INTRODUCTION

In contrast to surgical ablation, percutaneous catheter ablation of cardiac arrhythmias has evolved from the endocardium to the epicardium. The limitations of an endocardial-only ablation approach are highlighted by certain conditions such as Chagas disease, which is frequently associated wtih an epicardial substrate. Since its initial description by Sosa et al,¹ subxiphoid percutaneous epicardial mapping and ablation has become an important adjunct, and in some instances even the preferred strategy, for treatment of a wide range of cardiac arrhythmias, including scar-mediated ventricular tachycardia,^2,3 atrial fibrillation,^4,5 accessory pathways,^6,7 and idiopathic ventricular tachycardia.⁸ Additionally, the subxiphoid percutaneous approach has also been exploited for epicardial left atrial appendage closure,⁹ cardiac pacing,^10,11 drug delivery,^12,13 and displacement/protection of mediastinal collateral structures (such as the esophagus and the phrenic nerve) from the path of energy delivery during catheter ablation.^14,15 This chapter will examine the subxiphoid percutaneous approaches to epicardial access and puncture.

ACCESSING THE PERICARDIUM

The pericardial space normally contains 15 to 25 mL of serous, physiologic fluid.^16,17 The percutaneous approach to the pericardium is the only technique available that can afford unrestricted catheter access, mapping, and ablation of the epicardial surface. The percutaneous epicardial puncture is the most important step in this approach and one that can be performed safely in the electrophysiology laboratory. While the subxiphoid puncture technique remains the most widely described and used method for percutaneous epicardial access, other approaches to accessing the pericardium have also been reported, including the parasternal,^18,19 the apical,¹⁹ the transatrial,^20,21 transesophageal,²² and transbronchial²³ methods.

SUBXIPHOID APPROACH

Little has changed with regard to the technique of subxiphoid epicardial puncture for catheter mapping and ablation since its introduction by Sosa et al. over two decades ago.¹ Due to the high level of patient discomfort associated with a percutaneous epicardial puncture, it is recommended that this procedure be performed under deep procedural sedation or general anesthesia. Furthermore, urgent and on-site access to echocardiography, blood products, and cardiothoracic surgery is strongly advised.

A history of cardiac surgery or epicardial instrumentation may suggest the presence of diffuse pericardial adhesions. Hence, knowledge about the patient’s medical history as well as baseline blood coagulation profile is crucial. As a rule, a history of cardiac surgery represents the most common cause of access failure and a significant predictor of adverse events and complications during an epicardial procedure. Moreover, this necessitates an inferior epicardial puncture approach, as an intact anterior pericardial space is typically not encountered in patients with a history of anterior sternotomy. In such cases, a surgical subxiphoid pericardial window may prove helpful in performing epicardial mapping and ablation.

Before the puncture, the cutaneous tissue at the site of entry within the subxiphoid area should be cleansed and anesthetized. The site of the puncture is identified based on anatomical landmarks shown in Figure 3.1, and through accurate palpation. The “triangle” formed between the left border of the xiphoid process and the lower left rib represents the optimal puncture site. Next, a 17-/18-gauge, 120-/150-mm-long Tuohy needle is inserted under the skin and the rib cage, directed toward the left shoulder, and oriented according to the targeted ventricular surface (i.e., anterior versus inferior). Designed originally for epidural access, the Tuohy needle has a curved and relatively blunt, spatula-like tip intended to minimize vascular injury when accessing the epidural space (Figure 3.2). The angle between the needle and the skin determines the surface of the ventricle being accessed. Even though feasible as illustrated by Miyamoto and colleagues²⁴, the epicardial puncture should be performed preferably prior to the administration of systemic anticoagulation.

Figure 3.1 The subxiphoid approach is the most frequently used for percutaneous epicardial access. In this approach, the site of the puncture consists of a “triangle” formed by the left border of the xiphoid process and the lower left rib. The epicardial needle must always be introduced at an angle pointing toward the left shoulder.

Figure 3.2 The Tuohy needle was originally designed for epidural access. It has a curved and relatively blunt, spatula-like tip (arrow) intended to minimize vascular injury when performing an epidural puncture.

Once the needle is advanced under the skin, the stylet within the needle may be removed. The needle is then advanced gradually under fluoroscopy toward the cardiac silhouette with gentle aspiration to avoid vascular puncture, typically either in an anteroposterior or left anterior oblique projection. However, the operator may confirm the orientation of the needle in different projections. A left anterior oblique view confirms an anterior versus posterior orientation (right versus left cardiac chambers), whereas a right anterior oblique projections confirms a superior versus inferior orientation (atria versus ventricles). The space of Larrey is the target of the needle, which is bounded by the sternum anteriorly, the pericardium posteriorly, and the dome of the diaphragm inferiorly (Figure 3.3). It is important to note that the internal mammary artery passes through this space as it becomes the superior epigastric artery with its associated vein and lymphatics. The needle should always be advanced over the diaphragm, and never through it, as it is a highly vascular organ. The aorta gives rise just below the aortic hiatus to the inferior phrenic arteries that supply the diaphragm and in turn give rise to the suprarenal vessels to supply the adrenal glands. As such, a diaphragmatic puncture could lead to significant arterial bleeding complications. Fluoroscopic visualization of the needle in the left lateral projection can greatly aid to circumvent a diaphragmatic puncture (Figure 3.4). Furthermore, if the patient is intubated and placed under general anesthesia, the control of respirations through an “inspirational breath hold” can sometimes facilitate an epicardial puncture (Figure 3.5). Since the diaphragm moves away from the heart inferiorly at end-inspiration, the likelihood of a diaphragmatic puncture is further reduced by advancement of the needle toward the pericardium during end-inspiration. Another maneuver used by some operators is to apply gentle downward pressure at the epigastrium in order to reduce the distance that the needle has to advance to reach the pericardium (Figure 3.6). While this technique can prove helpful when performing an epicardial puncture in obese patients and also helps steer the left lobe of the liver away from the needle’s path, it may also unintentionally displace the diaphragm toward the heart and increase the likelihood of a diaphragmatic puncture.

Figure 3.3 When performing an epicardial puncture, the target is the space of Larrey, which is enclosed by the sternum anteriorly, the pericardium posteriorly, and the dome of the diaphragm inferiorly. The internal mammary artery passes through this space as it gives rise to the superior epigastric artery. Therefore, when performing an epicardial puncture, the needle should always be advanced over the diaphragm and never through it.

Figure 3.4 Fluoroscopic visualization of the needle in the left lateral projection can greatly facilitate epicardial access and help circumvent an unintended diaphragmatic puncture. As shown, a left lateral view can demonstrate the precise path of the needle in relation to the diaphragm and aid in validating the epicardial approach (“anterior” versus “inferior”).

Meanwhile, the angle of the needle may be adjusted according to the ventricular region that the operator wishes to access. This region is most frequently the medial third of the right ventricle, where typically no major coronary vessels are found (Figure 3.7). The presence of a diagnostic catheter in the right ventricular apex and/or the coronary sinus can serve as a reference in guiding the needle. The needle is then gently advanced under fluoroscopy (Figure 3.8A). The layers penetrated by the needle include the skin, the superficial fascia, the anterior rectus sheath/linea alba, the rectus abdominis muscle, and the posterior rectus sheath. Once the needle reaches the pericardium, cardiac pulsations can be appreciated. Initially, the pulsations may be felt intermittently. But as the tip of the needle is gently advanced toward the pericardium, cardiac pulsations can be sensed with each heartbeat. At this point, injection of a small amount of undiluted contrast medium will indicate the location of the needle tip (Figure 3.8, Panel B). If contrast injection results in staining of the pericardial fat or the pericardium itself, the needle may be slowly advanced 1–2 mm and contrast injection repeated until the pericardial cavity is accessed. However, care should be taken to avoid injecting a large amount of contrast medium as this can considerably obscure the fluoroscopic image (Figure 3.9). The authors typically advocate the use of a 3-cc Luer locktip syringe connected to the needle to avoid inadvertent injection of copious amounts of contrast. If an excessive amount of contrast is injected, the operator may consider waiting a period of time to allow this to dissipate before reattempting the puncture.

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