A Principal Component Regression Approach for Estimating Ventricular Repolarization Duration Variability
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Research Article A Principal Component Regression Approach for Estimating Ventricular Repolarization Duration Variability Mika P. Tarvainen,1 Tomi Laitinen,2 Tiina Lyyra-Laitinen,2 Juha-Pekka Niskanen,1 and Pasi A. Karjalainen1 1 Department 2 Department
of Physics, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital, P.O. Box 1777, 70211 Kuopio, Finland
Received 28 April 2006; Revised 27 September 2006; Accepted 29 October 2006 Recommended by Pablo Laguna Lasaosa Ventricular repolarization duration (VRD) is affected by heart rate and autonomic control, and thus VRD varies in time in a similar way as heart rate. VRD variability is commonly assessed by determining the time differences between successive R- and T-waves, that is, RT intervals. Traditional methods for RT interval detection necessitate the detection of either T-wave apexes or offsets. In this paper, we propose a principal-component-regression- (PCR-) based method for estimating RT variability. The main benefit of the method is that it does not necessitate T-wave detection. The proposed method is compared with traditional RT interval measures, and as a result, it is observed to estimate RT variability accurately and to be less sensitive to noise than the traditional methods. As a specific application, the method is applied to exercise electrocardiogram (ECG) recordings. Copyright © 2007 Mika P. Tarvainen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
1.
INTRODUCTION
Ventricular repolarization duration (VRD) is known to be affected by heart rate (HR) and autonomic control (mainly through sympathetic branch), and thus VRD varies in time in a similar way as HR [1, 2]. The time interval between Qwave onset and T-wave offset in an electrocardiogram (ECG), that is, QT interval, corresponds to the total ventricular activity including both depolarization and repolarization times, and thus QT interval may be used as an index of VRD. It has been suggested that abnormal QT variability could be a marker for a group of severe cardiac diseases such as ventricular arrhythmias [3]. In addition, it has been suggested that QT variability could yield such additional information which cannot be observed from HR variability [4]. Due to the difficulty in fixing automatically the Q-wave onset in VRD determination, RT interval is typically used instead of QT interval [5, 6]. The RT interval can be defined as the interval from R-wave apex either to T-wave apex (RTapex ) or to T-wave offset (RTend ). The T-wave apex is typically fixed by fitting a parabola around the T-wave maximum [5]. The T-wave offset, on the other hand, can be fixed with a number of methods. In threshold methods, the T-wave offset is fixed as an intercept of the T-wave or its derivative with a threshold level above the isoelectric line [7–9]. In the fitting methods,
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