Background:
Autonomic dysfunction (AD) as measured by heart rate variability (HRV) is associated with increased risk of cardiovascular disease (CVD) and breast cancer. No study has utilized a large prospective multi-center cohort of diverse women to assess differences in HRV associated with incident breast cancer.
Objectives:
To identify heart rate variability changes in women with breast cancer compared to controls in the Women’s Health Initiative (WHI).
Methods:
In a retrospective cohort study, we utilized 5,031 women in the WHI CT cohort who were breast cancer free at baseline and compared 1) those with incident breast cancer v. 2) those who were breast cancer free during the ECG follow-up period as controls. HRV was calculated utilizing 10-second ECG with two measures of two-domain HRV: standard deviation of all normal-to-normal RR intervals (SDNN) and the root mean square of successive differences in normal-to-normal RR intervals (rMSSD). HRV was measured from ECGs collected at baseline, years 3, 6, and 9 in the comparison groups. An adjusted mixed linear model was used to evaluate the differences in SDNN and rMSSD comparing women with incident breast cancer to controls. Cardiovascular risk factors utilized in the adjusted model were determined via questionnaire at baseline.
Results:
At baseline, women with incident breast cancer diagnosed by years 3, 6, or 9 were significantly older (median age 63 vs. 61, P<0.0001) and had a higher prevalence of hypertension (35% vs. 32%, P=0.02). SDNN at years 3 and 6 in women with breast cancer compared to controls was significantly lower (P=0.0002, P=0.03 respectively). As well, rMSSD was significantly lower at year 3 compared to controls (P<0.0001) (
Figure 1
).
Conclusions:
HRV as a measure of AD is significantly lower in women with incident breast cancer compared to women without breast cancer. Reduction in HRV is associated with CVD outcomes in the literature. Our study suggests HRV may predict CVD in breast cancer patients.
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