KS was first reported in the United States in 1991, but nationwide epidemiological data are still lacking, according to a recent report. The condition is defined as acute coronary syndrome (ACS) caused by an allergic reaction or a strong immune reaction to a drug or other substance. A study published in the International Journal of Cardiology assessed the prevalence of KS among patients primarily hospitalized for allergic/hypersensitivity/anaphylactic reactions.

Researchers from the Atlanta Veterans’ Affairs Medical Center and colleagues compared baseline demographics, comorbidities, and outcomes of KS with patients with only allergic, hypersensitivity, and/or anaphylactic reactions using the National Inpatient Sample, 2007-2014. Overall, the study team identified 235,420 patients primarily hospitalized with allergy/hypersensitivity/anaphylactic reactions.

Of these, 2,616 patients (1.1%) experienced ACS and were identified as having KS; 0.2% had unstable angina; 0.2% had ST-elevation myocardial infarction; and 0.7% had non–ST-elevation myocardial infarction.

Patients with KS tended to be older (mean age 65.9 ± 14.1 vs. 57.2 ± 17.8 years); more often white (71.1% vs. 58.6%); male (46.4% vs. 39.9%); enrolled in Medicare (58.9% vs. 41.5%), and admitted nonselectively (96.8% vs. 95.3%), compared with the non-KS group (P <.001).

Researchers pointed out that hospitalizations with KS led to:
• Higher all-cause in-hospital mortality (7.0% vs. 0.4%, P <.001)
• Prolonged hospital length-of-stay (mean 5.8 ± 6.0 vs. 3.0 ± 3.9 days, P <.001)
• Higher inpatient charges ($52,656 vs. $20,487, P <.001), and
• More frequent transfers to other facilities.

Also significantly higher in patients with KS were the rates of stroke (1.0% vs. 0.2%), arrhythmias (30.4% vs. 12.4%), venous thromboembolism (1.6% vs. 1.0%), and diagnostic and therapeutic coronary interventions.

The study notes that patients with KS had increased odds of in-hospital mortality (unadjusted odds ratio [OR]: 18.52; 95% CI, 15.74-21.80, P <.001 and adjusted OR: 9.74, 95% CI, 8.08-11.76, P <.001) compared with the non-KS group.

“Overall U.S. prevalence of KS among patients hospitalized for allergic/hypersensitivity/anaphylactic reactions is 1.1% with a subsequent all-cause inpatient mortality rate of 7.0%,” the study authors concluded.

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