Assessment of Cardiac Autonomic Regulation and Ventricular Repolarization after Off-Pump Coronary Artery Bypass Grafting

Multifractality in heartbeat dynamics in patients undergoing beating-heart myocardial revascularization

“…In the light of these findings the preoperative values of τ(q¼2), τ(q¼3) and h_top parameters in the current study indicate that a marked decay of multifractal behavior occurred already preoperatively in our patients, clearly showing that in these individuals a cardiac autonomic disbalance with a sympathetic predominance existed already prior to the surgical intervention. Such results are in accord with previous studies as well as with our own observations reporting on diminished linear and selected nonlinear HRV parameters in older patients with stable multivessel coronary artery disease [1][2][3][4]14,15]. Since the Δh parameter is known to strongly correlate also with the sympathetic activity, a higher preoperative values of parameter Δh in our group as compared to healthy subjects might suggest that the preoperative sympathovagal disbalance in our patients can be mainly attributed to sympathetic overdrive and to a lesser degree to parasympathetic decrement [24].…”

“…A breakdown of these loops due to advanced disease or surgical procedure might be responsible for the breakdown of multifractal complexity into monofractal [7][8][9]11]. However, the exact electrophysiological mechanisms causing such postoperative dysregulation remain unclear [14,15,33]. Significantly higher postoperative values of Δh parameter in our study indicate a considerable postoperative increase in sympathetic activity, which is in agreement with previous works describing sympathetic augmentation after surgical intervention [1,14,15,34].…”

“…However, since human heartbeat is essentially nonstationary and highly complex the nonlinear HRV techniques derived from mathematics of complex dynamics fractal geometry have been proven to be superior in clarifying changes of autonomic activity in coronary artery disease, rhythm disturbances, heart failure or following myocardial infarction and in independently predicting benign and malignant arrhythmias, sudden cardiac death and mortality after myocardial infarction [4,[26][27][28][29][30]. Furthermore, applying selected nonlinear HRV techniques in our earlier studies we have confirmed that a profound derangement of sympathovagal balance occurs not only as a result of underlying disease but also as a consequence of a surgical procedure be it with or without the utilization of extracorporeal circulation [14,15]. In the last decade it became evident that human heartbeat belongs to a special class of multifractal bio-signals displaying such an extraordinary complexity and self-similarity over multiple time and space scales that it cannot be indexed by a single global exponent [7,8].…”

“…However, the exact electrophysiological mechanisms causing such postoperative dysregulation remain unclear [14,15,33]. Significantly higher postoperative values of Δh parameter in our study indicate a considerable postoperative increase in sympathetic activity, which is in agreement with previous works describing sympathetic augmentation after surgical intervention [1,14,15,34]. Noteworthy, the profile of pre-and postoperative changes of Δh index might suggest, that in hyperadrenergic settings Δh is a marker of sympathetic modulation while in vagal settings it mirrors both branches of cardiac autonomous activity [24].…”

“…However, only few attempts have been made so far to evaluate multifractal dynamics in patients undergoing different cardiac procedures such as percutaneous coronary intervention or coronary artery bypass graft (CABG) surgery [12,13]. Using linear and nonlinear HRV approaches by several authors a significantly deranged autonomic modulation with vagal withdrawal and sympathetic predominance was observed following both beating and arrested heart procedures [14,15], however, currently it remains unsettled whether such medical interventions can substantially affect also the multifractal behavior and if doing so, what are the direction and the degree of potential disturbances.…”