This chapter on cardiac anatomy takes a practical approach for operators who are going to perform various procedures associated with structural heart disease. Rather than assume the traditional approach of describing the gross anatomy of the heart in isolation from the procedures performed, this chapter will attempt to provide useful information (Tips and Tricks) of how the anatomy, as seen by the percutaneous operator, affects the procedure results. Therefore, the emphasis is not only on gross anatomy, but also the anatomy that the interventionalist perceives using different imaging modalities. Whereas a surgeon can see and touch the anatomic structures, a cardiac interventionalist has to rely on indirect methods of visualization, which include fluoroscopy, echocardiography, and intracardiac ultrasound. Magnetic resonance or computed tomography images can be useful for orientation and diagnosis before the procedure (and, more recently, can be used as an overlay on the fluoroscopy monitor in the catheterization lab). However, the focus of this chapter is what the interventionalist has at his or her disposal at the time of the procedure to understand the anatomy. Accurate use of available imaging modalities in the catheterization laboratory and appreciation of relative orientations are important for optimal device sizing and placement.

Fluoroscopy provides a familiar image with the right atrium adjacent to the spine in the anteroposterior (AP) view, to the right in left anterior oblique (LAO) angulation, and anterior to the spine in the right anterior oblique (RAO) projection. The left upper pulmonary vein is just superior to the left atrial appendage and extends outside the cardiac shadow (Fig. 3-1). Transesophageal echocardiography (TEE) provides an image with the left atrium at the top of the screen because it is the closest structure to the probe, whereas the anterior cardiac structures, including the right atrium, are at the bottom of the screen. The left side of the image represents the inferior aspect of the heart leading to the inferior vena cava (IVC), and the right represents the superior aspects, including the superior vena cava (SVC) and aorta, all of which are not presented in the same orientation as the physical anatomy (Fig. 3-2). Rotating a TEE image 90° counterclockwise will orient the image similarly to a fluoroscopic image but with the plane of the image originating posteriorly from the esophagus to the anterior chest. The intracardiac echocardiography (ICE) probe is situated typically in the right atrium facing the atrial septum. The structure closest to the probe, and therefore at the top of the screen, is the right atrium. Similarly to TEE, the IVC is to the left of the screen, and the SVC is on the right. Rotating the ICE image 90° counterclockwise will present an image in the same anatomic orientation as fluoroscopy (see Fig. 3-1). TEE provides multiple tomographic cuts of the heart from different planes and angulations, which can be confusing for the interventionalist with a catheter in hand.

The secundum septal defect is the most common type of atrial septal defect (ASD) and involves the fossa ovalis border and the deficient edge of the ostium secundum. The defect may be circular, oval, or fenestrated, and the septum may be rigid or aneurysmal and floppy. Relative to the long axis of the body, the right atrium lays anterior to the left atrium, and the septum is oriented obliquely in the chest from the posterior right to the anterior left. The IVC enters the right atrium at an angle and is oriented roughly in a line through the inferior-posterior quadrant of the right atrium to the superior-anterior quadrant. In utero, this orientation helps direct returning placental blood from the IVC toward the foramen ovale on the septum (Fig. 3-3). The eustachian valve further helps to direct the oxygenated placental blood toward the still patent foramen ovale. A long residual eustachian valve can be misinterpreted as the atrial septum on TEE.

The rims surrounding the defect may be deficient in any of the quadrants if they measure less than 5 mm. The retroaortic rim is in the anterior-superior quadrant. The SVC and right pulmonary veins border the posterior-superior quadrant. The posterior free right atrial wall makes up the posterior rim. The tricuspid valve borders the inferior-anterior quadrant, and the IVC is contiguous with the posterior-inferior quadrant (Fig. 3-4).

Other types of septal defects are outside the fossa ovalis and can be close to other cardiac structures. These defects, such as the ostium primum and inferior and superior sinus venosus ASDs, are not correctable by percutaneous techniques and will not be covered in this chapter.¹

In the AP projection, an ASD is oriented slightly superior to the tricuspid valve. Because the atrial septum is oblique, a guide wire from the IVC will typically pass across an ASD to the left upper pulmonary vein, appearing slightly outside the heart border on fluoroscopy. Care must be taken not to advance the wire into the left atrial appendage oriented inferior and anterior to the pulmonary veins unless the operator is performing a left atrial appendage closure procedure (see Fig. 3-1; Fig. 3-5).² A sizing balloon should be used to obtain the stretch diameter and the Doppler stop-flow measurements in the LAO projection to minimize foreshortening. A mobile, aneurysmal septum can be difficult to assess on imaging, and balloon sizing ensures appropriate device size selection, thus reducing the risk of embolization or complications.

For a complete rim and defect evaluation using TEE in the midesophageal position, the omniplane transducer is rotated through approximately 0°, 45°, and 90°. Starting at 0°, the TEE shows the anterior-posterior rims including the mitral valve and posterior atrial wall. Rotating from 30° to 45° will show the anterior-superior or retroaortic rim, which is most commonly deficient in up to 42% of patients. Moving the TEE probe at this angle in and out brings into view the superior and inferior margins of the defect (see Fig. 3-2). Further rotation to 90° to 110° will show the SVC and IVC rims (bicaval view) (Fig. 3-6).³ Three-dimensional echocardiography can outline the defect and the rims surrounding it, making identification of deficient rims easier. This is also helpful after device deployment to judge the level of impingement on cardiac structures. The pulmonary venous connections can be evaluated by echocardiography and a pulmonary angiogram during the venous phase using a 45° LAO and 35° cranial projection.⁴

To use ICE in the assessment and positioning of a closure device, begin in the right atrial home view, keeping in mind that the most proximal structure at the top of the screen is the right atrium (Fig. 3-7A). This view shows the right atrium, right ventricle, and tricuspid valve. Placing a 20° retrograde angle on the ICE probe and rotating the probe clockwise will show the aorta in the short axis and the right ventricular outflow (Fig. 3-7B). Additional clockwise steering will also bring the foramen ovale into the field. Continuing to rotate brings the interatrial septum into view and the left atrial appendage in the right bottom of the image. The mitral valve may also be observed with slight right-left rotation of the probe (Fig. 3-7C). Further clockwise rotation will then bring the left pulmonary veins into view with the left upper pulmonary vein (LUPV) to the right of the screen and left inferior pulmonary vein to the left (Fig. 3-7D). Slight clockwise rotation will bring the guide wire into view traversing the septum and along its path in the left atrium. Additional clockwise rotation will then bring the right pulmonary veins into view in the short axis (Fig. 3-7E). Withdrawing the probe to the inferior right atrium and with additional posterior tilt will show the SVC and superior-posterior rim (Fig. 3-7F). Once the device is deployed, moving the probe in and out in the neutral position with slight right-left angulation is done to demonstrate capture of the rims by the occluder.

The orientation of the IVC relative to the atrial septum causes the device delivery sheath to place traction on the occluder inferiorly toward the IVC. During deployment of an Amplatzer septal occluder (St. Jude Medical, Saint Paul, MN), care must be taken to orient the left atrial disk parallel to the septum before pulling it against the septum. If the device is angulated perpendicular to the defect, the left atrial disk may prolapse across the septum and into the right atrium. This is of greater concern with the Amplatzer septal occluder, especially in cases of a deficient retroaortic rim. The TorqueView sheath (St. Jude Medical) typically used with the Amplatzer device may not orient in the ideal plane in horizontal or rotated hearts. The Hausdorf sheath (Cook Medical, Bloomington, IN) has 2 posterior curves and an angled tip designed to maintain the distal part of the sheath and the device parallel to the septum so the disk is less likely to prolapse into the right atrium when there is a large ASD.⁵ Once the sheath and left atrial disk are pulled as a unit against the septum, the right atrial disk is deployed. Until the device is released, the deployment cable places traction on the device and angulates the occluder. The tension placed on the device by the cable will press the right disk into the IVC rim and possibly push it across the septum. Conversely, the torque on the superior-anterior aspect of the device with a deficient retroaortic rim may prolapse the device into the right atrium. A clockwise rotation on the delivery sheath for deficient IVC rims and counterclockwise for deficient retroaortic rims may orient the deployed, but unreleased, device more parallel to the septum and capture the rims (Fig. 3-8).

Larger closure devices in small or geometrically unfavorable left atria can also make deployment of the left atrial disk challenging. With the delivery sheath in the LUPV, it is possible to deploy the left disk in the proximal pulmonary vein, then gently retract the disk out and oppose it to the defect ensuring the rims are captured. Finally, a deficient retroaortic rim should prompt some caution because it is associated with device-related complications including erosions, arrhythmias, and malposition. A large defect and aneurysmal septum are also risk factors because both of these issues require larger devices to be placed.⁶ The risk of erosion is rare, at 0.1% to 0.2%, but should be considered if the patient complains of chest pain, numbness, sudden weakness, dizziness, syncope, shortness of breath, or tachycardia (Fig. 3-9).

Patent foramen ovale (PFO) is present in 20% to 30% of the general population. In utero, the septum primum develops to pass to the left and under the septum secundum, creating a conduit shunting blood in the fetal circulation from the IVC across the interatrial septum into the left heart.⁷ The oxygen saturation of placental blood is only 67%. If the blood were to follow the usual pathway through the right heart and the unaerated fetal lung, the oxygen content would continue to fall and would not be able to sustain organogenesis. This mechanism is so important that it is preserved throughout evolution in all mammals. At birth, the drop in pulmonary pressure closes the tunnel as the left atrial pressure exceeds right atrial pressure, and in most people, the septum primum and septum secundum fuse.⁸ PFOs vary in shape, configuration, mobility, and size. An understanding of PFO anatomy is important for device closure procedures. PFO size increases with age in children until maximum growth is achieved. In the adult, there is no evidence that the PFO size changes over time. PFOs usually range in size from 3.4 to 5.8 mm but reportedly can be larger, and may be 3 to 18 mm in length.⁹ The variation depends partly on how a PFO is measured (eg, by echocardiography or by balloon sizing at cardiac catheterization).

The PFO has an oval shape and is formed by the crescent-shaped thicker (1 cm) septum secundum superiorly with the thin (1 mm) septum primum passing from the inferior aspect of the atrium, under the septum secundum, then entering the left atrium (Fig. 3-10). It extends superiorly and behind the limbus of the septum secundum (Fig. 3-11). Inferior-posterior to the PFO is the IVC, inferior-anterior is the tricuspid valve, and superior-anterior is the aortic root. The SVC enters the right atrium superior-posterior to the PFO and is about 1.2 cm away^10,11 (Fig. 3-12). To cross the PFO, a multipurpose catheter and either a 0.035 J or straight-tipped wire may be advanced up the IVC. Probing the septum about 1 cm below the SVC in a line inferior-posterior to the aorta should permit crossing the PFO tunnel as is done during a trans-septal puncture when the foramen ovale is closed (Fig. 3-13).

Accurate evaluation of the PFO tunnel length and morphology requires careful echocardiographic assessment. This is needed to assess the length and height of the PFO and the presence and extent of any septal aneurysm. This in turn can influence the choice of device size and to assure there are no other findings such as a secundum ASD, fenestrated septum, septal masses, or septal hypertrophy. To obtain the width of the PFO, it would be necessary to visualize the atrial septum directly en-face. This can be obtained currently only with 3-dimensional echocardiographic imaging. Alternatively, balloon sizing of the PFO can be performed during fluoroscopy, to obtain the stretched diameter and shape of the tunnel. It is important to decrease any foreshortening of the radiographic projection, and the LAO cranial view is usually the preferred projection (Fig. 3-14).¹² The shape and size of the PFO tunnel using a balloon will influence selection of the device and its size to close the PFO.¹³ The 2 currently available devices in the United States are the Amplatzer septal occluder, the Gore Cardioform, and the Gore Helex septal occluder (W. L. Gore & Associates, Flagstaff, AZ). These devices are approved by the US Food and Drug Administration (FDA) for closure of ASDs but are not approved for closure of PFOs. At the present time, PFO closure is performed either under an Investigational Device Exemption protocol or used off-label. The Amplatzer septal occluder is self-centering, so sizing is done 1:1 to the defect. The Gore Helex device has a narrow neck and is composed of expanded ePTFE material on a 0.012-inch nickel-titanium wire frame. For a typical small PFO less than 12 mm, we use the 25-mm Helex device because it is soft and well tolerated. Larger PFOs requiring the use of a 30- or 35-mm occluder result in the Helex device having too little compression force. This leaves a large residual shunt in 50% of people. Therefore, we prefer the newer Gore Cardioform, or the Amplatzer septal occluder for PFOs larger than 12 mm in diameter.¹⁴

During TEE imaging, the omniplane angle is rotated to the bicaval view (approximately 90–110°) to show the different aspects of the septum and bring the PFO tunnel into view (Figs. 3-15 and 3-16). We currently prefer using ICE for PFO closures, but some centers report using fluoroscopic guidance only, after they have assessed the anatomy with a preprocedure TEE.

A bubble study and color-flow Doppler are applied to assess the channel. The operator can also observe the wire crossing the tunnel and assess the extent of atrial septal aneurysm as well as the septal thickness and aortic morphology (Fig. 3-17).

PFO Morphology and Genetic Sequencing

A proposed classification of PFO morphology is shown in Table 3-1.¹⁵ Fenestrations and aneurysmal septal anatomy are associated with larger PFOs and are postulated to increase the risk of paradoxical emboli. In people who develop platypnea-orthodeoxia later in life, the proposed mechanism is that the anatomy is altered, such as with an enlarged aortic root or with hemidiaphragm paralysis. This in turn deforms the septum to enlarge the PFO and prolong the PFO opening during ventricular systole.¹⁵ The variation in PFO anatomy should influence the choice of the device and its size.¹⁶

A recent study of 48 people from 16 families who had PFO-related phenotypes (cryptogenic stroke or migraine with aura) was performed with exome sequencing to assess single nucleotide polymorphisms.¹⁷ There were 3 genes that were associated with the presence of a PFO and 5 genes that were more common in people with a closed foramen ovale. The inheritance suggests that PFO closure is determined by a polygenic basis, which may explain the variety of shapes and sizes of the septum primum and PFO.

Multiple procedures require crossing the interatrial septum including mitral valvuloplasty, left atrial appendage procedures, mitral valve clip, closure of mitral paravalvular leaks, and electrophysiologic studies. In complex PFO procedures where the tunnel is long and angulated, a transseptal puncture may permit a more effective placement of a device. In most interventional procedures, the puncture is aimed at the fossa ovalis. This is in contrast to pulmonary venous isolation procedures where the puncture may be angulated toward the pulmonary veins and thus away from the fossa ovalis. See the prior section on ASD and PFO closure for a more detailed description of the anatomy of the fossa ovalis and septum.

The septum is angulated in an oblique fashion from posterior-medially to anterior-laterally toward the left relative to the long axis of the body and is bordered by the posterior atrium on the right, right pulmonary veins on the left, ascending aorta anterior-superiorly, tricuspid valve anterior-inferiorly, and, a few centimeters away, the IVC posterior-inferiorly. The shape of the septum is variable and can be flat in normal atria or convex if the left atrial pressure is elevated as in mitral stenosis. The septum itself may be thickened or aneurysmal, increasing the difficulty associated with transseptal puncture.¹⁸

The equipment selection is dependent on the specifics of the anatomy. The standard Brockenbrough needle (BRK) is angled at 19°. For a curved septum, a more angulated needle (BRK-1) angled at 55° may be necessary to keep traction on the septum. Depending on the procedure planned, a Mullins catheter or the Swartz SL catheters (St. Jude Medical) may be needed. The SL0 catheter has a primary curve of 50°, whereas the SL1 has an additional secondary curve of 45° and the SL2 has a primary curve of 90°.¹⁹

The Transseptal Procedure

A 0.032 J-wire is advanced up the IVC, and the introducer sheath and dilator are advanced over it to the SVC. The wire is removed and the selected needle is advanced up the introducer until the needle is 1 cm inside the distal end of the dilator. The operator will feel the BRK needle curve fit in the introducer sheath’s curve. The sheath is rotated posteriorly to the 4 to 6 o’clock position to avoid the aortic root as it enters the right atrium. The catheter is withdrawn slowly under fluoroscopy until medial steps are observed; these steps are often felt as well. The first step corresponds to the introducer sheath entering the right atrium from the SVC. The needle then is moved medially and inferiorly within the right atrium. The sheath should be along the medial aspect of the right atrium and posterior to the noncoronary sinus of the aorta. On additional slow withdrawal, the sheath will drop again over the limbus of the septum secundum into the fossa ovalis.²⁰ This is observed on posteroanterior fluoroscopy as a second medial step. The tip of the introducer sheath is checked in the RAO and LAO projections. In the RAO projection, the tip should be lined up parallel to the spine. In the LAO projection, the tip should point to the left and posterior. Staining of the septum can be helpful to affirm on fluoroscopy the location of the sheath tip relative to other cardiac structures in 3 dimensions. The sheath is held stable, and with a swift movement, the needle is advanced forward to cross the septum. If the septum is aneurysmal or thickened, the needle may not puncture the septum easily. Excessive pressure on the sheath may cause it to slip out of the fossa, or if too much force is applied, the needle may puncture through the septum and then proceed to the posterior wall of the left atrium. Therefore, a bovie or radiofrequency energy may be needed to burn through the septum by applying energy to the back end of the needle for a few seconds as it rests against the tented septum. Contrast may be injected through the needle to confirm crossing into the left atrium, or the needle may be connected to a pressure transducer. Once across the septum, the needle is anchored to maintain access, and the sheath and dilator are advanced slowly together to the mid-left atrium. The needle is removed several inches and the sheath is advanced over the dilator. The dilator is then removed slowly to ensure no air is sucked into the left atrium. A Toray wire (Toray International, Tokyo, Japan) may be advanced to safely maintain wire access to the left atrium. Longer sheaths with a deflecting mechanism, such as an Agilis sheath (St. Jude Medical), may be necessary to achieve the appropriate orientation once across the septum (Fig. 3-18).

TEE or ICE imaging makes transseptal access safer but does require an understanding of the anatomy. Echocardiography can be used to “find” the tip of the transseptal sheath and observe tenting of the septum prior to extending the needle. In TEE, the omniplane is angulated from 0° showing the 4-chamber views to 65° showing the aortic root. If the sheath is observed at the same plane as the aortic root, then the operator will need to rotate the BRK needle clockwise (posteriorly) away from this area or risk a puncture into the aorta. Further angulation to 110° or the bicaval view will show how high up the septum the sheath tip is and allow the operator to monitor the tip location as the catheter is pulled down the septum (Fig. 3-19). Depending on the procedure, the operator may need to position the puncture a certain distance above the mitral valve annulus.

It is recommended that a patient undergo a full TEE evaluation prior to a transseptal puncture to assess the morphology of the septum, the possible anomalies, and for the presence of thrombus in the left atrial appendage, especially in the setting of atrial fibrillation or mitral stenosis. Once the puncture is done, the needle is connected to pressure to confirm it is not in the pericardial space or aorta before the dilator is advanced.²¹

ICE may also be used to localize the transseptal puncture. It is typically positioned in the “home view.” The probe is rotated clockwise until the aorta comes into view. It is then rotated further clockwise until the left pulmonary veins come into view (Fig. 3-20). A puncture at this plane will yield a posterior transseptal puncture typical for pulmonary vein isolation procedures. To perform a puncture appropriate for left atrial appendage procedures or mitral valve procedures, the catheter is gently rotated counterclockwise to show the left atrial appendage. The transseptal sheath may need to be rotated clockwise or counterclockwise until tenting is observed in this view. It is important to position the puncture in the correct plane to facilitate the intervention. Additional devices such as a more angulated sheath or an Agilis sheath may be needed for back-up support (Fig. 3-21).

The technique of percutaneous transvenous mitral valvuloplasty (PTMV) depends on adequate fracturing of the fused, rheumatic mitral leaflets. Success is defined as a final mitral valve area greater than 1.5 cm² with moderate or less regurgitation.²² Understanding the anatomic changes that take place in mitral stenosis and the specific valve pathology is important for the success of the procedure and long-term outcomes, as well as for avoiding complications during the procedure. Prior to the intervention, a full evaluation is required by echocardiographic imaging to assess the valve morphology. Although a precise number on the Wilkins score alone may not determine the success or advisability of performing the valvuloplasty, it provides a rough estimate of the severity of calcification and fibrosis, which are predictors of success with the procedure. The extent of mitral regurgitation also is important since it is likely that balloon valvuloplasty will result in some increase in the degree of regurgitation. The Wilkins score includes leaflet mobility, valve calcification, leaflet thickening, and disease of the subvalvular apparatus. It does not, however, include an important prognostic indicator, that is, commissural calcification.²³ Valvotomy of a highly calcified leaflet and commissure increases the risk of an unsuccessful result or worse: annular tearing and mitral regurgitation (Fig. 3-22). It is also important to identify unusual insertion of the papillary muscles at the leaflet tips and areas of restriction in the valvular apparatus. Finally, mitral stenosis significantly increases the risk for atrial fibrillation and for developing left atrial thrombus. The presence of left atrial thrombus is a relative contraindication to the procedure, and if present, it is safer to postpone the procedure until adequate anticoagulation is achieved (Fig. 3-23).²⁴ Mitral valvuloplasty has been performed safely in patients with thrombus in the left atrial appendage, but this should be attempted only after 3 months of adequate anticoagulation by operators who have extensive experience with the procedure. However, surgery may be the best option for these patients.

The percutaneous technique has 2 components. The first is a transseptal puncture in the optimal position for the intervention (see Fig. 3-18). The second part is passing the balloon through the mitral valve and performing the commissurotomy.

The presence of a PFO may obviate the need for a transseptal puncture, but due to the orientation of the PFO tunnel, it may not orient the device in the proper direction for crossing the mitral valve.²⁵ The transseptal puncture should be oriented in the direction just posterior to the left atrial appendage and the inferior part of the fossa ovalis as discussed in the preceding transseptal section (Figs. 3-24 and 3-25). Achieving an appropriate position for the puncture may be more difficult in mitral stenosis patients due to increased left atrial pressures and a convex septum bulging outward into the right atrium. This pushes the interatrial septum and fossa ovalis against the transseptal sheath, making anchoring of the sheath on the septum challenging, and the sheath may slide off (Fig. 3-26). A transseptal puncture in a patient with mitral stenosis is similar to trying to puncture the convex surface of a grapefruit, which makes precise needle tenting on the septum difficult (Fig. 3-27). Care must be taken not to allow the catheter to slip and puncture anteriorly near the ascending aorta or posteriorly into the transverse sinus and then into the left atrium.²⁶ This course may be catastrophic because the needle is within the left atrium and the operator may think it is safe to advance the large dilator and sheath. A problem will only be apparent upon removing the 14-Fr commissurotomy balloon when the pericardial effusion develops.