Radiofrequency catheter ablation has evolved to be a promising therapy for symptomatic drug resistant atrial fibrillation in the past decade. There have been a number of studies done to assess the efficacy and adverse effects of radiofrequency ablation, but very little data is available on the effect of radiofrequency ablation on the upper gastrointestinal system.
The impact of this procedure on the gastrointestinal system has been under-assessed and has been limited to anecdotal case reports. Therefore, we (Lakkireddy and a group at the University of Kansas Hospital in Kansas, USA) undertook the AF-GUT study to systematically assess the functional integrity of gastrointestinal system post-ablation procedure.
During left atrial ablation, radiofrequency energy delivered through the ablation catheter can extend into mediastinal space and therefore may involve the mediastinal structures surrounding the left atrium like oesophagus and peri-oesophageal nerves, which can have short-term or long-term effects on gastric motility and structural integrity of the upper gastrointestinal system. The myenteric plexus, buried within the wall of oesophagus, can be affected by thermal injury during atrial fibrillation ablation. Perio-esophageal vagal nerve injury can be seen in about 1–2% of patients. This damage can be structural (oedema, ulcer or rarely fistula) or functional (dysmotility, spasm) or a combination of both. It is also unknown whether oesophageal or gastric motility disturbances or vagal nerve injury with atrial fibrillation ablation are transient or long lasting.
The AF-GUT study
The AF-GUT study prospectively enrolled 27 patients that were tested at baseline, 24 hours and 90 days post ablation. In case of an abnormal test result, a subsequent follow-up at six months was scheduled. Patients with previous abdominal surgical procedures and history of either acute or chronic neuropathies were excluded. The primary outcomes were measured by three tests:1) LES (lower oesophageal sphincter) Manometry to assess the lower oesophageal sphincter tone. 2) Gastric scintigraphy, which evaluates the gastric emptying time. 3) Sham feeding test to evaluate vagal nerve function. The results of these tests were correlated with the gastrointestinal symptom questionnaire.
The study results demonstrated that five of 27 patients (18%) had some kind of baseline oesophageal abnormality. Twenty four hours post-ablation studies showed 74% of the people developed one or more new abnormality. There was no correlation between the severity and type of abnormality and the symptomatology. At 90 days, a vast majority of patients had improved vagus nerve integrity with 37% patients having an abnormal test result. Thirty three per cent of patients had new onset abnormalities from baseline and 18.5% had abnormality which did not exist at 24-hour testing.
The remaining 18% had an abnormal test result persistent at 90 days after first being detected at 24-hour post-ablation. These results suggest that vagal inputs to the gut might have spontaneously recovered overtime and the residual effects were due to the effect on oesophageal component of the vagus nerve.
The oesophagus has a complex network of nervous system forming the oesophageal plexus and there are inherent anatomical variations in how these are arranged in each individual. This determines the extent of effect radiofrequency energy delivered in the left atrium has on the upper gastrointestinal system, depending on the branching pattern of nerves in each individual.
Thus it is possible to infer that patients who had abnormal results in three tests could be due to the complex plexi that are innervated by both left and right sides of the vagus branches. These individual variations in vagal innervations can explain the reason for no vagal nerve dysfunction in some patients. The six month follow-up data of the patients who had abnormal test results has not been completed yet to comment on the long-term gastrointestinal effects of this procedure.
The effect of other potential contributing factors such as duration and intensity of radiofrequency energy needs to be evaluated in further studies. The lack of endoscopic data for correlating the functional and structural abnormalities has been a limiting factor.
Further studies are needed to better understand the variable effects of atrial fibrillation ablation on the gastrointestinal system and to enhance our understanding further. The study by Koruth et al (Journal of electrophysiology 2012), studied the feasibility of mechanical oesophageal displacement during the radiofrequency ablation procedure in 20 patients and endoscopy revealed no mucosal ulceration in the oesophagus from thermal injury in 18 out of 19 patients.
Other studies, like the one by Singh et al, concluded that luminal oesophageal temperature (LET) monitoring may decrease the risk of oesophageal injury when compared with other practice of power limitation alone. There is a greater need for future studies in this area to broaden our current knowledge on the mechanistic process involved in the pathophysiologic changes in gastrointestinal system after atrial fibrillation ablation.
Lakkireddy presented this topic at Boston AF 2012.
Dhanunjaya Lakkireddy is professor of Medicine, Mid America Cardiology, University of Kansas Hospitals, Kansas City, USA