Co-Occurrence of High Degree Atrioventricular Block and Facial Pain in Lateral Medullary Stroke

other peculiar symptoms might be associated with lateral bulbar infarction. Among these, ipsilateral facial pain, which often recalls Abstract Background: Besides the typical alternate clinical picture, Wallenberg syndrome may be rarely associated with facial pain due to the involvement of the trigeminal nucleus, and sudden death. Case: We report a case of lateral medullary infarction associated with potentially life threatening intermittent high degree atrioventricular block which occurred in close temporally association with severe facial pain exacerbations. The case required an urgent implantation of cardiac pacing. We hypothesized that the AV-block was triggered by vasovagal response to centrally-mediated pain. However, a direct involvement of the autonomic brainstem network (solitary tract nucleus and dorsal motor nucleus) could not be excluded. Conclusion: A similar sequence of events might explain at least part of the unexplained sudden deaths that seldom accompany Wallenberg syndrome. This report highlights the importance of continuous cardiac monitoring, in the acute phase of lateral bulbar ischemia, in order to prevent unfavorable outcome.

Although infrequent, sudden death might occur in Wallenberg syndrome, representing the most serious accompanying event [6,7].
Herein, we describe and speculate on the pathogenesis of a peculiar case of Wallenberg syndrome, in which fluctuating severe facial pain and high degree atrioventricular block co-occur with a close temporal relationship. Figure 1: EKG pattern recorded during the acute phase of bulbar stroke in three different conditions. (A) First-degree atrioventricular conduction block during asymptomatic (inter-critical) basal recording; (B) third-degree atrioventricular conduction block during one episode of facial pain (critical); (C) transition from a first-degree atrioventricular conduction block to a third-degree atrioventricular conduction block in coincidence with a sudden severe facial pain exacerbation.

Discussion
To the best of our knowledge, this is the first observation of to the heart. A further, albeit less probable mechanism, might involve the trigemino-cardiac reflex, which consists in a reflexive response to mechanical, electrical or chemical stimulation of the trigeminal nerve and/or ganglion or brainstem centers during surgery/angiography, leading to severe dysrhythmias and arterial hypotension [9,10]. Such reflex, however, is usually mediated by an external stimulus, which is missing in the present case.
Our first hypothesis (vasovagal response to pain) is supported by the tight temporal co-occurrence between stabbing pain exacerbations and AV blocks (Figure 1). Fibers from the trigeminal nerve have been shown to project to the STN and some authors described a connection between the trigeminal ganglion and the vagus nerve [9,11,12]. Moreover, against the second hypothesis (antero-medial medulla area) was spared, and this could explain the absence of bulbar motor symptoms (dysarthria, dysphagia and dysphonia) (Figure 2 c, d).
Trigeminal neuralgia secondary to lateral medullary infarction is a well-described rarity [2][3][4][5]. Vagal-mediated first-and seconddegree AV blocks have been observed [13], while a third-degree AV block secondary to a pain-related vagal activation has never been described. Koay et al. documented a case with several asymptomatic sinus arrests in a patient with left lateral medulla infarction. As well as in our case, the authors did not find any clear cardiac disease, and treated the patient with a permanent PM [6].
The present observations yield three interesting speculations: 1) At least part of the sudden deaths described in Wallenberg syndrome might indeed be due to a non-documented high-degree AV block. Even in our case, a delay of pacing intervention could have had lethal consequence; 2) Occurrence of intense facial pain possibly favors vasovagal responses with variable impairment of AV conduction; 3) Previous cases of sudden deaths in Wallenberg syndrome should be revisited in order to check for co-occurrence of severe facial pain. Based on these speculations, we recommend to monitor ECG already in ER in all cases of lateral medulla syndrome, being prepared for possible heart pacing, especially in cases accompanied by facial pain.

Conflicts of Interests
The authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers' bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patentlicensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.