[Paradoxical bradycardia and hemorrhagic shock]

We report two cases of paradoxical bradycardia associated with acute hemorrhage and hypotension in conscious patients who had no antecedents of myocardial disease. In some cases of massive and rapid hypovolemia the occurrence of bradycardia may constitute a protective reflex directed to improve ventricular filling. This reflex is probably mediated by a vagal mechanism which acts on a previously increased sympathetic nerve tone and tends to maintain systemic vascular resistances and keep a cerebral blood flow high enough to preserve conscience level. We discuss the differential diagnosis with vasovagal syncope which can also occur during the initial phases of acute hemorrhage and during the preterminal bradycardia that develops during the so called "irreversible phase" of shock. Paradoxical bradycardia during hemorrhagic shock is always a sign of important bleeding that requires a rapid reposition of volemia. Administration of vagolytic agents is contraindicated since they can favour the occurrence of severe cardiac arrhythmias.