The angina-relieving effects of sympathetic blockade

In the 1930's it was recognised by neurosurgeons performing destructive sympathectomies for angina pectoris that local anaesthetic infiltration around the stellate ganglion often resulted in pain relief outlasting the duration of action of the local anaesthetic drug^13. This observation has been more recently confirmed¹⁴, and is currently (June 1999) the subject of a large scale randomised double-blind placebo-controlled trial funded by the British Heart Foundation.

The pathogenesis of angina and myocardial infarction pain involves the activation of the afferent sympathetic pathway. A frequent and important consequence of pain (especially when severe) is the `flight or fight' response through activation of sympathetic efferents. The clinical image of the patient with an acute myocardial infarction (cold, clammy, sweaty, anxious, tachycardic) is secondary to this adrenergic activation. Therefore, angina might be regarded as the sensory component of a positive feedback loop, which cannot under these circumstances be conceived as resulting in benefit, and which may be considered to be a maladaption.

The angina-relieving effects of sympathetic blockade might be due to interference with this maladaptive feedback loop, in a similar manner to the way in which adenosine interrupts a re-entrant tachycardia. If such a loop exists, it may partly explain chronic refractory angina and the fact that temporary interruption of this pathway has a prolonged effect on pain¹⁴. Beneficial amelioration of angina can be achieved with repeated blocks¹⁴. There does not appear to be any predictability in the length of time a patient remains pain-free after successive blocks.

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