Swallow Syncope: A Case Report and Review of the Literature

Discussion

Swallow syncope is a relatively rare syndrome and belongs to the “reflectional syncope” syndromes. Omi et al2 reviewed 63 reported cases of swallow syncope in children and adults from the English-language literature between 1793 and 2005. Since then, another 17 cases have been reported in the English literature (table 1). This syndrome is more common in males, and most patients have been adults, but some cases were also noted in young children.2 Swallow syncope has been known to occur in patients with organic or functional disorders of the esophagus. These disorders include esophageal spasm, esophageal stricture, achalasia, esophageal diverticula, esophageal cancer, and hiatal hernia.2 Swallow syncope may also occur in the absence of esophageal diseases and has been observed in the setting of cardiac diseases like acute myocardial infarction, rheumatic carditis, and with digoxin use.2 Some reported cases were associated with ascending aortic aneurysm,3 thoracic surgery, advanced lung cancer, and transient hypoxia.2 However, in a significant number of cases, no underlying disease could be found.2 Table 2 shows the distribution of underlying disease in the previously reported 80 cases of swallow syncope.

The pathophysiology of swallow syncope is not completely understood, and several different mechanisms may exist. Vagal reflex plays a major role, as pretreatment with atropine is effective in preventing bradycardia and syncope in a significant number of patients. The common innervation of the esophagus and heart by the vagus nerve has been postulated to play an important role in swallow syncope. Mechanoreceptors in the esophagus, which are activated by stretching, may play an important role.4 They sense distension and send signals along the esophageal plexus via the vagus nerve to the brainstem. The efferent impulses from the brainstem reach the sinoatrial (SA) node via the right vagus nerve and the AV node via the left vagus nerve. The efferent signals lead to various types of paroxysmal bradyarrhythmias and temporary reduction of cardiac output, which leads to cerebral hypoperfusion and possibly to syncope. Others have observed that swallow syncope can occur even in the absence of bradycardia, as increased afferent vagal stimulation may lead to syncope via sympathetic withdrawal, resulting in peripheral vasodilation and hypotension.5 Although other arrhythmias such as sinus bradycardia, sinoatrial block, and complete atrial and ventricular asystole have been observed, AV block has been reported most frequently. Paroxysmal atrial fibrillation could also be associated with swallow syncope.6

The diagnosis of swallow syncope requires careful elicitation of the temporal relationship between swallowing liquids or solid foods and lightheadedness and syncope. Provocative testing with various types of liquid and solid foods should be attempted. As esophageal disorders may be associated with a majority of cases of swallow syncope, further work-up to exclude possible structural or functional esophageal pathology has been suggested. Echocardiogram and resting and ambulatory ECG should be performed to rule out any underlying cardiac pathology.

Management of swallow syncope involves withdrawal of all medications that can cause delay in cardiac conduction and inappropriate vasodepression. Avoidance of carbonated fluids or other agents associated with symptoms, as well as behavioral modification to change eating habits, may be successful in patients with infrequent episodes of syncope.7

Various anti-cholinergic medications like atropine, scopolamine, and propantheline have been used to prevent bradyarrhythmias by blocking vagal conduction. Sympathomimetic agents like adrenaline and isoprenaline have been used to increase the ventricular rate directly; however, the results have been inconsistent and limited by side effects.2 Beta-blockers may be effective in carefully selected patients.8 In the appropriate clinical setting, correction of any underlying esophageal pathology should be attempted. Permanent pacemaker placement is usually effective in patients in whom bradyarrhythmias are the major cause of syncope.

Because swallow syncope is a rare disease, there have been no randomized controlled trials comparing the efficacy of different treatment remedies such as medications, surgery, or pacemakers. However, it is logical to treat the underlying diseases of swallow syncope if they can be found and are treatable. For example, gastroesophageal reflux disease can be treated with proton pump inhibitors, and hiatal hernia can be treated with surgery. In the large majority of swallow syncope cases there is an associated reflex bradycardia leading to cerebral hypoperfusion and syncope. Of the previously reported 80 cases of swallow syncope, 68 cases (85%), including underlying causes such as digestive diseases as well as unknown causes, were found to have sinus arrest, sinus bradycardia, SA block, or AV block. Therefore, placement of a pacemaker represents a reasonable treatment option that allows for over-riding of the bradycardia, although it does not treat the cause of the problem. The 11 cases listed in table 1 who had pacemaker implantation, all had resolution of symptoms over a follow-up period of 2 to 26 months,9–20 indicating that pacemakers are an effective treatment. However, pacemaker implantation is not without risks that need to be balanced with the potential benefits. Approximately 4% to 5% of patients will have a complication during or following pacemaker placement, such as infection, lead dislodgment, pneumothorax, and cardiac perforations.21 There have been cases where pacemakers failed to resolve the symptoms. Armstrong et al22 reported a case of a patient with swallow syncope who had an esophageal web, moderate hiatal hernia, and spastic narrowing of the esophagus, but no bradycardia was documented. Pacemaker placement was unsuccessful in this case, and the patient died of congestive heart failure two years later. It is important that a definitive diagnosis of cardiac rhythm disturbance be established prior to insertion of a permanent cardiac pacemaker.22 In patients who do not respond to pacing therapy, volume repletion, increased salt intake, leg stockings, and avoiding ingestion of specific foods/beverages or behaviors associated with symptoms may be of value;22 however, no systematic study on this patient population has been reported. A careful search for underlying causes not involving bradycardia may be warranted. For instance, left atrial compression should be ruled out by echocardiography.23 A large hiatal hernia can cause extrinsic compression of the left atrium during meals and impede cardiac output leading to hypotension and syncope. These patients can get relief of their symptoms by surgical repair of the hernia.23,24 A pacemaker would not provide any benefit because bradycardia is not involved.

Swallow syncope, though generally considered a benign condition, can cause significant impairment of quality of life and can result in significant injury if it occurs at certain times like driving or operating heavy machinery. However, it is a treatable disease. A thorough history, including asking about any relationships between eating and syncope or lightheadedness, is important in the diagnosis of the disorder.