Background: Heart rate at 1 minute during the recovery period from an exercise stress test (EST) of less than 18 beats per minute is associated with poor prognosis. The mechanism is attributed to chronotropic incompetence and/or vagal reactivation. Aim: 1) To investigate the frequency of heart rate recovery (HRR) between individuals with "Normal", "Pathological" and "Fluctuated" HRR and, 2) to examine autonomic function in these individuals using heart rate variability (HRV) indices.
Methods: All individuals underwent multiple ESTs as a routine check-up. "Normal" HRR at 1 min was define as HRR >18 b/min (group 1); "Pathologic" HRR ≤18 b/min (group 2) and "Fluctuated" as having HRR either below or above 18 b/min (<>18b/min, group 3) during repeated ESTs. Autonomic function was calculated using Power Spectral Analysis of the very low frequency (VLF), low frequency (LF), high frequency (HF), and the ratio of LF/HF. Analysis of variance (ANOVA) was performed and a p value ≤0.05 was considered significant.
Results: Out of 66 individuals, 38 (57%) performing 186 ESTs during 17 years of follow up, demonstrated HRR> 18 (group 1); 2 individuals (3%) with 8 ESTs demonstrated HRR≤18 (group 2) and 26 individuals (40%) with 152 ESTs demonstrated HRR<>18 (group 3). 44 additional individuals that underwent autonomic function evaluation during a prospective EST demonstrated similar HRR differences between the 3 study groups. However, no significant differences were found between groups in Power LF and HF measures at rest, at peak exercise, and during the recovery period at 1 and 5 min (P>0.05) post exercise.
Conclusion:
Our results demonstrate that HRR ≤18b/min is not a constant value and may fluctuate between tests. Despite significant differences in HRR between groups, no differences were found in autonomic function indices. These data, if reproduced in larger studies, may question the clinical significance and prognostic value of HRR post exercise.
