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Biomedical subjects

R M Allan

Publications and source records attributed to R M Allan.

18 recordsLinked to original sources
PubMed1998

Impact of an aggressive coronary stenting strategy on the incidence of target lesion revascularization.

Coronary stenting has been shown to reduce the incidence of target lesion revascularization (TLR) compared with balloon angioplasty in highly selected patients. However, the impact of an aggressive coronary stenting strategy in unselected patients on the overall incidence of TLR is unclear. We assessed the effect of increased stenting by comparing long-term results in consecutive patients who underwent successful percutaneous revascularization (with or without stents) during June to December 1995 (n=347) with those in June to December 1996 (n=401). Stents were used in 22.5% of patients in 1995 versus 66.1% in 1996 (p <0.0001). Mean age of the patients was 62+/-11 years (71% men) in 1995 versus 63+/-10 in 1996 (76% men) (p=NS). The 2 groups were well matched with the exception that the 1996 cohort included more patients with unstable coronary syndromes (25% in 1995 vs 34% in 1996 (p=0.003). There was no significant difference in the incidence of in-hospital adverse events. After 12 months of follow-up (complete in 95% of patients in each group), the incidence of TLR was significantly lower in the 1996 cohort than in the 1995 cohort (8.5% vs 14.7%, p=0.0075). This was mainly due to reduced requirement for repeat angioplasty in 1996 patients compared with 1995 (6.5% vs 11.8%, p=0.011). It is concluded that in an unselected patient population, an aggressive coronary stenting strategy was associated with a marked overall reduction in requirement for TLR over a 12-month period.

Aged↗
PubMed1998

Percutaneous transseptal mitral valvotomy--progress report.

BACKGROUND: Percutaneous transseptal mitral valvotomy (PTMV) has been established as an alternative to surgery in the treatment of mitral stenosis. AIM: To review our experience in the first 200 attempted PTMV procedures in patients with mitral stenosis, and the short and medium term follow-up. METHODS: PTMV was attempted on 200 occasions in 189 patients with significant mitral stenosis between May 1988 and May 1994. There were 156 females and 33 males, mean age 53.5 years (range 14 to 83 years). Six patients were pregnant at the time of the procedure. RESULTS: Valve split was achieved at the initial attempt in 183/189 procedures (97%). Clinical improvement of at least one New York Heart Association (NYHA) functional class was achieved in 172/189 patients (91%). The mean mitral valve gradient (mean +/- SD) decreased from 11.5 +/- 5.1 mmHg to 4.9 +/- 4.1 mmHg, mean cardiac output rose from 3.9 +/- 1.1 L/minute to 4.4 +/- 1.4 L/minute and mean calculated mitral valve area increased from 1.0 +/- 0.3 cm2 to 2.1 +/- 0.9 cm2. Ten patients developed clinically significant mitral incompetence requiring surgical mitral valve replacement. There were two transient cerebral embolic events. Small atrial septal defects were detected echocardiographically in 42 patients, but none has been a clinical problem. There were no early deaths; there were 11 late deaths, four of which were non-cardiac. Twenty patients have had repeat PTMV for re-stenosis, four to 67 months after the first. CONCLUSIONS: PTMV provides significant haemodynamic and clinical improvement with low risk and should be considered the treatment of choice in patients with mitral stenosis.

Adolescent↗
PubMed1996

Activated clotting time differential is a superior method of monitoring anticoagulation following coronary angioplasty.

The standard high-range activated clotting time (sHR ACT) is used to monitor anticoagulation postangioplasty (PTCA), but may be unreliable. We assessed the accuracy of a new method we termed the ACT differential (ACT Diff), obtained by measuring the difference between an sHR ACT and a heparinase ACT from the same sample. Heparinase removes heparin from its sample and provides a current heparin-free baseline. For phase 1 of the study, the sHR ACT, ACT Diff, and laboratory APTT were measured in 250 samples from 75 PTCA patients. In 125 samples with an APTT prolonged but within measurement range, linear regression against the APTT was performed. The correlation coefficient was 0.74 for the ACT Diff and 0.24 for the sHR ACT. An ACT Diff of 15-25 sec was found to equal an APTT of 2.5-3.5 x control. In 50 samples with a normal activated partial thromboplastin time (APT), there was good differentiation by the ACT Diff of results from those adequately heparinized, with a value of 0.9 +/- 4.4 sec. The sHR ACT was 114 +/- 15.5 sec, and could not reliably distinguish between anticoagulated and nonanticoagulated samples. In 75 samples obtained with a high APTT (above measurement range), the ACT Diff was > 30 sec in 95% of samples, and again this allowed differentiation from therapeutic samples. The equivalent sHR ACT was 148 sec, and could not reliably distinguish between anticoagulated and overanticoagulated samples as the ACT Diff could. In phase 2, to examine the clinical usefulness of the ACT Diff, 286 patients were managed post-PTCA by starting heparin when ACT Diff fell to < 50 sec, maintaining ACT Diff at 15-25 sec during heparin infusions, and following cessation of heparin, by removing sheaths when the ACT Diff was < 7 sec. These patients were compared to a control group of 250 patients. Major bleeding (5% vs. 0.5%, P < 0.005) and minor bleeding (30% vs. 13%, P < 0.001) were significantly reduced in the group managed using the ACT Diff. The reduction in bleeding was thought to be due to the rapid availability of reliable results. Abrupt closure was low in both groups (0% with ACT Diff vs. 0.8%). No other thrombotic events occurred. Following phases 1 and 2, the ACT Diff replaced the APTT in all PTCA patients at this institution. In the 18 mo from July 1993, 1,104 patients were managed this way. Incidence of major bleeding (0.2%), transfusion requirement (0.1%), false anneurysm (0.6%), and abrupt closure during heparin infusion (0.1%) remained low. In conclusion, the ACT Diff is more accurate than an sHR ACT, and its clinical use in PTCA patients is associated with a very low incidence of complications from anticoagulation. Its routine use should be considered by units unable to obtain rapid APTT results.

Adult↗
PubMed1994

Modifying fluoroscopic views reduces operator radiation exposure during coronary angioplasty.

OBJECTIVES: This three-part study examined the feasibility of reducing operator radiation exposure during coronary angioplasty. BACKGROUND: As case loads and complexity increase, some cardiologists are receiving increasing radiation scatter doses. Techniques to reduce this are therefore becoming more important. METHODS: First, the determinants of the operator dose were assessed by measuring the differences in scatter dose with different camera views. The relative contribution of fluoroscopy as opposed to cine was then quantified. Finally, operators were provided with these data, and subsequent changes in technique were evaluated. RESULTS: Left anterior oblique views resulted in 2.6 to 6.1 times the operator dose of equivalently angled right anterior oblique views. Increasing steepness of the left anterior oblique view also resulted in a progressive increase in operator dose, with left anterior oblique 90 degrees causing eight times the dose of left anterior oblique 30 degrees and three times that of left anterior oblique 60 degrees. In the 45 coronary angioplasty cases prospectively analyzed, fluoroscopy was found to be a greater source of total radiation than cine by a 6.3:1 ratio (range 1.1 to 15.8). Once operators were made aware of the importance of left anterior oblique fluoroscopy, there was a marked reduction in its use. When this was not feasible, there was a reduction in the steepness of the angulation. Left anterior oblique fluoroscopy during angioplasty of the left anterior descending and circumflex coronary arteries was reduced from 40% of total screening time to approximately 5%, and left anterior oblique angulation for fluoroscopy during angioplasty of the right coronary artery decreased from 43.6 degrees (+/- 9.1 degrees) to 29.4 degrees (+/- 2.2 degrees). Success rates (90% vs. 89%) and screening times (19.5 vs. 20.7 min) remained unchanged in 200 coronary angioplasties performed after the study. Average operator radiation dose (measured by radiation badges worn under lead at waist level) was reduced from 32.6 to 14.3 microSv/operator per week despite a slight increase in case load. CONCLUSIONS: Fluoroscopy is the major source of total radiation exposure during coronary angioplasty, with left anterior oblique views providing the highest dose. Modification of views is feasible and will result in significant reduction of operator radiation dose.

Angioplasty, Balloon↗
PubMed1992

Percutaneous aortic valvuloplasty.

OBJECTIVE: To determine the short-term and long-term results of percutaneous aortic valvuloplasty. DESIGN: A retrospective follow-up study. SETTING: The Cardiac Catheterisation Laboratory and Cardiovascular Medicine Unit of a teaching hospital. PATIENTS: Eighteen patients with severe aortic stenosis who were not accepted for surgery; there were 11 men and 7 women, mean age 79 +/- 4.5 years. INTERVENTIONS: Percutaneous transluminal aortic valvuloplasty (PTAV) by means of balloon catheter techniques. MAIN OUTCOME MEASURES: Patient survival and symptomatic status. RESULTS: PTAV resulted in a significant decrease in the aortic valve pressure gradient from 64.8 +/- 23.2 mmHg to 38 +/- 14.7 mmHg (mean +/- SD) (P less than 0.00001) in the 18 patients and a significant increase in the mean aortic valve area from 0.4 +/- 0.16 cm2 to 0.6 +/- 0.18 cm2 (P less than 0.0001) in 14 patients. Complications occurred in seven patients; two of them, who had been in terminal heart failure with a low output state before PTAV, died. Fifteen patients improved in at least one New York Heart Association functional class early after PTAV and one patient had an aortic valve replacement. In follow-up of between 5 and 32 months (mean, 13.3 +/- 7.7 months) six patients are in a better functional class than before PTAV, one patient is in Class IV, one patient had an aortic valve replacement and seven patients died (three died of cardiac failure and four of non-cardiac causes). CONCLUSIONS: PTAV has a place as a palliative procedure in selected patients with aortic stenosis in whom another condition precludes aortic valve replacement.

Aged↗
PubMed1990

Non-surgical mitral valvotomy.

Percutaneous transseptal mitral valvotomy was performed on 14 occasions in 13 patients; in one patient, the procedure was unsuccessful at the first attempt, but was repeated successfully. All other attempts were successful, giving a procedure success rate of 93% and a patient success rate of 100%. The only complication was transient diplopia in one patient, presumably due to a small cerebral embolus. This early experience confirms that this procedure is easily learnt, and can be performed with good results and low risk in selected patients with mitral stenosis.

Adult↗
PubMed1987

Regional extravascular density of the lung in patients with acute pulmonary edema.

The regional distribution of extravascular lung density (lung tissue and interstitial or alveolar fluid per unit thoracic volume) and fractional pulmonary blood volume (volume of blood per unit thoracic volume) was measured in five patients with acute interstitial pulmonary edema and two patients with acute alveolar edema. We found a uniform increase in extravascular lung density in the patients with acute interstitial edema but a preferentially dependent distribution in the patients with alveolar edema. Fractional blood volume had an abnormally uniform distribution in patients with interstitial edema. In alveolar edema, there was marked redistribution of blood volume away from severely edematous regions. The results are in agreement with previous experimental work with animal models. The distribution of extravascular lung density and fractional blood volume in subjects with acute interstitial edema is, however, different from that found in subjects with chronic interstitial edema, suggesting that the pathophysiological characteristics of the two conditions may be different.

Acute Disease↗
PubMed1984

Regional pulmonary blood volume in patients with abnormal blood pressure or flow in the pulmonary circulation.

We studied the effects of a chronic increase in flow and of chronic hypertension on regional pulmonary blood volume and extravascular lung density (lung tissue and interstitial water per unit thoracic volume) in one group of patients with intracardiac, left-to-right shunt and in another group with Eisenmenger's syndrome or primary pulmonary hypertension. We used positron computerized tomography to measure regional lung density (transmission scans) and blood volume (labelling with 11CO). The distribution of pulmonary blood volume was more uniform in patients with a chronic increase in pulmonary blood flow than in normal subjects. There were also indications of an absolute increase in intrapulmonary blood volume. In patients with chronic pulmonary arterial hypertension, the regional distribution of blood volume was abnormally uniform, but there were no indications of substantial abnormalities in overall intrapulmonary blood volume.

Adolescent↗
PubMed1983

Regional extravascular lung density and fractional pulmonary blood volume in patients with chronic pulmonary venous hypertension.

Using a technique based on positron transmission and emission tomography, we measured regional extravascular lung density (lung tissue and interstitial water per unit thoracic volume) and fractional pulmonary blood volume (volume of blood per unit thoracic volume) in normal subjects and in patients with cardiomyopathy and chronic pulmonary venous hypertension. We found an increase in extravascular lung density in the patients. Extravascular density was increased in all parts of the lung studied, but higher values were seen in the dorsocaudal portion than in the ventrocaudal portion of the lung (average 151% and 130% of normal, respectively). Fractional blood volume was markedly reduced in the dorsocaudal part of the lung (mean 74% of normal). The increase in extravascular density probably reflects structural changes in the lung as well as accumulation of interstitial fluid. The distribution of extravascular density is consistent with previous radiological and morphological studies, and may reflect a higher tendency to oedema formation in the dependent parts of the lung. The measurements of fractional blood volume suggest that intrapulmonary blood volume is reduced in chronic pulmonary venous hypertension. This may reflect a decrease in the distensibility of the pulmonary vessels due to structural abnormalities, as well as functional changes in the pulmonary vasculature.

Adult↗
PubMed1982

Relation between regional myocardial uptake of rubidium-82 and perfusion: absolute reduction of cation uptake in ischemia.

Experiments were undertaken using rubidium-82 and position tomography to examine the relation between myocardial perfusion and cation uptake during acute ischemia. Rubidium-82 was repeatedly eluted from a strontium-82-rubidium-82 generator. In six dogs emission tomograms were used to measure the delivered arterial and myocardial concentrations at rest and after coronary stenosis, stress and ischemia. There was a poor overall relation between regional myocardial uptake and flow measured by microspheres and a large individual variability. Extraction of rubidium-82 was inversely related to flow. Significant regional reduction of cation uptake was detected in the tomograms when regional flow decreased by more than 35 percent. This reduction was significantly greater when ischemia was present. A small but significantly greater when ischemia was present. A small but significant decrease (33.0 +/- 9.1 percent, mean +/- standard deviation) in the myocardial uptake of rubidium-82 was detected only when flow was increased by more than 120 percent in relation to a control area after administration of dypiridamole. The technique using rubidum-82 and tomography was applied in five volunteers and five patients with angina pectoris and coronary artery disease. Myocardial tomograms recorded at rest and after exercise in the volunteers showed homogeneous uptake of cation in reproducible and repeatable scans. In contrast, the patients with coronary artery disease showed an absolute mean decrease of 36 +/- 14 percent in regional myocardial uptake of rubidium-82 after exercise. These abnormalities persisted in serial tomograms for more than 20 minutes after the symptoms and electrocardiographic signs of ischemia.

Adult↗
PubMed1982

Preparation of [1-11C]acetate--an agent for the study of myocardial metabolism by positron emission tomography.

A method of obtaining an injectable solution of acetate labelled in the carboxyl group with the short-lived positron-emitting radionuclide, 11C (t12 = 20.4 min), is described. In the method labelling is achieved via the carbonation of freshly prepared methylmagnesium bromide with 11C-labelled carbon dioxide produced by the 14N(p, alpha)11C nuclear reaction. The method is fast (20 min) and produces sterile, apyrogenic [1-11C]acetate in high radiochemical yield (72 +/- 12%) and in high specific activity (greater than 18.5 GBq/mumol: greater than 0.5 Ci/mumol). The radiochemical purity of the radiopharmaceutical was found to exceed 95% by thin layer and high pressure liquid chromatography. Evidence presented shows that [1-11C]acetate has considerable value as an agent for investigating myocardial metabolism by positron emission tomography.

Acetates↗
PubMed1982

Measurement of serum C-reactive protein concentration in myocardial ischaemia and infarction.

Serum C-reactive protein (CRP) and creatine kinase (CK) MB levels were measured prospectively in patients with definite myocardial infarction, patients with spontaneous or exercise-induced angina, subjects undergoing coronary arteriography, and patients with non-cardiac chest pain. All individuals with infarction developed raised CRP levels and there was a significant correlation between the peak CRP and CK MB values. The CRP, however, peaked around 50 hours after the onset of pain at a time when the CK MB, which peaked after about 15 hours, had already returned to normal. In 20 patients who recovered uneventfully, CRP levels fell, returning to normal about seven days after infarction in four cases who were followed to this point. In eight complicated cases, including four who died within the first 10 days, the CRP level remained high. Angina alone or coronary arteriography did not cause a rise in the CRP or CK MB concentrations. Increased CRP production is a non-specific response to tissue injury and raised CRP levels in cases of chest pain with a normal CK MB indicated a pathological process other than myocardial infarction. Regular monitoring of CRP levels may also assist in early recognition of intercurrent complications occurring after myocardial infarction.

Angina Pectoris↗
PubMed1980

Proteolysis of isolated mitochondria by myocardial lysosomal enzymes.

1. Solubilized mitochondria and lysosomal fractions were obtained from guinea-pig heart by differential centrifugation and selective membrane disruption. 2. Mitochondria incubated at 37 degrees C in the presence of lysosomal enzymes underwent proteolysis. The rate of protein degradation was inversely dependent on pH. 3. The use of proteinase inhibitors showed that at low pH the major enzyme involved in mitochondrial digestion was cathepsin D. 4. At neutral pH carboxyl proteinases were still active, but thiol proteinases accounted for most of the protein breakdown. 5. The role of lysosomal enzymes as mediators of mitochondrial damage in ischaemic myocardium is discussed.

Amino Acids↗
PubMed1979

An enzyme-immunoassay for myoglobin in human serum and urine. Method development, normal values and application to acute myocardial infarction.

An enzyme-immunoassay has been developed for the detection of myoglobin in human serum and urine which is specific, accurate, precise, and has a sensitivity of 3 ng/ml. When compared with radioimmunoassay, the enzyme-immunoassay gives markedly similar results. Sera from normal adults had a myoglobin concentration in the range 3-65 ng/ml, and 64% of the same group had detectable myoglobinuria (range 3-11.5 ng/ml). All of 8 patients with definite acute myocardial infarction had raised serum myoglobin levels (range 200-1125 ng/ml) either at admission or 4 h later. Myoglobin concentration returned to normal in 6 patients, and in the remaining 2 patients there was evidence of infarct extension. Urinary myoglobin excretion was variable. One patient with possible acute myocardial infarction had elevated serum myoglobin (413 ng/ml 4 h post admission) and 5 patients with no evidence of infarction had normal levels (15-53 ng/ml). The results suggest that detection of serum myoglobin by enzyme-immunoassay may be a valuable test in the early diagnosis of acute myocardial infarction.

Acute Disease↗