# Influence of Ectopic Beats on Heart Rate Variability Analysis

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## Abstract

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## 1. Introduction

## 2. Methods

#### 2.1. Data and Preprocessing

#### 2.2. HRV Indices

- SDNN: SDNN is the standard deviation of a 5 min RR segment, and was calculated as follows:$$\mathrm{SDNN}=\sqrt{\frac{{\sum}_{i=1}^{N}{\left(R{R}_{i}-R{R}_{mean}\right)}^{2}}{N}}$$
- LF/HF: The frequency-domain features were calculated using power spectral density. Prior to the frequency-domain analysis, spline interpolation was used to resample the RR intervals time series evenly at 4 Hz. HRV spectrum was produced using Burg’s method with an order of 10 [24]. It was then decomposed into two separate frequency bands: a low-frequency band (LF, 0.04 to 0.15 Hz) and a high-frequency band (HF, 0.15 to 0.4 Hz). The ratio of low-frequency power to high-frequency power (LF/HF) was calculated, which reflected the balance between the sympathetic and parasympathetic (or vagal) activity.
- Sample entropy: SampEn is a widely used index for HRV analysis and can reflect the inherent complexity or regularity of RR interval time series. The calculation for SampEn was summarized as follows [20]:For a 5 min RR segment $X=\left\{{x}_{1},{x}_{2},\cdots ,{x}_{N}\right\}$, given the parameters m and r, first form the vector sequences ${X}_{m}\left(i\right)$, which represented m consecutive ${x}_{i}$ values:$${X}_{m}\left(i\right)=\left[{x}_{i},{x}_{i+1},\cdots ,{x}_{i+m-1}\right]\left(1\le i\le N-m\right).$$The distance between ${X}_{m}\left(i\right)$ and ${X}_{m}\left(j\right)$ was defined using the maximum absolute difference:$${d}_{i,j}^{m}=d({X}_{m}\left(i\right),{X}_{m}\left(j\right))=\mathrm{max}\left(\left|{x}_{i+k}-{x}_{j+k}\right|\right)\left(0\le k\le m-1\right).$$For each ${X}_{m}\left(i\right)$, denote ${B}_{i}^{m}\left(r\right)$ as (N-m)-1 times the number of ${X}_{m}\left(j\right)$ ($1\le j\le N-m$, $j\ne i$) that meets ${d}_{i,j}^{m}\le r$. Similarly, set ${A}_{i}^{m}\left(r\right)$ is ${\left(N-m\right)}^{-1}$ times the number of ${X}_{m+1}\left(j\right)$ that meets ${d}_{i,j}^{m+1}\le r$ for all $1\le j\le N-m$.Then SampEn is defined by:$$\mathrm{SampEn}\left(m,r,N\right)=-\mathrm{ln}\left({\sum}_{i=1}^{N-m}{A}_{i}^{m}\left(r\right)/{\sum}_{i=1}^{N-m}{B}_{i}^{m}\left(r\right)\right).$$In the current study, the parameter settings for SampEn used the recommendation from our previous study [22], i.e., embedding dimension m = 2 and tolerance threshold r = 0.10 times the standard deviation (SD) of the time series.
- Physical threshold-based SampEn (Pt-SampEn): For entropy analysis, three intrinsic parameters (embedding dimension 𝑚, tolerance threshold r, and time-series length N) needed to be initialized. SampEn was reported not sensitive to the time series length if $N\ge 200~300$ but sensitive to the parameter tolerance threshold. Since parameter m is based on the length N ($N\approx {10}^{m}~{20}^{m}$), SampEn was also not sensitive to m. Tolerance threshold r was difficult to be determined and was recommended between 0.10 and 0.25 times the SD of the time series. However, in practice, if the r value was too small, the number of matched vectors was small, and, on the contrary, if the r value was too large, detailed information within the time series was ignored. RR interval time series usually have variable SD values, and it is not easy to find an appropriate r value to achieve an optimal result. Hence, simply use the suggested range of 0.10 to 0.25 times the SD. Herein, a physical threshold r was used to form a unified comparison baseline for determining the vector similarity, and, thus, the Pt-SampEn was developed in our previous study [28].

#### 2.3. Evaluation Method

#### 2.4. Statistical Analysis

## 3. Results

#### 3.1. C_{SDNN}

_{SDNN}for both NSR subjects and CHF patients. SDNN decreased as expected when the ectopic beats were removed, and its change rate index C

_{SDNN}significantly increased with the increase of the number of ectopic beats. The increasing trend in the two groups was similar. For NSR subjects, C

_{SDNN}results were 5.2% (2.2–11.4%) when only one ectopic beat was included in each 5 min RR segment and increased to 42.1% (26.4–58.8%) when more than 10 ectopic beats were included. For CHF patients, C

_{SDNN}results were 5.2% (1.5–13.8%) when only one ectopic beat was included and increased to 52.6% (27.3–69.3%) when more than 10 ectopic beats were included. The C

_{SDNN}results from the two groups indicated that the influence of ectopic beat burden for SDNN appeared to grow with the increasing number of ectopic beats.

#### 3.2. C_{LF/HF}

_{LF/HF}for the two groups. The change rate index C

_{LF/HF}also increased with the increase of the number of ectopic beats, and the influence appeared to be more profound compared with that of SDNN. For NSR subjects, C

_{LF/HF}results were 69.8% (24.5–166.2%) when only one ectopic beat was included in each 5 min RR segment and fluctuated to 501.2% (278.1–1091.7%) when more than 10 ectopic beats were included. For CHF patients, C

_{LF/HF}results were 25.0% (4.7–102.9%) when only one ectopic beat was included and increased to 291.2% (64.0–609.4%) when more than 10 ectopic beats were included. The C

_{LF/HF}results from the two groups indicated that the frequency-domain index of LF/HF was heavily influenced by ectopic beats, and the influence became heavier when the number of ectopic beats increased.

#### 3.3. C_{SampEn}

_{SampEn}for the two groups. The change rate index C

_{SampEn}still increased with the increase in the number of ectopic beats. For NSR subjects, the C

_{SampEn}results were 0.3% (0.1–1.6%) when only with one ectopic beat and became larger as the ectopic number increased, yielding a maximum value of 46.2% (17.1–101.8%) when the ectopic number was more than 10. For CHF patients, the C

_{SampEn}results were 0.2% (0.04–0.7%) when there was only one ectopic beat and achieved maximum results of 65.4% (21.8–154.3%) when the ectopic number was more than 10. Variation of C

_{SampEn}also had a general increasing trend related to the ectopic numbers, indicated by the increased IQR range with the increase in the number of ectopic beats.

#### 3.4. C_{PT-SampEn}

_{Pt-SampEn}for the two groups. C

_{Pt-SampEn}shows significantly lower values compared with the other three indices. For NSR subjects, C

_{Pt-SampEn}was only 0.3% (0.1–0.6%) when only one ectopic beat was included and increased to 6.6% (3.3–11.6%) when more than 10 ectopic beats were included. For CHF patients, C

_{Pt-SampEn}was 0.6% (0.2–1.0%) when there was only one ectopic beat and increased to 11.4% (7.6–18.2%) when more than 10 ectopic beats were included. The C

_{Pt-SampEn}results from the two groups indicated that the influence of ectopic beat burden on Pt-SampEn appeared to be relatively small. An obvious change in C

_{Pt-SampEn}was only observed from the RR segments with lots of ectopic beats (>10 in this study).

#### 3.5. Comparison of Variances of the Change Rate Index

_{LF/HF}was the largest with 730.5% for NSR subjects and 388.0% for CHF patients, respectively. The std of C

_{SDNN}and C

_{SampEn}were also large and were 16.4% and 58.3% for NSR subjects, 20.3% and 74.9% for CHF patients. The std of C

_{Pt-SampEn}was relatively small, only 2.3% for NSR subjects and 3.3% for CHF patients. These results further confirmed that, compared to other indices, Pt-SampEn had better robustness to ectopic beats in each ectopic number group and, thus, had better stability.

## 4. Discussion and Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**Distribution of the ectopic-free and ectopic 5 min RR segments classified by the number of ectopic beats in the NSR group. # Number of.

**Figure 2.**Distribution of the ectopic-free and ectopic 5 min RR segments classified by the number of ectopic beats in the CHF group. # Number of.

**Figure 3.**Examples of 5 min RR segments from an NSR subject: (

**A**) 5 min RR segment without ectopic beats and (

**B**) 5 min RR segment with premature atrial contraction (ectopic type A). The x-axes show the real-time window from the raw RR interval recordings, facilitating the readers to locate these selected 5 min RR segments.

**Figure 4.**Examples of 5 min RR segments from a CHF patient: (

**A**) 5 min RR segment without ectopic beats and (

**B**) 5 min RR segment with premature ventricular contraction (ectopic type: V). The x-axes show the real-time window from the raw RR interval recordings, facilitating the readers to locate these selected 5 min RR segments.

**Figure 5.**Demonstration of the changes of HRV indices before (

**A**) and after (

**B**) ectopic beats removal in a 5 min RR segment of subject NSR003. The corresponding HRV results were given in each sub-figure. “ectopic type: A” means premature atrial contraction.

**Figure 6.**Demonstration of the changes of HRV indices before (

**A**) and after (

**B**) ectopic beats removal in a 5 min RR segment of patient CHF205. The corresponding HRV results were given in each sub-figure. “ectopic type: V” means premature ventricular contraction.

**Figure 7.**Trends of C

_{SDNN}under different ectopic beat burdens, i.e., the number of ectopic beats increase from 1 to more than 10: (

**A**) NSR group and (

**B**) CHF group.

**Figure 8.**Trends of C

_{LF/HF}under different ectopic beat burdens, i.e., the number of ectopic beats increase from 1 to more than 10: (

**A**) NSR group and (

**B**) CHF group.

**Figure 9.**Trends of C

_{SampEn}under different ectopic beat burdens, i.e., the number of ectopic beats increase from 1 to more than 10: (

**A**) NSR group and (

**B**) CHF group.

**Figure 10.**Trends of C

_{Pt-SampEn}under different ectopic beat burdens, i.e., the number of ectopic beats increase from 1 to more than 10: (

**A**) NSR group and (

**B**) CHF group.

**Table 1.**Data profile for the normal sinus rhythm (NSR) group from the PhysioNet/MIT RR Interval Database. # Number of.

Record | # Ectopic-Free 5 min Segments | # Ectopic 5 min Segments | Record | # Ectopic-Free 5 min Segments | # Ectopic 5 min Segments |
---|---|---|---|---|---|

NSR001 | 212 | 58 | NSR028 | 190 | 95 |

NSR002 | 134 | 146 | NSR029 | 269 | 18 |

NSR003 | 247 | 37 | NSR030 | 229 | 58 |

NSR004 | 245 | 33 | NSR031 | 97 | 191 |

NSR005 | 89 | 198 | NSR032 | 99 | 188 |

NSR006 | 239 | 40 | NSR033 | 261 | 14 |

NSR007 | 203 | 81 | NSR034 | 265 | 18 |

NSR008 | 237 | 50 | NSR035 | 258 | 29 |

NSR009 | 262 | 25 | NSR036 | 254 | 28 |

NSR010 | 168 | 107 | NSR037 | 246 | 29 |

NSR011 | 195 | 92 | NSR038 | 251 | 4 |

NSR012 | 247 | 40 | NSR039 | 200 | 87 |

NSR013 | 249 | 32 | NSR040 | 266 | 17 |

NSR014 | 175 | 112 | NSR041 | 253 | 29 |

NSR015 | 263 | 24 | NSR042 | 277 | 10 |

NSR016 | 245 | 42 | NSR043 | 159 | 123 |

NSR017 | 22 | 265 | NSR044 | 17 | 270 |

NSR018 | 73 | 213 | NSR045 | 135 | 149 |

NSR019 | 254 | 33 | NSR046 | 181 | 94 |

NSR020 | 172 | 108 | NSR047 | 266 | 22 |

NSR021 | 275 | 12 | NSR048 | 268 | 21 |

NSR022 | 236 | 47 | NSR049 | 285 | 3 |

NSR023 | 253 | 34 | NSR050 | 285 | 3 |

NSR024 | 15 | 272 | NSR051 | 281 | 6 |

NSR025 | 166 | 120 | NSR052 | 274 | 10 |

NSR026 | 243 | 44 | NSR053 | 269 | 1 |

NSR027 | 280 | 5 | NSR054 | 271 | 8 |

**Table 2.**Data profile for the congestive heart failure (CHF) group from the PhysioNet/MIT RR Interval Database. # Number of.

Record | # Ectopic-Free 5 min Segments | # Ectopic 5 min Segments | Record | # Ectopic-Free 5 min Segments | # Ectopic 5 min Segments |
---|---|---|---|---|---|

CHF201 | 240 | 36 | CHF216 | 250 | 14 |

CHF202 | 97 | 150 | CHF217 | 53 | 228 |

CHF203 | 75 | 187 | CHF218 | 47 | 217 |

CHF204 | 0 | 247 | CHF219 | 236 | 28 |

CHF205 | 31 | 245 | CHF220 | 138 | 143 |

CHF206 | 11 | 240 | CHF221 | 0 | 276 |

CHF207 | 1 | 249 | CHF222 | 1 | 274 |

CHF208 | 31 | 257 | CHF223 | 0 | 274 |

CHF209 | 70 | 156 | CHF224 | 137 | 150 |

CHF210 | 16 | 258 | CHF225 | 97 | 121 |

CHF211 | 275 | 11 | CHF226 | 18 | 257 |

CHF212 | 0 | 205 | CHF227 | 0 | 275 |

CHF213 | 7 | 281 | CHF228 | 71 | 204 |

CHF214 | 0 | 204 | CHF229 | 267 | 20 |

CHF215 | 110 | 166 |

**Table 3.**The standard deviation (std) of the change rate index of different HRV indices. # Number of.

# Ectopic Beat | Variances in NSR Subjects (%), std | Variances in CHF Patients (%), std | ||||||
---|---|---|---|---|---|---|---|---|

C_{SDNN} | C_{LF/HF} | C_{SampEn} | C_{Pt-SampEn} | C_{SDNN} | C_{LF/HF} | C_{SampEn} | C_{Pt-SampEn} | |

1 | 9.3 | 222.5 | 29.5 | 0.4 | 13.3 | 177.7 | 26.7 | 0.6 |

2 | 12.1 | 415.3 | 40.2 | 0.6 | 16.9 | 262.2 | 41.8 | 1.1 |

3 | 14.5 | 547.9 | 49.2 | 1.0 | 18.6 | 334.2 | 61.6 | 1.6 |

4 | 16.3 | 483.5 | 55.5 | 1.2 | 20.3 | 385.4 | 68.2 | 2.1 |

5 | 16.4 | 742.1 | 59.7 | 1.7 | 20.8 | 354.4 | 71.4 | 2.4 |

6 | 15.1 | 520.7 | 47.9 | 1.7 | 21.0 | 338.2 | 79.1 | 2.2 |

7 | 18.5 | 679.5 | 55.7 | 1.3 | 22.0 | 356.1 | 71.2 | 2.5 |

8 | 18.2 | 1001.8 | 65.9 | 1.9 | 21.0 | 375.3 | 91.2 | 2.8 |

9 | 21.1 | 818.6 | 77.0 | 2.4 | 22.0 | 571.1 | 86.5 | 2.7 |

10 | 19.3 | 1037.3 | 84.8 | 3.2 | 22.2 | 524.1 | 92.1 | 3.4 |

>10 | 19.7 | 1566.0 | 75.4 | 9.4 | 25.3 | 589.7 | 134.0 | 15.0 |

Mean | 16.4 | 730.5 | 58.3 | 2.3 | 20.3 | 388.0 | 74.9 | 3.3 |

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Zhao, L.; Li, P.; Li, J.; Liu, C. Influence of Ectopic Beats on Heart Rate Variability Analysis. *Entropy* **2021**, *23*, 648.
https://doi.org/10.3390/e23060648

**AMA Style**

Zhao L, Li P, Li J, Liu C. Influence of Ectopic Beats on Heart Rate Variability Analysis. *Entropy*. 2021; 23(6):648.
https://doi.org/10.3390/e23060648

**Chicago/Turabian Style**

Zhao, Lina, Peng Li, Jianqing Li, and Chengyu Liu. 2021. "Influence of Ectopic Beats on Heart Rate Variability Analysis" *Entropy* 23, no. 6: 648.
https://doi.org/10.3390/e23060648