Study objectives: To compare the independent and additive data provided by initial and final heart rate (HR) exercise transients, and to analyze both according to gender, aerobic fitness, clinical status, and medication usage.
Design: Retrospective study.
Setting: Exercise medicine clinic.
Patients: A total of 544 subjects (363 men) with a mean (± SD) age of 50 ± 14 years (age range, 10 to 91 years), including asymptomatic and coronary artery disease patients.
Measurements and results: HR transients were obtained from the following two exercise protocols: 4-s exercise test (4sET) followed by a maximal cardiopulmonary cycling exercise test (CPET). The initial HR transient was represented by the cardiac vagal index (CVI), which was obtained by the 4sET, and the final transient (ie, HR recovery [HRR]) was determined by the following equation: CPET maximal HR − the 1-min postexercise HR. Transients were modestly related (r = 0.22; p < 0.001) when adjusted for age, aerobic fitness, clinical status, and negative chronotropic action drug usage. The transients were unrelated to gender (vs CVI, p = 0.10; vs HRR, p = 0.15). Subjects with a measured maximum oxygen uptake (V̇o2max) exceeding 100% of the predicted maximal aerobic power showed higher CVIs than those in less aerobically fit subjects (V̇o2max < 50% subgroup, p = 0.009; V̇o2max < 75% subgroup, p = 0.034). Both transient results differed for asymptomatic and cardiac subjects (CVI, 1.32 ± 0.02 vs 1.42 ± 0.02, respectively [p = 0.001]; HRR, 33 ± 1 beats/min (bpm) vs 37 ± 1 bpm, respectively [p = 0.009]).
Conclusions: The initial and final HR transients were modestly related, suggesting a potentially complementary clinical role for both measurements in the assessment of autonomic function in patients with coronary artery disease. Although both HR transients tended to behave similarly under the influence of several variables, the initial HR transient, measured during 4sET, was more likely to discriminate distinct subgroups compared with the final HR transient.