Perioperative bradycardia and asystole: relationship to vasovagal syncope and the Bezold-Jarisch reflex

Reflex cardiovascular depression with vasodilation and bradycardia has been variously termed vasovagal syncope, the Bezold-Jarisch reflex and neurocar diogenic syncope. The circulatory response changes from the normal maintena nce of arterial pressure, to parasympathetic activation and sympathetic inh ibition, causing hypotension. This change is triggered by reduced cardiac v enous return as well as through affective mechanisms such as pain or fear. It is probably mediated in pan via afferent nerves from the heart, but also by various non-cardiac baroreceptors which may become paradoxically active . This response may occur during regional anaesthesia, haemorrhage or supin e inferior vena cava compression in pregnancy; these factors are additive w hen combined. In these circumstances hypotension may be more severe than th at caused by bradycardia alone, because of unappreciated vasodilation. Trea tment includes the restoration of venous return and correction of absolute blood volume deficits. Ephedrine is the most logical choice of single drug to correct the changes because of its combined action on the heart and peri pheral blood vessels. Epinephrine must be used early in established cardiac arrest, especially after high regional anaesthesia.