Table 3.
Comparison of 24‐Hour HRV Measures and Ectopy Counts Between Participants With and Without Incident Stroke on Follow‐Up
| Time Domain HRV Variables | No Stroke (N=816) | Incident Stroke (N=68) | P Value |
|---|---|---|---|
| Heart rate, beats per min | 73.5±9.7 | 73.1±9.5 | NS |
| SDNN, ms | 115.9±34.5 | 106.9±36.6 | 0.054 |
| SDANN, ms | 105.2±33 | 97.8±36.9 | NS |
| CV, % | 13.9±3.6 | 12.8±3.9 | 0.019 |
| SDNN index, ms | 41.9±15.4 | 38.1±13.2 | 0.025 |
| RMSSD, ms | 26.1±15.9 | 24±12.5 | NS |
| Frequency domain HRV variables | |||
| ln (total power) | 4.1±0.28 | 4.0±0.29 | 0.035 |
| ln (ultra‐low‐frequency power) | 4.0±0.29 | 3.9±0.30 | 0.048 |
| ln (very‐low‐frequency power) | 2.9±0.30 | 2.8±0.33 | 0.033 |
| Normalized low‐frequency power (5‐min averages) | 59.2±11 | 57.2±10.3 | NS |
| Normalized high‐frequency power (5‐min averages) | 26.6±9.6 | 27.8±9.2 | NS |
| ln (low‐frequency power) (5‐min averages) | 2.5±0.39 | 2.4±0.41 | 0.052 |
| ln (high‐frequency power) (5‐min averages) | 2.1±0.46 | 2.0±0.42 | NS |
| Nonlinear HRV variables | |||
| Short‐term fractal scaling exponent (DFA1) | 1.13±0.21 | 1.10±0.20 | NS |
| Intermediate‐term fractal scaling exponent (DFA2) | 1.23±0.15 | 1.24±0.13 | NS |
| SD1/SD2 | 0.28±0.11 | 0.29±0.09 | NS |
| Power law slope (SLOPE) | −1.36±0.15 | −1.42±0.14 | 0.003 |
| Ectopy counts | N=816 | N=68 | |
| ln (VPC+1) | 3.7±2.3 | 4.0±2.3 | NS |
| ln (APC+1) | 4.5±1.6 | 4.5±1.4 | NS |
Time domain heart rate variability (HRV) variables: SDNN (ms)=SD of all normal‐to‐normal (N‐N) intervals; SDANN (ms)=SD of the averages of N‐N intervals for all 5‐min segments; CV (%)=average coefficient of variance of N‐Ns for 5‐min segments for 24 ; SDNN Index (ms)=mean of 5‐min SDs of all N‐N intervals for 24 h; RMSSD (ms)=square root of the mean of the squared differences between successive N‐N intervals for 24 h. Frequency domain HRV: Total Power=all of the variance in HRV; Ultra‐low‐frequency power=all variance in 24‐h HRV at frequencies of every 5 min to every 24 h, thus reflecting primarily circadian HRV; Very‐low‐frequency power=variance in HRV at underlying frequencies of every 25 s to every 5 min calculated for every 15‐min segment and averaged; Normalized low‐frequency power=the average proportion of HRV in each 5 min that is explained by oscillations at underlying frequencies of 0.04 to 0.15 Hz (the low‐frequency band) divided by the total HRV in that 5‐min period; Normalized high‐frequency power=the average amount of HRV in each 5 minutes that is explained by oscillations at underlying frequencies 0.15 to 0.4 Hz (high‐frequency or respiratory frequency band) divided by total HRV in that 5‐min period; ln (LF)=natural log of low‐frequency power. LF captures the variance in HRV at underlying frequencies of 0.04 to 0.15 Hz; ln (HF)=natural log of high‐frequency power. High frequency captures the variance in HRV at underlying frequencies of 0.18 to 0.4 Hz. Nonlinear HRV variables: DFA1=short‐term fractal scaling exponent calculated over 3 to 11 beats and averaged over 1000 beats for 24 h; DFA2=longer‐term fractal exponent calculated over 12 to 20 beats and averaged over 1000 beats for 24 h; SD12=Poincaré ratio. The Poincaré plot is a scatterplot of each N‐N interval vs the next. SD1 is the short axis of an ellipse fitted to the Poincaré plot. SD2 is the long axis of the same ellipse. SD12 (SD1/SD2) is the ratio of the short and long axes of ellipse and reflects the organization of the N‐N interval time series. SD12 was calculated for each 1000 beats and averaged; Power law slope=slope of a line fitted to a plot of log spectral power vs log of underlying frequency between 10−2 and 10−4 Hz over 24 h. Ectopy counts: ln (VPC+1)=natural log transformation of the number of premature ventricular contractions +1; ln (APC+1)=natural log transformation of the number of premature atrial contractions +1. NS indicates Not Significant.