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Biomedical subjects

Tsair Kao

Publications and source records attributed to Tsair Kao.

8 recordsLinked to original sources
PubMed2006

Frequency analysis in different types of paroxysmal atrial fibrillation.

OBJECTIVES: This study sought to investigate the regional frequency distribution from multiple bi-atrial sites in different types of paroxysmal atrial fibrillation (AF). BACKGROUND: A previous study showed a left atrium (LA) to right atrium (RA) frequency gradient in patients with paroxysmal AF. METHODS: Forty-four patients (age = 60 +/- 16, male patients = 27) with paroxysmal AF originating from the pulmonary veins (PVs) (n = 31) or superior vena cava (SVC) (n = 13) were included. Frequency analysis was performed on the intracardiac electrograms (7 s, 1 kHz/channel) recorded from PV, posterior LA, coronary sinus (CS), posterolateral RA, and SVC. The largest peak frequency was identified as the dominant frequency (DF). RESULTS: In the PV-AF patients, there was a frequency gradient from the PV ostium to the LA, RA, and SVC (8.5 +/- 3.3 Hz vs. 5.9 +/- 1.1 Hz vs. 5.2 +/- 0.85 Hz vs. 5.5 +/- 0.48 Hz, respectively, p < 0.001). The highest DFs were mostly located at the arrhythmogenic PV ostium (58%). The DFs of the arrhythmogenic PV and PV ostium were significantly higher than those of the non-arrhythmogenic PVs and PV ostia (p < 0.05). In the SVC-AF patients, there was a frequency gradient from the SVC to the RA, LA, and PV (8.0 +/- 2.4 Hz vs. 5.9 +/- 1.1 Hz vs. 5.9 +/- 0.7 Hz vs. 5.8 +/- 0.7 Hz, respectively, p = 0.001). The highest DFs were mostly located inside the SVC (77%) instead of the SVC ostium (as compared with PV-AF patients, p = 0.035). CONCLUSIONS: The location of the highest DF depended on the arrhythmogenic PV or SVC. A frequency gradient was present between the arrhythmogenic thoracic vein and atrium in all patients.

Atrial Fibrillation↗
PubMed2005

Electrophysiological characteristics and catheter ablation in patients with paroxysmal right atrial fibrillation.

BACKGROUND: Catheter ablation of the right atrial (RA) substrate has had variable efficacy in curing paroxysmal atrial fibrillation (PAF), suggesting that RA substrate ablation can play an important role in the treatment of atrial fibrillation (AF) in some patients. The aim of this study was to investigate the electrophysiological characteristics and ablation strategy and its results in a specific group of patients with paroxysmal RA-AF. METHODS AND RESULTS: The study population consisted of 13 patients (8 men; age, 64+/-15 years) with drug-refractory (2+/-1 drugs), frequent episodes of PAF. Provocation maneuvers did not reveal any ectopic beat-initiating AF. However, rapid atrial pacing easily induced AF. Activation mapping during sinus rhythm, atrial pacing, and AF was visualized by using a noncontact mapping system. Noncontact mapping revealed RA reentry (6 patients with single-loop circuits and 7 with double-loop circuits) with conduction through channels between lines of block, crista terminalis gaps, and the cavotricuspid isthmus, which could be identified during sinus rhythm and atrial pacing, resulting in fibrillatory conduction in other parts of the RA. The consistency of wavefront activation was confirmed by frequency analysis from equally distributed mapping sites in the RA. Short lines of ablation lesions were aimed at the conduction channels between the lines of block, crista terminalis gaps, and the cavotricuspid isthmus, resulting in bidirectional block. AF was eliminated in 11 (85%) of 13 patients, and those 11 patients with acute success were free of AF without any antiarrhythmic drugs during the long-term follow-up period (16+/-6 months). CONCLUSIONS: RA ablation still can cure selected patients with PAF. Linear ablation of the RA substrate guided by the electrophysiological characteristics of RA-AF is an effective approach for treating this specific group of patients with AF.

Aged↗
PubMed2005

System integration and DICOM image creation for PET-MR fusion.

This article demonstrates a gateway system for converting image fusion results to digital imaging and communication in medicine (DICOM) objects. For the purpose of standardization and integration, we have followed the guidelines of the Integrated Healthcare Enterprise technical framework and developed a DICOM gateway. The gateway system combines data from hospital information system, image fusion results, and the information generated itself to constitute new DICOM objects. All the mandatory tags defined in standard DICOM object were generated in the gateway system. The gateway system will generate two series of SOP instances of each PET-MR fusion result; SOP (Service Object Pair) one for the reconstructed magnetic resonance (MR) images and the other for position emission tomography (PET) images. The size, resolution, spatial coordinates, and number of frames are the same in both series of SOP instances. Every new generated MR image exactly fits with one of the reconstructed PET images. Those DICOM images are stored to the picture archiving and communication system (PACS) server by means of standard DICOM protocols. When those images are retrieved and viewed by standard DICOM viewing systems, both images can be viewed at the same anatomy location. This system is useful for precise diagnosis and therapy.

Computer Communication Networks↗
PubMed2004

Estimating the input function non-invasively for FDG-PET quantification with multiple linear regression analysis: simulation and verification with in vivo data.

A novel statistical method, namely Regression-Estimated Input Function (REIF), is proposed in this study for the purpose of non-invasive estimation of the input function for fluorine-18 2-fluoro-2-deoxy- d-glucose positron emission tomography (FDG-PET) quantitative analysis. We collected 44 patients who had undergone a blood sampling procedure during their FDG-PET scans. First, we generated tissue time-activity curves of the grey matter and the whole brain with a segmentation technique for every subject. Summations of different intervals of these two curves were used as a feature vector, which also included the net injection dose. Multiple linear regression analysis was then applied to find the correlation between the input function and the feature vector. After a simulation study with in vivo data, the data of 29 patients were applied to calculate the regression coefficients, which were then used to estimate the input functions of the other 15 subjects. Comparing the estimated input functions with the corresponding real input functions, the averaged error percentages of the area under the curve and the cerebral metabolic rate of glucose (CMRGlc) were 12.13+/-8.85 and 16.60+/-9.61, respectively. Regression analysis of the CMRGlc values derived from the real and estimated input functions revealed a high correlation (r=0.91). No significant difference was found between the real CMRGlc and that derived from our regression-estimated input function (Student's t test, P>0.05). The proposed REIF method demonstrated good abilities for input function and CMRGlc estimation, and represents a reliable replacement for the blood sampling procedures in FDG-PET quantification.

Algorithms↗
PubMed2003

The influence of mean heart rate on measures of heart rate variability as markers of autonomic function: a model study.

Some studies have demonstrated that the assessments of autonomic activities from the alterations of heart rate variations (HRVs) after autonomic blockade and during exercise of high intensity by the spectral analysis of HRV seemed inconsistent with actual situation. The inconsistency is probably caused by the contributions of fluctuating magnitudes and mean levels of autonomic activities on HRV having not been clarified. The alterations of HRV after autonomic blockade and during exercise of high intensity using a mathematical model were simulated. The autonomic activity in normal condition was assumed first according to some experimental evidence. Then autonomic activities after sympathetic blockade, vagal blockade and during exercise of high intensity were appropriately adjusted accordingly. The HRVs in response to these given autonomic activities were simulated. We found that the effect on HRV influenced by the mean level of autonomic activity is helpful to explain alterations of HRV in these conditions. After vagal blockade, a largely reduced low frequency (LF) power could be caused by the reduced mean heartbeat interval induced by a decreased mean level of vagal activity. Increased low and high frequency powers after sympathetic blockade could be caused by the increased mean heartbeat interval induced by a decreased mean level of sympathetic activity. A decreased LF power during exercise of high intensity, in addition to the withdrawal of vagal activity, could also be caused by the decreased mean heartbeat interval induced by an increased mean level of sympathetic activity.

Animals↗
PubMed2002

Spectral analysis of chronic atrial fibrillation and its relation to minimal defibrillation energy.

The average rate of fibrillatory activity may reflect the global activation pattern of AF. Electrical cardioversion is the most effective method of converting chronic AF to sinus rhythm. The aim of this study was to investigate the relation between the minimal defibrillation energy requirement and the dominant frequency of chronic AF. Twenty-nine patients with chronic AF (mean duration 57.9 +/- 7.7 months) underwent external electrical cardioversion. Before cardioversion, the frequency content of the 60-second AF in ECG lead V1 was quantified using digital signal processing. After band-pass filtering, QRST complexes were cancelled using a recursive lease squares algorithm. The resulting fibrillatory baseline signal was subjected to fast Fourier transform and was displayed as a power spectrum. The dominant AF frequency was found to range from 4.9 to 8.7 Hz (mean 6.7 +/- 0.9 Hz). Twenty-six patients had successful conversion of AF to sinus rhythm without immediate recurrence. There was a positive correlation between the minimal defibrillation energy and the dominant frequency of chronic AF (rho = 0.414, P = 0.035). Thus, power spectral analysis of AF using the surface ECG is feasible and may be useful in predicting the minimal shock energy required for successful cardioversion of chronic AF.

Aged↗