Increased arterial stiffness and heart rate variability over time in heart transplant recipients: A cross-sectional study using peripheral arterial tonometry

Abstract

Background: Arterial stiffness represented by Augmentation index (AIx) and heart rate variability (HRV) are established predictors of cardiovascular risk in heart transplant (HTx) recipients. However, the relationship between AIx and HRV in this population remains insufficiently explored, and factors such as time after transplantation may influence both metrics.

Objective: The purpose of this study was to evaluate vascular function through Aix and HRV parameters in HTx patients, both assessed by peripheral arterial tonometry (PAT).

Methods: A cross-sectional study was conducted with 35 adults aged 18 to 65 years, HTx ≥ 6 months after surgery, with stable clinical condition and no changes over the last 3 months of immunosuppressive treatment. AIx and HRV were assessed using PAT.

Results: Participants were categorized into 2 groups based on AIx values: high AIx (n = 19, AIx > -5%) and low AIx (n = 16, AIx ≤ -5%). The high AIx group had a significantly longer time after transplantation (p = 0.00). HRV analysis revealed that the standard deviation of all normal NN intervals (SDNN, p = 0.044), and lower frequency to high-frequency ratio (LF/HF, p = 0.034) were significantly higher (p = 0.03) and HR was significantly lower (p = 0.04) in the high AIx group compared to low AIx.

Conclusions: Arterial stiffness assessed by PAT was higher in patients with a longer time after heart transplantation. Similarly, HRV indices, which reflect several cardiovascular health conditions, such as SDNN and sympathovagal balance (LF/HF ratio) were higher in the group with higher arterial stiffness in individuals after heart transplantation.

Keywords: arterial stiffness; augmentation index; endothelial function; heart rate variability; heart transplant.

Figure 1

Acquisition of the Augmentation index (AIx) signal, where P₂ represents the peak of the reflection wave and P₁ the peak of the systolic wave (P1), AIx = (P2 - P1)/P1 × 100 (Image obtained from the exam result generated by EndoPAT2000).

Figure 2

Acquisition of heart rate variability indices. A: Acquisition of NN intervals. B: Acquisition of HRV indices in the frequency domain. LF, low frequency; HF, high frequency. (Image obtained from the exam result generated by EndoPAT2000).

Figure 3

Flowchart of sample selection.

Figure 4

Comparison of arterial stiffness measured by augmentation index of heart transplant recipients separate in High Augmentation Index (high AIx) and Low Augmentation Index (low AIx) for time of transplant.

Figure 5

Comparison of arterial stiffness measured by augmentation index of heart transplant recipients separate in High Augmentation Index (high AIx) and Low Augmentation Index (low AIx) for standard deviation of all normal NN intervals (SDNN) and low frequency to high frequency ratio (LF/HF).