Background: Heart rate variability (HRV) is a non-invasive marker of autonomic nervous system function that is based on the analysis of length differences between subsequent RR intervals of the electrocardiogram. The aim of this systematic review was to assess the current knowledge gap in the utility of HRV parameters and their value as predictors of the acute stroke course.Methods: A systematic review was performed in accordance with the PRISMA guidelines. Relevant articles published between 1 January 2016 and 1 November 2022 available in the PubMed, Web of Science, Scopus, and Cochrane Library databases were obtained using a systematic search strategy. The following keywords were used to screen the publications: “heart rate variability” AND/OR “HRV” AND “stroke.” The eligibility criteria that clearly identified and described outcomes and outlined restrictions on HRV measurement were pre-established by the authors. Articles assessing the relationship between HRV measured in the acute phase of stroke and at least one stroke outcome were considered. The observation period did not exceed 12 months. Studies that included patients with medical conditions influencing HRV with no established stroke etiology and non-human subjects were excluded from the analysis. To minimize the risk of bias, disagreements throughout the search and analysis were resolved by two independent supervisors.Results: Of the 1,305 records obtained from the systematic search based on keywords, 36 were included in the final review. These publications provided insight into the usability of linear and non-linear HRV analysis in predicting the course, complications, and mortality of stroke. Furthermore, some modern techniques, such as HRV biofeedback, for the improvement of cognition performance after a stroke are discussed.Discussion: The present study showed that HRV could be considered a promising biomarker of a stroke outcome and its complications. However, further research is needed to establish a methodology for appropriate quantification and interpretation of HRV-derived parameters.

The aim of this study was to assess whether heart rate variability (HRV) could predict which hemisphere of the brain was affected during an acute ischemic stroke (AIS). To achieve this goal, we compared HRV between patients with a right (RH) and left hemispheric (LH) stroke. The studied group consisted of 64 patients with AIS (25 with RH and 39 with LH stroke, with a mean age of 64 ± 12 and 66 ± 13, p = 0.3, respectively) using 24 h Holter ECG records at NN intervals performed at a mean of 4.3 ± 2 days following their AIS. Standard linear methods were used to analyze HRV in the time and frequency domains, as well as nonlinear methods, including sample entropy, detrended fluctuation analysis, and asymmetry measures. Patients with an LH stroke had significantly greater values for sample entropy compared to subjects with an RH stroke (1.31 ± 0.53 vs. 0.92 ± 0.46, p = 0.003, Bonferroni-corrected p = 0.033, effect size = 0.8). The LH stroke group also had higher RMSSD (113 ± 81 vs. 76 ± 61, p = 0.06), pNN50 (33.35 ± 28.54 vs. 18.52 ± 23.75, p = 0.02), and HF_nu (48.42 ± 16.41 vs. 42.66 ± 17.88, p = 0.11) values, when compared to the RH group, which was possibly related to higher activity in the parasympathetic system in the LH group. Conversely, subjects with RH stroke had higher LF_nu (57.34 ± 17.88 vs. 51.58 ± 16.41, p-value = 0.11) and LF/HF ratios (2.24 ± 2.87 vs. 1.68 ± 2.50, p-value = 0.11), which were likely related to higher activity in the sympathetic nervous system, when compared to the LH stroke group. Our pilot study demonstrated that patients with RH stroke had lower HRV complexity than those with LH stroke, indicating that HRV could be useful in the discrimination of hemispheric involvement in AIS.

The aim of this study was to assess whether the heart rate variability (HRV) could predict a favorable or unfavorable stroke outcome. The endpoint was based on the National Institutes of Health Stroke Scale (NIHSS). The patient’s health condition was assessed upon discharge from the hospital. An unfavorable stroke outcome was defined as death or NIHSS ≥ 9, while NIHSS < 9 meant a favorable stroke outcome. The studied group consisted of 59 patients with acute ischemic stroke AIS (mean age of 65.6 ± 13.2; 58% were females). An original and innovative non-linear measure was used to analyze HRV. It was based on symbolic dynamics consisting of comparing the “length of the longest words” in the night recording of HRV. “The length of the longest word” meant the longest sequence of identical adjacent symbols possible for a patient. An unfavorable stroke outcome occurred in 22 patients, whereas the majority of patients (37) had a favorable stroke outcome. The average hospitalization time of patients with clinical progression was 29 ± 14 days, and with favorable outcomes was 10 ± 3 days. Patients with long words (more than 150 adjacent RR intervals having the same symbol) were hospitalized no longer than 14 days and they had no clinical progression. The patients with a favorable stroke outcome were characterized by longer words. Our pilot study may be the beginning of work on the development of a non-linear, symbolic method as a predictor of prolonged hospitalization and increased risk of clinical progression in patients with AIS.

Objective: Can the localization of an ischemic stroke in the hemisphere of the brain be assessed on the basis of the heart rate variability? Is there a difference in heart rate variability between people with right hemisphere stroke and people with left hemisphere stroke? Methods: 24h analysis of RR intervals of people in the acute phase of stroke. The research group consisted of 25 people after ischemic stroke of the right hemisphere and 39 people after ischemic stroke of the left hemisphere. Standard linear methods were used to analyze heart rate variability in the time and frequency domains, as well as nonlinear methods - Sample Entropy, Detrended Fluctuation Analysis and asymmetry measures. Results: Statistically significant results between right and left hemispheric stroke subjects are shown for the pNN50(p-value=0.028) and Sample Entropy (p-value=0.010). The results for the RMSSD (0.052) are also close to statistical significance. People with a right hemisphere stroke are characterized by reduced parasympathetic activity and a lower complexity of heart rate variability compared to the group of people with left hemispheric ischemic stroke. Conclusion: Based on the heart rate variability in the acute phase of an ischemic stroke, it is possible to determine the location of the stroke in the right brain hemisphere or the left brain hemisphere.