Introduction

The persistence of a left superior vena cava into adulthood has been well-described, however, the clinical implications are not completely understood.  The majority of available cases are in the context of incidental discovery during routine central venous access, cardiac pacemaker placement or non-invasive imaging.  The incidence of a persistent left superior vena cava (PLSVC) ranges between 0.3 – 0.5% of the general population and is the most common thoracic vascular anomaly [1].  Persistence of fetal vasculature is normally asymptomatic, however there is a high association with other structural heart defects.  Depending on the insertion into the left-sided or right-sided circulation, a PLSVC can have profound hemodynamic effects [2, 3].  Several subtypes of tachyarrhythmias have been associated with this condition and are thought to originate from either residual pacemaker tissue or re-entrant pathways.  We present a challenging case of a critically-ill patient with an incidentally discovered PLSVC causing persistent and unstable supraventricular tachycardia. 

Case Report

A 48-year-old male with no prior cardiac history was admitted to the Arizona Burn Center for 45% total body surface area (TBSA) full thickness burns after a motor vehicle collision.  The patient was resuscitated per protocol and central venous access was indicated for intravenous delivery of multiple infusions and intravenous resuscitation.  A 7 French triple-lumen central venous catheter was placed into the left subclavian vein in the usual, sterile fashion.  Post procedural chest radiograph, revealed the catheter coursing caudally on the left aspect of the thoracic spine (Figure 1).

Figure 1

Portable AP chest radiograph demonstrating the course of the left subclavian central venous catheter.

Further investigation of the catheter placement consisted of a simultaneous arterial blood gases (ABG) and venous blood gases (VBG) (Table 1), and examining the transduction of the catheter (Figure 2).  The VBG was consistent with venous blood and the tracing was consistent with a central blood venous pressure.  Due to uncertainty of the anatomy, the catheter was withdrawn and relocated.  Subsequently, an echocardiogram demonstrated a dilated coronary sinus (CS) (Figure 3).

Table 1

Arterial (radial arterial line) and venous blood gases (left subclavian central line) obtained simultaneously to verify the location of the central line within the central venous circuit.

Figure 2

Venous tracing (blue line) revealing central venous pressures at 5 mmHg.

Figure 3

Echocardiogram showing a dilated CS (white arrow).

The diagnosis of PLSVC was suspected and confirmed shortly after with a CT angiogram of the chest which was being obtained for another clinical issue.  The left subclavian vein and left internal jugular vein converged into the PLSVC and clearly emptied into the CS in proximity to the right atrium (Figure 4).  

Figure 4a&b

CT angiogram of the chest (a - coronal; b – axial) showing PLSVC inserting into the CS.

The patient’s operative course consisted of multiple tangential excisions and split thickness skin graftings.  Early in his second hospital week there were multiple episodes of unstable, supraventricular tachycardia (SVT) and an EKG revealed a narrow QRS complex supraventricular tachycardia.  Initially managed with intravenous adenosine, he had a return to normal sinus rhythm, however, continued hemodynamic instability precluded the use of beta-blockers and calcium channel blockers for rate control.  Therefore, the patient continued to receive multiple administrations of adenosine to combat his frequent episodes of SVT.  He was eventually started on an amiodarone infusion at 1mg/min for 48 hours and transitioned to 400mg amiodarone twice daily with resolution of his tachyarrhythmia. 

Discussion

This difficult case raises questions regarding the anatomy, physiology and long-term management of arrhythmias arising from a PLSVC.  Embryologically, a PLSVC results from failure of the left superior cardinal vein to regress.  During development, the anterior cardinal veins drain cephalic fetal blood while the posterior cardinal veins drain the caudal portions of the fetus.  These veins constitute the fetal venous return and drain into the left and right horn of the sinus venosus.  The left and right anterior cardinal veins anastomose to form the left brachiocephalic vein.  In normal embryogenesis, the right anterior cardinal vein becomes the normal superior vena cava and the obliterated left anterior cardinal vein becomes the ligament of Marshall.  Importantly, the left horn of the sinus venosus becomes the coronary sinus which is why the vast majority of PLSVCs drain into the right atrium via the coronary sinus [4, 5]. 

Supraventricular tachycardia is a broad term that describes multiple tachyarrhythmias that originate at or above the atrioventricular (AV) node.  The most common subtypes of SVT are atrial fibrillation and atrial flutter.  Other subtypes that fall under the umbrella of paroxysmal supraventricular tachycardia (PSVT) are atrioventricular nodal re-entrant tachycardia (AVNRT), atrioventricular re-entrant tachycardia (AVRT) and atrial tachycardia (AT).  These rhythms are created from either re-entry circuits, automaticity, or triggered activity.  Re-entry arrhythmias preferentially utilize a fast pathway while the slow pathway is blocked.  Automaticity is due to ectopic foci within the endocardium other than the AV node that set the atrial rate [6].   Triggered activity refers to arrhythmias caused by enhanced intracellular calcium due to cardiac glycosides leading to delayed repolarizations, extrasystoles and tacharrythmias [7].

Shortly after his admission, our patient exhibited new onset narrow-complex supraventricular tachycardia with no previous diagnosis of arrhythmia and no structural heart defects on echocardiogram.  According to guidelines from the American Heart Association (AHA), acute termination of a re-entrant rhythm can typically be achieved with 6 - 12mg of IV adenosine.  This causes a temporary block at the AV node that restores its intrinsic rate.  Intravenous beta-blockers and calcium channel blockers such as diltiazem and verapamil can be used with equal efficacy in the acute setting, however, they are normally reserved for stable SVT since they can potentiate hypotension.  Long-term suppression can be achieved with either monotherapy or combined therapy of a class 1c (flecanine, propafenone) or class 4 antiarrhythmic drugs (diltiazem, verapamil).  Digoxin and amiodarone are second line agents when there is no clinical response after initiation of beta-blockers or calcium-channel blockers and in patients that are not candidates for cardiac ablation.  We opted to avoid calcium channel blockers in our patient due to ongoing hypotension and utilized amiodarone with complete resolution.  Presently, amiodarone is reserved for persistent or refractory cases since long-term use has been repeatedly associated with hepatic dysfunction, thyrotoxicosis, and pulmonary interstitial fibrosis [7, 8].  

Catheter-based radiofrequency ablation is being increasingly used for multiple subtypes of supraventricular tachycardia, however, there is limited data specific to arrhythmias arising from a PLSVC.  Interestingly, areas of electrical potential have been observed within the PLSVC and CS on electro-anatomic mapping.  The sinoatrial (SA) node forms from the embryonic right horn and right common cardinal vein coming off the sinus venosus.  The pacemaker tissue at the SA node is present to a lesser degree within the left cardinal vein which could explain why its persistence is associated with arrhythmias [9].  Several reports have described successful ablation of the slow pathways in re-entrant supraventricular tachycardia [10-12].  Even though the presence of a PLSVC causes deviation of slow nerve fibers and skews the anatomical boundaries of the triangle of Koch, success rates after ablation are greater than 80% [13].   Commonly the fibers are found to course near the orifice of the dilated CS on electrophysiology (EP) and mapping studies [10, 11].  Excitable ectopic foci leading to supraventricular tachycardia have also been successfully ablated with good long-term follow-up.  Endocardial mapping studies have shown abnormal electrical activity within the CS and at the distal extent of the anomalous vena cava [12, 13]. 

Conclusion

This case raises questions regarding the short and long term management of patients with tachyarrhythmias thought to originate from a PLSVC.  Ablation in this setting for either re-entrant pathways or ectopic foci have been associated with acceptable success rates and presents a better alternative to long-term pharmacology.  After review of available research, we believe the patient would benefit from evocative testing and evaluation by an interventional cardiologist after this hospitalization and rehabilitation.  Early ablation prevents the undesirable effects of long-term amiodarone use.