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C N Thomas

Publications and source records attributed to C N Thomas.

16 recordsLinked to original sources
PubMed2003

Provision of anaesthesia for porcine cardiac transplantation at the veterinary school in Trinidad and Tobago.

A successful heterotopic cardiac transplantation was performed between sibling female Yorkshire Juvenile swine. Adequate pre-medication with azaperone and a smooth induction were ensured for both pigs, which were anaesthetized simultaneously with sodium thiopentone followed by endotracheal intubation and intermittent positive pressure ventilation. Inhalation anaesthetic agents were used for maintenance, neuromuscular blockade was achieved with cisatracurium and both fentanyl and tramadol were used to provide analgesia. Invasive monitoring was used in both the donor and recipient. Central venous pressure (CVP) was maintained at > 10 cm H2O and mean arterial pressure (MAP) > 60 mmHg. Heparin was injected during the surgical dissection of the heart in the donor to prevent coronary thrombosis and prior to aortic side clamping for end-to-side anastomosis of the donor heart in the recipient abdomen. After transplantation, the cardiovascular parameters of the recipient showed a MAP of 85-105 mmHg and a CVP of 8-10 cm H2O while echocardiography of the transplanted heart confirmed an ejection fraction (EF) of 80%. A functional anaesthetic team was assembled and trained to provide anaesthesia for porcine cardiac transplantation. The transplanted heart suffered pump failure after 69 days and was excised for performance of tissue analysis.

Anesthesia, General↗
PubMed2002

Bioaccumulation, elimination, and tissue distribution of chlorpyrifos by red hybrid Tilapia in fresh and brackish waters.

Bioaccumulation, degradation, elimination and tissue partitioning of chlorpyrifos (Dursban 25E) was studied under static conditions for 3-4 days, in fresh (FW) and brackish (BW) waters by two methods: in the renewal method, fish were transferred every 24 h to FW or BW aquaria containing 0.05 mg l(-1) of the insecticide; in the spiking method, the original concentration of 0.005 mg l(-1) was spiked every 8 h. Samples of fish and water were collected at regular intervals and residues determined gas chromatographically. In the renewal experiments with 0.05 mg l(-1), bioconcentration reached its peak within 8 h of exposure in FW (1.25 mg l(-1)) and within 1 h in BW (0.95 mg g(-1)); in spiking experiments with 0.005 mg l(-1), these peaks were attained in 48 h in FW (3.8 mg g(-1)) and 8-24 h in BW (1.67 mg g(-1)). Thereafter, the concentrations declined. The concentrations of an unidentified metabolite were generally but not always correlated with that of the parent compound. Upon exposure of contaminated fish to uncontaminated waters, 72% was eliminated within the first 12 h and 4% later in 60 h in FW, and only 23% in 1 h and another 21% in the following 60 h in BW. Concentration of the metabolite was very high during the elimination. In the renewal experiment with 0.05 mg l(-1) of chlorpyrifos, tissue distribution was much higher in FW than in BW, while the reverse was true in spiking experiments with 0.005 mg l(-1) of the chemical. Testis, heart and brain had the highest levels of residues, followed by ovaries and other tissues.

Animals↗
PubMed2002

The initial Trinidad experience with Cine MRI in clinical cardiology.

We describe the initial Trinidad experience with Magnetic Resonance Imaging (MRI) and Cine MRI as a diagnostic tool in clinical cardiology. Six patients from the following categories were referred for Cine MRI evaluation: congenital heart disease, valvular heart disease, aortic diseases, cardiomyopathy and intracardiac mass. All patients underwent echocardiography. MRI and Cine MRI were performed on all patients using a Siemens Magnetom 1.0 Tesla MR system at MRI Trinidad and Tobago Ltd. Selected patients underwent Angiography and/or computed tomography (CT) scanning. Clinical data and images of the six patients evaluated are described. MRI and Cine MRI provided excellent anatomical and functional details of the heart and aorta in five patients with dissection of the aorta, aneurysm of the ascending aorta, suspected left ventricular apical thrombus, infiltrative cardiomyopathy and arrhythmogenic right ventricular dysplasia. Technical difficulty was experienced with one patient who had a congenital defect (common atrium). In this study, Cine MRI provided excellent images in all but one patient. This new noninvasive technique enhanced diagnostic capabilities and facilitated management in patients with certain cardiovascular diseases.

Adult↗
PubMed2001

Stenting of partial and total coronary occlusions in Trinidad and Tobago.

In order to evaluate the efficacy and safety of coronary stenting, we reviewed the first 32 consecutive patients (34 vessels) who underwent elective coronary stenting during the period August 1999 to August 2000 inclusive at the Digital Lab installed at the Eric Williams Medical Sciences Complex, Trinidad and Tobago. Aspirin, heparin and ticlopidine were used routinely. Abciximab was used in selected cases (38%). The mean age of patients was 55 +/- 10 years. Eighty-one per cent were male, 52% were hypertensive and 21% were diabetic. Sixty-five per cent had severe angina. Prior Coronary Artery Bypass Grafting (CABG) was performed in 3% and previous Percutaneous Transluminal Coronary Angioplasty (PTCA) in 3%. Multivessel disease was present in 43%. The mean left ventricular ejection fraction was 53 +/- 12%. The culprit lesion was located in either the native left anterior descending (LAD) coronary artery (53%), right coronary artery (RCA) (31%), circumflex artery 13% and saphenous vein graft (3%). The mean baseline diameter stenosis was 91 +/- 9% and this was reduced to 13 +/- 33% after stenting. Procedural success was 100% for 26 partially occluded vs 50% for 8 totally occluded vessels. For the total occlusions, procedural success was inversely related to the duration of the occlusion. There were no cases of death, acute vessel closure, Q-wave myocardial infarction, repeat PTCA or emergent Coronary Artery Bypass Graft (CABG) during and following the procedure. Distal embolization occurred in one patient. The mean duration of hospital stay was one day (for 30 outpatient cases). One patient had recurrence of symptoms with a negative stress test. No patient underwent repeat angiography during the first year of follow-up. Coronary stents were successfully implanted at a tertiary care facility in the Caribbean with low in-hospital morbidity and mortality. Stents markedly reduced the diameter stenosis of the coronary lesion during PTCA. The incidence of clinical restenosis was low. Coronary revascularisation can be successfully achieved by coronary stenting in the Caribbean.

Angioplasty, Balloon, Coronary↗
PubMed2000

Two-year mortality and its determinants following acute myocardial infarction in Trinidad and Tobago.

The purpose of this study was to determine the occurrence of coronary artery disease risk factors in patients presenting with acute myocardial infarction (AMI) to a tertiary care institution in Trinidad and to determine the factors associated with increased mortality following AMI. All patients admitted to the Eric Williams Medical Sciences Complex (EWMSC) between January 1 and December 31, 1996, with a diagnosis of AMI were identified using the hospital admissions and discharge diagnosis databases. Demographic, clinical and laboratory variables were extracted from the hospital case records of patients with confirmed AMI. Sixty-one AMI patients (38 men) were admitted during the study period. Mean age at admission was 60 +/- 11 years with an ethnic case mix of thirty-nine (62%) of East Indian descent, eight (13%) of African descent, twelve (20%) mixed ethnicity and three (5%) of Caucasian descent. Thirty patients (49%) were hypertensive. Thirty-two patients (53%) were diabetic and eighteen patients (30%) gave a history of cigarette smoking. The mean left ventricular ejection fraction was 53 +/- 14%. The mean serum cholesterol from 29 patients was 228.2 +/- 49.0 mg/dl. Increasing age, female gender, an ejection fraction less than 40%, non treatment with streptokinase and in-hospital ventricular fibrillation were associated with poor survival. Multiple regression analyses identified three independent predictors of mortality. These were gender (p = 0.04), in-hospital ventricular fibrillation (p = 0.001) and an ejection fraction less than 40% (p = 0.02). Diabetes mellitus, hypertension, hyperlipidaemia and cigarette smoking were prevalent amongst patients presenting with AMI. Ventricular function was a major determinant of two-year mortality following AMI. Aggressive risk factor modification is recommended to prevent both first and recurrent coronary events.

Adult↗
PubMed2000

The feasibility of a porcine model of acute coronary occlusion and reperfusion using off-pump coronary artery bypass grafting.

We developed an open-chest porcine model of acute coronary occlusion and surgical reperfusion, and attempted to prevent intra-operative ischaemic ventricular fibrillation (VF) by a Retrograde Intracoronary Glyceryl trinitrate (RIG) infusion into the occluded vessel. Five Yorkshire pigs (weight 50 +/- 1.1 kg), randomized into 3 groups, underwent median sternotomy under general anaesthesia. One pig (Group 1, control) underwent sternotomy and pericardiotomy only. Four pigs underwent acute left anterior descending (LAD) coronary occlusion. Two pigs were not reperfused (Group 2). Two pigs underwent surgical reperfusion (Group 3) via left internal mammary artery (LIMA) grafting to the LAD using the Off-Pump Coronary Artery Bypass (OPCAB) technique. Ischaemic injury was assessed using 7-lead electrocardiography (ECG) and transthoracic/epimyocardial echocardiography (ECHO). Group 1: transient intraoperative hypotension and VF occurred. Successful resuscitation and 10-week survival (until sacrifice) with normal left ventricular (LV) function was achieved. Group 2: there were ECG and ECHO evidence of acute LV ischaemic dysfunction in both pigs. The surviving pig had persistent anterior hypokinesis at 8 1/2 months. The other died intra-operatively following progressive ischaemic LV dysfunction despite resuscitative attempts. Group 3: the surviving pig had normal LV function at 8 months. Initial anterior LV akinesis normalized within 7 days. The other developed post-occlusion haemodynamic instability and died intra-operatively despite reperfusion. In this porcine model, acute LAD artery occlusion modified by the novel RIG infusion technique, followed by surgical reperfusion (OPCAB) is feasible. This model would facilitate further development of OPCAB surgical expertise and understanding of the pathophysiology of ischaemia-reperfusion injury.

Animals↗
PubMed2000

Coronary artery bypass graft outcome: the Trinidad and Tobago experience.

The study is retrospective review of the demographic, clinical, angiographic, and operative data of the first 205 consecutive CABG operations performed by Caribbean Heart Care at the Eric Williams Medical Sciences Complex (EWMSC), Trinidad and Tobago, between November 1993 and December 1997. The aim of the study was to determine the in-hospital and intermediate-term follow-up results. The mean age of patients was 59 +/- 10 years and 78% were male. Sixty-four per cent were of East Indian descent, whereas 16% were of African descent. Forty-eight per cent of the patients were hypertensive, 46% were diabetic, 33% had hyperlipidaemia, 20% had a recent history of cigarette smoking and 16% were obese. Sixty-five per cent had a positive family history of ischaemic heart disease. The average time interval between angiography and surgery was 2.3 months. At the time of angiography, 63.5% of patients had Canadian Cardiac Society (CCS) class 3 or 4 angina. The mean ejection fraction was 61 +/- 15%. Wall motion abnormalities were seen in 67% of patients. Significant stenoses of the left anterior descending artery, right circumflex artery, circumflex and ramus coronary arteries were present in 91%, 78%, 54% and 5%, respectively. Many patients (67%) had severe diffuse disease on angiography. The mean intensive care stay was 2.2 +/- 0.8 days. In-hospital mortality was 3.9% (8/205). The most frequent post-operative complication was haemorrhage (2.6%). Acute renal failure occurred in 2.1%; pulmonary collapse, 1.6%; stroke, 1% and cardiac arrest, 1%. Both sternal wound infections and systemic sepsis occurred in 0.5%. Intermediate-term follow-up data were obtained for 92% (189/205). The duration of follow-up ranged from 1 to 5 years (mean 3.7 years). During the follow-up period, 7 patients (3.4%) died. Angina severity was reduced from a mean CCS score of 2.61 +/- 0.95 before CABG to 1.22 +/- 0.55 at the time of follow-up (p < 0.0001). Overall 4-year mortality compared favourably with data from international studies. Among survivors, quality of life improved as evidenced by the reduction in the mean angina score.

Angina Pectoris↗
PubMed1997

Inhibition of platelet deposition with local delivery of heparin using a double balloon catheter.

Heparin is an effective agent in the treatment of unstable angina and myocardial infarction. The clinical utility of heparin is limited by bleeding complications. This study was performed to determine whether static delivery of heparin could effectively inhibit further platelet deposition. Thrombogenic graft segments were incorporated into chronic arteriovenous shunts in pigs. Autologous platelets were labeled with 111Indium. Platelet deposition was quantitated with gamma camera imaging. The grafts were exposed to blood flow for 15 min in order to induce platelet deposition on the thrombogenic surface. Heparin was delivered locally either by direct exposure or with a double balloon catheter. After a 15 minute exposure period, the heparin solution was removed and subsequent platelet deposition was monitored for 90 minutes. Heparin, administered with the double balloon catheter in doses as low as 12.5 U, effectively inhibited further platelet deposition. An intravenous injection of 100 U of heparin, the highest dose use for local delivery, did not perturb bleeding time or the activated partial thromboplastin time. In conclusion, platelet deposition can be inhibited with static local delivery of heparin at doses that are not associated with systemic bleeding.

Animals↗
PubMed1996

"Bailout" coronary stenting in patients with a recent myocardial infarction.

Patients who underwent bailout intracoronary stenting within 7 days of a myocardial infarction had lower clinical and angiographic success rates and a higher incidence of emergent coronary artery bypass graft surgery than patients who underwent bailout stenting without a history of a recent myocardial infarction. In addition, there was a trend toward more cardiac events after discharge in patients who received stents after a recent myocardial infarction.

Aged↗
PubMed1996

Local intracoronary heparin delivery with a microporous balloon catheter.

Arterial thrombosis plays a major role in the pathogenesis of acute coronary syndromes such as unstable angina and acute myocardial infarction. Heparin is efficacious in treating both disorders; however, systemically administered heparin is associated with bleeding complications. Local intracoronary delivery of heparin may be a safer, more effective method of administration. This study was performed to determine the fate of heparin infused with a specially designed catheter for local intracoronary delivery. To quantitate heparin delivery, tritiated-labeled heparin was dissolved in a solution of unlabeled heparin (1,000 U/ml). A microporous balloon catheter was placed in the left anterior descending (LAD) and left circumflex arteries of anesthetized pigs (n = 15), and 1 ml of the heparin solution was infused. The animals were euthanized within 1 hour, and the treated arteries and controls were harvested, processed, and the tritiated activity was measured. To assess the distribution of the heparin in the arterial wall, 1 ml of fluorescein-isothiocyanate (FITC)-labeled heparin was locally delivered into the walls of the LAD and left circumflex arteries with the microporous balloon catheter. To visualize the dynamic fluid transfer of the device, a microporous balloon catheter was inflated in the LAD, and 1 ml of diluted contrast medium was infused under cinefluoroscopy. The arteries treated with tritiated-labeled heparin contained 0.6% +/- 0.2% of the infused heparin dose. Control arteries contained 0.01% of the administered heparin. Animals that were infused with FITC-labeled heparin displayed fluorescence throughout all layers of the artery, especially in the adventitia. In animals that were injected with 1 ml of diluted contrast medium through the microporous balloon, a relatively large amount of the infusate appeared in the arterial lumen proximal to the balloon. In conclusion, these results suggest that heparin can be delivered to coronary arteries with a microporous balloon catheter. However, <1% of the infused dose can be found in the artery 1 hour after delivery. Infused heparin is distributed throughout the arterial wall, but most of the infused solution appears in the arterial lumen proximal to the inflated balloon and is probably washed downstream after balloon deflation.

Animals↗
PubMed1995

Inhibition of platelet-dependent thrombosis by local delivery of heparin with a hydrogel-coated balloon.

BACKGROUND: Systemic administration of heparin can decrease mortality and morbidity of acute ischemic coronary syndromes such as unstable angina and myocardial infarction. Hemorrhage is the major limiting factor in the clinical use of systemic heparin. The objective of the present study was to determine whether local delivery of heparin could inhibit platelet-dependent thrombosis without altering systemic bleeding parameters. METHODS AND RESULTS: Hydrogel-coated angioplasty balloon catheters were dipped in a heparin solution, dried, and applied to a platelet-rich mural thrombus in a chronic ex vivo porcine arteriovenous shunt. 111In-labeled platelet deposition was quantified by gamma camera imaging. In a separate series of experiments, 3H-heparin was used to estimate the amount of heparin delivered to the thrombus with the coated balloon. Systemic heparin administration produced a dose-dependent decrease in platelet-dependent thrombus formation that was maximal at 200 units/kg. Bleeding times and activated partial thromboplastin times were prolonged at this dose. An equal inhibition of thrombus formation was achieved after the coated balloon was dipped in a heparin solution (10,000 units/mL) and deployed at the mural thrombus. In contrast to systemic heparin administration, there was no alteration in bleeding parameters associated with local heparin delivery. The estimated amount of heparin delivered with the coated balloon was 40 units. CONCLUSIONS: Local delivery of heparin in amounts sufficient to inhibit platelet-dependent thrombosis can be accomplished with a hydrogel-coated coronary angioplasty balloon catheter. Local heparin delivery can inhibit thrombus formation in amounts that are several orders of magnitude lower than the required systemic dose. Local delivery of heparin was not associated with prolongation of bleeding parameters.

Acrylic Resins↗
PubMed1995

Comparison of the thrombogenicity of stainless steel and tantalum coronary stents.

This study was designed to compare the thrombogenicity of stainless steel and tantalum coronary stents of the same design. Stainless steel and tantalum coronary stents are being evaluated for their utility in treating acute closure and restenosis. A major disadvantage of stainless steel stents is radiolucency. To determine whether radioopaque tantalum stents may be safely substituted for stainless steel stents, we compared the relative thrombogenicity of these materials in stents of identical design. Total platelet and fibrin deposition on the stents were determined from measurements of indium 111-labeled platelet and iodine 125-labeled fibrinogen accumulation after deployment into exteriorized chronic arteriovenous shunts in seven untreated baboons. In another series of experiments, 111In-platelet deposition was compared 2 hours after stent implantation in coronary arteries of pigs. In baboons, platelet thrombus formation on stainless steel and tantalum stents was equivalent and plateaued at approximately 2.5 x 10(9) platelets after 1 hour (p > 0.05). Fibrin deposition averaged approximately 1 mg/stent and did not differ between the stainless steel and tantalum stents (p > 0.05). In the porcine coronary model there was no significant difference in 111In-labeled platelet deposition between the stainless steel and tantalum stents (p > 0.05). This result was confirmed by scanning electron microscopic analysis of the coronary stents. Based on these two models, we conclude that there is no significant difference in the thrombogenicity of stainless steel and tantalum wire coil stents.

Animals↗
PubMed1976

Propranolol as primary therapy for thyrotoxicosis.

It has been suggested that propranolol hydrochloride alone is effective in the treatment of thyrotoxicosis. To test this hypothesis, eight mildly thyrotoxic individuals were prospectively studied for an average of eight months, during which propranolol alone was administered and thyroid function tests, cardiac systolic time intervals, and body densities were sequentially measured. Two patients became euthyroid. The others had adequate but incomplete symptomatic control. Weight loss was not corrected, but no changes in lean body mass were induced. The augmented myocardial contractility of thyrotoxicosis, as determined by systolic time intervals, improved but failed to return completely to normal. Thus, systolic time intervals are a practical means of following the peripheral response to chronic beta-adrenergic blockage in thyrotoxic patients. However, these observations do not support the use of propranolol alone as the first choice of therapy for thyrotoxicosis.

Adult↗