What are the cardiovascular findings characteristic of anaphylaxis?

Updated: May 16, 2018
  • Author: S Shahzad Mustafa, MD; Chief Editor: Michael A Kaliner, MD  more...
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Tachycardia is present in one fourth of patients, usually as a compensatory response to reduced intravascular volume or to stress from compensatory catecholamine release.

Bradycardia, in contrast, is more suggestive of a vasodepressor (vasovagal) reaction. Although tachycardia is the rule, bradycardia has also been observed in anaphylaxis (see Pathophysiology). Thus, bradycardia may not be as useful for distinguishing anaphylaxis from a vasodepressor reaction as was previously thought. Relative bradycardia (initial tachycardia followed by diminished heart rate despite worsening hypotension) has been reported previously in experimental settings of insect sting anaphylaxis, as well as in trauma patients. [6, 7, 57, 58, 59]

Hypotension (and resultant loss of consciousness) may be observed secondary to capillary leak, vasodilation, and hypoxic myocardial depression. Cardiovascular collapse and shock can occur immediately, without any other findings. This is an especially important consideration in the surgical setting. Because shock may develop without prominent skin manifestations or history of exposure, anaphylaxis is part of the differential diagnosis for patients who present with shock and no obvious cause.

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