Bradycardia–asystole during neck dissection

EDITOR:

During radical neck dissection, bradycardia and asystole are life-threatening signs of an exaggerated carotid sinus reflex (CSR) that may occasionally be observed in certain patients. This may be seen before, during or after head and neck surgery.

A 40-yr-old (smoker for 20yr) male presented with difficulty in swallowing for 4 months and neck swelling for 1 month. Indirect laryngoscopy revealed a growth involving the right aryepiglottic fold, extending to the epiglottis and pyriform sinus. A single hard immobile lymph node of 3 cm was found in the jugulodigastric triangle. A clinical diagnosis of carcinoma of the hypopharynx was made. A biopsy was performed under local anaesthesia, and histopathology confirmed the growth to be a squamous cell carcinoma. He received external radiation to the head and neck (60 Gy in 30 fractions over a period of 6 weeks). Direct laryngoscopy at the end of the treatment showed regression of the primary. He was then scheduled to undergo neck dissection for the residual nodal disease. Preoperative anaesthetic evaluation was unremarkable and no airway problems were anticipated.

In the operating room, monitoring was instituted and anaesthesia induced. After tracheal intubation anaesthesia was maintained with inhalational anaesthetics and controlled ventilation. The heart rate and blood pressure remained stable at induction (80–90 min⁻¹ and 130/80–110/70 mmHg, respectively) and throughout the initial part of the surgery. Using a modified McFee’s incision, the surgeons proceeded to perform a radical neck dissection. During the dissection of level II nodes, bradycardia and junctional rhythm was noted. The heart rate decreased to 60 min⁻¹ and despite cessation of surgical stimulus; within 5 s the heart rate was 30 min⁻¹. The blood pressure recorded was 60/40 mmHg and the inhalational agents were immediately discontinued. The administration of glycopyrollate (0.2 mg i.v.) did not increase the heart rate and this was followed by an asystolic pause. Atropine (0.6 mg i.v.) was administered and preparation for external cardiac massage was made. Within 3 min of the initial event, the electrocardiogram monitor showed return of sinus rhythm and the heart rate increased to 60 min⁻¹. Anaesthetics were re-instituted and surgery proceeded after infiltration of the area with lidocaine. The remainder of the anaesthetic was uneventful, he made satisfactory recovery with no haemodynamic events in the postoperative period and was discharged to continue follow-up as an outpatient.

This patient’s episode of bradycardia preceding the hypotension and asystole occurring during neck dissection is typical of an exaggerated CSR [1]. The normal reflex plays a central role in blood pressure homoeostasis and there are three subtypes. The cardio-inhibitory type (70–75% of cases) is where the predominant manifestation is sinus bradycardia, atrio-ventricular block or asystole. The response is due to exaggerated vagal action and can be abolished with atropine and treated with transvenous pacing. The second is the vasodepressor type, seen in 5–10% of cases. The predominant manifestation is a decrease in vasomotor tone without a change in heart rate. The third type is the mixed type (20–25% of cases) where a decrease in heart rate and vasomotor tone occurs simultaneously.

Patients with head and neck malignancies may present with recurrent episodes related to an exaggerated CSR [2]. Mechanical deformation of the carotid sinus (located at the bifurcation of the common carotid artery) by the tumour or metastatic nodal mass may result in an exaggerated response – bradycardia, hypotension, cardiac arrhythmia presenting as seizures, presyncope or syncope. These episodes can occur during neck examination, surgery or rarely occur spontaneously [3]. Preoperative radiation therapy is useful to treat metastatic head and neck malignancies that may otherwise be inoperable. Additionally, external radiation therapy to the neck may provide relief from symptoms of CSR [4]. External radiation therapy is especially useful in treating metastatic tumour around the carotid sinus and those infiltrations of the carotid sheath which preclude surgical excision [5]. Unfortunately, the radiation itself can result in a variety of haemodynamic conditions [4,5] (including CSR) and significant carotid artery stenosis in patients who were previously asymptomatic.

During surgery (neck dissection), episodes of bradycardia–asystole have been previously reported [6]. Such events are reported to occur sporadically during head and neck surgery, but occasionally may prove fatal [7]. Once this exaggerated CSR occurs intra-operatively, as in this case, it can be corrected in most instances by a combination of cessation of surgical stimulus and administration of vagolytics. Low-dose vagolytics may paradoxically increase vagal tone and precipitate a cardiac arrest [8].

Though these exaggerated CSR’s are often they are either infrequent or rarely reported or both. We reviewed the previous consecutive 150 neck dissections done in this hospital over past 36 months. No other episodes of bradycardia–asystole had been observed during surgery. This patient belonged to a small subset of 18 patients who had received radiation therapy before the surgery (mostly for advanced pharyngeal malignancies). We therefore speculate that preoperative external radiation therapy treatment may predispose patients to an exaggerated CSR during radical neck dissection. Further, in this patient, the preoperative disease (advanced pharyngeal malignancy with neck nodal metastasis), treatment (external radiation) and or intra-operative surgical procedure (radical neck dissection) individually or together may have contributed to this adverse event. Investigative studies would be required to determine the contribution of each of the above in the development of bradycardia–asystole during neck dissection.