Biomedical subjects

A T Tan

Publications and source records attributed to A T Tan.

At least 19 recordsLinked to original sources

PubMed2000

A comparison of indices of respiratory failure in ventilated preterm infants.

AIM: To compare indices of respiratory failure in terms of their ability to predict adverse respiratory outcomes in preterm infants. The indices evaluated were: (a) the alveolar-arterial oxygen tension difference (A-aDO(2)); (b) the ratio of arterial to alveolar oxygen tension (a/A ratio); (c) the oxygenation index (OI); (d) the fractional inspired oxygen concentration (FIO(2)). METHODS: Details of respiratory support and arterial blood gas data in the first 24 hours of life were collected in ventilated infants below 34 weeks gestation. The worst single value of a particular index in the first 24 hours was chosen to quantify the severity of respiratory failure in each infant. Receiver operating characteristic curves were constructed and areas under the curve (AUC) calculated to compare the performance of the indices in predicting death from respiratory failure and/or the development of chronic lung disease (CLD). RESULTS: A total of 155 preterm infants were studied, of whom 35 (23%) died primarily from respiratory failure and 53 of the 120 survivors (44%) developed CLD. The overall performance of the four indices in predicting death from respiratory failure ranged from 0. 77 (AUC for maximum FIO(2)) to 0.88 (AUC for minimum a/A ratio). The corresponding AUCs for gestational age and birth weight were 0.75 and 0.76 respectively. In contrast, demographic variables tended to perform better than indices of respiratory failure in predicting CLD/death. CONCLUSIONS: There was no evidence of a significant difference between the performance of the a/A ratio, A-aDO(2), and OI in predicting adverse respiratory outcomes. Use of the OI is recommended because of its ease of calculation.

Chronic Disease↗

PubMed2000

Technetium-99m sestamibi for the assessment of myocardial salvage following reperfusion therapy in acute myocardial infarction.

INTRODUCTION: Reperfusion therapy with either thrombolysis or angioplasty has been shown to be beneficial in acute myocardial infarction. Tc-99m sestamibi is a myocardial tracer that can be used to assess myocardial salvage because of its property of very limited redistribution. MATERIALS AND METHODS: To assess the feasibility of this technique locally, Tc-99m sestamibi was injected before and after reperfusion therapy with angioplasty (n = 11) or streptokinase (n = 18) in 29 patients with acute myocardial infarction (anterior = 25, inferior = 4). Single-photon emission computed tomography (SPECT) was performed within 4 hours of reperfusion and repeated 5 to 7 days later. RESULTS: Initial perfusion defect size ranged from 6% to 78% (mean 36.3 +/- 18.7%), and final defect size from 0% to 50% of the left ventricle (mean 23.7 +/- 14.8%, P < 0.001). Patients with proximal left anterior descending artery (LAD) lesions had larger defects compared to those with mid LAD lesions (mean defect size 52% for pLAD versus 28% for mLAD, P < 0.013). However, there were wide variations in initial defect size (myocardium at risk) for a given infarct-related artery location. The mean decrease in defect size was 12% in the 28 patients with patent arteries compared to only 2% in the patient with an occluded artery (47% to 45%). There was no significant difference in amount of salvage between patients who had thrombolysis (mean 13%, P = 0.0003) and patients who had percutaneous transluminal coronary angioplasty (PTCA) (mean 12%, P = 0.005). CONCLUSIONS: Assessment of myocardial salvage is feasible using Tc-99m sestamibi SPECT imaging. It allows for quantitation of myocardium at risk and the amount of myocardial salvage, which is not possible by angiography alone.

Adult↗

PubMed1999

Ovarian response after laparoscopic ovarian cystectomy for endometriotic cysts in 132 monitored cycles.

OBJECTIVE: To investigate the follicular response of ovaries after laparoscopic ovarian cystectomy for endometriotic cysts. DESIGN: A retrospective, controlled study. SETTING: Obstetrics and Gynaecology Department of a university hospital. PATIENT(S): Patients with history of infertility who had laparoscopic ovarian cystectomy for endometriotic cysts. INTERVENTION(S): Laparoscopic ovarian cystectomy, transvaginal ultrasound monitoring of follicles in natural cycles, stimulated cycles using clomiphene citrate (CC), chronic low-dose FSH, and "flare down" regimen. MAIN OUTCOME MEASURE(S): Follicular response of postcystectomy and normal ovaries. RESULT(S): For women < 35 years of age, the mean follicular response of postcystectomy ovaries was reduced significantly when compared with normal ovaries in natural cycles (0.30 versus 1.00 follicle per cycle) and in CC-stimulated cycles (0.87 versus 1.27 follicles per cycle). The mean follicular response was not statistically significantly different when the ovaries were stimulated with chronic low-dose FSH or with the flare down regimen. For women > or = 35 years, postcystectomy ovaries responded with a comparable number of follicles as the normal ovaries in natural cycles and the three different ovarian stimulation regimens. CONCLUSION(S): Postcystectomy ovaries showed reduced follicular response in natural and CC-stimulated cycles for women < 35 years of age. Postcystectomy ovaries produced a comparable number of follicles as normal ovaries when stimulated with gonadotropins.

Adult↗

PubMed1999

Factors related to outcome after pneumonectomy: retrospective study of 62 patients.

OBJECTIVE: To find out which risk factors affect outcome after pneumonectomy. DESIGN: Retrospective study. SETTING: Teaching hospital, The Netherlands. SUBJECTS: 62 patients who were treated for bronchial cancer by pneumonectomy between 1984 and 1995. MAIN OUTCOME MEASURE: Hospital mortality and postoperative complications. RESULTS: Hospital mortality increased with age, being 5/51 (10%) in the 40-69 age group and 4/11 (36%) in patients aged 70 or more. In the American Society of Anesthesiologists (ASA) class I group hospital mortality was 8% (2/26), in class II 12% (3/26) and in class III 40% (4/10). Hospital mortality was highest when the FEV1:FVC-ratio was below 55%. Cardiac arrhythmias developed in 8 (13%), early bronchopleural fistulas in 7 (11%), and postpneumonectomy syndrome in 5 (8%). These major complications had a high mortality. CONCLUSION: Respiratory function, ASA class, and age over 70 years are the main prognostic factors for hospital morbidity and mortality after pneumonectomy.

Adult↗

PubMed1998

Lovastatin induces apoptosis in malignant mesothelioma cells.

Malignant mesothelioma causes profound morbidity and nearly universal mortality that is refractory to conventional treatment with aggressive surgery, radiotherapy, or chemotherapy. We report that pharmacologic concentrations of lovastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitor, induced apoptosis in human malignant mesothelioma cell lines. Mesothelioma cell viability was decreased in a dose-dependent manner by lovastatin (5 to 30 microM). These effects were not reversed by exogenous growth factors or cholesterol, but were reversed by addition of 100 microM mevalonate, confirming that lovastatin affected mesothelioma viability by inhibiting mevalonate synthesis. Lovastatin appeared to decrease mesothelioma viability by inducing apoptosis, as indicated by morphologic changes, histologic evidence of nuclear condensation and degeneration, and flow-cytometric analysis of DNA content. Lovastatin's effects on cell viability were partially reversed in the presence of farnesol, and treatment of mesothelioma cells with a specific farnesyl-protein transferase (FTP) inhibitor decreased cell viability and induced morphologic changes indistinguishable from those caused by lovastatin. In addition, lovastatin-treated cells showed translocation of ras guanosine triphosphate (GTP)-binding proteins from membrane to cytosolic fractions on Western blots, suggesting that lovastatin's effects on mesothelioma were mediated in part by disrupting acylation of GTP-binding proteins. Thus, lovastatin is a commercially available and clinically well-tolerated agent that reduces viability and induces apoptosis of mesothelioma cells, and may provide the basis for adjunctive treatments of patients with mesothelioma.

Alkyl and Aryl Transferases↗

PubMed1998

The clinical impact of platelet glycoprotein IIb/IIIa receptor blockade in cardiovascular medicine.

Several of the adverse events that occur in acute coronary syndromes and after percutaneous coronary revascularization procedures are believed to be mediated by platelets. Recently, using molecular biology techniques, the platelet glycoprotein IIb/IIIa receptor was identified as the final common pathway for platelet aggregation. Thus, blocking the action of this receptor would seem to be an attractive proposition for reducing ischemic complications. A monoclonal antibody was the first agent in this new pharmacological family to be designed, but several peptide and peptide-like substances have subsequently been developed. This paper reviews the development of this class of agents and the various preclinical and clinical trials that have been undertaken. Early studies evaluated such agents during percutaneous coronary revascularization procedures. Because of the overwhelming benefits observed in such patients, together with the current limitations of treatments for acute coronary syndromes, the scope of investigations has been extended. Preliminary reports have been encouraging.

Blood Platelets↗

PubMed1998

Comparison of treatment of supraventricular tachycardia by Valsalva maneuver and carotid sinus massage.

STUDY OBJECTIVE: To compare the efficacy of the Valsalva maneuver with that of carotid sinus massage (CSM) in terminating paroxysmal supraventricular tachycardia (SVT) in the ED. METHODS: This prospective, randomized case study was performed in the ED of a tertiary care institution. Patients were at least 10 years of age with regular narrow complex tachycardia and had an ECG diagnosis of SVT. Patients with regular narrow complex tachycardia were randomly assigned to undergo either the Valsalva maneuver or CSM. If the tachycardia was not terminated by the method chosen by randomization, then the alternative method of vagal maneuver was used. If the tachycardia was not converted by both methods of vagal stimulation, patients would undergo either synchronized electrical cardioversion or a pharmacologic method of conversion at the discretion of the treating physician, depending on the patient's hemodynamic status. RESULTS: One hundred forty-eight instances of SVT were studied Sixty-two patients underwent Valsalva maneuver first with conversion in 12 (success rate of 19.4%). Eighty-six underwent CSM first with conversion in 9 (success rate 10.5%). Carotid sinus massage was used in the 50 cases of SVT in which conversion was not achieved with the Valsalva maneuver. Conversion occurred in 7 cases (success rate 14.0%). For the 77 cases of SVT in which initial CSM did not achieve conversion, conversion occurred in 13 with the Valsalva maneuver (success rate 16.9%). The Valsalva maneuver and CSM achieved conversion in a total of 41 instances of SVT (success rate 27.7%). CONCLUSION: Vagal maneuvers are efficacious in terminating about one quarter of spontaneous SVT cases. There is no detectable difference in efficacy between the Valsalva maneuver and CSM.

Adult↗

PubMed1996

Translational control of programmed cell death: eukaryotic translation initiation factor 4E blocks apoptosis in growth-factor-restricted fibroblasts with physiologically expressed or deregulated Myc.

There is increasing evidence that cell cycle transit is potentially lethal, with survival depending on the activation of metabolic pathways which block apoptosis. However, the identities of those pathways coupling cell cycle transit to survival remain undefined. Here we show that the eukaryotic translation initiation factor 4E (eIF4E) can mediate both proliferative and survival signaling. Overexpression of eIF4E completely substituted for serum or individual growth factors in preserving the viability of established NIH 3T3 fibroblasts. An eIF4E mutant (Ser-53 changed to Ala) defective in mediating its growth-factor-regulated functions was also defective in its survival signaling. Survival signaling by enforced expression of eIF4E did not result from autocrine release of survival factors, nor did it lead to increased expression of the apoptosis antagonists Bcl-2 and Bcl-XL. In addition, the execution apparatus of the apoptotic response in eIF4E-overexpressing cells was found to be intact. Increased expression of eIF4E was sufficient to inhibit apoptosis in serum-restricted primary fibroblasts with enforced expression of Myc. In contrast, activation of Ha-Ras, which is required for eIF4E proliferative signaling, did not suppress Myc-induced apoptosis. These data suggest that the eIF4E-activated pathways leading to survival and cell cycle progression are distinct. This dual signaling of proliferation and survival might be the basis for the potency of eIF4E as an inducer of neoplastic transformation.

3T3 Cells↗

PubMed1995

Intracoronary stenting in the treatment of acute or threatened closure in angiographically small coronary arteries (< 3.0 mm) complicating percutaneous transluminal coronary angioplasty.

The effect of the Flex-Stent on immediate and long-term angiographic and clinical results for acute and threatened closure was evaluated in 42 consecutive patients with coronary arterial segments < 3.0 mm in diameter after percutaneous transluminal coronary angioplasty (PTCA). Forty-two consecutive patients were treated with Flex-Stent (2.0 or 2.5 mm) for acute or threatened closure complicating PTCA. Ten patients (24%) had acute closure and 32 (76%) had threatened closure with a residual luminal stenosis of > 50%. Successful stent deployment was achieved in 40 patients (95%) with a primary clinical success rate of 90% (freedom from myocardial infarction, coronary artery surgery, and death). In-hospital complications occurred in 5 patients (some patients fell into more than one category): 3 (7.1%) had coronary bypass surgery, 1 (2.4%) had acute stent thrombosis, 1 (2.4%) had subacute stent thrombosis, 2 (4.8%) had myocardial infarction, and 1 (2.4%) had dextran allergy. There was no hospital death. Clinical follow-up was complete at a mean of 14.8 +/- 7.6 months, and recurrence of angina was noted in 20 of 38 eligible patients (53%). Angiographic restenosis was found in 19 of 29 patients (66%) (76.3% of eligible patients) on follow-up angiography (mean 5.9 +/- 4.6 months). Fourteen patients (74%) underwent successful repeat PTCA at the stented site, 4 of 38 patients (11%) had bypass surgery. Intracoronary stenting in the treatment of acute or threatened closure in arteries < 3.0 mm is effective in improving the acute clinical outcome and is a viable nonsurgical alternative for this subset of patients.

Acute Disease↗

PubMed1995

Myocardial perfusion imaging with technetium-99m sestamibi SPECT in the evaluation of coronary artery disease.

Technetium-99m hexakis-2-methoxy-isobutyl-isonitrile (99mTc sestamibi) has been used for myocardial perfusion imaging in the evaluation of coronary artery disease (CAD) since 1990. The experience of its use in an Asian population with and without previous myocardial infarction (MI), diabetes mellitus (DM), hypertension (HPT) and collateral circulation (COL) is reported. One hundred and thirty-nine patients who underwent treadmill exercise testing with 99mTc sestamibi single photon emission computed tomography (SPECT) and coronary angiogram were studied. The overall sensitivity for the detection of CAD was 91.0% and specificity was 64.7%. For patient without previous myocardial infarction, the sensitivity was 83.8% and specificity was 83.3%. Patients with COL had a higher sensitivity while those with HPT had a lower specificity. Sensitivity was higher in patients with multi-vessel disease (MVD) than single vessel disease (SVD). The overall detection for individual artery stenosis was 74.1% with a specificity of 73.1%. Amongst the three major coronary arteries, sensitivity was highest for the right coronary artery and specificity was highest for the left circumflex artery. Specificity was higher in patients without MI or COL. We found that the agreement between 99mTc sestamibi SPECT and coronary angiogram for the extent of CAD was only 52.5%. The concordance rate was higher for patients with MVD than SVD. It is concluded that 99mTc sestamibi SPECT is a sensitive and specific test for the detection of CAD and localization of disease to individual coronary arteries in our patients with some differences in the subgroups. Agreement between coronary angiogram and 99mTc sestamibi for the extent of coronary artery disease was also satisfactory.

Adult↗

PubMed1995

Outpatient coronary angiography using 7 French catheters in Singapore.

PURPOSE: Out-patient coronary angiogram (OCA) is commonly performed in many centres using 5 or 6 French (F) catheters. Though this small catheter may reduce bleeding complications, manipulatability and adequate vessel visualisation are problems which may increase procedure time. 7 or 8 F catheters have been used in Caucasians. We report our experience with OCA using 7 F catheters in an Asian centre. METHODS: Sixty-six patients with low procedural risk were consecutively recruited. They were pre-medicated with oral diazepam. Selective coronary angiogram (SCA) and left ventriculogram were performed via the femoral artery. Parenteral heparin was administered after the arterial puncture. After the procedure, haemostasis was secured by at least ten minutes of manual compression. The patients were immobilised for six hours and thereafter encouraged to walk for about an hour. The groin was inspected by a doctor before discharge and reviewed the following day. RESULTS: The age ranged from 27 to 73 years with a mean of 52.6. There were 48 men and 18 women. Seventeen patients had previous SCA or angioplasty. There was no significant coronary artery disease (CAD) in 26 patients (39.4%). Thirteen patients (19.7%) had minor CAD, 20 (30.3%) had single or double vessel and 7 (10.6%) had triple vessel disease. The mean procedural time was 16.6 +/- 7.3 minutes, ranging from 7 to 54. Seven (10.6%) of the patients had a small haematoma prior to discharge. None of the haematoma deteriorated at review. We did not find sex, age, history of diabetes mellitus or hypertension, height, weight, body mass index, use of anti-platelet agents, systolic blood pressure at and after the procedure and coronary artery anatomy to be associated with an increased risk of haematoma. The estimated cost savings for a non-subsidized patient was S$285 and for a subsidized patient was S$66. CONCLUSION: We conclude that OCA using 7 F catheters is a safe and efficacious procedure in our patients.

Adult↗

PubMed1995

Upright tilt table testing in the evaluation of syncope.

OBJECTIVES: To review our experience with the upright tilt table test for the diagnosis of vasovagal syncope in a group of unselected patients with a history of syncope or presyncope. METHODS: 179 patients with a history of syncope or presyncope were subjected to upright tilt test. After carotid sinus massage to exclude carotid sinus hypersensitivity, the patients were tilted on a motorised tilt table with footplate support to an angle of sixty to seventy degrees for thirty minutes. If syncope was not induced, isoprenaline was then infused for a further fifteen minutes. A positive response was defined as fulfilling at least two out of three criteria: (i) syncope or presyncope similar to the spontaneous episodes of syncope, (ii) relative slowing of the heart rate at the onset of symptoms, (iii) drop of systolic pressure to less than 90 mmHg or by more than 50 mmHg. STATISTICAL METHODS: Continuous variables are expressed as mean values +/- one standard deviation and analysed for statistical significance by the unpaired Student's t-test. Chi-squared test with continuity correction was used for dichotomous variables. RESULTS: Ninety-four patients (53%) were positive for vasovagal syncope. Fourteen patients (8%) were positive at baseline tilt. An additional 80 patients (45%) were positive with the use of isoprenaline. Ten percent of the positive responses were purely cardioinhibitory, 10% purely vasodepressor and 80% mixed. The commonest cardiac rhythm during a positive response was junctional rhythm (46%) followed by sinus rhythm (44%). Sinus arrest with ventricular standstill occurred in only 5%. Accelerated idioventricular rhythm, 2:1 atrioventricular block and ventricular bigeminy accounted for the remaining 5%. CONCLUSION: The upright tilt table test is useful for the diagnosis of vasovagal syncope.

Adolescent↗

PubMed1994

Simultaneous ST-segment elevation in lead V1 and depression in lead V2. A discordant ECG pattern indicating right ventricular infarction.

The major electrocardiographic change in right ventricular infarction (RVI) is ST-segment elevation in leads V4R-V6R. The authors describe a discordant electrocardiographic pattern of ST-segment elevation in lead V1 and ST-segment depression in lead V2 in five patients presenting with acute transmural (Q wave) inferior infarction and RVI. There were 51 patients with transmural inferior infarction from a thrombolytic trial. In 25 patients, the ST-segment in the right-sided precordial leads was elevated by > or = 1 mm indicating the presence of RVI. In 5 of these 25 patients, simultaneous ST-segment elevation of 1.0-8.0 mm (mean, 2.8 +/- 2.9 mm) in lead V1 and ST-segment depression of 2.5 to 4.0 mm (mean, 3.3 +/- 0.6 mm) in lead V2 were also present. The discordant pattern of the ST-segments in leads V1 and V2 is an important and specific sign for RVI.

Adult↗

PubMed1994

Massive acute pulmonary embolism in protein S deficiency--a case report.

A young man with a history of deep vein thrombosis and pulmonary embolism 11 years ago presented again with acute pulmonary embolism and was treated initially with intravenous heparin at our institution. Five days later he had another massive bout of pulmonary embolism causing hypotension. Pulmonary angiography confirmed the presence of thrombi in both pulmonary arteries, with complete obstruction of the left pulmonary artery. He was treated successfully by emergency pulmonary embolectomy. Blood investigations later confirmed the diagnosis of protein S deficiency and he was started on warfarin therapy for life. Massive pulmonary embolism should be treated aggressively. Thrombolytic therapy accelerates clot lysis, reduces pulmonary pressures, restores pulmonary capillary volume and reverses right heart failure faster than heparin alone. There is also a trend towards decreased mortality with thrombolysis. In the presence of shock, the patient should be resuscitated and if facilities for emergency embolectomy are available, surgery is a viable alternative to thrombolysis, especially if the clot burden is massive. In young patients with recurrent venous thromboembolism in the absence of obvious predisposing factors, it is important to exclude inherited plasma protein deficiencies of protein S, protein C, antithrombin III, plasminogen and fibrinogen.

Acute Disease↗

PubMed1993

An unusual cause for cyanosis.

Cyanosis is a common physical sign in clinical medicine. Cardiac or respiratory conditions are the usual causes. We report a patient with an unusual cause for cyanosis and highlight the salient clues that lead to the diagnosis.

Adult↗

PubMed1993

Percutaneous transseptal balloon mitral valvotomy: initial experience in Singapore.

Between June 1990 and August 1991, 28 percutaneous transseptal balloon mitral valvotomy procedures were attempted in 27 patients (23 women and 4 men; mean age 39.8 +/- 9.3 years) with severe mitral stenosis. Successful mitral valvotomy was achieved in 25 patients (primary success rate of 92%). Mitral valve area increased from 0.82 +/- 0.17 cm2 to 1.53 +/- 0.48 cm2 (p < 0.001) and the mean mitral valve gradient decreased from 13.4 +/- 7.4 to 6.0 +/- 5.4 mmHg (p < 0.05). There were no deaths, one patient had cardiac tamponade after transseptal puncture and required emergency pericardiocentesis with successful percutaneous balloon valvotomy 6 months later. One patient had an unsuccessful valvotomy because the mitral valve could not be crossed and another patient had an inadequate dilatation. Our initial experience in percutaneous transseptal mitral valvotomy confirms the safety and efficacy of this new technique for the treatment of rheumatic mitral stenosis.

Adult↗

PubMed1993

Percutaneous balloon aortic valvotomy.

We report our first case of percutaneous balloon aortic valvotomy in a 72-year-old Chinese female with critical aortic stenosis and carcinoma of the stomach. The presence of critical aortic stenosis (mean aortic pressure gradient of 65 mmHg and an aortic valve area of 0.5 cm2) placed her at a high risk for gastrectomy. After balloon valvotomy of the aortic valve, the mean pressure gradient fell to 21 mmHg and the aortic valvular area increased to 1.0 cm2. She improved clinically and subsequently underwent surgery with no haemodynamic complication. Overseas experience has shown that percutaneous balloon valvotomy can be done with little technical difficulty and excellent patient tolerance, resulting in good haemodynamic and clinical improvement and a low acute complication rate. Present follow-up data however suggest significant mortality and restenosis rates at the end of one year. Percutaneous balloon aortic valvotomy (PBAV) has a significant though narrowly defined role in the management of patients with severe calcific aortic stenosis.

Adenocarcinoma↗

PubMed1992

Surgery for cardiac arrhythmias.

From March 1989 to March 1991, 17 patients underwent curative surgical ablation of cardiac arrhythmias at the Singapore General Hospital. In the supraventricular tachycardia group, 13 patients with the Wolff-Parkinson White syndrome (WPW) underwent surgical ablation of the accessory conduction pathway by the classical endocardial approach. Two patients who had atrioventricular nodal tachycardia (AVNRT) underwent surgical dissection around the atrioventricular node to divide one of the dual conduction pathway responsible for the tachycardia. In the ventricular tachycardia group, two patients underwent surgical ablation of the arrhythmic focus. There was no operative mortality in the supraventricular tachycardia group and there were no late deaths to date. All these patients underwent electrophysiological study just before discharge and most of them had a repeat test six months later. In the Wolff-Parkinson White group, surgical ablation was completely successful in 12 patients (92%), preexcitation recurred in one patient (8%) but non had recurrence of supraventricular tachycardia. The two patients who had atrioventricular nodal tachycardia were completely cured of recurrent supraventricular tachycardia and had normal atrioventricular conduction. In the ventricular tachycardia group, one was cured with no recurrence of tachycardia, is not on medication and is in New York Heart Association Class I status. The other died postoperatively of recurrent ventricular tachycardia and low cardiac output syndrome.

Adult↗