Analysis of QRS-T subtraction in unipolar atrial fibrillation electrograms

This paper presents a QRS-T subtraction approach for atrial fibrillation (AF) intracardiac atrial electrograms (AEG). It also presents a comparison between the proposed method and two alternative ventricular subtraction techniques: average beat subtraction (ABS) using a fixed length window and an approach based on flat interpolation for QRS cancellation. Areas of the atrium close to the mitral valve showed stronger ventricular influence on the AEGs when compared with the remaining atrial regions. Ventricular influence affects the spectral power distribution of the AEG and can also affect the estimation of the dominant frequency unless the whole ventricular activity influence (QRS-T) is removed. The average power after QRS-T subtraction is significantly reduced for frequencies above 10 Hz (mostly associated with QRS complexes), as well as for frequencies between 3 and 5.5 Hz, (mostly related to T waves). The results indicate that the proposed approach removes ventricular influence on the AF AEGs better than the QRS cancellation method. Spectral analysis showed that both the ABS and the proposed method do well and no method should be preferred to the other. In the time domain, the proposed approach is matched to the lengths and timings of onset and offset for individual QRS-T segments while the ABS approach uses an arbitrary length around the QRS for the pattern used for QRS-T removal.     

Complex fragment atrial electrograms, not pulmonary vein, the ideal ablation targets for chronic atrial fibrillation

Complex fragment atrial electrograms (CFAEs) are fractionated or discrete atrial wave fronts that frequently mapped in chronic atrial fibrillation (CAF). The CFAEs areas represent slow conduction and/or functional blocks that play substrate role in AF. Compared with the limited efficacy of pulmonary veins (PVs) oriented ablation strategy for CAF, few attempts of adjunctive ablation on CFAEs gain promising outcome. We hypothesized that CFAEs, not PVs, are the ideal ablation targets for CAF.     

Computational method for high resolution spectral analysis of fractionated atrial electrograms

BackgroundThe discrete Fourier transform (DFT) is often used as a spectral estimator for analysis of complex fractionated atrial electrograms (CFAE) acquired during atrial fibrillation (AF). However, time resolution can be unsatisfactory, as the frequency resolution is proportional to rate/time interval. In this study we compared the DFT to a new spectral estimator with improved time-frequency resolution.MethodRecently, a novel spectral estimator (NSE) based upon signal averaging was derived and implemented computationally. The NSE is similar to the DFT in that both estimators model the autocorrelation function to form the power spectrum. However, as derived in this study, NSE frequency resolution is proportional to rate/period² and thus unlike the DFT, is not directly dependent on the window length. We hypothesized that the NSE would provide improved time resolution while maintaining satisfactory frequency resolution for computation of CFAE spectral parameters. Window lengths of 8 s, 4 s, 2 s, 1 s, and 0.5 s were used for analysis. Two criteria gauged estimator performance. Firstly, a periodic electrogram pattern with phase jitter was embedded in interference. The error in detecting the frequency of the periodic pattern was determined. Secondly, significant differences in spectral parameters for paroxysmal versus persistent AF data, which have known dissimilarities, were determined using the DFT versus NSE methods. The parameters measured were the dominant amplitude, dominant frequency, and mean spectral profile.ResultsAt all time resolutions, the error in detecting the frequency of the repeating electrogram pattern was less for NSE than for DFT (p<0.001). The DFT was accurate to 2 s time resolution/0.5 Hz frequency resolution, while the NSE was accurate to 0.5 s time resolution/0.05 Hz frequency resolution. At all time resolutions, significant differences in the dominant amplitude spectral parameter for paroxysmal versus persistent CFAE were greater using NSE than DFT (p<0.0001). For three of five time resolutions, the NSE had greater significant differences than DFT for discriminating the dominant frequency and mean spectral profile parameters between AF types.ConclusionsThe results suggest that the NSE has improved performance versus DFT for measurement of CFAE spectral properties.     

The temporal behavior and consistency of bipolar atrial electrograms in human persistent atrial fibrillation

The unstable temporal behavior of atrial electrical activity during persistent atrial fibrillation (persAF) might influence ablation target identification, which could explain the conflicting persAF ablation outcomes in previous studies. We sought to investigate the temporal behavior and consistency of atrial electrogram (AEG) fractionation using different segment lengths. Seven hundred ninety-seven bipolar AEGs were collected with three segment lengths (2.5, 5,and 8 s) from 18 patients undergoing persAF ablation. The AEGs with 8-s duration were divided into three 2.5-s consecutive segments. AEG fractionation classification was applied off-line to all cases following the CARTO criteria; 43% of the AEGs remained fractionated for the three consecutive AEG segments, while nearly 30% were temporally unstable. AEG classification within the consecutive segments had moderate correlation (segment 1 vs 2: Spearman’s correlation ρ = 0.74, kappa score κ = 0.62; segment 1 vs 3: ρ = 0.726, κ = 0.62; segment 2 vs 3: ρ = 0.75, κ = 0.68). AEG classifications were more similar between AEGs with 5 and 8 s (ρ = 0.96, κ = 0.87) than 2.5 versus 5 s (ρ = 0.93, κ = 0.84) and 2.5 versus 8 s (ρ = 0.90, κ = 0.78). Our results show that the CARTO criteria should be revisited and consider recording duration longer than 2.5 s for consistent ablation target identification in persAF.     

Improving spatial resolution in skin-contact thermography: comparison between a spline based and linear interpolation

A wearable device for skin-contact thermography [Giansanti D, Maccioni G. Development and testing of a wearable integrated thermometer sensor for skin contact thermography. Med Eng Phys 2006 [ahead of print]] using a 2-D array of 4x4 integrated silicon sensors has been designed and constructed. The thermal resolution was equal to 0.03 degrees C and the spatial resolution equal to 1.6x10(-5)m(2) in the range 25-41 degrees C. The improvement of spatial resolution is strongly needed in several medical correlated applications of skin-contact thermography such as the breast cancer monitoring and the feature recognition. A cubic-spline interpolation procedure has been designed to improve the spatial resolution. The performances have been investigated in a significant medical application. Results were compared to those ones obtained by means of an infrared digital video camera and a linear based interpolation procedure. The comparison showed that: (1) the spline based interpolation procedure permitted to improve the spatial resolution of the device to 1.5x10(-8)m(2) with an interpolating number of pixels equal to 128x. (2) The accuracy of the thermal reconstruction obtained by means of the spline interpolation in each one of the pixels was better than the one obtained by a pure linear interpolation; in particular the maximal error was equal to, 81x10(-3) degrees C.     

Comparison of methods for adaptive sampling of cardiac electrograms and electrocardiograms

Digital sampling of cardiac electrograms and electrocardiograms is usually performed by sampling at uniform intervals with rates high enough to record the fastest signal components. Numerous redundant samples are recorded during slower deflections and baseline intervals, particularly for direct cardiac measurements that include fast Purkinje deflections. In this report, five adaptive sampling methods (voltage triggered, two-point projection, second differences, the fan and CORTES) are compared with uniform sampling for cardiac waveforms. For the electrogram, the results indicated that adaptive sampling based on the fan method might be used effectively to limit average data rates to moderate values during original data acquisition     

Application of temporal subtraction for detection of interval changes on chest radiographs: Improvement of subtraction images using automated initial image matching

The authors developed a temporal subtraction scheme based on a nonlinear geometric warping technique to assist radiologists in the detection of interval changes in chest radiographs obtained on different occasions. The performance of the current temporal subtraction scheme is reasonably good; however, severe misregistration can occur in some cases. The authors evaluated the quality of 100 chest temporal subtraction images selected from their clinical image database. Severe misregistration was mainly attributable to initial incorrect global matching. Therefore, they attempted to improve the quality of the subtraction images by applying a new initial image matching technique to determine the global shift value between the current and the previous chest images. A cross-correlation method was employed for the initial image matching by use of blurred low-resolution chest images. Nineteen cases (40.4%) among 47 poor registered subtraction images were improved. These results show that the new initial image matching technique is very effective for improving the quality of chest temporal subtraction images, which can greatly enhance subtle changes in chest radiographs.     

Sex- and age-related normal limits for the QRS complex in vectorcardiography

In order to provide reference values for vectorcardiography (VCG), which are relevant with regard to sex, age and available computer technology. VCG from a normal material were studied. VCG according to Frank were recorded in 159 men and 193 women, healthy and randomly selected from a defined caucasian urban population. The technique used includes noise reduction by averaging and a spatial algorithm for QRS delineation. The results are given separately for men and women and for young and old subjects. Significant differences between these groups were found to be common and of potential importance for interpretation of VCG. Discrepancies between our results and other reports on normal ranges can be explained by both different techniques used and different composition of the material studied. On the basis of our data normal limits for a number of measurements, commonly used in diagnostic criteria for myocardial infarction and ventricular hypertrophy are reported.     

Mandibular transformations in prepubertal patients following treatment for craniofacial microsomia: thin-plate spline analysis

To analyze correction of mandibular deformity using an inverted L osteotomy and autogenous bone graft in patients exhibiting unilateral craniofacial microsomia (CFM), thin-plate spline analysis was undertaken. Preoperative, early postoperative, and approximately 3.5-year postoperative posteroanterior cephalographs of 15 children (age 10+/-3 years) with CFM were scanned, and eight homologous mandibular landmarks digitized. Average mandibular geometries, scaled to an equivalent size, were generated using Procrustes superimposition. Results indicated that the mean pre- and postoperative mandibular configurations differed statistically (P<0.05). Thin-plate spline analysis indicated that the total spline (Cartesian transformation grid) of the pre- to early postoperative configuration showed mandibular body elongation on the treated side and inferior symphyseal displacement. The affine component of the total spline revealed a clockwise rotation of the preoperative configuration, whereas the nonaffine component was responsible for ramus, body, and symphyseal displacements. The transformation grid for the early and late postoperative comparison showed bilateral ramus elongation. A superior symphyseal displacement contrasted with its earlier inferior displacement, the affine component had translocated the symphyseal landmarks towards the midline. The nonaffine component demonstrated bilateral ramus lengthening, and partial warps suggested that these elongations were slightly greater on the nontreated side. The affine component of the pre- and late postoperative comparison also demonstrated a clockwise rotation. The nonaffine component produced the bilateral ramus elongations-the nontreated side ramus lengthening slightly more than the treated side. It is concluded that an inverted L osteotomy improves mandibular morphology significantly in CFM patients and permits continued bilateral ramus growth.     

HeartSaver: a mobile cardiac monitoring system for auto-detection of atrial fibrillation, myocardial infarction, and atrio-ventricular block

A mobile medical device, dubbed HeartSaver, is developed for real-time monitoring of a patient's electrocardiogram (ECG) and automatic detection of several cardiac pathologies, including atrial fibrillation, myocardial infarction and atrio-ventricular block. HeartSaver is based on adroit integration of four different modern technologies: electronics, wireless communication, computer, and information technologies in the service of medicine. The physical device consists of four modules: sensor and ECG processing unit, a microcontroller, a link between the microcontroller and the cell phone, and mobile software associated with the system. HeartSaver includes automated cardiac pathology detection algorithms. These algorithms are simple enough to be implemented on a low-cost, limited-power microcontroller but powerful enough to detect the relevant cardiac pathologies. When an abnormality is detected, the microcontroller sends a signal to a cell phone. This operation triggers an application software on the cell phone that sends a text message transmitting information about patient's physiological condition and location promptly to a physician or a guardian. HeartSaver can be used by millions of cardiac patients with the potential to transform the cardiac diagnosis, care, and treatment and save thousands of lives.     

Fast and reliable QRS alignment technique for high-frequency analysis of signal-averaged ECG

The process of QRS alignment as required in signal-averaged ECG can impose serious limitations on the spectral range of the signal output. This effect depends basically on the particular alignment technique being used and on the level and type of noise present in the recorded ECG. In clinical studies where a wide-band (1000 Hz) ECG averager is required, the conventional QRS alignment technique, based on maximum coherence matching (MCM) with a template beat, may not perform consistently well. An alternative QRS alignment technique based on the accurate detection of a single fiducial point (SFP) in the bandpass filtered (3–30 Hz) QRS complex was developed. Using computer simulation methods, a comparative assessment of the frequency bandwidths (3 dB points) offered by both MCM and SFP techniques as a function of noise level (15–100 μ RMS) and type (EMG and 50 Hz interference), was carried out. The results of the comparative assessment indicated a better performance by the SFP technique in all cases of noise. Hence, the SFP technique would perform more reliably for high-frequency analysis of a noisy ECG, especially when 50 Hz interference is high. Furthermore, SFP is considerably faster than MCM (about four times) when implemented digitially, and its analogue realisation is feasible. The SFP technique is suitable for late-potential analysis in the signal-averaged ECG.