Abbreviations:AF (atrial fibrillation), ECG (electrocardiogram), NSR (normal sinus rhythm), RMSSD (root mean square of successive RR difference), ShE (Shannon entropy)
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Approaches to pulse waveform analysis
where l is the length of RR intervals and a(j) is the jth RR interval in the segment with length l, where j = 1, 2, …, l. The normalized RMSSD is expected to be higher in a segment recorded from a patient with an irregular pulse due to AF since AF is associated with higher variability of RR intervals than is NSR. ShE provides a quantitative measure of uncertainty for a random variable in the following:
where N is the number of bins and N(i) is the number of beats in the i-th bin. We used N = 16, which provided the best accuracy.
where THRMSSD and THShE are the threshold values of RMSSD/mean and ShE, respectively (Figure 3).
|Baseline characteristics||Total (N = 76)|
|Age (y) mean (SD)||65.3 (11.6)|
|Male, n (%)||59 (77)|
|White, n (%)||73 (96)|
|Body mass index (kg/m2), mean (SD)||31.0 (8.3)|
|Medical characteristics, n (%)|
|Current smoking||6 (8)|
|Diabetes mellitus||21 (28)|
|Coronary artery disease||22 (29)|
|Congestive heart failure||16 (21)|
|Sleep apnea||12 (16)|
|Coronary artery bypass||8 (11)|
|Prior cardioversion||20 (27)|
|Treatment characteristics, n (%)|
|Calcium channel blocker||15 (20)|
|Antiarrhythmic drug||19 (31)|
|Class I||5 (7)|
|Class III||18 (24)|
|Procedural characteristics, mean (SD)|
|Number of shock||1.1 (0.4)|
|Joules delivered, mean (SD)||226 (86)|
|Clinical and pulse recording characteristics||Mean (SD)||P|
|Systolic blood pressure (mm Hg)||131 (18)||112 (18)||<.001|
|Diastolic blood pressure (mm Hg)||81 (14)||68 (12)||<.001|
|Heart rate (beats/min)||91 (22)||70 (16)||<.001|
|Respiration rate (breaths/min)||19 (3)||16 (4)||<.001|
|0.29 (0.09)||0.08 (0.08)||<.001|
|Shannon entropy||0.80 (0.09)||0.45 (0.13)||<.001|
|Pulse recording characteristics||Adjusted beta coefficient|
|95% confidence interval|
|Shannon entropy||−0.38||−0.43 to−0.33|
|RMSSD/mean + Shannon entropy||0.9619||0.9752||0.9676|
Strengths and limitations
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This work was funded in part by the Office of Naval Research work unit N00014-12-1-0171. Dr McManus’s time was funded by National Institutes of Health through grants 1U01HL105268-01 and KL2RR031981.
Dr McManus, Dr Lee, and Dr Chon have ownership stake in DxMe, Inc. Dr Chon has a patent on the algorithm described in the article.
The first 2 authors contributed equally to this article.