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T Chua

Publications and source records attributed to T Chua.

At least 19 recordsLinked to original sources
PubMed2006

Association analysis of endothelial nitric oxide synthase gene polymorphism with primary hypertension in a Singapore population.

Vascular endothelial cells produce nitric oxide (NO), which contributes to the regulation of blood pressure and regional blood flow. Endothelial nitric oxide synthase (eNOS) gene polymorphisms are associated with coronary artery disease, but their linkage with primary hypertension is controversial. A total of 103 individuals with primary hypertension and 104 normotensive control subjects were studied in Singapore. The specific genotypes for G894T missense variant in exon 7, variable number tandem repeats (VNTR) in intron 4 (eNOS 4A/B/C) and T-786C in the promoter were isolated using allele-specific gene amplification and restriction fragment length polymorphism to examine the association of genotype and allelic frequency in both groups. Logistic regression analysis was also used to detect the association between genotypes and hypertension. Five genotypes of intron 4 VNTR (AA, AB, BB, AC and BC) were observed. Intron 4 B/B genotype was significantly associated with the hypertension group (P = 0.035), but disequilibrium of G894T and T-786C was absent between the two groups (P = 0.419 and P = 0.227), respectively. The overall distribution of allelic frequency differed significantly between the two groups, with four-repeat allele (4A) of intron 4 more frequent in the normotensive group than the hypertensive group (P = 0.019). Logistic regression analysis showed that intron 4 B/B genotype was significantly associated with systolic blood pressure of individuals with body mass index greater than 25 kg/m2 (P = 0.04). In conclusion, the eNOS 4 B/B genotype is a genetic susceptibility factor for primary hypertension in a Singapore population.

Blood Pressure↗
PubMed2003

Ethnic differences in acute myocardial infarction in Singapore.

AIMS: We compare the myocardial infarction (MI) event and mortality rates among Chinese, Malay and Indian residents of Singapore. METHODS: Residents, aged 20 to 64 years, with an MI event were identified from hospital discharge listings, postmortem reports, and the Registry of Births and Deaths. All pathology laboratories flagged patients with elevated creatine phosphokinase (CPK) levels. Modified MONICA (multinational monitoring of trends and determinants in cardiovascular disease) criteria were used for determining MI events. RESULTS: From 1991 to 1999, 12 481 MI events were identified. Chinese patients were older and less likely to have typical symptoms or previous MI. Malays had the highest peak CPK level. Among all three ethnic groups, MI event and age-adjusted case-fatality rates declined. Compared with Chinese, MI event rates were >2-fold and >3-fold higher, and age-standardized coronary mortality rates were 2.4 and 3.0 higher times for Malays and Indians, respectively. Malays have the highest 3.1-year case-fatality, with an adjusted hazard ratio of 1.26 (95% confidence interval, 1.14 to 1.38) compared with Chinese. CONCLUSION: We found strong ethnic differences in MI event, case-fatality and coronary mortality rates among the three ethnic groups in Singapore. While Indians have the greatest MI event rates, Malays have the highest case-fatality.

Adult↗
PubMed2003

A case series of sotalol-induced torsade de pointes in patients with atrial fibrillation--a tale with a twist.

INTRODUCTION: Sotalol is a potent antiarrhythmic often used in patients with atrial fibrillation. However, it has been associated with a risk of provoking other potentially dangerous arrhythmias, especially if used in high doses and in patients with uncorrected electrolyte imbalance or impaired renal and cardiac function. CLINICAL PICTURE: We present 4 patients with atrial fibrillation treated with sotalol who developed torsade de pointes due to marked prolongation of the QT interval. While 1 patient had renal failure, all had normal left ventricular function. One patient had been treated with sotalol for more than 10 months before developing torsade de pointes precipitated by hypokalaemia, while another had tolerated sotalol for a 3-month period before the drug was discontinued, and only developed torsade de pointes when the drug was restarted 2 years later. Significantly, the doses used in all patients were relatively low, in contrast to most other reported cases where higher doses were used. CONCLUSION: As with all antiarrhythmic therapy, these cases illustrate the need for close follow-up of patients treated with sotalol, even if relatively low doses are used. In addition, patients who had previously tolerated the drug well are still susceptible to its proarrhythmic effects.

Aged↗
PubMed2002

An outbreak of multidrug-resistant Salmonella enterica subsp. enterica serotype Typhimurium, DT104L linked to dried anchovy in Singapore.

Multidrug-resistant Salmonella enterica subsp. enterica serotype Typhimurium DT104L was first reported in Singapore from mid-July to mid-October 2000. Salmonella strains isolated from clinical laboratories were submitted to a reference laboratory for serotyping, phage-typing and pulsed-field gel electrophoresis (PFGE) using XbaI restriction endonuclease. An epidemiological investigation was conducted to determine the source of infection and mode of transmission using a structured questionnaire. A total of 33 cases involving mainly infants and toddlers were detected in the 3-month long outbreak. The outbreak strain was of the R-type ACGSTSu, i.e. resistant to ampicillin, chloramphenicol, gentamicin, streptomycin, tetracycline and sulphonamide. PFGE showed all isolates had an indistinguishable pattern, indicating a common source of infection. Consumption of imported dried anchovy was found to be the vehicle of transmission after adjusting for all confounding variables in the case-control study using stepwise logistic regression (OR 25.6; 95% CI 3.9-167.9; P = 0.001). Imported dried seafood should be properly processed, packed, labelled, and thoroughly cooked to prevent transmission of multidrug-resistant S. Typhimurium.

Adolescent↗
PubMed2001

Giant coronary aneurysms with multiple vascular aneurysms: a rare manifestation of hyperhomocysteinemia.

Hyperhomocysteinemia is associated with accelerated atherosclerosis, which leads to an increased incidence of premature vascular disease. Although multiple vascular aneurysms have been linked to hyperhomocysteinemia, coronary artery aneurysms have not. We report a case of giant coronary artery aneurysm associated with multiple peripheral vascular aneurysms in a patient with hyperhomocysteinemia.

Aged↗
PubMed2001

Leopard syndrome.

The Leopard syndrome is a complex of multisystemic congenital abnormalities characterised by lentiginosis, electrocardiographic conduction abnormalities, ocular hypertelorism, pulmonary stenosis, abnormalities of genitalia, retardation of growth and deafness (sensorineural). Hypertrophic cardiomyopathy, though not included in the mnemonic, is often associated. Although the Leopard syndrome is rare, it is important to recognise it since it can be associated with serious cardiac disease. It is advisable to follow up patients with Leopard syndrome for new onset of cardiac abnormalities and to monitor the progression of existing cardiac disease. We present a case report and review of the literature of this syndrome.

Abnormalities, Multiple↗
PubMed1994

Gated technetium-99m sestamibi for simultaneous assessment of stress myocardial perfusion, postexercise regional ventricular function and myocardial viability. Correlation with echocardiography and rest thallium-201 scintigraphy.

OBJECTIVES: This study compares technetium-99m sestamibi (sestamibi) electrocardiographic (ECG) gated single-photon emission computed tomography (gated SPECT) and echocardiography for the evaluation of myocardial function and assesses the feasibility of single-injection, single-acquisition stress perfusion/rest function technetium-99m sestamibi-gated SPECT as an alternative to conventional stress/rest imaging for assessment of myocardial perfusion and viability. BACKGROUND: Simultaneous assessment of stress perfusion and rest function is possible with gated SPECT acquisition of stress-injected technetium-99m sestamibi. METHODS: Rest thallium-201 SPECT followed by stress sestamibi-gated SPECT (acquired 0.5 to 1 h after sestamibi injection) was performed in 58 patients. Echocardiography was performed immediately after or before gated SPECT in 43 of the patients. All studies were analyzed by semiquantitative visual scoring. Sestamibi-gated SPECT studies were read for stress perfusion and rest wall motion and thickening. Reversibility on sestamibi-gated SPECT was defined as the presence of a definite stress defect with normal or mildly impaired wall motion or thickening on gated SPECT: RESULTS: There was high segmental score agreement between gated SPECT and echocardiography for wall motion (91%, kappa = 0.68, p < 0.001) and thickening (90%, kappa = 0.62, p < 0.001). Correlation for global wall motion (r = 0.98, p < 0.001) and thickening (r = 0.96, p < 0.001) scores between the two modalities was excellent. In 32 patients without previous myocardial infarction, there was excellent agreement for reversibility between stress sestamibi-gated SPECT and rest thallium-201/stress sestamibi (98%, kappa = 0.93, p < 0.01). However, in 26 patients with previous infarction, discordance between the two approaches was frequent, with 26% (20 of 78) of nonreversible defects by stress sestamibi-gated SPECT being reversible by rest thallium-201/stress sestamibi and 21% (23 of 112) of reversible defects by stress sestamibi-gated SPECT being nonreversible by rest thallium-201/stress sestamibi. CONCLUSIONS: Gated SPECT of stress-injected sestamibi correlates well with echocardiographic assessment of regional function and thus adds information to perfusion SPECT: In patients without previous myocardial infarction, a single-injection stress perfusion/rest function approach using sestamibi-gated SPECT can substitute for conventional stress/rest myocardial perfusion imaging, adding a rest perfusion study only if there are nonreversible defects or consideration of attenuation artifacts. In patients with previous myocardial infarction, the gated SPECT approach does not replace the need for a rest perfusion study.

Aged↗
PubMed1994

A quantitative phantom analysis of artifacts due to hepatic activity in technetium-99m myocardial perfusion SPECT studies.

UNLABELLED: We have observed that filtered backprojection may cause artifactual decreased myocardial wall uptake in the reconstructed images if the hepatic-to-cardiac activity ratio (HCR) in 99mTc clinical myocardial SPECT studies is sufficiently high (> 1). METHODS: To quantitatively relate hepatic uptake to this phenomenon, a commercial chest and heart phantom was modified with the addition of a customized liver insert, which was filled with various concentrations of 99mTc to simulate HCRs of 0:1, 1:1 and 2:1. The phantom was imaged with a high-sensitivity, three-detector camera, low-energy, high-resolution (LEHR) collimation and 180 degrees noncircular orbits. RESULTS: Quantitative circumferential profile analysis of the reoriented SPECT images demonstrated artifactual inferior/inferoseptal maximal activity decreases of 17.8% and 46.2% for the 1:1 and 2:1 HCRs, compared to the 0:1 HCR. Hepatic scatter probably partly mitigates the decrease. Smoothing the projection data before reconstruction worsened the artifacts' severity. Using Butterworth filters of order 5 and cutoff frequencies of 0.1, 0.2 and 0.215 Nyquist (clinical standard) resulted in artifactual inferior wall activity decreases of 5%, 8% and 16%, compared to using the same filter with a cutoff of 0.3 for an HCR of 2:1. CONCLUSION: These data indicate that if count statistics are good and liver uptake is high, higher frequency cutoffs in pre-reconstruction filters may improve specificity in 99mTc-labeled myocardial perfusion SPECT studies.

Artifacts↗
PubMed1993

Technetium-99m teboroxime regional myocardial washout in subjects with and without coronary artery disease.

The aim of this study was to test the hypothesis that regional myocardial washout of technetium-99m teboroxime is slowed in the presence of coronary stenosis. Washout was assessed in 33 catheterized patients and in 13 with a low likelihood of coronary artery disease, using a triple detector camera and dynamic single-photon emission computed tomography, with serial 1-minute acquisitions after injection of 20 to 25 mCi of teboroxime at the third minute of adenosine-induced hyperemia. Washout was measured as the percent change in counts between the first, second and third minutes after injection, as measured in 6 short-axis myocardial regions of interest. Myocardial regions were classified as ischemic (> or = 50% diameter stenosis and no prior myocardial infarct), infarcted, normal (no significant coronary stenosis) or "low likelihood" (from the 13 patients with a low likelihood of coronary artery disease). Teboroxime washout was significantly (p < 0.001) slowed in the ischemic myocardium (12.7 +/- 8.3%) compared with the normal (18.5 +/- 5.7%), low-likelihood (17.8 +/- 6.1%) and infarcted (17.8 +/- 4.4%) zones. There was regional variability in washout rates (% washout/min), with the anterior wall having the lowest (13.8 +/- 3.4%/min) and the inferior wall the highest (20.7 +/- 7.9%/min) values. In regard to individual coronary territories, 21 of 41 ischemic, noninfarcted territories (51%) had abnormal washout compared with 3 of 43 normal territories (7%) (p = 0.001). In conclusion, regional washout of teboroxime is detectably slowed in ischemic, noninfarcted myocardium. The clinical value of washout analysis in teboroxime single-photon emission computed tomography warrants further investigation.

Cohort Studies↗
PubMed1993

Posterior pituitary of the newborn marsupial possum, Trichosurus vulpecula.

The fetal anterior pituitary-adrenal axis is thought to be involved in the initiation of birth in both eutherian and marsupial mammals. Little is known about the structure and function of the posterior pituitary at birth in the marsupial. Immunocytochemistry, high pressure liquid chromatography, and radioimmunoassay were used to identify vasopressin and mesotocin in the posterior pituitary of a newborn marsupial, the brushtail possum, Trichosurus vulpecula. The concentrations of vasopressin and mesotocin in the head of the newborn possum were 0.34 and 0.28 ng, respectively. The concentration of vasopressin was always greater than that of mesotocin, and the amounts of neuropeptides present in the head increased as the possum developed.

Aging↗
PubMed1993

Detection and correction of patient motion in dynamic and static myocardial SPECT using a multi-detector camera.

We have developed a method for the detection and correction of translational patient motion in dynamic and static myocardial SPECT studies. The method uses a low activity 99mTc point source and is especially designed for multi-detector cameras. The source's centroid coordinates are measured or derived for all projection images in a temporal frame. The coordinate curves fitted to predicted distributions and the projection images shifted to realign measured to fitted values, with sub-pixel accuracy. In dynamic studies, the frame with the best fits serves as reference for all others. The accuracy of this method, measured with cardiac phantom experiments, was found to be +/- 0.37 mm and +/- 0.44 mm in the axial and transaxial dimension, respectively. By comparison, overall motion in 42 patients undergoing 99mTc-teboroxime dynamic cardiac SPECT studies was +/- 1.6 mm and +/- 1.2 mm, respectively (average on 39,272 projection views). Application of the method to phantom experiments, 99mTc-sestamibi and 99mTc-teboroxime human studies visually eliminated artifactual perfusion defects from simulated phantom motion and actual patient motion.

Gamma Cameras↗
PubMed1993

Rapid back to back adenosine stress/rest technetium-99m teboroxime myocardial perfusion SPECT using a triple-detector camera.

Technetium-99m-teboroxime is characterized by a high extraction fraction over a wide range of blood flow rates, rapid myocardial clearance and avid hepatic uptake. This study determined the imaging parameters and examined the clinical efficacy of a rapid back to back adenosine stress/rest teboroxime myocardial perfusion SPECT protocol using a triple-detector camera. Acquisition parameters were determined using cardiac phantom studies which were then applied in SPECT studies of 51 catheterized patients (22 with prior myocardial infarction) and 20 patients with a "low" (7.9% +/- 4.3%) likelihood of coronary artery disease. Technetium-99m-teboroxime (20-25 mCi) was injected at the third minute of adenosine infusion. Teboroxime (20-25 mCi) was also injected at rest, 15 min later. Stress followed by rest SPECT were completed within 25 min using a triple-detector camera and sequential, 1-min continuous rotations in alternating directions. Summed raw data from the first to second (1-2 min), second to third (2-3 min) and second to fifth (2-5 min) minutes of imaging following stress teboroxime injection were reconstructed and compared for image quality, degree of liver interference, and accuracy for diagnostic efficacy. In a subgroup of 30 patients, 2-8-min summed images were also reconstructed to compare this more conventional imaging protocol with our rapid acquisition. Image quality was fair to good in 75% of the 1-2-min, 84% of the 2-3-min and 2-5-min studies and 53% of the 2-8-min scans. The frequency of severe liver interference appeared to increase with the duration of imaging time (1-2 min: 3%; 2-3 min: 7%; 2-5 min: 8%) and was greatest (30%, p = 0.08) with 2-8-min images. Three patients (4%) had uninterpretable studies due to intense hepatic uptake. Overall sensitivity (95%) and specificity (71%) were equal for the 2-3-min and 2-5-min stress images and appeared better than in the 1-2-min images (84% and 57%, respectively). For the 2-8-min scans, vessel sensitivity (69%) and specificity (63%) appeared poorer than with 2-3-min studies (83% and 81%, respectively). Normalcy rates were 89% for the 2-3-min and 2-5-min and 79% for 1-2-min images. The back to back adenosine stress/rest teboroxime SPECT can be performed in 30 min using a triple-detector camera. Although overall high sensitivity and normalcy rates were achieved, the protocol is technically demanding. Interference due to intense liver uptake remains problematic.

Adenosine↗
PubMed1992

Analysis of supradiaphragmatic clinical stage I and II Hodgkin's disease treated with radiation alone.

Patients with clinical Stage I and II Hodgkin's disease have been managed at the Princess Margaret Hospital for over 20 years, without the use of routine staging laparotomy. Our experience identified as adverse prognostic factors presence of a large mediastinal mass, B symptoms, and advanced age in presence of unfavorable histology (20). We had suggested previously that the use of extended field radiation therapy (XRT) was associated with a lower risk of relapse than involved field XRT or mantle XRT. There has been a trend over the past decade to select those patients with favorable prognostic factors for treatment with XRT alone and to use mantle plus upper abdominal XRT (extended field XRT) to treat them. A retrospective study of patients with clinical Stage I and II Hodgkin's disease treated at the Princess Margaret Hospital between 1978 and 1986 was conducted to determine the impact of patient selection and extended field radiation on outcome. The study involved 250 patients with supradiaphragmatic disease selected for treatment with radiation alone on the absence of adverse prognostic factors. Radiation techniques included involved field radiation in selected patients (those with upper neck involvement), mantle radiation in the earlier years, and mantle plus upper abdominal radiation in the later years of the study. Actuarial survival was 83.3% at 8 years; cause-specific survival was 90.1% and the relapse-free rate 71.6%. Local tumor control was 94.6%; only two patients had true infield failure. Multivariate analysis showed that significant prognostic factors included age, histology, and erythrocyte sedimentation rate. Extent of the radiation treatment volume was significant and influenced the risk of relapse, particularly out-of-field relapse, independently of other factors. A dose of 35 Gy was found to be sufficient for control of clinical disease. This study validated a previously developed model for the selection of clinically staged patients with Stage I and II Hodgkin's disease for treatment with radiation alone. Careful selection of these patients can yield excellent results without requiring that staging laparotomy be routinely performed or the use of systemic chemotherapy as the initial treatment.

Adolescent↗
PubMed1992

Radiation therapy in clinical stage I and II Hodgkin's disease. The Princess Margaret Hospital Lymphoma Group.

A review of the Princess Margaret Hospital experience over the last 20 years in treating clinically staged patients with stage I and II Hodgkin's disease was performed to analyse the impact of patient selection and extended field radiation on relapse and survival. Of the 878 patients with stage I and II Hodgkin's disease, 521 with clinical stages I and II received radiation alone as the initial treatment. The actuarial survival for all stage I and II patients was 85.1% at 5 years and 76.2% at 10 years, and for clinically staged patients treated with radiation alone, 87.2 and 77.6%, respectively. The relapse-free rate (RFR) for all clinical stage I and II patients treated with radiotherapy (RT) alone was 70.1% at 5 years and 65.8% at 10 years. Significant prognostic factors for RFR and survival included age, stage and histology. In addition, the extent of radiation was identified as an independent prognostic factor for survival as well as for relapse. The RFR for those treated with involved field RT was 58.4% at 5 years and 50.5% at 10 years; for patients treated with mantle RT, 69.9 and 65.6%, and those treated with extended field RT 77.4 and 75.8%, respectively. In a highly selected group of patients with no adverse features, i.e. with stages IA-IIA, lymphocyte predominant or nodular sclerosis histology, erythrocyte sedimentation rate < 40, age < 50, no large mediastinal mass, and no E-lesions--the policy of mantle RT (M) and extended field RT (EF) produced comparable 5-year relapse-free rates (M, 84.9%; EF, 87.1%; P = 0.53). We conclude that a policy of treatment selection based upon clinicopathological prognostic factors and the use of extended field RT confers excellent results in the treatment of clinical stage I and II Hodgkin's disease.

Adolescent↗
PubMed1991

Bladder cancer: long-term follow-up results of patients treated with radical radiation.

Carcinoma of the bladder is commonly treated for cure with external beam radiation. Whilst short-term results are associated with a good chance of disease control there is little information about the long-term results of such therapy. We present a retrospective review of the Princess Margaret Hospital experience in treating transitional cell carcinoma of the bladder and emphasis on the long-term follow-up of patients treated with radiotherapy (XRT). Between 1972 and 1980, 355 patients were treated with a radical course of external beam radiation. The overall survival was 20% at 10 years and the cause-specific survival was 32%. Radiation treatment resulted in a long-term bladder preservation in at least 25% of patients. The majority of long-term survivors without evidence of relapse were patients with T1 (solitary tumours), T2 and T3a tumours. This subgroup represents patients with disease favourable for treatment with radiation. Factors affecting response to the XRT and survival included T stage and tumour bulk. Radiation complications were frequent and were usually associated with local disease recurrence.

Adult↗
PubMed1990

Outcome analysis of localized gastrointestinal lymphoma treated with surgery and postoperative irradiation.

One hundred thirteen patients with localized gastrointestinal lymphoma treated by surgery and postoperative irradiation between 1967 and 1985 were reviewed. At 15 years, actuarial survival of this group was 40.6%, with a cause-specific survival of 69.2% and a relapse-free rate of 64%. Two-thirds of relapses occurred at distant sites. In Stage IA and IIA patients with no residuum or with positive resection margins, (N = 90) only site of involvement and stage predicted for relapse. Age, histologic subtype group, and depth of bowel wall invasion did not affect relapse risk. In the very favorable group (Stage IA, IIA, no residuum or microscopic residuum), 8.4% of patients with stomach lymphoma relapsed compared to 25% of patients with small bowel lymphoma. The risk of early relapse was higher in those with Stage IIA small bowel lymphoma than those with Stage IA small bowel lymphoma. We continue to recommend adjuvant abdominal irradiation for patients with Stage IA, IIA completely resected stomach lymphoma and Stage IA completely resected small bowel lymphoma. We recommend combined modality therapy for patients with completely resected Stage IIA small bowel lymphoma and all other localized gastrointestinal lymphoma where visible residual disease is present.

Adolescent↗
PubMed1989

Radical radiotherapy for muscle invasive transitional cell carcinoma of the bladder: failure analysis.

Patients with muscle invasive carcinoma of the bladder treated with radical radiation were prospectively documented and followed in an attempt to identify prognostic factors predictive of the response to treatment. Data on 121 consecutive patients treated with radical radiation between 1981 and 1985 are presented. Over-all actuarial survival of the patient population (median age 70 years) was 31.6% at 5 years and cause-specific survival was 44.8%. At analysis 33 of 121 patients (27.3%) were alive with preserved bladder function. Independent prognostic factors for cause-specific survival and for complete response with radical radiation were tumor configuration, hemoglobin level and clinical stage. The rate free of local relapse was significantly influenced by stage and presence of coexistent carcinoma in situ. The study suggests that factors other than stage and grade influence prognosis in invasive bladder cancer and should be considered in interpreting treatment results.

Adult↗