Swallow syncope: a case report and review of literature

Background Swallow or deglutition syncope is an unusual type of neurally-mediated syncope associated with life-threatening bradyarrhythmia and hypotension. It is a difficult condition to diagnose with commonly delayed diagnosis and management. There is lack of review articles that elucidate the basic demographics, clinical characteristics and management of this rare condition. This publication systematically reviews the 101 case reports published since 1793 on swallow syncope. Case presentation A 59-year-old man presented with the complaint of recurrent dizziness associated with meals. A 24-h ambulatory ECG recording confirmed an episode of p-wave asystole at the time of food intake. Oesophagogastroduodenoscopy with balloon inflation in the mid to lower oesophagus resulted in a 5.6 s sinus pause. The patient’s symptoms resolved completely following insertion of a permanent dual chamber pacemaker. Conclusions Swallow syncope is extremely rare, but still needs to be considered during diagnostic workup. It is commonly associated with gastro-intestinal disease. Permanent pacemaker implantation is the first line treatment.


Background
Swallow syncope is a rare cause of a neurally mediated syncope that is frequently associated with life-threatening bradyarrhythmia [1]. The underlying mechanism is believed to be an exaggerated vagal stimulation during swallowing resulting in suppression of the cardiac conduction system. Swallow syncope has been reported in all age groups and occurs with or without underlying esophageal or cardiac pathology. A diagnosis of swallow syncope is frequently missed by physicians, often resulting in delayed diagnosis and treatment. The first case of swallow syncope was reported by Spens in 1793 [2]. Since then, another 117 cases have been reported in the literature.
We present a case of recurrent swallow syncope with a review and summary of the entire literature available regarding this rare condition.

Case presentation
A 59-year-old Chinese male presented with a 6-month history of intermittent dizziness. The dizziness occurred exclusively at meal times and was worst when swallowing large quantities of solid food, such as rice or bread. He initially was symptom free when consuming smaller quantities of solids or fluids, but his condition worsened progressively with presyncopal events occurring even while eating smaller quantities of solid food. The patient described a sensation of increasing difficulty in swallowing despite reducing the size of his meals. He denied any associated syncope or seizures. His past medical history and physical examination were unremarkable and blood investigations were within normal limits. Echocardiography revealed a structurally normal heart with normal systolic and diastolic function. 24-h electrocardiogram (ECG) monitoring recorded a sinus pause of 4.5 s at the time the patient had his meal (Fig. 1). A provisional diagnosis of swallow syncope was made and a permanent pacemaker (PPM) implantation was scheduled.
Tilt table testing prior to pacemaker insertion resulted in a hypotensive response 5 min after provocation with 400 micrograms of sublingual glycerin trinitrate administered sublingually, with reproduction of symptoms of syncope. The minimal blood pressure was 32.9/29.2 mmHg and the heart rate 75.3 bpm. No asystole was observed during tilt table testing (Fig. 2).
The patient's symptoms resolved completely after implantation of a dual chamber PPM. A diagnostic workup to exclude gastrointestinal disease was performed. A barium swallow test was normal and effectively ruled out achalasia. The oesophagus appeared healthy with no structural disease on oesophagogastroduodenoscopy (OGD). The pacemaker was continuously interrogated during the OGD. Increased pacing requirements were noted when the endoscope was advanced into the esophagus (Fig. 3b). Subsequently, a 20 mm diameter TTS (through-the-scope), CRE™ (controlled radial expansion) balloon (Boston scientific) was sequentially inflated in the proximal, mid and distal esophagus while the pacemaker was programmed "OFF" to assess the physiologic response. Inflation in both distal and mid oesophagus resulted in significant sinus pauses of up to 5.6 s (Fig. 3c) confirming the cardio-inhibitory response to oesophageal distension as the underlying pathophysiological mechanism of this patient's syncopal events.

Discussion
Swallow syncope is more common in males (59.4%, n = 60), and in the older age group (55.4%, n = 56, more than 60 years old). The mean age at presentation was 57.5 years with the youngest patient described in the literature being 5 years old [3] and the eldest 89 years old [4]. All of the patient presented with either presyncope or syncope. Only one patient was diagnosed incidentally, when a high degree atrioventricular (AV) block associated with meal times was found during a diagnostic workup for lung carcinoma [5]. Swallow syncope is strongly associated with gastrointestinal diseases (32.7%, n = 33). Hiatal hernia (18.8%, n = 19), oesophageal stricture (3%, n = 3), achalasia (3%, n = 3) and oesophageal    , atrial fibrillation (5%, n = 5), sick sinus syndrome (3%, n = 3), aortic aneurysm, rheumatic heart disease and digitalis toxicity. Twenty-eight patients (27.7%) had metabolic diseases like hypertension, diabetes mellitus, dyslipidaemia or obesity. In most patients (54.5%, n = 55), any type of foodbe it liquids or solids -triggered syncope. Atrioventricular conduction blocks (34.7%, n = 35) including first, second and third-degree AV blocks are the most common electrophysiological problems, followed closely by sinus node dysfunctions (33.7%, n = 34) including sinus bradycardia, sinus arrest and asystole. Second degree AV block, complete heart block (=3rd degree AV block) and asystole were the most frequently reported bradyarrhythmia in the literature. However, there are several cases where both sinus and atrioventricular dysfunction concurred. Paroxysmal atrial fibrillation and atrial tachycardia were rare causes of syncope. Table 1.
Pacemaker implantation is the most popular treatment modality. More than half of the patients (55.5%, n = 56) were treated with a permanent pacemaker. Almost all (98.1%, n = 52) of the patients treated with pacemakers reported resolution of syncopal symptoms. One patient passed away shortly following a PPM implant due to asystole despite a reportedly normal functioning pacemaker [71]. Treatment of an underlying causative factor (15.8%, n = 16) was the second most common treatment modality. Treatment of an underlying gastrointestinal   Table 2.
Various mechanisms regarding the pathogenesis of swallow syncope have been postulated.
The most common postulated mechanism is increased and excessive vagal reflex activation during swallowing causing cardio inhibition [86]. During swallowing, the afferent impulses from the oesophageal plexus travel via the vagus nerve to the nucleus solitarius tract in the Fig. 4 Approach to the diagnostic work-up and management of patients with symptoms suggestive of swallow syncope medulla oblongata. Subsequently, a corresponding signal that regulates involuntary peristalsis will travel down the parasympathetic efferent fibers through the oesophageal branch of the vagus nerve [87]. The presence of reflex arcs between afferent sensory fibers and efferent parasympathetic fibers of the cardiac branch results in inappropriate vagal activation with bradycardia, disturbance to the conduction system and hypotension secondary to vasodilation [27,88]. The exact mechanism remains to be elucidated, however, excessive parasympathetic stimulation to the heart seems to be the central mechanism. The fact that atropine, a potent anticholinergic agent, prevents bradyarrhythmia effectively in cases of swallow syncope supports the theory of excessive vagal stimulations [5,29,66,79].
Abnormal oesophageal mechanoreceptors have been postulated to be the primary cause of swallow syncope in individuals with underlying structural and functional disorders of the gastrointestinal system. We demonstrated a reproducible cardio-inhibition with balloon inflation in the mid to lower oesophagus in our patient [48,89]. The bradyarrhythmia was terminated upon deflation of the balloon suggesting that mechanoreceptors in the midlower oesophagus may play a role in the pathogenesis of swallow syncope.
Investigations of neurally-mediated syncope should be tailored based on actual precipitants. While a tilt-table test confirmed the presence of a vasovagal response with reproduction of syncope, it did not demonstrate any periods of asystole. The diagnosis in this case was confirmed during OGD with cardiac monitoring and hence investigation with an OGD with haemodynamic monitoring should be considered for individuals with suspected swallow syncope. A diagram depicting a proposed approach to the diagnostic work-up and management of patients with symptoms suggestive of swallow syncope is depicted in (Fig. 4).

Conclusions
Swallow syncope is a rare cause for syncopal events and should be considered as part of the diagnostic workup. Pacemakers are a safe and efficacious therapeutic option for all patients with that condition. In patients with associated gastrointestinal disease, specific treatment of the underlying disease has a high likelihood of resolving the swallow syncope without the need for permanent pacing.