Pamela Taggart

Comparison of linear-stochastic and nonlinear-deterministic algorithms in the analysis of 15-minute clinical ECGs to predict risk of arrhythmic death.

Objective: Comparative algorithmic evaluation of heartbeat series in low-to-high risk cardiac patients for the prospective prediction of risk of arrhythmic death (AD). Background: Heartbeat variation reflects cardiac autonomic function and risk of AD. Indices based on linear stochastic models are independent risk factors for AD in post-myocardial infarction (post-MI) cohorts. Indices based on nonlinear deterministic models have superior predictability in retrospective data. Methods: Patients were enrolled (N = 397) in three emergency departments upon presenting with chest pain and were determined to be at low-to-high risk of acute MI (>7%). Brief ECGs were recorded (15 min) and R-R intervals assessed by three nonlinear algorithms (PD2i, DFA, and ApEn) and four conventional linear-stochastic measures (SDNN, MNN, 1/f-Slope, LF/HF). Out-of-hospital AD was determined by modified Hinkle–Thaler criteria. Results: All-cause mortality at one-year follow-up was 10.3%, with 7.7% adjudicated to be AD. The sensitivity and relative risk for predicting AD was highest at all time-points for the nonlinear PD2i algorithm (p ≤0.001). The sensitivity at 30 days was 100%, specificity 58%, and relative risk >100 (p ≤0.001); sensitivity at 360 days was 95%, specificity 58%, and relative risk >11.4 (p ≤0.001). Conclusions: Heartbeat analysis by the time-dependent nonlinear PD2i algorithm is comparatively the superior test.

The Expression of the CD18 Leucocyte Integrin in a Rabbit Model of Acute Myocardial Infarction: A Pilot Study of Temporal Changes and Relationship to Infarct Size

CD18 integrins mediate leucocyte adhesion to vascular endothelium. This represents the initial step in inflammatory cell infiltration following myocardial necrosis. The current studyassessed whether the expression of these rapidly activated and readily measured adhesion receptors on circulating neutrophils would reflect the extent of cardiac damage in a rabbit model of acute myocardial infarction. Myocardial ischaemia/infarction was induced in anaesthetised adult male New Zealand white rabbits (n = 8) by ligation of the circumflex or marginal coronary artery. To control for the effects of anaesthesia and surgery, 4 rabbits underwent identical procedures without the induction of infarction. Absolute infarct size (in mg) and infarct size as a percentage of total left ventricular mass (relative infarct size) were calculated by differential staining and weighing of necrotic myocardium. Flow cytometry was used to determine cell surface expression of CD18 at six time points (baseline, 20 and 45 min of ischaemia and 20, 60 and 180 min of reperfusion). Absolute neutrophil CD18 expression and changes in expression over baseline were correlated with absolute and relative infarct size. Mean neutrophil CD18 expression increased significantly (from 2.42 ± 0.20 to 3.07 ± 0.29; p = 0.04) within 20 min of ischaemia. CD18 expression at 3 h did not predict absolute or relative infarct size (r = 0.40 and 0.37, respectively). The percentage change in cell surface CD18 expression (above baseline levels) was, however, correlated with both measures of infarct size (r = 0.76, p = 0.03, and r = 0.92, p = 0.001, respectively). In conclusion, in this rabbit model of myocardial infarction, neutrophil CD18 expression rises within 20 min of the induction of ischaemia but absolute values after 3 h of reperfusion are poor indicators of infarct size. Although percentage change in neutrophil CD18 levels over baseline correlates with infarct size there is considerable variation between individuals, limiting any clinical application.

Inflammatory cytokines provide limited early prognostic information in emergency department patients with suspected myocardial ischemia

STUDY OBJECTIVE The aim of this study was to assess the early prognostic value of the inflammatory cytokines interleukin 6, interleukin 8, and tumor necrosis factor alpha in a cohort of emergency department (ED) patients with chest pain who have suspected myocardial ischemia. METHODS One hundred eighteen patients with chest pain presenting to 2 urban EDs were studied. Interleukin 6, interleukin 8, and tumor necrosis factor alpha levels were assayed at presentation. The end point was the occurrence of a serious cardiac event (death, nonfatal acute myocardial infarction, myocardial revascularization, or readmission with an acute coronary syndrome) during the index admission or subsequent 3 months. RESULTS Mean levels of all 3 cytokines were higher among patients experiencing a serious cardiac event, with the greatest differences observed in levels of interleukin 6 (mean 2.5 pg/mL [95% confidence interval (CI) 1.2 to 3.7 pg/mL] versus mean 9.8 pg/mL [95% CI 2.4 to 17.2 pg/mL]). Interleukin 6 had a sensitivity of 35% (95% CI 20% to 54%), a specificity of 86% (95% CI 76% to 92%), and an overall prognostic accuracy of 71% (95% CI 63% to 79%) for predicting serious cardiac events. However, logistic regression analysis revealed that the only independent predictor of an adverse outcome was an ECG suggestive of ischemia at presentation. CONCLUSION Among patients presenting to the ED with suspected myocardial ischemia, higher levels of inflammatory cytokines are associated with an increased risk of a serious cardiac event during the subsequent 3 months. There is, however, considerable overlap in levels among patients who do and do not have a serious cardiac event, limiting their utility as predictors of outcome in individual patients.