MP-5 - NEURALLY-MEDIATED SYNCOPE ASSOCIATED WITH NECK SARCOMA

Case background: A 60-year-old male presented with right-sided neck swelling and a recent onset of syncope. He had no previous history of syncope or bradyarrhythmias. His syncope was characterized by cardioinhibitory and hypotensive features, suggesting a mechanical interaction of a neck mass with the carotid sinus. He quickly deteriorated, developing profound intermittent complete heart block, sinus bradycardia, and worsening hypotension, with a documented blood pressure as low as 57/31 mm Hg. A sinus pause lasting more than 30 seconds precipitated his transfer to the Coronary Care Unit (CCU).

Attempts to place a temporary pacemaker via the right internal jugular vein were unsuccessful due to difficulty in cannulating the sheath, so a temporary pacemaker wire was inserted via the right femoral vein. Despite this intervention, the patient continued to deteriorate, requiring intravenous vasopressor support with phenylephrine and dopamine.

Computed tomographic imaging revealed right neck lymphadenopathy and a separate mass measuring 3.6 cm, causing compression of the right internal jugular vein and right internal carotid artery. A venogram confirmed the occlusion of the right internal carotid artery. An ultrasound-guided lymph node biopsy caused hemodynamic collapse, syncope, and myoclonic seizures, necessitating the use of intravenous fluids, atropine, and dopamine infusion.

After further stabilization, the transvenous pacemaker was eventually removed, and a dual-chamber pacemaker was inserted. However, despite adequate pacing, the patient continued to experience symptoms due to the autonomic disturbances caused by the neck mass, particularly hypotension.

The patient underwent a right lateral neck dissection, including partial tumor resection, ligation of the right internal jugular vein, and resection of the right vagus nerve. The tumor adhered to the carotid sheath and encased the jugular vein. The final diagnosis was Stage II (T1N2M0) p16-positive squamous cell carcinoma of the right base of the tongue. He subsequently underwent radiation therapy and cisplatin chemotherapy. He was discharged on caffeine 200 mg twice daily, fludrocortisone 0.1 mg daily, and midodrine 20 mg three times daily.

Three months post-discharge, the patient remained symptom-free. His caffeine regimen was discontinued, and midodrine was reduced to 5 mg three times daily while continuing fludrocortisone 0.1 mg daily. These adjustments effectively managed his presyncopal and syncopal symptoms.

Management Challenges: This case represents a highly atypical presentation of carotid sinus syncope. The reasons for invoking the carotid sinus baroreceptor reflex arc include the hypotension and bradycardia, its fluctuating course, the anatomical involvement of the carotid baroreceptor, and the relief provided by surgical excision and decompression. However, the carotid sinus baroreceptor reflex arc responds to changes in transmural pressure very rapidly, while the heart rate and blood pressure changes in this patient lasted many hours. These receptors are essential in modulating blood pressure and executing reflex responses in heart rate and vascular tone in response to arterial wall stretching. The mechanical compression exerted by the tumor on the carotid sinus may have induced an intensified baroreflex response with fluctuating resetting. Although the baroreceptor set points for blood pressure and heart rate can reset chronically, as is common in hypertension, a set point resetting to extremely low levels remains unusual.

The unique physiological presentation of this case demands a closer examination of the autonomic influences on cardiac function, particularly the differential effects of carotid sinus stimulation on the sinus and atrioventricular nodes. There is a right-sided predominance in hypersensitivity reactions to carotid sinus massage, with asystole more commonly induced on the right side than the left. In a cohort of 130 patients, asystole occurred for three seconds or longer in 21 patients during right-sided massage compared to 15 on the left. The case is highlighted by the unusual severity of the patient's condition, marked by reliance on artificial rate support and vasopressors. Additionally, parasympathetic activation results in a negative dromotropic effect, slowing AV node conduction velocity.

Although surgical decompression of the affected area alleviated some mechanical pressure on the carotid sinus, symptoms persisted, indicating that the removal did not immediately resolve the underlying physiological disruptions. The continued symptoms post-mass removal might have stemmed from a variety of factors, such as the interaction of residual cancer cells with baroreceptor neurons, altered baroreceptor sensitivity due to prolonged compression, or residual inflammation affecting baroreceptor activity and function.

This case highlights the need to consider a broader spectrum of rare neck mass tumors that could induce syncope, such as thyroid enlargements, lymphadenopathy, paragangliomas, neurogenic tumors, salivary gland tumors, vascular anomalies, and cystic lesions. Each of these entities has the potential to compress the carotid sinus or its associated structures, mimicking or exacerbating the cardiovascular symptoms observed in this patient. The literature on cardiac complications from mechanical compression in head and neck cancer is scarce. This case contributes to our understanding of the intricate relationship between neck masses, carotid sinus function, and syncope. It underlines the importance of considering mechanical compression of the carotid sinus in the differential diagnosis of syncope, particularly in patients with neck masses.

Moreover, this case emphasizes the necessity of a personalized cardiovascular management plan for cancer patients, particularly when traditional cardiac interventions fail to alleviate symptoms. A multidisciplinary approach is imperative for comprehensive care in patients with overlapping cardiological and oncological conditions.