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Biomedical subjects

A C Tweddel

Publications and source records attributed to A C Tweddel.

18 recordsLinked to original sources
PubMed1992

A comparison of maximal exercise and dipyridamole thallium-201 planar gated scintigraphy.

Both symptom-limited maximal exercise and intravenously given dipyridamole stress (0.56 mg/kg over 4 min with a 2 min walk) gated thallium scans were performed in 22 patients undergoing coronary arteriography for the assessment of chest pain. All scans were acquired gated to the electrocardiogram in 3 projections and were reported for the presence and extent of defects in 5 myocardial segments in each view. In addition, left and right ventricular myocardial uptake and estimates of right and left lung and liver to left ventricular uptake were assessed relative to the injected dose of thallium-201. Overall, 190/310 segments were abnormal with exercise compared with 169/310 with dipyridamole. Segments were scored greater in extent in 90/310 cases with exercise, compared with 46/310 in which the defect was more extensive with dipyridamole (P less than 0.0005). Non-attenuation corrected percentage myocardial thallium uptakes were similar for both stresses: anterior percentage uptakes, 0.785% +/- 0.230% with exercise versus 0.870% +/- 0.217% with dipyridamole (NSD). Left and right lung and liver to left ventricle ratios were all significantly higher with dipyridamole than with exercise (1.587 +/- 0.408 versus 1.446 +/- 0.518, P less than 0.02; 1.78 +/- 0.479 versus 1.46 +/- 0.502, P less than 0.002; 2.598 +/- 0.788 versus 1.265 +/- 0.386, P less than 0.001, respectively). High right and left lung uptakes with dipyridamole were strongly correlated with high exercise values (r = 0.756, P less than 0.001; r = 0.809, P less than 0.001). The liver uptake was weakly correlated between the 2 different stress tests (r = 0.483, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The influence of arm position and cardiac output on bolus clearance from the arm.

The importance of arm position and cardiac output on the clearance of a bolus injection from the arm was assessed in 63 patients using technetium-99m. Injections were made in the left arm which was either adducted, abducted or adducted with the forearm flexed over the lower chest. The clearance of isotope was assessed by measuring the amount of radioactivity remaining in the arm at 10 s intervals and calculating it as a fraction of the injected dose. The clearance of Tc-99m was significantly faster and more complete from the abducted arm than from the adducted arm. There was no correlation between clearance and cardiac output.

Arm↗
PubMed1992

Symptomatic and silent myocardial ischaemia in hypertensive patients with left ventricular hypertrophy.

OBJECTIVE: To assess the prevalence of symptomatic and silent myocardial ischaemia in patients with hypertensive left ventricular hypertrophy. DESIGN: Cross sectional study. SETTING: University department of medical cardiology. PATIENTS: 90 patients (68 men and 22 women; mean age 57 (range 25 to 79)) with left ventricular hypertrophy due to essential hypertension. INTERVENTIONS: 48 hour ambulatory ST segment monitoring (all patients), exercise electrocardiography (n = 79), stress thallium scintigraphy (n = 80), coronary arteriography (n = 35). RESULTS: 43 patients had at least one episode of ST segment depression on ambulatory electrocardiographic monitoring. The median number of episodes was 16 (range 1 to 84) with a median duration of 8.6 (range 2 to 17) min. Over 90% of these episodes were clinically silent. 26 patients had positive exercise electrocardiography and 48 patients had reversible thallium perfusion defects despite chest pain during exercise in only five patients. 18 of the 35 patients who had coronary arteriography had important coronary artery disease. Seven of these patients gave no history of chest pain. CONCLUSIONS: Symptomatic and silent myocardial ischaemia are common in hypertensive patients with left ventricular hypertrophy, even in the absence of epicardial coronary artery disease.

Adult↗
PubMed1992

Thallium scans in syndrome X.

OBJECTIVE: To review thallium scans in patients with angina and normal coronary arteriograms. DESIGN: Retrospective review of data. SETTING: Regional cardiac centre in Glasgow. PATIENTS: 100 patients selected from those undergoing diagnostic angiography for typical angina who had normal arteriograms (around 10%), no other cardiovascular abnormality, and available thallium scans (performed routinely before angiography). MAIN OUTCOME MEASURES: Coronary arteriography, exercise tests, and gated thallium scans at peak exercise. RESULTS: The exercise test was positive in 30 and negative in 70 patients. Thallium defects were found in 98 patients, but no consistent pattern and no significant correlation existed between the extent of thallium defect and positive exercise test or exercise tolerance. CONCLUSIONS: Thallium defects described in 98 of 100 patients with angina and normal coronary arteriograms suggest that microvascular angina may be commoner than is generally appreciated.

Adult↗
PubMed1992

Balanced triple-vessel disease: enhanced detection by estimated myocardial thallium uptake.

Maximal stress thallium scans may prove to be 'normal' in some patients with triple-vessel disease due to global reduction in flow resulting in no focal perfusion defect. The aim of this study was to attempt to identify patients with global reduction in flow by estimating total thallium delivery to the left ventricle. Myocardial thallium uptake was calculated as a percentage of injected dose as a mean of three projections in 90 patients undergoing diagnostic arteriography and in 10 normal volunteers. These volunteers and nine patients who proved to have normal coronary arteries established a normal range. Values for myocardial thallium uptake were: 1.166 +/- 0.352% in normals (n = 19); 0.671 +/- 0.184% in patients with single- or double-vessel disease (n = 26); 0.708 +/- 0.245% in patients with triple-vessel disease (n = 55). Thallium scans were normal in 11 of 55 patients with triple-vessel disease and eight of 26 with single- or double-vessel disease. However, eight of these 11 and 5 of the eight proved to have abnormal myocardial thallium uptake. Thus combining the tests improved sensitivity from 76.5% for the scan alone to 94.5% for the scan and myocardial thallium uptake, with no reduction in specificity. Measurement of myocardial thallium uptake is a readily and reliably quantified parameter from a thallium scan which leads to enhanced detection of coronary artery disease.

Adult↗
PubMed1989

Improved detection of coronary artery disease by estimated myocardial thallium uptake.

Myocardial thallium uptake has been assessed at the time of thallium scanning in a group of 50 male patients undergoing coronary arteriography and 10 young healthy volunteers. The net thallium dose injected was obtained by counting the dose prior to injection using the gamma camera and counting the syringe and IV cannula after injection. Significantly higher levels of myocardial thallium uptake were obtained in both the volunteers and patients with normal coronary anatomy (1.36% +/- 0.32%, n = 10 and 0.93% +/- 0.26%, n = 9, respectively) compared to patients with single, double or triple vessel coronary artery disease (0.63% +/- 0.19%, n = 11; 0.70% +/- 0.20%, n = 15; 0.67 +/- 0.18, n = 15, respectively). Exercise tests were positive in 46% of patients with coronary artery disease with an overall predictive accuracy of 56%. Thallium scans were positive in 68% of patients at a specificity of 89%. If the range of myocardial thallium uptake from the patients with normal coronary arteries is used to define a lower limit of normal, then the sensitivity of the thallium scan with thallium uptake is 90% with a predictive accuracy of 90% in the detection of significant coronary artery disease in this group of patients. Thus, estimation of total % thallium uptake is a simple index which yields useful diagnostic clinical information.

Adult↗
PubMed1989

An automated analysis technique for thallium images.

The use of stress thallium-201 scans in the non-invasive assessment of myocardial perfusion is well established, despite several reports of considerable inter-observer variability in the assessment of perfusion defects. By applying a simple statistical algorithm to a set of normal thallium images and using a well defined criterion of abnormality, the threshold of normality in these 'statistical images' was obtained for each of four projections. Subsequently a test set of images from both normal volunteers and patients with arteriographically documented coronary artery disease were reported using statistical images at four levels (70, 75, 80 and 85% of the mean of the hottest pixels) and standard thallium images viewed on the computer monitor in both colour and black and white. Significant reductions in the inter-observer disagreement and enhanced predictive accuracy in the detection of significant coronary artery disease were obtained using the statistical images. The technique described and assessed would permit the reporting of thallium scans at a preselected value of sensitivity and specificity depending on the requirements of the particular study. It could be readily implemented, after local validation, in any department performing thallium scans where the gamma camera is interfaced to a computer.

Adult↗
PubMed1989

Perfusion imaging.

The term perfusion has varied connotations in different situations. The word perfusion comes from the Latin to pour or diffuse through or over. Myocardial perfusion depends on (a) coronary artery or vessel flow, and (b) myocardial or muscle flow. The factors which determine perfusion at rest and during stress in coronary vessels and within the myocardium are clearly related but not with a predictable linear relationship. In animals there is extensive literature concerning the regulation of coronary flow and perfusion obtained by many sophisticated methods. In contrast, the techniques that are applicable to humans are relatively crude. To date, the clinical data available suggests that the normal control of coronary flow in man and in dogs is fairly similar but that models of pathology in animals bear little relation to the compensatory changes found in the coronary circulation in man. Although the data available is limited and subject to many technical inaccuracies, this article is confined to the assessment of myocardial perfusion in clinical practice.

Coronary Circulation↗
PubMed1988

Sustained haemodynamic effects of felodipine in patients with chronic cardiac failure.

1. The efficacy of felodipine a new calcium channel blocker with selective vasodilator activity in the management of severe low output cardiac failure, secondary to coronary heart disease, was determined in 10 patients. 2. Haemodynamic measurements were made at rest and during dynamic exercise and left ventricular function was assessed by radionuclide ventriculography. 3. Significant increases in cardiac index, stroke volume index and ejection fraction were found particularly during exercise, both acutely and following 4 weeks administration of felodipine therapy. 4. Felodipine could well have a significant role in the long term management of the patient with chronic cardiac failure.

Adult↗
PubMed1987

Gated thallium scintigraphy in patients with coronary artery disease: an improved planar imaging technique.

The use of thallium scanning in the assessment of myocardial perfusion is well established. However, myocardial contraction leads to significant blurring of standard static images. By using electrocardiographic gating and a high sensitivity collimator, multiple view gated scans can be acquired prior to thallium redistribution. Reporting of these images on cine loop display in 100 consecutive patients undergoing coronary arteriography and 14 volunteers results in improved visual assessment of regional myocardial perfusion (with reduced interobserver variability) and, in addition, yields useful and accurate information on left ventricular function. The combination of better assessment of perfusion and information on wall motion results in improved detection of patients with significant coronary disease with no loss of specificity when compared with static images. Predictive accuracy improves from 85% to 94% with gated imaging. Gated thallium scanning could be readily applied in most centres using thallium at no extra cost and with improved predictive accuracy in the non-invasive detection of significant coronary disease.

Coronary Disease↗
PubMed1987

A comparison of intravenous elantan and frusemide in patients with chronic cardiac failure.

Opiates and loop diuretics are the mainstay of treatment of acute pulmonary oedema, but it is now recognized that immediate response to intravenous loop diuretics is acute vasoconstriction with impaired cardiac performance. It therefore seemed appropriate to compare the effects of intravenous isosorbide 5-mononitrate and frusemide on systemic and coronary haemodynamics in a group of patients with chronic cardiac failure at cardiac catheterization. Intra-arterial blood pressure was recorded from the ascending aorta, pulmonary capillary wedge pressure and cardiac output were measured using a Swan-Ganz thermodilution catheter. Coronary venous blood flow was measured using a thermodilution technique and A-V oxygen difference across the myocardium was obtained from simultaneous blood sampling in the aorta and coronary sinus. Absolute myocardial nutrient blood flow was measured using a 133Xe clearance technique. Frusemide in a dosage of 0.5 mg/kg given intravenously provoked acute vasoconstriction with falls in cardiac output and stroke volume. Pulmonary capillary wedge pressure was unchanged in the first 60 min after administration of frusemide. Isosorbide 5-mononitrate in a dosage of 15 mg intravenously, significantly reduced the pulmonary capillary wedge pressure within 5 min, and with the subsequent fall in systolic arterial blood pressure, cardiac output was maintained. These results suggest that intravenous isosorbide 5-mononitrate could well be of value in the immediate management of the patient with acute pulmonary oedema.

Blood Pressure↗
PubMed1987

Calcium channel blocker and isosorbide 5-mononitrate in the management of chronic cardiac failure.

In the management of the patient with chronic cardiac failure, the combination of an arteriolar vasodilator and venodilator should be beneficial. 8 patients with NYHA grade III-IV chronic cardiac failure were studied following placebo, after 4 weeks' therapy with the arteriolar vasodilator felodipine, and with the combination of felodipine and oral isosorbide 5-mononitrate. Haemodynamic measurements were made at rest and during dynamic exercise at an individual, fixed, near maximal workload. Ejection fraction (EF) was obtained by gated radionuclide ventriculography. At rest, heart rate was unchanged 73 +/- 6 at control, 72 +/- 4 with felodipine and 74 +/- 4 beats/min with the addition of isosorbide 5-mononitrate. Mean arterial pressure fell from 98 +/- 5 to 84 +/- 4 (p less than 0.02) and 84 +/- 3 mm Hg (p less than 0.02) with nitrate. Cardiac index increased from 2.2 +/- 0.1 to 2.5 +/- 0.2 litres/min/m2 with felodipine and further to 2.6 +/- 0.2 litres/min/m2 (p less than 0.02) with nitrate. Exercise tachycardia and mean arterial pressure were not significantly affected by therapy. Cardiac index increased on exercise from 4.4 +/- 0.3 to 4.8 +/- 0.3 litres/min/m2 with felodipine and 4.9 +/- 0.3 litres/min/m2 (p less than 0.05) with the addition of nitrate. Stroke volume index increased from 35.4 +/- 4 to 40.8 +/- 4 beats/min/m2 and further to 41.0 +/- 4 beats/min/m2 (p less than 0.05) and EF from 14 +/- 3 to 18 +/- 3% with nitrate. In conclusion, in patients with chronic cardiac failure, treatment with a calcium channel blocker produced sustained haemodynamic improvement, particularly on exercise, and combination with nitrate produced further benefit.

Chronic Disease↗
PubMed1986

Gated xenon scans for right ventricular function.

The complex geometry of the right ventricle makes the use of radionuclides an attractive method for assessing right ventricular function. The use of the gated 133Xe technique for this purpose offers several advantages. A short i.v. infusion over 20 sec of 133Xe permits scans to be obtained, gated to the electrocardiogram at rest and during maximal exercise using a standard gamma camera. The method is both reproducible (3.5%) and repeatable (2.8%), and because of the short half-life within the patient with most of the radioisotope being excreted by the lungs, scans may be repeated within a few minutes and the radiation dose to the patient is small. Right ventricular ejection fraction obtained from gated xenon scans is shown to correlate well with measurements obtained from both standard gated technetium scans and first-pass studies.

Female↗
PubMedDate not supplied

The potential impact of patient self-referral on mortality in acute myocardial infarction.

Audit is now an important component of the provision of acute cardiology services. In particular, the desire to administer thrombolytic treatment early in acute myocardial infarction has led to a reappraisal of admission procedures. Using records collected prospectively onto a computerized coronary care database for 36 months to December 1991, median delay before arrival at the emergency department and delay between admission and thrombolytic treatment was calculated. Of 1993 consecutive admissions to the coronary care unit, 816 patients had an initial diagnosis of myocardial infarction (later confirmed in 89.6 per cent), and 608 (74.5 per cent) of these received thrombolytic treatment. Overall median delay before arrival at hospital was 147 min. Randomization during the ISIS-3 trial significantly prolonged delays after arrival at hospital (64 vs. 50 min; p < 0.007). General practitioner referral delayed arrival at the emergency department (175 vs. 100 min self-referred; p < 0.0001) and was associated with similar hospital delay (54 vs. 55 min self-referred). Older patients ( > 65 years) presented later in the self-referred group (120 vs. 99 min for age < 65 years; p < 0.04), but there was no difference in the GP-referred group. Previous ischaemic heart disease did not predict type of referral. If delays before thrombolytic treatment are to be reduced significantly patients should be encouraged to seek early medical assistance by telephoning for an ambulance. Delays for patients arriving at the hospital following referral by a GP should be reduced by facilities for direct admission to the cardiologist.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗