Surgical interventions and studies of the carotid sinus

Abstract

Background: The carotid baroreflex buffers acute changes in blood pressure and is triggered by baroreceptors in the carotid sinus. Baroreceptor firing results in an increased parasympathetic tone and a decreased sympathetic tone leading to reduced heart rate and blood pressure. Under normal conditions, sympathetic and parasympathetic action at the level of the carotid sinus is balanced. In contrast, patients suffering from a carotid sinus syndrome (CSS) may demonstrate an exaggerated carotid baroreflex response. Symptoms of dizziness and syncope may occur because of episodes of a brief asystole or a profound drop in blood pressure. In a mostly elderly patient group these syncopes may be associated with frequent falls leading to serious sequelae.Pacemaker implantation is nowadays considered ‘gold standard’ for treating CSS patients with repetitive syncope, but may not always be effective. The sympathetic nervous system also plays a crucial role in the pathofysiology of hypertension. An association was found between systemic hypertension and the presence of an abnormal baroreflex. Large clinical trials indicate that up to 30% of hypertensive patients do not reach normotension despite life style changes in combination with the use of pharmacological agents these measures. This therapy resistant hypertension is a major risk factor for the development of cardiovascular events. Aims Aims of this thesis are: first to study the effects of carotid sinus denervation by means of adventitial stripping in patients suffering from carotid sinus syndrome (CSS) and second, to explore the concept of mechanical carotid sinus stimulation in the treatment of hypertension. Methods A literature study was performed on technique, efficacy and safety of a surgical technique termed adventitial stripping of the carotid sinus as a treatment of CSS. Second, the anatomy of nerve structures surrounding the carotid bifurcation with special emphasis on the carotid sinus nerve (CSN) and its branches was studied, followed by a microscopic study of baroreceptor distribution in the carotid bifurcation. Next, short and long term efficacy and safety of adventitial carotid stripping was studied in a cohort of 27 CSS patients. Finally, a first-in-man study of mechanical carotid sinus stimulation was performed. Conclusions -Substantial or complete relief of CSS associated symptoms was achieved by adventitial carotid stripping in 85% of the patients reported in the literature. -Carotid sinus nerve (CSN) anatomy is characterized by a great variability. Therefore, CSN transection as a single treatment for patients with CSS may be insufficient. -Baroreceptor density is highest in the first cm portion of the medial internal carotid artery (ICA). Therefore, adventitial stripping of the proximal ICA is sufficient for CSS. -Adventitial stripping of the proximal 3 cm of the ICA appears effective in 93% of our CSS patient cohort (n=27),whereas CSS recurrence was absent on the long term. -Carotid denervation by adventitial stripping is safe. -Mechanical carotid stimulation lowers blood pressure in an acute human model.