DOI: 10.14457/tu.the.2016.1333
title: Determination of abnormal QTc and silent atrial fibrillation by hybrid signal processing methods and improvement of HRV analysis in acute stroke

description: Previous studies have reported that atrial arrhythmia (AF), prolonged QT interval and tachycardia are the most common cardiac arrhythmia during ischemic stroke with the severity of recurrent stroke and sudden death.  Cardiac autonomic derangement is commonly found and showed significant characteristic of AF stroke. R-R intervals (RRIs) are a series of beat to beat of heart contraction which composes of two cardiac cycles. Hence, abnormal ECG waves behave as any noise or showing missing beat are very interesting which they may influence cardiac autonomic modulation. Ventricular repolarization affects QT interval variation and might affect the next P wave on the second ECG cycle.  In stroke, missing beats of R-R interval have been shown contributing abnormal QTc and AF.  Silent AF, prolonged or shorten QTc or even ventricular tachycardia during acute stroke is poorly elucidated. Recently, an increasing heart rate and changes in ST and T wave were obviously found in QT interval variation during Day 1 or 24 hours acute stroke. These findings lead to investigate the significant meaningful missing beats which may impact on QTc variation and arrhythmia event. In this study, we develop a hybrid signal processing by Pan Tompkins QRS detection and Kalman filter estimator for missing beat correction in order to examine searching AF with abnormal QTc and improving HRV. Meaningful missing beat is investigated by HRV analysis.Participants were classified as normal QTc (NQTc), short QTc (SQTc) and long QTc (LQTc) of   large artery ischemic stroke patients (by fMRI studies) with matching control in general characteristics and carotid stenosis flow velocity whom were recruited from 165 acute ischemic stroke. These QTc variation patients were classified by AF and considered as NQTc-stroke AF, SQTc-stroke A, LQTc-stroke AF and NQTc-stroke nonAF. They were excluded a history of AF before. All   participants gave informed consent NO. MTU-EC-IM-4-018/54.   QTc is determined by Bazett’s method. R-R intervals of Lead II ECG recordings were performed by Power Lab.  RR intervals were examined by hybrid signal processing (Pan Tomkins + Kalman filter) compared with those by LabChart (FFT-LabChart) and then by HRV. For validation of a hybrid model, NQTc-stroke non AF (15) was compared with SQTc-stroke AF (5), NQTc-stroke AF (4) and LQTc-stroke AF (5). Moreover, for verification, a hybrid model was compared to a conventional LabChart program by using corrected missing beats and uncorrected missing beats in QTc-variation with AF, respectively.The results of corrected missing beats in all QTc groups showed distinguishable tracing between corrected vs uncorrected missing beats of RRIs.  Validation finding studied in NQTc-stroke AF vs NQTc-stroke nonAF showed significant differences in mean HR, mean RRIs, total power of frequency domain, VLF and SD1. Negative correlation of mean HR and mean RRIs were noticed meanwhile VLF and SD1 showed positively significant correlation. This findings indicate that our hybrid model was fitted for discrimination of sinus rhythm (NQTc) and atrial activity of two experiment groups through predominant parasympathetic drive (SD1). Missing beats correction impacts   on SD1 which it reflects parasympathetic activity that possibly acts on repolarization of cardiac action potential during relative refractory period.  For  a hybrid model validation :  When compared NQTc-stroke AF with NQTc-stroke non AF, our model is able to distinguish SD1 of NQTc-stroke AF and those in NQTc-stroke non AF. SD1 (nonlinear HRV) reflects parasympathetic activity on Poincare’ plot. High value (0.8) correlation between SD1 of NQTc-stroke AF and     NQTc-stroke non AF suggests that the significant difference of parasympathetic drive is positively correlated. Mean HR and mean RRIs are significant difference and show negative correlation between both groups. This finding is from AF signal that it obviously differs from normal atrial activity in NQTc-stroke non AF. The meaningful missing beat   influence on parasympathetic drive which trigger at repolarization process of cardiac action potential. When compared SQTc-stroke AF and NQTc-stroke non AF, there were a significant difference of time domain (SDNN, RMSSD, pNN50%), total power of frequency domain, SD1, SD2, and an irregularity of signals by ApEn and SamEn. Corresponding to a wide range of RRIs in NQTc- stroke  non AF compared with a narrow range of SQTc-stroke AF ( less than 1 sec) our hybrid model can distinguish HRV variables such as SDNN, RMSSD, pNN 50% in time domain; total power of   frequency domain; nonlinear SD1,  SD2, ApEn and SamEn.  Significant difference in SDNN and total power of frequency domain suggest that two components of autonomic nervous system, sympathetic   and parasympathetic activities, are predominant.  Negative correlation of pNN 50% (-0.7) and of SD2 (-0.8) indicates greater parasympathetic and sympathetic drives in SQTc-stroke AF than in NQTc-stroke non AF. Changes in cardiac autonomic modulation in aspect of time, frequency and nonlinear domains are recognized by our hybrid model.For LQTc group, when compared LQTc-stroke AF and NQTc-stroke non AF, our hybrid model shown a significant difference of time domain (SDNN, RMSSD, pNN50%), total power of frequency domain, SD1, SD1/SD2,   an irregularity of signals by ApEn, SamEn and short term α1. Our hybrid model verified that LQTc-stroke AF revealed a predominant parasympathetic drive indicated by RMSSD, pNN 50%, SD1, SD1/SD2. An irregularity of signals is also found in ApEn and SamEn.  Interestingly, α 1 that represented an intrinsic factor of hemodynamic response was detected. Significant correlations of those variables were strongly confirmedFor a hybrid model verification:Verification of corrected missing beats after Kalman estimator compared with those after LabChart was studied in QTc variation – stroke AF groups.  When compared NQTc-stroke AF with and without reconstruction RRIs data, the SamEn was significant difference verifying the hybrid model.  Since NQTc represents a sinus node activity governing the heart rate, different value of SamEn by our hybrid model indicates a different complexity level of an irregularity, inconsistency and randomness of signals. In SQTc-stroke AF with and without reconstruction RRIs data, predominant sympathetic activity was detected by high values of LF, LF/HF ratio and SD2/SD1. Confirmed results by low values of pNN50 % and HF were evident. When compared LQTc-stroke AF with and without reconstruction RRIs data, SDNN, RMSSD, pNN 50, SD1, SD1/SD2, SD2/SD1 and α1 were significant difference between  LQTc-stroke AF (Kalman) vs LQTc-stroke AF (Labchart). The results indicate predominant parasympathetic activity detected by our model. Value of short term α1 is 1.01 + 0.09 suggests the intrinsic factor of physiological response that it presents in LQTc-stroke AF (Kalman). Positive correlation of those variable   suggests trend in autonomic modulation.In conclusion, the findings   suggest  that a hybrid  signal processing model that we have developed for better RRI detection and estimation by  correction of missing beats during QTc variation and arrhythmic event in 24 hours acute stroke  fits  firmly to searching silent AF and  improving HRV especially, nonlinear function and  it is able to distinguish  distinctively  those corrected  and uncorrected signals in  QTc variation group with AF and NQTc-stroke non AF.  Predominant sympathetic drive is evident in SQTc-stroke AF as indicated by high value of LF, LF/HF ratio and SD2/SD1 in Poincaré plot. Greater parasympathetic activity in LQTc-AF Kalman stroke plays a vital role in sympatho-vagal balance of an inconsistency and irregularity signals. High values of sample entropy corresponding with more scatter gram of Poincaré plot indicate signal turbulence and more variation in QTc with AF stroke.  This study will be useful method for early detection and estimation of missing beats in QTc variation and arrhythmic event especially in acute stroke that there is modulation of autonomic nervous system. Corrected missing beats influences HRV interpretation. Further study in arrhythmic event in other case such as cardiac arrest and treated with hypothermia will be recommended.