterial pressure waveform indicates intraaortic position of the needle. Absence of a pressure wave recording can indicate needle passage into the pericardial space or sliding up and not puncturing through the atrial septum. A second method is injection of contrast through the needle to assess the position of the needle tip. Opacification of the LA (rather than the pericardium or the aorta) verifies the successful transseptal access. Alternatively, passing a 0.014-inch floppy guidewire through the Brockenbrough needle into a left-sided PV (beyond the cardiac silhouette in the LAO fluoroscopy view) helps verify that needle tip position is within the LA (see Video 4 ). If the guidewire cannot be advanced beyond the fluoroscopic border of the heart, pericardial puncture should be suspected. In addition, aortic puncture should be suspected if the guidewire seems to follow the course of the aorta. In these situations, contrast should be injected to assess the position of the Brockenbrough needle before advancing the transseptal dilator. Sometimes, the guidewire enters the LA appendage rather than a PV; in this setting, a clockwise torque of the sheath and dilator assembly can help direct the guidewire posteriorly toward the ostium of the left superior or left inferior PV.

FIGURE 4-11 Left anterior oblique (LAO) fluoroscopic views and simultaneous electrical and pressure (P) recordings during transseptal catheterization. Left, The transseptal assembly is in the right atrium (RA), indicated by typical A and V waves of right-heart pressure tracing. Middle, The pressure waveform is dampened somewhat as the catheter tip abuts the septum. Right, The needle is across the atrial septum, and characteristic waves (V larger than A) are seen. CSdist = distal coronary sinus; CSprox = proximal coronary sinus; LA = left atrium.

Once the position of the needle tip is confirmed to be in the LA, both the sheath and dilator are advanced as a single unit over the needle by using one hand while fixing the Brockenbrough needle in position with the other hand (to prevent any further advancement of the needle). Preferably, the sheath and dilator assembly is advanced into the LA over a guidewire placed distally into a left-sided PV, which helps direct the path of the assembly as it enters the LA and minimize the risk of inadvertent puncture of the lateral LA wall. Once the dilator tip is advanced into the LA over the needle tip, the needle and dilator are firmly stabilized as a unit—to prevent any further advancement of the needle and dilator—and the sheath is advanced over the dilator into the LA. Once the transseptal sheath tip is within the LA, the dilator and needle are withdrawn slowly during continuous flushing through the needle or while suction is maintained through a syringe placed on the sheath side port to minimize the risk of air embolism and while fixing the sheath with the other hand to prevent dislodgment outside the LA. The sheath should be aspirated until blood appears without further bubbles; this usually requires aspiration of approximately 5 mL. The sheath is then flushed with heparinized saline at a flow rate of 3 mL/min during the entire procedure.

The mapping-ablation catheter is advanced through the sheath into the LA. Flexing the catheter tip and applying clockwise and counterclockwise torque to the sheath help confirm free movement of the catheter tip within the LA, rather than possibly in the pericardium. It is important to recognize that merely recording atrial electrograms does not confirm an LA catheter location because an LA recording can be obtained from the epicardial surface of the LA, from the RA, or even the aortic root.

When two transseptal accesses are required, the second access can be obtained through a separate transseptal puncture performed in a fashion similar to that described for the first puncture. Alternatively, the first transseptal puncture can be used for the second sheath. This technique entails passing a guidewire or thin catheter through the first transseptal sheath into the LA, preferably into the left inferior or superior PV, and then the sheath is pulled back into the RA. Subsequently, a deflectable tip catheter is used through the second long sheath to interrogate the fossa ovalis and to try to access the LA through the initial puncture site. Once this is accomplished, the first sheath is advanced back into the LA, and the guidewire is replaced with the mapping catheter. Alternatively, instead of using a deflectable catheter, the needle, dilator, and sheath assembly is advanced into the SVC and pulled back and positioned at the fossa ovalis (as described earlier for the first transseptal puncture). Once the tip of the dilator falls into the fossa ovalis, gentle manipulation of the assembly under biplane fluoroscopy guidance is performed until the dilator tip passes along the guidewire through the existing transseptal puncture, without advancing the needle through the dilator. The assembly is then advanced as a single unit into the LA.

An intravenous heparin bolus is administered just before or immediately after puncturing the atrial septum, followed by intermittent boluses or continuous heparin infusion to maintain an elevated ACT (more than 250 to 300 seconds).

Intracardiac Echocardiography–Guided Transseptal Catheterization

The intent of ICE-guided transseptal catheterization is to image intracardiac anatomy and identify the exact position of the distal aspect of the transseptal dilator along the atrial septum—in particular, to assess for tenting of the fossa ovalis with the dilator tip.

Two types of ICE imaging systems are currently available, the electronic phased-array ultrasound catheter and the mechanical ultrasound catheter.⁸ The electronic phased-array ultrasound catheter sector imaging system (AcuNav, Siemens Medical Solutions, Malvern, Pa.) uses an 8 or 10 Fr catheter that has a forward-facing 64-element vector phased-array transducer scanning in the longitudinal plane. The catheter has a four-way steerable tip (160-degree anteroposterior or left-right deflections). The catheter images a sector field oriented in the plane of the catheter. The mechanical ultrasound catheter radial imaging system (Ultra ICE, EP Technologies, Boston Scientific, San Jose, Calif.) uses a 9-MHz catheter-based ultrasound transducer contained within a 9 Fr (110-cm length) catheter shaft. It has a single rotating crystal ultrasound transducer that images circumferentially for 360 degrees in the horizontal plane. The catheter is not freely deflectable.

When using the mechanical radial ICE imaging system, a 9 Fr sheath, preferably a long, preshaped sheath, for the ICE catheter is advanced via a femoral venous access. To enhance image quality, all air must be eliminated from the distal tip of the ICE catheter by flushing vigorously with 5 to 10 mL of sterile water. The catheter then is connected to the ultrasound console and advanced until the tip of the rotary ICE catheter images the fossa ovalis. Satisfactory imaging of the fossa ovalis for guiding transseptal puncture is viewed from the mid-RA (Fig. 4-12).⁸

FIGURE 4-12 Intracardiac echocardiography (ICE)-guided transseptal puncture using the Ultra-ICE catheter. These ICE images, with the transducer placed in the right atrium (RA), show (A) the RA, fossa ovalis (arrowheads), left atrium (LA), and aorta (AO). B, The transseptal needle is properly positioned, with tenting (yellow arrow) against the midinteratrial septum at the fossa ovalis. RV= right ventricle.

The AcuNav ICE catheter is introduced under fluoroscopy guidance through a 23-cm femoral venous sheath. Once the catheter is advanced into the mid-RA with the catheter tension controls in neutral position (the ultrasound transducer oriented anteriorly and to the left), the RA, tricuspid valve, and RV are viewed. This is called the home view (Fig. 4-13A; see Video 5 ). Gradual clockwise rotation of a straight catheter from the home view allows sequential visualization of the aortic root and the pulmonary artery (see Fig. 4-13B), followed by the CS, the mitral valve, the LA appendage orifice, and a cross-sectional view of the fossa ovalis (see Fig. 4-13C and D). The mitral valve and interatrial septum are usually seen in the same plane as the LA appendage. Posterior deflection or right-left steering of the imaging tip in the RA, or both, is occasionally required to optimize visualization of the fossa ovalis; the tension knob (lock function) can then be used to hold the catheter tip in position. Further clockwise rotation beyond this location demonstrates images of the left PV ostia (see Fig. 4-13E). The optimal ICE image to guide transseptal puncture demonstrates adequate space behind the interatrial septum on the LA side and clearly identify adjacent structures, but it does not include the aortic root because it would be too anterior for the interatrial septum to be punctured safely. In patients with an enlarged LA, a cross-sectional view that includes the LA appendage is also optimal if adequate space exists behind the atrial septum on the LA side.⁸

FIGURE 4-13 Phased-array intracardiac echocardiography (ICE) AcuNav serial images with the transducer placed in the middle right atrium (RA) demonstrate serial changes in tomographic imaging views following clockwise rotation of the transducer. Each view displays a left-right (L-R) orientation marker to the operator’s left side (i.e., craniocaudal axis projects from image right to left). A, Starting from the home view, the RA, tricuspid valve (yellow arrowheads), and right ventricle (RV) are visualized. B, Clockwise rotation brings the aorta (AO) into view. PA = pulmonary artery. C, Further rotation allows visualization of the interatrial septum (green arrows), left atrium (LA), coronary sinus (CS), left ventricle (LV), and mitral valve (red arrowheads). D, Subsequently, the left atrium appendage (LAA) becomes visible. E, The ostia of the left superior pulmonary vein (LSPV) and left inferior PV (LIPV) can be visualized with further clockwise rotation.

(Courtesy of AcuNav, Siemens Medical Solutions, Malvern, Pa.)

The sheath, dilator, and needle assembly is introduced into the RA, and the dilator tip is positioned against the fossa ovale, as described earlier. Before advancing the Brockenbrough needle, continuous ICE imaging should direct further adjustments in the dilator tip position until ICE confirms that the tip is in intimate contact with the middle of the fossa, confirms proper lateral movement of the dilator toward the fossa, and excludes inadvertent superior displacement toward the muscular septum and aortic valve. With further advancement of the dilator, ICE demonstrates tenting of the fossa (Fig. 4-14 and see Fig. 4-12). If the distance from the tented fossa to the LA free wall is small, minor adjustments in the dilator tip position can be made to maximize the space. The Brockenbrough needle is then advanced. With successful transseptal puncture, a palpable pop is felt, and sudden collapse of the tented fossa is observed (see Fig. 4-14). Advancement of the needle is then immediately stopped. Saline infusion through the needle is visualized on ICE as bubbles in the LA, thus confirming successful septal puncture (see Video 6 ). With no change in position of the Brockenbrough needle, the transseptal dilator and sheath are advanced over the guidewire into the LA, as described earlier.

FIGURE 4-14 Phased-array intracardiac echocardiography (ICE)-guided transseptal puncture. A, These ICE images, with the transducer placed in the right atrium (RA), show a transseptal dilator tip (yellow arrowhead) lying against the interatrial septum (green arrows). B, With further advancement of the dilator, ICE demonstrates tenting of the interatrial septum at the fossa ovalis. C, Advancement of the transseptal needle is then performed, with the needle tip visualized in the left atrium (LA), and tenting of the interatrial septum is lost.

Alternative Methods for Difficult Transseptal Catheterization

In some cases, the conventional approach using a Brockenbrough needle sheath fails to pierce the septum because of the presence of a small fossa area, a thick interatrial septum, fibrosis and scarring of the septum from previous interventions, or an aneurysmal septum with excessive laxity. Applying excessive force to the needle, dilator, and sheath assembly against a resistant septum (which can be seen as bending and buckling of the assembly in the RA) can lead to building pressure of the needle tip on the septum, which can potentially lead to an uncontrolled sudden jump of the assembly once across the stiff or fibrotic fossa ovalis, thus perforating the opposing lateral LA wall. Similarly, excessive tenting of the interatrial septum (beyond halfway into the LA) can bring it in close proximity to the lateral LA wall, so that the needle can potentially puncture the lateral LA wall once across the septum. Some of these difficulties can sometimes be overcome by manual reshaping of the curvature of the Brockenbrough needle tip, applying slight rotation on the needle and sheath assembly to puncture a different point on the fossa ovalis, using a sharper transseptal needle type (BRK-1 extra sharp), or utilizing a 0.014-inch, sharp-tipped, J-shaped transseptal guidewire (Safe Sept, Pressure Products, Inc., San Pedro, Calif.).⁹^–¹³

Other techniques to facilitate transseptal puncture include radiofrequency (RF) perforation of the fossa ovalis and the application of pulses of electrosurgical cautery or RF energy to the proximal end of the Brockenbrough needle. Once the position of the dilator tip is confirmed at the fossa ovalis (under ICE guidance), the needle is advanced beyond the tip of the dilator in contact with the septum until resistance is met. RF energy (5 to 30 W for 1 to 11 seconds) can be applied through a conventional ablation catheter electrode brought manually in contact with the proximal hub of the transseptal needle. Typically, the fossa is punctured almost instantaneously (within 1 to 2 seconds) following RF application. Alternatively, electrosurgical cautery (set to 15 to 20 W for a 1- to 2-second pulse of cut-mode cautery) is applied to the proximal hub of the needle as its tip is advanced out of the dilator. Importantly, the cautery should be initiated on the needle handle prior to pushing the needle tip beyond the dilator tip to help minimize the power needed to puncture the septum, and it should be stopped as soon as the needle is pushed out fully.¹⁴^–¹⁶

Additionally, a specialized, electrically insulated RF-powered needle (Baylis Medical Company, Inc., Montreal) has been developed to facilitate transseptal puncture. The needle is connected to a proprietary RF generator (RFP-100 RF Puncture Generator, Baylis Medical), which delivers RF energy to the rounded, closed tip of the needle positioned at the interatrial septum. Once septal tenting is visualized on the ICE, RF energy is applied at 10 W for 2 seconds. The RF perforation generators apply a higher voltage for short durations, resulting in a high-energy electric field and an almost instantaneous temperature rise to 100°C, leading to steam popping and septal perforation with minimal collateral tissue damage. In contrast, conventional RF generators deliver a higher power with a lower voltage and impedance range for longer periods of time, with resulting thermal destruction of the local tissue around the needle tip, rather than perforation.^17,¹⁸

These methods help minimize pressure application to the needle as it crosses the septum and tenting of the septum, which can potentially reduce the chances of sudden advancement through the lateral LA as the needle crosses the septum. Nonetheless, the powered needle can potentially be more traumatic at the puncture site than a standard needle, and it is possible that the transseptal puncture site created with a powered needle is less likely to close spontaneously. Similarly, inadvertent cardiac perforation occurring in the setting of powered needles can potentially be associated with greater consequences. Whether RF is more likely to cause a thrombus at the puncture site compared with a standard needle is unknown.¹⁷^–¹⁹

Complications of Atrial Transseptal Puncture

Injury to cardiac and extracardiac structures is the most feared complication. Because of its stiffness and large caliber, the transseptal dilator should never be advanced until the position of the Brockenbrough needle is confirmed with confidence. Advancing the dilator into an improper position can be fatal. Therefore, many operators recommend the use of ICE-guided transseptal puncture, especially for patients with normal atrial size.¹⁹

When the aorta is advertently punctured by the Brockenbrough needle—an arterial waveform is recorded from the needle tip and dye injected through the needle is carried away from the heart—the needle should be withdrawn back into the dilator. If the patient remains stable for 15 minutes and echocardiography shows no pericardial effusion, another attempt at LA access can be made. Advancing the dilator and sheath assembly into the aorta can lead to catastrophic consequences.

It is important to recognize that successful atrial septal puncture is a painless procedure for the patient. If the patient experiences significant discomfort, careful assessment should be made of the catheter and sheath locations (pericardial space, aorta).

Another potential complication is embolism of thrombus or air. To avoid air embolism, catheters must be advanced and withdrawn slowly so as not to introduce air into the assembly. Sheaths must be aspirated with a syringe on a stopcock to the amount of their volume (e.g., an 8 Fr sheath contains 5 mL when filled) to remove any retained air. Thromboembolic complications can be avoided by flushing all sheaths and guidewire with heparinized saline and maintaining the ACT at longer than 300 seconds. In addition, a guidewire should not be left in the LA for more than 1 minute, especially if no systemic heparin has been administered. Administration of heparin before, rather than after, the atrial septal puncture can also help reduce thromboembolism.¹⁹

Occasionally, ST segment elevation in the inferior ECG leads (with or without transient bradycardia or AV block) can occur following transseptal catheterization, potentially secondary to air embolism in coronary arteries, although a Bezold-Jarisch–like reflex mechanism can also be implicated.

Importantly, the presence of an LA thrombus is an absolute contraindication for transseptal catheterization. Additionally, caution should be used in the setting of the presence cardiac or thoracic malformation (e.g., congenital heart disease, kyphoscoliosis).

Transseptal catheterization is feasible and safe in most patients with atrial septal defect or patent foramen ovale repair. Nonetheless, because of the altered anatomical landmarks after repair, fluoroscopic guidance for transseptal puncture can be unreliable, and the procedure can be challenging. In these patients, an understanding of the method of repair and utilization of ICE guidance are essential.

In patients with atrial septal defect closure devices, puncture is preferably performed at the portion of the septum located inferior and posterior to the closure device and not through the device itself. In patients with a septal stitch or pericardial or Dacron patch, puncture can be achieved through the thickened septum or the patch. However, transseptal access is typically not achievable through a Gore-Tex patch (W.L. Gore & Associates, Flagstaff, Ariz.) because of its resistant texture; instead, puncture can be performed directly through neighboring native interatrial tissue. When the patch is wide, sufficient free septal tissue for transseptal puncture may not be available, in which setting transseptal access to the LA may not be feasible.^19,²⁰

Epicardial Approach

Coronary veins can be used to perform epicardial mapping, but manipulation of the mapping catheter is limited by the anatomical distribution of these vessels. Therefore, the subxiphoid percutaneous approach to the epicardial space is the only technique currently available that allows extensive and unrestricted mapping of the epicardial surface of both ventricles, and it has been used most commonly for VT mapping and ablation. The epicardial approach for mapping and ablation is discussed in Chapter 27.⁶

Baseline Measurements

Intracardiac Electrograms

Whereas the surface ECG records a summation of the electrical activity of the entire heart, intracardiac electrograms recorded by the electrode catheter represent only the electrical activity (phase 0 of the action potential) of the local cardiac tissue in the immediate vicinity of the catheter’s electrodes. Cardiac electrograms are generated by the potential (voltage) differences recorded at two recording electrodes during the cardiac cycle. All clinical electrogram recordings are differential recordings from one source that is connected to the anodal (positive) input of the recording amplifier and a second source that is connected to the cathodal (negative) input.²¹

Recorded electrograms can provide three important pieces of information: (1) the local activation time (i.e., the time of activation of myocardium immediately adjacent to the recording electrode relative to a reference), (2) the direction of propagation of electrical activation within the field of view of the recording electrode, and (3) the complexity of myocardial activation within the field of view of the recording electrode.

Analog Versus Digital Recordings

Intracardiac electrograms are recorded with amplifiers that have high-input impedances (more than 1010 Ω), to decrease unwanted electrical interference and ensure high-quality recordings.²¹ Analog recording systems directly amplify the potential from the recording electrodes, plot the potential on a display oscilloscope, and write it to recording paper or store it on magnetic tape, or both. Analog systems have largely been replaced by digital recording systems that use an analog to digital (A/D) converter that converts the amplitude of the potential recorded at each point in time to a number that is stored.

The quality of digital data is influenced by the sampling frequency and precision of the amplitude measurement.²¹ The most common digital recording systems sample the signal approximately every 1 millisecond (i.e., 1000 Hz), which is generally adequate for practical purposes of activation mapping. However, higher sampling frequencies can be required for high-quality recording of high-frequency, rapid potentials that can originate from the Purkinje system or areas of infarction. The faster sampling places greater demands on the computer processor and increases the size of the stored data files.

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