Introduction 

Persistent left superior vena cava is the most common congenital anomaly of the thoracic venous system. Isolation of this vein, which is usually required to eliminate atrial fibrillation (AF), is a challenging procedure with either radiofrequency or cryoablation energy.   

Clinical case

A 47-year-old man underwent catheter ablation of drug-refractory symptomatic paroxysmal AF. A persistent left superior vena cava (PLSVC) was confirmed during the electrophysiology study. An ablation catheter with a fiber optic-based force sensor mounted on the tip that measures microdeformations of an elastic body when in contact with tissue was used (TactiCath Quartz Ablation Catheter, St. Jude Medical). Pulmonary vein (PV) and PLSVC isolation were guided by a 20-electrode circular mapping catheter. Spontaneous atrial premature contractions (APCs) with negative P waves in lead II and positive in lead V1 and earliest atrial electrogram within the PLSVC were observed (Figure 1A). There was a double potential on the PLSVC elec-trograms comprising of a far-field (FF) left atrial signal and a sharp potential, which sequence was reversed during APCs (Figure 1A, black arrow). An atrial tachycardia was induced (Figure 1B, red stars) with isoproterenol infusion that rapidly degenerated into AF (brown arrow). The earliest atrial electrogram was recorded at electrode 7 (bipolar 13-14) placed at the lower portion of the PLSVC.

Catheter ablation around the antrum of the left upper PV did not eliminate all the existing sharp potentials (Figure IC). A second circular catheter was placed at the upper portion of the PLSVC. Note the close proximity of these veins depicted on the LA geometry created with EnSite^™ NavX^™ technology (St. Jude Medical). When pacing from the PLSVC 9-10 electrode, the left upper PV potentials were brought in closer to the pacing spike and were gone once the PLSVC was isolated, confirming they were far-field signals (Figure 1C). Isolation of the lower portion of the PLSVC is shown in Figure 1D.

Ablation of the PLSVC was performed at two sites (see LA geometry): proximally to the great cardiac vein and distally at the level of the left superior PV, where LA-PLSVC connections have been described. Ablation lesions are represented by red dots. Contact force (CF) in the left atrial posterior wall was 32g ± 12 and 18g ± 6 in the anterior portion around the left upper PV. CF was 26g ± 5 and 40g ± 6 on the upper and lower portion of the PLSVC, respectively, with relatively easy catheter manipulation. Ablation time was 9 minutes and 20 seconds to isolate the lower portion of the PLSVC, and 6 minutes to isolate the upper portion of the PLSVC. Power was titrated to 10 and 20 watts when CF was >10g and >20 g, respectively. At 8-month follow-up, the patient has been free of any arrhythmias. 

Figure 1 highlights the importance of the PLSVC as an AF trigger. PLSVC isolation with either radiofrequency or cryoablation has been associated with major intraprocedural complications and high reconnection rate.¹ To our knowledge, this is the first time a CF catheter was used to isolate the PLSVC.

Discussion

Impedance drop, electrogram amplitude reduction, and loss of pace capture, routinely used at the time of ablation, have a modest predictor value of tissue contact and lesion formation, which likely account for a high PV reconnection rate and AF recurrence.²

However, experimental studies have shown a robust correlation between CF and lesion size. CF correlated linearly with lesion size, thrombus formation, cardiac tamponade, phrenic nerve paralysis, and coronary injury in a canine preparation.³ Not only the quantity but the quality of CF also influences lesion size, mainly the angle, axial versus lateral, and the average force-time integral (FTI) 

TOCCATA⁴ and SMART-AF⁵ were key clinical trials to prove the value of CF in catheter ablation of AF. When CF was >10g, FTI=400 value, PV reconnection was less than 20% with lower recurrences of AF at one year. 

Although more CF means deeper lesions and more collateral damage, it is likely the minimum CF required is region and tissue specific, and there is still a lack of CF value standards for VT ablation. It is important not to ignore all the other ablation parameters, particularly impedance, as they have a complementary role in enhancing safety and efficacy. CF is a measure of contact tissue and impedance of tissue heating.

We have incorporated use of CF into our routine AF ablation practice. We strive for a CF=10-40g, FTI>400g, and 10 ohm impedance drop, as in our case report. Power is titrated according to contact force and impedance. Intracardiac echocardiography is routinely used for catheter stability and anatomic location. Post ablation, we look for electrogram voltage reduction and lack of local capture at high output pacing. Adenosine is used to test for dormant conduction. 

Although this is only one case using CF, this technology is likely to improve safety and durability of PV and PLSVC isolation. 

Disclosure: Dr. Navarrete reports consultancy (modest) with St. Jude Medical. Dr. Isthidar has no conflicts of interest to report. 

References

1. Wissner, E, Tilz R, Konstantinidou M, et al. Catheter ablation of atrial fibrillation in patients with persistent left superior vena cava is associated with major intraprocedural complications. Heart Rhythm. 2010;7:1755-1760. 
2. Nakagawa H, Kautzner J, Natale A, et al. Locations of high contact force during left atrial mapping in atrial fibrillation patients: electrogram amplitude and impedance are poor predictors of electrode-tissue contact force for ablation of atrial fibrillation. Circ Arrhythm Electrophysiol. 2013;6:746-753. 
3. Katsuaki Y, Hiroshi N, Dipen S, et al. Chronic atrial fibrillation is a biatrial arrhythmia: data from catheter ablation of chronic atrial fibrillation aiming arrhythmia termination using a sequen-tial ablation approach. Circ Arrhythm Electrophysiol. 2008;1:344-362.
4. Reddy VY, Dipen S, Josef K, et al. The relationship between contact force and clinical out-come during radiofrequency catheter ablation of atrial fibrillation in the TOCCATA study. Heart Rhythm. 2012;9:1789-1795.
5. Natale A, Reddy VY, Monir G, et al. Paroxysmal AF catheter ablation with a contact force sensing catheter: results of the prospective, multicenter SMART-AF trial. J Am Coll Cardiol. 2014;64:647-656.