Complexity of preoperative blood pressure dynamics: possible utility in cardiac surgical risk assessment.

Complexity measures are intended to assess the cardiovascular system's capacity to respond to stressors. We sought to determine if decreased BP complexity is associated with increased estimated risk as obtained from two standard instruments: the Society of Thoracic Surgeons' (STS) Risk of Mortality and Morbidity Index and the European System for Cardiac Operative Risk Evaluation Score (EuroSCORE II). In this observational cohort study, preoperative systolic, diastolic, mean (MAP) and pulse pressure (PP) time series were derived in 147 patients undergoing cardiac surgery. The complexity of the fluctuations of these four variables was quantified using multiscale entropy (MSE) analysis. In addition, the traditional time series measures, mean and standard deviation (SD) were also computed. The relationships between time series measures and the risk indices (after logarithmic transformation) were then assessed using nonparametric (Spearman correlation, rs) and linear regression methods. A one standard deviation change in the complexity of systolic, diastolic and MAP time series was negatively associated (p < 0.05) with the STS and EuroSCORE indices in both unadjusted (21-34%) and models adjusted for age, gender and SD of the BP time series (15-31%). The mean and SD of BP time series were not significantly associated with the risk index except for a positive association with the SD of the diastolic BP. Lower preoperative BP complexity was associated with a higher estimated risk of adverse cardiovascular outcomes and may provide a novel approach to assessing cardiovascular risk. Future studies are needed to determine whether dynamical risk indices can improve current risk prediction tools.

The Association Between Preoperative Hemoglobin A1C and Postoperative Glycemic Variability on 30-Day Major Adverse Outcomes Following Isolated Cardiac Valvular Surgery.

BACKGROUND: Preoperative hemoglobin A1c (HbA1c) and postoperative glycemic variability predict major adverse events (MAEs) after coronary artery bypass grafting in a protocolized glycemic control setting. However, the influence of preoperative HbA1c and postoperative glycemic variability in isolated cardiac valvular surgery is unknown. In this study, we sought to establish (a) whether preoperative HbA1c could identify patients at increased risk of MAEs and (b) whether postoperative glycemic variability was associated with MAEs after isolated cardiac valvular surgery. METHODS: Patients >18 years of age undergoing isolated valve surgery from January 2008 to December 2013 were enrolled in this prospective, single-center, observational cohort study with IRB approval. Patient demographics, intraoperative data, and postoperative MAEs were extracted from the institutional Society of Thoracic Surgery (STS) database. The primary outcome, MAEs, was a composite of in-hospital death, myocardial infarction, reoperations, sternal infection, cardiac tamponade, pneumonia, stroke, or renal failure. Glycemic variability in the postoperative period was assessed by the coefficient of variation. Patents were stratified by HbA1c levels (<6.5% or ≥6.5%) and assessed using multivariable logistic regression. RESULTS: Of the enrolled 763 patients, 109 (14.3%) had a preoperative HbA1c level ≥6.5%. Patients with HbA1c ≥6.5% were older (70 [63-79] vs 66 [56-75], P < .001) and had a higher incidence of dyslipidemia (83.5% vs 57.0%, P < .001) and congestive heart failure (39.5% vs 27.8%, P = .01). The calculated STS risk score for morbidity and mortality was also statistically higher in this group (0.18 [0.13-0.27] vs 0.13 [0.09-0.21], P < .001). The occurrence of MAEs was similar between the 2 groups (13.8% in HbA1c ≥6.5% vs 11.0% in HbA1c <6.5%, P = .40). Multivariate logistic regression analysis revealed that neither preoperative HbA1c ≥ 6.5% (odds ratio [OR] 1.48, 95% confidence interval [CI]: 0.78-2.82; P = .23) nor postoperative glycemic variability (CV per quartile; OR 1.05, 95% CI: 0.85-1.30; P = .67) was found to be associated with MAEs. An HbA1c ≥ 6.5% was associated with the increased glycemic variability in the postoperative period (0.173 [0.129-0.217] vs 0.141 [0.106-0.178], P < .0001). CONCLUSIONS: This study did not show an association between preoperative HbA1c and postoperative glycemic variability with MAEs after isolated cardiac valvular surgery. Specifically, lack of association between postoperative glycemic variability and MAEs is noteworthy and is in contrast to our previous finding in CABG patients. Future studies should focus a targeted glycemic variability reduction in CABG patients and evaluate the reduction in MAEs, without risk of employing a one-size fits all approach when approaching other cardiac procedures.

Blood pressure fragmentation as a new measure of blood pressure variability: association with predictors of cardiac surgery outcomes.

Background: Fluctuations in beat-to-beat blood pressure variability (BPV) encode untapped information of clinical utility. A need exists for developing new methods to quantify the dynamical properties of these fluctuations beyond their mean and variance. Objectives: Introduction of a new beat-to-beat BPV measure, termed blood pressure fragmentation (BPF), and testing of whether increased preoperative BPF is associated with (i) older age; (ii) higher cardiac surgical risk, assessed using the Society of Thoracic Surgeons' (STS) Risk of Morbidity and Mortality index and the European System for Cardiac Operative Risk Evaluation Score (EuroSCORE II); and (iii) longer ICU length of stay (LOS) following cardiac surgery. The secondary objective was to use standard BPV measures, specifically, mean, SD, coefficient of variation (CV), average real variability (ARV), as well a short-term scaling index, the detrended fluctuation analysis (DFA) ⍺1 exponent, in the same type of analyses to compare the results with those obtained using BPF. Methods: Consecutive sample of 497 adult patients (72% male; age, median [inter-quartile range]: 67 [59-75] years) undergoing cardiac surgery with cardiopulmonary bypass. Fragmentation, standard BPV and DFA ⍺1 measures were derived from preoperative systolic blood pressure (SBP) time series obtained from radial artery recordings. Results: Increased preoperative systolic BPF was associated with older age, higher STS Risk of Morbidity and Mortality and EuroSCORE II values, and longer ICU LOS in all models. Specifically, a one-SD increase in systolic BPF (9%) was associated with a 26% (13%-40%) higher likelihood of longer ICU LOS (>2 days). Among the other measures, only ARV and DFA ⍺1 tended to be associated with longer ICU LOS. However, the associations did not reach significance in the most adjusted models. Conclusion: Preoperative BPF was significantly associated with preoperative predictors of cardiac surgical outcomes as well as with ICU LOS. Our findings encourage future studies of preoperative BPF for assessment of health status and risk stratification of surgical and non-surgical patients.