Quantification of the heart rate-independent vasodepressor component in carotid sinus syndrome

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Abstract
In 45 patients with carotid sinus syndrome, the heart rate-independent vasodepressor component under ventricular and av-sequential pacing of the heart was investigated both in supine and in standing patients. Under both forms of pacing, the carotid pressure determination has led to a marked lowering of systolic and diastolic arterial blood pressure which is significantly more pronounced under orthostasis. The blood pressure values reached both in supine and in standing patients are significantly higher under av-sequential pacing than under ventricular pacing. Accordingly, the proportion of symptomatic patients is less under av-sequential pacing in the supine position (17% versus 29%) and in standing (65% versus 83%). The heart rate-independent vasodepressor reaction is maximal on average between 11 s and 16 s after the beginning of the carotid pressure test and persists for 3 s to 7 s. The blood pressure reaches initial values again after 14 s to 20 s. To summarize, these data document that a clinically relevant heart rate-independent vasodepressor reaction is to be reckoned with in the majority of patients with carotid sinus syndrome. This shows a different time course than the vagally determined effect of the carotid sinus reflex on heart rate. Orthostasis intensifies the vasodepressor reaction so that the hemodynamically more favorable avsequential pacing which is actually more favorable in hemodynamic terms cannot guarantee freedom from symptoms in the majority of patients in the upright standing position.