Risk stratification after myocardial infarction: a new method of determining the neural component of the baroreflex is potentially more discriminative in distinguishing patients at high and low risk for arrhythmias

Abstract

We hypothesize that the neural component (NC) of the baroreflex sensitivity (BRS) is a better risk stratifier for ventricular tachycardia/fibrillation (VT/VF) than conventional BRS itself, because it is both independent of vessel wall stiffness and can be measured non-invasively. NC was determined by correlating spontaneous carotid artery diameter variations with R-R interval variations using spectral analyses. In consecutive outpatient populations with chronic coronary artery disease the ability of the NC to distinguish post-myocardial infarction (MI) patients at risk for VT/VF (post-MI(HIGH RISK)) from post-MI less prone to arrhythmias (post-MI(LOW RISK)) was compared with the pressure-derived BRS(phenyl) and BRS(spectral) method. Ninety-six patients, i.e. 28 post-MI(LOW RISK), 28 post-MI(HIGH RISK) [a LVEF(left ventricular ejection fraction) <30% and/or history of VT/VF] and 40 healthy controls were enrolled. With NC, rather than with BRS methods, median values for post-MI(HIGH RISK) were smaller than for post-MI(LOW RISK) patients (NC, P = 0.03; BRS(spectral), P = 0.35; BRS(phenyl), P = 0.63). Variability of R-R interval (LF = 0.04-0.15 Hz) was significantly larger in the control group than in the post-MI(HIGH RISK) and post-MI(LOW RISK) group (P < 0.01 and P < 0.01). To separate post-MI(HIGH RISK) from post-MI(LOW RISK) patients, a linear combination of age and the logarithm of the NC measurement was constructed as a risk index. By optimizing the intercept of this line, an optimal sensitivity and specificity pair was determined. The sum of optimal specificity and sensitivity was higher for NC (155) than for BRS(spectral) (133) and BRS(phenyl) method (132). With all methods, values for post-MI patients were significantly smaller than for controls. NC may be superior to conventional BRS measures in identifying post-MI patients at high risk for VT/VF.