The protective suits needed by Hazmat workers often cause heat stress, so graded exercise testing (GXT) has been recommended in their medical evaluation. Since such workers are relatively young and healthy, false-positive indications of cardiac ischemia are common. One must therefore look beyond ST-segment depression alone, in analyzing their GXT results. Among 206 potential Hazmat candidates (93% male, age 34.6, BMI 29.1, 8% smokers), 11 men's GXT had ≥2 mv of horizontal ST depression in multiple leads. Cardiac imaging was normal in seven and not done in four who are working in non-Hazmat jobs, 5 years later. Heart rate recovery (HRR, 30 ± 9SD), Chronotropic Index (CI, 1.0 ± 0.2), and Duke Treadmill Score (DTS, 1.0 ± 4) in these 11 men indicated maximal 5-year all-cause mortality of 3%, compared to 0.9% and 0.3%, in candidates with 1 to 1.9 mv, and < 1 mv of ST depression, respectively. While the use of HRR, CI, andDTS can minimize the need for cardiac imaging in this application of GXT, the Bruce Protocol (BP) induced little heat stress in a subset of 52 potential candidates so evaluated. That is, during BP GXT lasting 11.1 ± 2.3 min (Stage 4, 12.9 METS), tympanic and oral temperatures rose by only 0.7 ± 0.9 and 0.4 ± 0.8°F, respectively, with little thermal discomfort or sweating.
Conclusions BP GXT typically involves such brief duration and attire that it creates little heat stress, which is the raison d'etre for using GXT in Hazmat candidates. Other approaches are needed.
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