Predictors and Clinical Impacts of Impaired Heart Rate Variability in Women with Breast Cancer

<i>Background and Objectives</i>: Breast cancer (BC) is the most prevalent cancer globally, with a significant mortality rate, especially among women. While advances in treatment have reduced BC mortality, cardiovascular complications resulting from anticancer therapies have become a major concern. The autonomic nervous system (ANS) may be affected in BC patients and it is assessed with heart rate variability (HRV). The aim of this study was to investigate the prevalence of impaired HRV, its predictors, and its clinical impacts in BC patients. <i>Materials and Methods</i>: We retrospectively screened all female BC patients and enrolled cases who underwent 24 h Holter electrocardiography monitoring with accessible clinical follow-up data. <i>Results</i>: This study included 136 BC patients, and the mean age was 56.8 ± 10.8 years old. Impaired HRV was present in 36.8% of patients, and hypertension was identified as a significant predictor of reduced HRV (OR = 3.61, CI: 1.01-12.92, <i>p</i> = 0.048). Furthermore, de novo atrial fibrillation (AF) occurred more frequently in patients with impaired HRV (20% vs. 8.1%; <i>p</i> = 0.044). None of the HRV parameters were associated with all-cause mortality, and cancer stage was found to be the only independent predictor of all-cause mortality (HR = 3.93, CI: 1.81-8.55; <i>p</i> < 0.001). <i>Conclusions</i>: HRV is impaired in a significant proportion of patients with BC. Hypertension plays a crucial role in the deterioration of HRV in patients with BC, and de novo AF is more common in patients with impaired HRV. However, HRV does not appear to predict all-cause mortality in patients with BC. This study highlights the importance of the optimal management of cardiovascular risk factors, such as hypertension, to prevent ANS dysfunction in cancer patients.