Congenital anomalies of superior vena cava and their implications in central venous catheterization

Introduction

The insertion of central venous catheters (CVCs) is a common, often life-saving medical procedure. Although rare, the presence of vascular anomalies may determine failure and/or complications of CVC implantation. Thus, knowledge of normal vascular anatomy and its possible variants is crucial for the success of the procedure (1).

Congenital anomalies of the superior vena cava (SVC) are caused by variations in the development of the embryologic thoracic venous system (2-3-4). In most cases, these variations are clinically silent and may be discovered incidentally in radiological studies done for other reasons. However, they should be kept in mind when these patients are candidate to CVC insertion or to cardiothoracic surgery (5). In this perspective, we describe the embryological origin of SVC, its normal anatomy and possible congenital anomalies, diagnosis of PLSVC, and the clinical and technical impact of SVC congenital anomalies for CVC placement.

Embryology

During the fourth week of gestation, two major symmetrical vein systems, the right and the left precardinal veins, drain the upper portion of the embryo (head and ­upper limb bulbs). Each precardinal vein drains into a common cardinal vein before entering the embryological heart (Fig. 1a). By the eighth week of gestation, a vein anastomosis connects the two precardinal veins and the left common cardinal vein atrophies progressively until complete regression, becoming the ligament of Marshall (6, 7) (Fig. 1b). With this regression, the anastomotic vein between the two precardinal veins becomes the left innominate (brachio-cefalic) vein and the right precardinal vein and the right common cardinal vein form the SVC (5-6-7) (Fig. 1c). The failure of this normal regression can lead to the formation of a persistent left SVC (PLSVC), determining the clinical situation of double SVC (8, 9) (Fig. 1d). This PLSVC runs between the left atrial appendage and left pulmonary veins, and down the back of the left atrium, entering the right atrium through the orifice of an enlarged coronary sinus (10, 11), although in about 10% of cases, it drains in the left atrium. In addition, if the normally persistent right cardinal vein undergoes regression, then there is only an LSVC (Fig. 1e). This anatomical variant is the rarest, with a right innominate (brachio-cefalic) vein draining blood from the right to the left (12).

Fig. 1 -

Incidence

The persistence of LSVC is described as the most common central venous anomaly, which may be associated with congenital heart anomalies (6, 13-14-15-16). The true overall incidence of this anatomical condition is difficult to establish. On the basis of previous reports, its prevalence in the general population was estimated at 0.1-0.3% (13, 14). In patients with congenital heart disease, the reported prevalence ranges between 2.1 and 5% (6, 13-14-15-16).

Diagnosis

Detectable signs of a PLSVC, either with a coexistent right SVC (double SVC) or alone, depend upon its hemodynamic effects and consequently on venous blood pressure (1, 2). Congenital anomalies of SVC, when isolated, very rarely cause clinical symptoms and may be never diagnosed. In more than 90% of cases, LSVC drains into the right atrium via the coronary sinus. This anatomical situation generally gives no clinical consequences and it is hemodynamically insignificant (10, 17). However, in the remaining 10% of cases, the LSVC drains into the left atrium, causing right-to-left shunting, which may determine cyanosis and may be associated with cardiac malformations, such as coronary sinus atrial septal defect (unroofed coronary sinus) (10, 17). Arrhythmias, including atrial fibrillation (18) and Wolff–Parkinson–White syndrome (19), have also been reported.

Even if generally not symptomatic, this situation may cause difficulties and potential complications in case the subject undergoes CVC placement, angiography, or cardio-­thoracic surgery (14). Thus, awareness and prompt identification of this condition is crucial before or during these procedures. Most commonly, the diagnosis of such anatomic anomalies is achieved by imaging. For patients with congenital heart disease, fetal echocardiography is the first image modality leading to the diagnosis (20). In the adult population, LSVC persistence can be suspected in a plain chest radiography as a focal widening of the mediastinum superior to the left side of the aortic knob. In these cases, confirmation and better definition of the anomaly is achieved by computed tomography, magnetic resonance, or angiography (3, 5) (Figs. 2 and 3). More often, these anomalies are detected incidentally during imaging studies performed for other reasons (1-2-3-4-5-6, 21). A dilated coronary sinus seen on echocardiography should raise the suspicion of PLSVC (22). Saline contrast echocardiography can confirm or exclude the hypothesis. On physical examination, distention of the left external jugular vein may be observed.

Fig. 2 -Fig. 3 -

Clinical significance of PLSVC

Congenital anomalies of SVC are generally discovered incidentally during CVC insertion, pacemaker electrode placement, and cardiopulmonary bypass surgery (1). The presence of PLSVC may cause difficulties or possible complications during access to the right atrium, especially with a left internal jugular and a left subclavian approach, which are common sites of access for hemodialysis catheters or when placing pacemakers and Swan-Ganz catheters (22, 23).

Serious complications have been described, such as angina, arrhythmia, shock, and even cardiac arrest (18, 19, 24, 25). The latter may occur because during these maneuvers, there is the possibility to irritate the coronary sinus, where an ectopic pacemaker (conduction system) can be present (26). Another clinical implication in persistent LSVC is the inadequate myocardial perfusion during retrograde cardioplegia (27).

Therefore, when congenital anomalies of the SVC are suspected, an accurate anatomical assessment of the SVC system with possible coexistent cardiac anomalies is useful before insertion of CVCs, pacemakers, or defibrillator leads. To achieve central venous access in the rare cases where the diagnosis of PSLVC is already known, an imaging preoperative planning is strongly recommended for determining the best percutaneous access, the safer route and CVC future course and length, venous diameters, and possible congenital heart disease. This approach will avoid futile attempts and misinterpretation of the final chest X-ray and, consequently, unnecessary removal of appropriately placed catheters (4). A relatively more common situation is noticing, during an insertion procedure done under fluoroscopy, that the catheter follows an anomalous left-sided course. This may not only represent the presence of a PLSVC but also an intra-arterial catheter placement, as well as other ectopic positions (intra-pericardial, mediastinum, pleural space, superior intercostal vein, pericardiophrenic vein, or the left internal mammary vein) (28). A correct differential diagnosis is necessary, using simple tools (clinical observation of blood flow characteristics, blood gas analysis, waveform transduction) and/or injection of radiological contrast medium. For procedures completed without fluoroscopic guidance, a similar diagnostic approach should be followed when a left-sided anomalous position is discovered at the post-procedure X-ray control.

In patients suspected of PLSVC at CVC placement, before using their CVC, the pattern of cardiac venous return should be clarified because of the possibility of venous return to the left atrium in about 10% of cases, which is often associated with right to left cardiac shunting. Patients with right to left cardiac shunting are at a significant risk for subsequent embolic complications to the arterial system (29, 30), either from thromboemboli or air emboli, with resultant neurologic, cardiac, renal, mesenteric, and/or peripheral complications.

Technical aspects for a successful CVC implantation

To enhance the success of CVC positioning, the procedure should always be performed by physicians with adequate training, using ultrasound guidance for direct vein puncture. Immediate fluoroscopic control of correct catheter placement is preferable, but post-procedure chest X-ray is also an accepted approach and it is commonly used for non-tunneled CVCs.

Ultrasound guidance can now be considered a mandatory tool for CVC insertion, as indicated by most guidelines, especially in difficult cases, in patients with coagulation disorders or congenital vascular anomalies (31-32-33-34-35-36).

Verification of guidewire direction and consequently catheter tip location under fluoroscopic guidance is recommended in all patients for tunneled dialysis catheters. This may be particularly helpful in case of presence of vein anomalies (Figs. 2b, 3c). In case of doubt or technical problems, injection of contrast medium will help in delineating the venous anatomy during the procedure (Fig. 3b). At the end of the procedure, correct CVC functioning must also be verified by aspiration of blood and infusion of saline.

Conclusion

In patients with known congenital anomalies of the SVC undergoing CVC placement, several important aspects should be considered for a safe and effective procedure: an accurate preoperative planning with imaging description of veins anomalies, a careful selection of the most adequate vascular access, and use of ultrasound and fluoroscopic guidance by skilled operators.

In routine CVC placement, ultrasound guidance is also a standard, with the exception of emergency when no ultrasound device is available, while fluoroscopic guidance is strongly recommended in tunneled or permanent (ports) catheter placement. Fluoroscopy allows direct visualization of the guidewire and correct catheter tip placement. Recognition during the procedure of an unexpected course of the guidewire will indicate the possibility of performing a phlebography to confirm the possible diagnosis of congenital anomaly of SVC.

(a) Posterior view of the embryological vein system on the fifth week of gestation. (b) Posterior view of the vein system on the eighth week of gestation. (c) Posterior view of normal superior vena cava. (d) Posterior view of persistent left superior vena cava (double superior vena cava). (e) Posterior view of left superior vena cava.

(a) Chest venography demonstrating the presence of a right superior vena cava (°) and a persistent left superior vena cava (*) (double superior vena cava). (b) Before the insertion of a right side central venous catheter (arrowheads) and a left side pacemaker (arrows).

(a) Multi-detector computed tomography coronal multiplanar reconstruction demonstrating a left superior vena cava (*). (b) Chest venography confirming the presence of the left superior vena cava (*). (c) Final chest X-ray showing the right insertion of the central venous catheter, its course into the right innominate vein, and finally into the left superior vena cava (arrowheads).

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