Expert Commentary

DOI: 10.19102/icrm.2013.040307

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Superior Vena Cava Obstruction caused by Catheter Ablation: Primum Non Nocere?

As health-care professionals, we are often reminded of one of the fundamental paradigms in medicine, “primum non nocere.” This premise to first “do no harm” is especially important for proceduralists, as we constantly weigh the potential risks and benefits for the invasive procedures we recommend to our patients.

In this issue of the Journal, a case of superior vena cava (SVC) syndrome caused by repeated ablations for inappropriate sinus tachycardia (IST) is described. This complication, though seemingly rare, has been reported previously,¹ and raises concerns regarding the treatment of this unfortunate patient. Do the risks of this procedure outweigh potential benefits? Was the appropriate imaging modality used to minimize the risk of complications? Should the patient have been evaluated for SVC narrowing prior to the final procedure? The authors point out that repeated ablations may have worsened a pre-existing stenosis, as the clinical presentation may be subtle or asymptomatic. This patient is a good example that when presenting the therapeutic option of a repeat ablation, the potential risks and benefits need to be considered.

Ablation for IST is an established therapeutic option, but is not without limitations. The definition of “inappropriate” of a resting heart rate greater than 100 bpm is arbitrary. The mechanisms are also not clearly defined and may be multifactorial. Potential “intracardiac” mechanisms such as increased sinus node automaticity, increased sympathetic tone or increased sympathetic receptor sensitivity, and blunted parasympathetic tone are usually targeted for therapy.² The “extracardiac” mechanisms such as length-dependent autonomic neuropathy, excessive venous pooling (similar to postural orthodromic tachycardia syndrome), beta-receptor hypersensitivity or alpha-receptor hyposensitivity, and altered systemic autonomic balance or brainstem deregulation are even less understood. More importantly, the nature of any dysautomia is difficult to quantify and even more difficult to target for treatment. So how can simply ablating the sinus node lead to improvement?

Acute procedural success for ablation, defined as reduction in heart rate by 25%, is reported: 66–100% in small series.^3–5 However, symptoms often recur a few months after the procedure in a high percentage of patients.⁴ Long-term success is certainly less with only a small percentage of patients remaining symptom-free after a year, and has not yet been systematically defined in a large series of patients. Marrouche and colleagues⁶ have described in a series of 39 patients with IST and a mean follow-up of 32 months only a 21% incidence of recurrence when ablation employed three-dimensional mapping. However, 28% of patients required a second procedure, and one patient had SVC narrowing requiring balloon dilatation. Ablation for IST is not without risks. Most series have reported SVC stenosis as a potential risk of the procedure,^3–6 and this likely underestimates the true incidence given the potential for subtle or asymptomatic occurrence. In a report of 35 patients, three patients were seen to have SVC syndrome, with testing and diagnosis prompted by symptoms.⁷ A series of 13 procedures in 10 patients utilizing intracardiac echocardiography (ICE) demonstrated an overall reduction in the SVC–right atrial orifice of 24% and a narrowing of >30% in five of the 10 patients.⁸ Transient and long-term phrenic nerve has also been reported.^3–4 Finally, much like case presented here, pacemaker implantation from sinus node dysfunction has been reported in most series.^3–5 This does not take in account patients who ultimately have ablate and pace therapy performed.

Given the multiple potential mechanisms and variables in IST and the limited long-term efficacy of catheter ablation, most experts recommend a multimodality approach in treating patients with this disorder.^2,9–10 The diagnosis may be aided by full autonomic testing and is generally recommended. Treatment may include cardiac rehabilitation (in our experience, swimming is particularly helpful), pharmacological treatment, and in our practice only rarely is ablation considered in the severely debilitated patients. Recently, the drug ivabradine, the selective I_f blocker, has shown promise in a small randomized double-blinded clinical trial, showing reduction of symptoms in 70% of patients and elimination of symptoms in 50% corresponding to significant reduction in heart rate at rest and on standing.¹¹

Regardless of the treatment approach, the case presented here consisting of three catheter ablations for IST resulting in SVC obstruction is a clear example of when considering a treatment option, we must keep in mind primum non nocere and should consider that we should first do no harm to our patients. Better risk stratification, such as imaging for pre-existing stenosis, may have prevented a significant detrimental outcome from occurring.

Rahul N. Doshi, MD, FHRS
Fullerton Cardiovascular Medical Group
Fullerton, CA
University of California
Irvine, CA

Jill Harris, ACNP
Fullerton Cardiovascular Medical Group
Fullerton, CA

References

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