Myocardial perfusion scintigraphy: the evidence.

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Fractal dimensions of laser doppler flowmetry time series.

Laser Doppler flowmetry (LDF) provides a non-invasive method of assessing cutaneous perfusion. As the microvasculature under the probe is not defined the measured flux cannot be given absolute units, but the technique has nevertheless proved valuable for assessing relative changes in perfusion in response to physiological stress. LDF signals normally show pronounced temporal variability, both as a consequence of the pulsatile nature of blood flow and local changes in dynamic vasomotor activity. The aim of the present study was to investigate the use of methods of nonlinear analysis in characterizing temporal fluctuations in LDF signals. Data were collected under standardised conditions from the forearm of 16 normal subjects at rest, during exercise and on recovery. Surrogate data was then generated from the original time series by phase randomization. Dispersional analysis demonstrated that the LDF data was fractal with two distinct scaling regions, thus allowing the calculation of a fractal dimension which decreased significantly from 1.23 +/- 0.09 to 1.04 +/- 0.02 during exercise. By contrast, dispersional analysis of the surrogate data showed no scaling region.

Adenosine provokes diastolic dysfunction in microvascular angina.

Adenosine stress echocardiography was performed in nine patients (58 (+/-3) years, eight women) with documented microvascular angina. Global ventricular function was assessed by Tc(99m) blood pool imaging and Doppler, whereas longitudinal ventricular function was assessed by simultaneous tissue Doppler echocardiography of the lateral mitral annulus. Adenosine was infused incrementally to onset of chest pain in all patients. There was no significant change in global or longitudinal systolic function. Adenosine induced global diastolic dysfunction, demonstrated by blood pool imaging and by Doppler of the transmitral flow. All patients had long axis diastolic dysfunction at peak adenosine, revealed by a ratio of early to late diastolic velocity of lateral mitral annulus <1, which was absent at rest. Adenosine, as a stress agent, provokes regional and global diastolic dysfunction in microvascular angina, which may be a consequence of subendocardial ischaemia. Long axis diastolic dysfunction can be easily revealed by tissue Doppler of the lateral annular motion.

Differentiation between pathologic and physiologic left ventricular hypertrophy by tissue Doppler assessment of long-axis function in patients with hypertrophic cardiomyopathy or systemic hypertension and in athletes.

To identify new echocardiographic indexes of long-axis function that might differentiate between pathologic and physiologic left ventricular (LV) hypertrophy, we compared 60 subjects with different types of LV hypertrophy (group I: 15 patients with hypertrophic cardiomyopathy, group II: 15 patients with systemic hypertension, and group III: 30 athletes) with 20 normal subjects (group IV). The peak velocities of mitral annular motion at 4 sites were measured from the apex by tissue Doppler echocardiography. There were no differences in mean age and global ejection fraction between groups. Groups I and II had lower long-axis systolic and early diastolic velocities than the athletes (p <0.01) for all 4 sites. The best differentiation of pathologic from physiologic hypertrophy was provided by a mean systolic annular velocity <9 cm/s (sensitivity 87%, specificity 97%). Heterogeneity of annular velocities discriminated between group I and group II. Thus, long-axis systolic and early diastolic velocities are decreased in patients with pathologic hypertrophy, but preserved in athletes. These simple new echocardiographic parameters can differentiate between pathologic and physiologic hypertrophy.

Relatively low red cell folate levels and acute coronary syndromes.

BACKGROUND: Low folate levels are related to increased risk for coronary artery disease in humans, while experimental work has shown that folate deficiency is thrombogenic. We hypothesized that relatively low folate levels are related to the development of acute coronary syndromes in patients with previously stable coronary artery disease. METHODS: One hundred and forty-one men were studied: 53 consecutive patients with acute coronary syndromes, 41 with stable coronary artery disease and 47 control participants. Known clinical and lipid risk factors were identified in all subjects and in addition plasma B12, plasma and red cell folate levels were measured. RESULTS: Red cell folate levels were significantly lower in patients with acute coronary syndromes (510+/-178 nmol/l) than in both stable coronary artery disease patients (638+/-264 nmol/l, P< 0.005) and controls (615+/-193 nmol/l, P< 0.05 respectively). Plasma folate and B12 levels were similar in all three groups. Multiple logistic regression analysis identified red cell folate levels as the only independent predictor of acute coronary events in the whole population of patients with known coronary artery disease and in the subgroup of non-smokers (P=0.010 and P=0.031). CONCLUSIONS: The present study suggests that relatively low red cell folate levels are associated with acute coronary syndromes and are an independent predictor of acute coronary events.

Nuclear cardiology in the UK: British Nuclear Cardiology Society survey 1994.

This study surveyed practice in nuclear cardiology in the UK in 1994. A questionnaire was sent to 219 centres performing nuclear imaging asking for details of current practice in nuclear cardiology. Replies were received from 192 centres (88%). Activity in performance of myocardial perfusion imaging (MPI) and radionuclide ventriculography (RNV), anticipated changes in activity, differences between regional and district general hospitals, technical imaging parameters and referral sources were surveyed. Of the responding centres, 125 (65%) performed nuclear cardiology. More regional centres (85 vs 55%, P < 0.0003) performed a higher proportion (62 vs 24%, P < 0.001) of nuclear cardiology activity compared with district general hospitals. Nuclear medicine activity was estimated at 9.3 scans/1000/year, of which 8.9% was cardiology (0.82/1000/year; MPI, 0.56/1000/year; RNV, 0.26/1000/year). A comparison with previous surveys showed a significant increase of 24% in nuclear cardiology since 1988, with a strong rise in MPI (350%); however, RNV has fallen by 47%. Myocardial perfusion activity in the UK remains very low (25 and 5% for MPI and RNV respectively) when compared with the average of 2.2/1000/year for Europe and 10.8/1000/year for the USA. In conclusion, MPI has increased on average by 23% per annum (compound rate) since 1988, but in 1994 was still only 32% of the British Cardiac Society target of 2.6 scans/1000/year. Proper resourcing for capital expenditure on new equipment and new staff will be important to maintain momentum in closing the gap. Also important is clinical understanding, as already implemented by including nuclear cardiology in guidelines for specialist cardiology training.

Nuclear cardiology in the UK 1994: activity relative to Europe, USA, and British Cardiac Society targets.

OBJECTIVE: To survey practice in nuclear cardiology in the UK in 1994. DESIGN: A questionnaire was sent to 219 centres performing nuclear imaging asking for details of current practice in nuclear cardiology. Replies were received from 192 centres (88%). MAIN OUTCOME MEASURES: Activity in performance of myocardial perfusion imaging (MPI) and radionuclide ventriculography (RNV), anticipated changes in activity, differences between regional and district hospitals, technical imaging parameters, and referral sources. RESULTS: Of the responding centres, 125 (65%) performed nuclear cardiology procedures. More regional than district hospitals performed nuclear cardiology procedures (85% v 55%, p < 0.0003) and regional centres performed a higher proportion (62% v 24%, p < 0.001) of nuclear cardiology activity. Nuclear cardiology activity was 0.82 scans per 1000 population per year (MPI 0.56, RNV 0.26). There has been a significant increase (24%) in nuclear cardiology since 1988. There has been a pronounced rise in MPI (350%) while RNV has fallen by 47%. Myocardial perfusion activity in the UK remains very low (25% and 5% in regional and district hospitals, respectively) compared with the 1994 figures of 2.2/1000/year for Europe or 10.8/1000/year for the USA. CONCLUSIONS: MPI has increased on average by 23%/annum (compound rate) since 1988, but in 1994 was still only 32% of the British Cardiac Society target of 2.6/1000/year. Proper resources for capital expenditure on new equipment and new staff will be important to maintain momentum in closing the gap. Also important is improved clinical understanding, as already implemented by including nuclear cardiology in guidelines for specialist cardiology training.

Syndrome X and endothelial dysfunction.

OBJECTIVE: Syndrome X (angina, normal coronary arteriogram and positive exercise test) remains an enigma with unexplained features and apparent conflicts of evidence. The present study addressed whether (i) the Syndrome is characterised by generalised flow-related endothelial dysfunction, (ii) myocardial thallium201 defects reflect myocardial or microvascular dysfunction, (iii) endothelial dysfunction and its consequences can be improved by oral L-arginine. METHODS: Flow-mediated brachial artery dilatation was measured by ultrasonic 'wall-tracking' in 7 Syndrome X patients, further characterised as having thallium201 defects and no known cause of endothelial dysfunction, and a normal control group. Syndrome X patients entered a 4-week randomised double-blind placebo-controlled cross-over trial of oral L-arginine (7 g twice daily), with brachial artery studies, exercise tests and technetium99 tetrafosmin scans. RESULTS: Flow-mediated dilatation was absent in Syndrome X vs. normal. Stress technetium99 tetrafosmin and thallium201 scans showed similar defects. Flow-mediated dilatation, symptom-limited exercise duration and peak oxygen consumption (VO2max) were increased but rate-pressure-product (RPP) and radionuclide defects were unchanged after L-arginine vs. placebo. CONCLUSIONS: The study supports coronary microvascular rather than myocardial dysfunction and shows loss of flow-mediated dilatation in systemic arteries. Oral L-arginine improved flow-mediated dilatation, exercise capacity and VO2max (by ca. 17%) despite unchanged RPP. The findings support generalised endothelial dysfunction. The arginine effects imply NO-mediated improvement of skeletal muscle perfusion suggesting improved homogeneity of microvascular distribution.

Small artery structural alterations of patients with microvascular angina (syndrome X).

1. There is increasing evidence that a substantial number of patients who suffer from angina have normal epicardial arteries (Syndrome X), and it has been suggested that these individuals have a generalized disorder of small vessels not confined to the intramyocardial vasculature. 2. Small arteries were therefore obtained from biopsies of skin and subcutaneous fat from nine normotensive patients with Syndrome X and nine matched control subjects. Vessels were dissected and mounted as ring preparations in a myograph for morphological and functional assessment. 3. Morphological measurements revealed a significant increase in media thickness/lumen diameter ratio in arteries from patients with Syndrome X. Contractile responses to U46619 were similar in arteries from patients and control subjects. Endothelium-dependent relaxation induced with acetylcholine and bradykinin was greater in arteries from patients although differences were not statistically significant. Endothelium-independent relaxation induced by forskolin and sodium nitroprusside was not different. 4. In conclusion, these data demonstrate that subcutaneous small arteries from patients with Syndrome X are characterized by increased media thickness/lumen diameter ratios, although contractile responses were normal. Additionally, endothelium-dependent relaxation was not impaired in arteries from these patients. Thus, no significant functional abnormalities were associated with the observed structural differences.

Quantification of extracorporeal white cell and platelet deposition in cardiopulmonary bypass: comparison of membrane and bubble oxygenators.

Cardiopulmonary bypass is known to activate both white cells and platelets. The aim of this study was to investigate whether the use of bubble and membrane oxygenators results in different degrees of deposition in the filter and oxygenator of the bypass circuit. Dual-isotope imaging techniques were employed, with white cells labelled with 99Tcm and platelets with 111In, and with subsequent imaging of the filters and oxygenators on a gamma camera fitted with a medium-energy, parallel-hole collimator, relative to a known standard. The percentage white cell oxygenator deposition ranged from 0.011 to 4.91% in the bubble group (n = 20) and was not different from the membrane group (0.001 to 4.22%). Similarly, no difference in platelet deposition was found, with 0.605-45.17% deposited in the bubble oxygenators and 0.001-15.26% deposited in the membrane oxygenators. Filter deposition of both types of cell was substantially lower in both membrane and bubble groups with no difference between groups. The striking feature of the data is the non-normal distribution of the deposition in both types of oxygenator. This study demonstrated that both white cell and platelet deposition in the cardiopulmonary bypass circuit can be quantified using radiolabelled cells. No differences in oxygenator or filter deposition were found in patients randomly allocated to membrane or bubble oxygenation.

Respiratory dysfunction and white cell activation following cardiopulmonary bypass: comparison of membrane and bubble oxygenators.

OBJECTIVE: Cardiopulmonary bypass induces respiratory dysfunction postoperatively, with activation of both the complement system and white cells implicated. This study compared the effects of bubble and membrane oxygenators for cardiopulmonary bypass in terms of respiratory dysfunction and markers of white cell activation and endothelial damage. METHODS: Fifty patients undergoing cardiopulmonary bypass were randomly allocated either membrane or bubble oxygenation. Respiratory function was assessed serially by arterial oxygen tension and alveolar-arterial oxygen gradient. Complement activation was measured by serial sampling of serum C3a levels. White cell activation was assessed by serial measurement granulocyte elastase; other markers investigated were levels of thromboxane B2, von Willebrand factor and malondialdehyde. All sample measurements were made preoperatively, early and late during bypass, 4-6 h postoperatively and then on the 1st, 2nd and 6th postoperative day. All samples were corrected for haemodilution, and differences between groups tested non-parametrically. RESULTS: In both groups of patients there was a highly significant fall (P < 0.001) in arterial oxygen tension accompanied by a highly significant rise (P < 0.0001) in aleveolar-arterial oxygen gradient at 18 h compared to preoperative values persisting until 6 days postoperatively. Levels of C3a increased significantly in both groups at 10 min post bypass, increased further at 60 min peaking at 4-6 h post bypass. Granulocyte elastase serum levels increased significantly at 10 min postoperatively in both groups compared to control levels, remaining elevated till 48 h, but returning to control levels by 6 days. There was a small difference (P < 0.04) between the groups at 4-6 h only. Levels of von Willebrand factor increased significantly at 60 min post bypass in both groups, remaining elevated 6 days postoperatively. Levels of malondialdehyde increased at 10 min post bypass, remaining elevated until 6 days post bypass. Thromboxane levels showed no significant changes. For all markers measured, there were no significant differences between the groups other than those already indicated. CONCLUSIONS: This study demonstrated marked respiratory dysfunction, complement activation and white cell activation in patients undergoing cardiopulmonary bypass with either bubble or membrane oxygenators. There was marked variability in the response of individual patients with either oxygenation technique, but overall no significant differences between the groups.

Ventilatory and gas exchange abnormalities on exercise in chronic heart failure.

The mechanism of breathlessness on exertion in patients with chronic heart failure are still not fully understood. We therefore investigated the effects of ventilatory and gas exchange abnormalities on exercise capacity in chronic heart failure. Exercise testing was performed in 30 patients with exertional breathlessness due to chronic heart failure and in 30 controls, using continuous transcutaneous blood gas monitoring. Maximal symptom-limited oxygen consumption as (V'O2) as a percentage predicted was reduced in patients (45 +/- 10%; mean +/- SD) compared to controls (87 +/- 7). The ventilatory response (minute ventilation/carbon dioxide production (V'E/V'CO2)) was significantly increased in patients compared to controls (39.9 +/- 7.7 and 25.9 +/- 3.6, respectively). The dead space to tidal volume ratio (VD/VT) was raised in patients compared to controls at rest (0.45 +/- 0.04 vs 0.35 +/- 0.02, respectively) and this persisted on exertion (0.40 +/- 0.05 in patients and 0.20 +/- 0.05 in controls). At maximal symptom-limited exercise, V'E/V'CO2 was inversely related to the % predicted V'O2 in patients, but not in controls (r = -0.62 and r = -0.24, respectively). In patients, V'E/V'CO2 was significantly correlated with VD/VT at maximum exercise (r = 0.82). Patients with chronic heart failure have a significant degree of "wasted ventilation" on exertion, which is associated with increased ventilatory response. The increased ventilatory response on exertion appears to contribute to exercise limitation in these patients.

Breathlessness in microvascular angina.

In patients with microvascular angina (MA), there is some evidence from studies of plethysmography, that there are widespread microvascular abnormalities. In addition to exertional chest pain, all these patients complain of breathlessness, with no evidence of airways obstruction or resting left ventricular dysfunction. Progressive exercise testing was performed in 12 age and sex matched controls and 12 patients (three males), in whom the diagnosis of MA was established on the basis of exertional chest pain, abnormal thallium scans, and an attenuated myocardial flow response to a vasodilator challenge, with angiographically entirely normal epicardial vessels. Symptom limited exercise was performed with on line ventilation and expired gas analysis, measuring minute ventilation, oxygen consumption and carbon dioxide production and arterial blood gas values using a transcutaneous system. Anaerobic threshold was calculated by curve fitting a plot of oxygen consumption against carbon dioxide production. Compared to controls (49.7 +/- 7.3 SD% predicted maximum VO2) in patients with MA, the anaerobic threshold was reduced (41.6 +/- 5.82; P < 0.02) although still within accepted normal limits. Maximal (symptom limited) oxygen consumption, as a percentage of predicted, was reduced 60.73 +/- 16.51 compared to 87.21 +/- 5.2 (P < 0.003). The ventilatory response (VE/VCO2 l l-1 CO2 output) was significantly increased in the MA patients compared to controls (35.9 +/- 8.01 and 27.5 +/- 3.08, respectively; P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of adenosine and exercise stress 201T1 scintigraphy.

A detailed comparison of stress thallium images utilizing exercise (symptom-limited bicycle ergonometer) and adenosine (infused at 50 micrograms kg-1 min-1 increasing by 25 micrograms kg-1 min-1 every 2 min to a maximum tolerated dose) was performed in 20 patients with angiographically documented coronary disease. Ten patients were receiving beta-blockade at the time of both tests. Triple-, double- and single-vessel disease was present in eight, seven and five patients, respectively. Exercise produced a large increase in double product (8970 +/- 288 to 20,-984 +/- 690 mm Hg min-1) while adenosine produced no significant change (8440 +/- 280 to 9086 +/- 600 mm Hg min-1). Each of the three gated planar images (anterior 40 degrees and 70 degrees left anterior oblique) was divided into five equal segments. Exercise produced 44/90, 44/95 and 45/95 abnormal segments in the anterior, 40 degrees and 70 degrees views while adenosine produced 53/100, 44/100 and 52/100 abnormal segments for the same views. The total number of abnormal segments was similar in both groups (133/280 exercise and 149/300 adenosine). Each abnormal segment was analysed for degree of change between stresses using a five-point scoring system. Exercise produced eight segments which were larger by one point and 44 segments larger by two points while adenosine produced 17 and 44 segments larger by one and two points respectively. Left ventricular uptake (as % injected dose) was significantly greater in the adenosine group (1.12 +/- 0.06% versus 0.64 +/- 0.05%, P < 0.01) but right ventricular uptake was similar (0.15 +/- 0.1% versus 0.14 +/- 0.09%).(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility of cardiopulmonary bypass: influence on blood compatibility of device type, mode of blood flow and duration of application.

The biocompatibility of artificial organs is recognised as an area presenting difficulties in terms of the complexity of the situation. The nature of the blood response involving interactions of systems, pattern and extent of change, patient status and the influence of the whole device contribute to the complexity. Recognising these, the profile of the blood response to cardiopulmonary bypass (CPB), with respect to type of device, mode of blood flow, duration of the procedure and patient status, has been evaluated by monitoring contact phase activation [Factor XII-like activity (FXIIA)], fibrinolytic activity [Fibrin degradation products (X-FDP's)], complement activation (C3a, C5a), leucocyte activation [Granulocyte elastase (GE)] and platelet and white cell imaging. FXIIA, X-FDP's, and GE rose gradually during CPB, with levels remaining elevated post-operatively for up to 48 h. In contrast, C3a levels rose sharply with no significant elevation in the post-operative period, while C5a did not show significant changes during bypass. The use of pulsatile perfusion resulted in lesser activation of the parameters, although these were significantly less only for GE. The alterations in FXIIA, X-FDP's, C3a and GE correlated positively with the duration of CPB, with this effect pronounced in the post-operative period for FXIIA, X-FDP's and GE. However, these changes had no apparent influence on clinical outcome and the majority of patients had uncomplicated post-operative recoveries. With respect to the use of bubble/membrane oxygenators, platelet and white cell deposition and the patterns of change for FXIIA and C3a were similar in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of dobutamine and maximal exercise as stress for thallium scintigraphy.

In the assessment and evaluation of patients with suspected coronary artery disease there is a need for pharmacological stress combined with thallium scintigraphy. Thallium images were obtained following stress both with dobutamine infusion (5-20 micrograms kg-1 min-1) and with symptom-limited bicycle ergometry in 20 patients (age 39-70 years) with chest pain who had been admitted for coronary angiography. Percentage thallium uptake was calculated using a region of interest technique. Detailed comparison was performed of the presence, size and distribution of left ventricular thallium perfusion defects; the percentage thallium uptake in ventricles, lung and liver; and the haemodynamic response to stress. Each stress produced a similar number of abnormal segments in each of three views (total EX 166/300; DOB 167/295), but exercise produced larger defects in the anterior view (P < 0.025). Thallium uptake in left and right ventricles and relative uptake to lungs were similar, but dobutamine produced higher relative liver uptake [EX 1.55 (0.67); DOB 2.97 (1.23) P < 0.0001]. Fourteen patients were able to tolerate dobutamine 20 micrograms kg-1 min-1. The ratio of peak stress to rest double product was smaller with dobutamine in both patients with (DOB 1.3; EX 2.0; P < 0.0047) and patients without beta-blockade (DOB 1.5; EX 2.4; P < 0.008). Dobutamine produced fewer conventional stress endpoints of chest pain and ST depression. In conclusion, dobutamine produces a well-tolerated incremental pharmacological stress with thallium images similar to maximal exercise, and provides a useful alternative stress in patients unable to perform adequate dynamic exercise.

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)

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.