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Biomedical subjects

R H Swanton

Publications and source records attributed to R H Swanton.

At least 37 records · Page 2Linked to original sources
PubMed1990

Monophasic action potential recordings in response to rapid transient elevation of extracellular potassium and their modification by beta-adrenoceptor blockade in the anaesthetized dog.

1. Monophasic action potentials (MAPs) were recorded simultaneously from the endocardium and the epicardium in open-chested dogs (n = 16) during bolus intravenous injections of potassium chloride at 0.1 mmol/kg and 0.2 mmol/kg. MAP duration was measured at 90% repolarization. Local conduction was measured as the delay between the pacing artefact and upstroke of the MAP. 2. The animals were anaesthetized with alpha-chloralose and urethane. Heart block was created by atrioventricular nodal ablation with 0.1% (v/v) formalin. Infra-nodal pacing was established. 3. Bolus injections of potassium chloride at 0.1 mmol/kg shortened MAP duration. The effect was maximal at 15 s after the injection [epicardium: 171.5 +/- 3.0 (control) and 148.9 +/- 5.2 ms at 15 s (P less than 0.001); endocardium: 178.7 +/- 4.4 (control) and 165.6 +/- 5.3 ms (P less than 0.001)]. The shortening on the epicardium was significantly greater than on the endocardium (P less than 0.05). 4. Local conduction time showed no significant change [epicardium: 37.8 +/- 1.8 (control) and 41.2 +/- 2.4 at 15 s; endocardium: 41.1 +/- 1.6 (control) and 45.0 +/- 3.4 at 15 s]. 5. After beta-adrenoceptor blockade, MAP duration shortened, exhibiting a maximum effect at 20 s after a bolus injection of potassium chloride at 0.1 mmol/kg [epicardium: 184.7 +/- 7.1 (control) and 130.7 +/- 9.0 ms at 20 s (P less than 0.001); endocardium 192.0 +/- 7.4 (control) and 148.6 +/- 10.8 ms at 20 s (P less than 0.001)]. The greater shortening observed on the epicardial surface did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1990

Echocardiographic abnormalities in type IV mucopolysaccharidosis.

Cardiac involvement is well recognised in most forms of the mucopolysaccharidoses but there is poor documentation of abnormalities specific to Morquio's syndrome (type IV mucopolysaccharidosis). Ten patients with the classic form or type A Morquio's syndrome with a median age of 12.5 years underwent echocardiographic assessment. Abnormalities were detected in six (60%) cases with mitral valve involvement in five patients and aortic valve disease in four. One patient had severe mitral leaflet thickening to the point of mitral stenosis. Two patients had evidence for myocardial involvement by way of echocardiographic ventricular hypertrophy. The cardiac lesions were haemodynamically mild. A cardiac murmur was audible in only three of the six cases. It is concluded that there is a high prevalence of silent cardiac abnormalities in patients with Morquio's syndrome with predominantly left sided valve involvement. Echocardiography should be part of the assessment of these patients and bacterial endocarditis prophylaxis should be advised for those with cardiac abnormalities.

Adolescent↗
PubMed1990

Pseudoxanthoma elasticum presenting with myocardial infarction.

A 31 year old man presented with an anterior myocardial infarction. He had a history of recurrent gastrointestinal bleeding of obscure cause since childhood and peripheral vascular disease. A clinical diagnosis of the type 1 dominant form of pseudoxanthoma elasticum was supported by histological data from skin biopsy.

Adult↗
PubMed1990

Dipyridamole magnetic resonance imaging: a comparison with thallium-201 emission tomography.

Limitation of space and motion artefact make magnetic resonance imaging during dynamic exercise difficult. Pharmacological stress with dipyridamole can be used as an alternative to exercise for thallium scanning. Forty patients with a history of angina and an abnormal exercise electrocardiogram were studied by dipyridamole thallium myocardial perfusion tomography and dipyridamole magnetic resonance wall motion imaging with a cine gradient refocused sequence. Images for both scans were obtained in the oblique horizontal and vertical long axis and short axis planes before and after pharmacological stress with dipyridamole. The myocardium was divided into nine segments for direct comparison of perfusion with wall motion. Segments were assessed visually into grades--normal, hypokinesis or reduced perfusion, and akinesis or very reduced perfusion. After dipyridamole there were reversible wall motion abnormalities in 24 (62%) of 39 patients with coronary artery disease and 24 (67%) of 36 patients with reversible thallium defects. The site of wall motion deterioration was always the site of a reversible thallium defect. Thallium defects affecting more than two segments were always associated with wall motion deterioration but most single segment thallium defects were undetected by magnetic resonance imaging. There was a significant correlation between detection of wall motion abnormality, the angiographic severity of coronary artery disease, and the induction of chest pain by dipyridamole. There were no significant differences in ventricular volume or ejection fraction changes after dipyridamole between the groups with and without detectable reversible wall motion changes but the normalised magnetic resonance signal intensity of the abnormally moving segments was significantly less than the signal intensity of the normal segments. In nine patients the change was apparent visually and it was maximal in the subendocardial region. Magnetic resonance imaging of reversible wall motion abnormalities in patients with coronary artery disease is feasible during pharmacological stress with dipyridamole and may be associated with a reduced magnetic resonance signal. The failure to show wall motion abnormalities in all cases of reversible thallium defects may be because the defect was small or because dipyridamole caused perfusion defects in the absence of myocardial ischaemia.

Adult↗
PubMed1990

Anticoagulants in cardiovascular diseases.

Anticoagulants form an important group of drugs in the management of cardiovascular diseases. These drugs are being increasingly employed but the indications and therapeutic regimens for their use remain unclear in certain situations. This review summarizes the currently accepted practice and aims to provide a balanced view of the ill-defined areas of anticoagulant therapy in cardiovascular diseases.

Anticoagulants↗
PubMed1989

Quantitative phase analysis in the assessment of coronary artery disease.

The phase image in radionuclide ventriculography shows the timing of ventricular contraction and is valuable in the detection of abnormalities induced by coronary artery disease. The image is usually interpreted subjectively, and in the present study a histogram of left ventricular phase values was used to make interpretation more objective. The left ventricular ejection fraction and the standard deviation, skewness, and kurtosis of the phase histogram were measured at rest, during isometric exercise, and during the final two stages of maximal dynamic exercise in 25 controls and 27 patients with coronary artery disease without previous infarction. The ejection fraction and the standard deviation of the phase had the same predictive accuracy for the presence of disease when measured during the penultimate stage of dynamic exercise (89%) as during the final stage, but their accuracy was lower during maximal exercise (77%) because of motion artefact at high exercise levels. Skewness and kurtosis of the histogram were of no value for the detection of disease, and isometric exercise was of only limited value. It is concluded that the phase histogram provides an objective measurement of the synchronicity of left ventricular contraction and can increase sensitivity for the detection of abnormality. Data should be acquired at all stages of dynamic exercise, and the penultimate stage should be used if there is any doubt about the validity of the final stage.

Adult↗
PubMed1989

Monophasic action potential recordings in response to graded hyperkalemia in dogs.

Recent interest in sudden cardiac death during exercise in normal healthy people has highlighted the possible role of swings of extracellular potassium in arrhythmogenesis in conditions other than ischemia. Regional differences in action potential duration and conduction may be important. We have recorded monophasic action potentials (MAPs) from the endocardium and epicardium in nine open-chest dogs during graded intravenous infusion of potassium up to a plasma level of 9 mM. The animals were anesthetized with alpha-chloralose and urethan. Continuous, online arterial potassium monitoring was employed. MAP duration showed a biphasic response with initial shortening up to 7 mM, which tended to be more obvious on the epicardium. Regional activation time was measured as the difference between the onset of depolarization of the endocardial and epicardial MAP. Regional activation time also showed a biphasic response with initial shortening and subsequent delay. The QRS width of the scalar lead II electrocardiogram also showed biphasic changes, and the T wave amplitude progressively decreased. Our results suggest that regional differences in repolarization time may develop in the nonischemic myocardium in response to increased extracellular potassium levels mainly as a result of local changes in regional activation time rather than as a result of a direct effect on action potential duration.

Action Potentials↗
PubMed1988

Simultaneous endocardial and epicardial monophasic action potential recordings during brief periods of coronary artery ligation in the dog: influence of adrenaline, beta blockade and alpha blockade.

Local differences in the time course of recovery of excitability during the early phase of myocardial ischaemia are important in the genesis of arrhythmias. Catecholamines are known to encourage the formation of arrhythmias and adrenergic blockade is a recognised therapeutic regime. The purpose of this study was to compare the effect of short periods of coronary artery ligation on endocardial and epicardial repolarisation time, to assess any disparity between the two surfaces, and investigate the influence of catecholamines and adrenergic blockade. Simultaneous left ventricular endocardial and epicardial monophasic action potentials (MAPs) were recorded during short periods of left anterior descending coronary artery (LAD) ligation in 9 open chested dogs. Recordings were made during two 90 s periods of LAD ligation. Two further ligations were made during infusion of adrenaline (1 microgram.kg-1.min-1). Subsequently ligations were made after beta blockade with propranolol (0.25 mg.kg-1) and then in the presence of a combination of alpha blockade (phentolamine, 0.15 mg.kg-1) and beta blockade. MAP duration was measured at 90% repolarisation. LAD ligation produced a marked shortening of MAP duration epicardially with only minimal shortening endocardially, which resulted in a highly significant difference between the repolarisation times on the two surfaces. The disparity between surfaces tended to be augmented by adrenaline and was significantly minimised by either beta blockade alone or in combination with alpha blockade. Our results show rapid development of substantial regional differences in repolarisation time between endocardium and epicardium in response to "ischaemia".(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1988

Sarcoidosis of the heart.

Patients who have bilateral hilar lymphadenopathy (BHL) alone need annual follow-up with chest X-ray, ECG, 24-h monitoring, exercise testing, lung function and possible thallium 201 scanning. Provided these tests are normal or negative, there is no evidence of other organ or parenchymal lung involvement and the extent of BHL is stable or regressing, then restriction to multicrew operation should be required until regression has occurred or a period of two years has elapsed. Although a patient with generalized or systemic sarcoidosis and no apparent cardiac involvement should be allowed to drive a car, certification to fly should be dependent on physical well being and restricted to multicrew operation. With our present inability to diagnose cardiac involvement in sarcoidosis with complete sensitivity, this restriction should be indefinite as cardiac involvement in sarcoidosis may only become apparent many years after the diagnosis of systemic sarcoidosis has been made. Patients with known cardiac involvement in sarcoidosis should also be refused a driving licence unless they are under regular and close supervision for possible arrhythmic complications. Permanent pacing may be needed. Patients with known cardiac sarcoid should be refused certification to fly.

Cardiomyopathies↗
PubMed1988

Demonstration of the ascending aorta in infective endocarditis by intravenous digital subtraction angiography.

Four patients with infective endocarditis were examined by digital subtraction angiography immediately before operation. In three a root abscess was suspected and the remaining patient was believed to have a false aneurysm at an infected aortic cannulation site. In all the cases digital subtraction angiography showed the structure in several projections and confirmed the presence of a cavity. Subsequent operation confirmed the site and nature of the lesions.

Adult↗
PubMed1988

Differential sensitivity of radionuclide ventriculography for the detection of anterior and inferior infarction.

Attenuation of counts from the more distant inferior portion of the left ventricular blood pool in equilibrium radionuclide ventriculography may mean that inferior infarction is less likely to be detected than anterior infarction. Fourier amplitude and phase images can be used to map the extent and timing of regional ventricular wall motion and this study assesses their use for the detection of anterior and inferior infarction. Normal regional values of amplitude and phase were established in 38 individuals without evidence of cardiac abnormality. In 20 patients with anterior infarcts, though the sensitivity of the combined left anterior oblique amplitude and phase images was high (95%) it was lower (77%) in 39 with inferior infarcts, principally because the sensitivity of the phase image for the detection of inferior infarcts was only 39%. Right anterior oblique images generated from a first pass study detected all 13 patients with inferior infarcts. The mean left ventricular ejection fraction was significantly lower in the patients with anterior infarcts (37%) than in those with inferior infarcts (48%). Although the mean wall motion score on x ray contrast ventriculography was slightly lower in the patients with anterior infarction, the high sensitivity of the right anterior oblique amplitude and phase images in inferior infarction suggests that attenuation of counts is an important cause of reduced sensitivity of the left anterior oblique images. This may also partly explain the lower ejection fractions in inferior infarction. It follows that both a right anterior oblique first pass study and a left anterior oblique equilibrium study are necessary for an accurate description of regional wall motion.

Adult↗
PubMed1988

Monophasic action potentials at discontinuation of cardiopulmonary bypass: evidence for contraction-excitation feedback in man.

Mechanical dysfunction is the strongest predictor of sudden cardiac death due to arrhythmia. Contraction-excitation feedback whereby changes in myocardial length/tension influence the time course of repolarization and excitability would provide a possible mechanism. Such a relationship has been shown in animals but has yet to be demonstrated in man. A useful model for studying this relationship is provided by the process of weaning off cardiopulmonary bypass after routine coronary artery surgery. During this weaning period of approximately 1 min, the heart is converted from being partially empty and flaccid (i.e., a "nonworking" state) to being filled and stretched to support the circulation (i.e., a "working" state). Monophasic action potentials (MAPs) were recorded from the left ventricular epicardium as a measure of repolarization time in 16 patients at discontinuation of cardiopulmonary bypass. Systolic pressure was recorded from the radial artery line. Measurements were made at three stages that related to different dynamic states of the heart: (1) starting to come off bypass ("minimally working"), defined as the time of first appearance of an inflection on the arterial pressure trace indicating the start of left ventricular ejection and valve opening, when arterial pressures represent left ventricular pressure, (2) half off bypass ("partially working"), and (3) off bypass ("wholly working"). During the process of discontinuing bypass MAP duration shortened, while systolic pressure increased. MAP duration at 90% and 60% repolarization (MAP D90, MAP D60) decreased from 288.0 +/- 29.5 msec (mean +/- SEM) and 235.0 +/- 27.9 msec in the minimally working heart to 274.5 +/- 30.2 msec and 224.2 +/- 27.3 msec in the partially working heart (p less than .001), with a subsequent decrease to 261.0 +/- 28.8 and 214.0 +/- 28.7 when the heart was wholly working (p less than .001). Systolic pressure increased from 54.1 +/- 9.3 mm Hg in the minimally working heart to 65.9 +/- 13.8 mm Hg in the partially working heart (p less than .001) and subsequently increased to 75.5 +/- 13.3 mm Hg when the heart was wholly working (p less than .001). Mean heart rates did not change significantly. A strong correlation was obtained between absolute MAP duration and systolic pressure. Regression analysis revealed: MAP D90 vs systolic pressure (p less than .001) and MAP D60 vs systolic pressure (p less than .01).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Stress induced right ventricular dysfunction: an indication of reversible right ventricular ischaemia.

Stress induced changes in left ventricular ejection fraction are widely used in the detection and assessment of coronary artery disease. This study demonstrates that right ventricular dysfunction may also occur, and assesses its significance in terms of coronary artery anatomy. This study involved 14 normal subjects and 26 with coronary artery disease investigated by equilibrium radionuclide ventriculography, at rest and during maximal dynamic exercise. Mean normal resting right ventricular ejection fraction (RVEF) was 0.40 (SD 0.118), and all normal subjects increased RVEF with stress (mean delta RVEF + 0.13 SD 0.099). Mean delta RVEF in the subjects with coronary artery disease was significantly lower at 0.00 (SD 0.080), but there was overlap between the two groups. The largest falls in RVEF were seen if the right coronary artery was occluded without retrograde filling. In this subgroup with the most severely compromised right ventricular perfusion (nine subjects), RVEF always fell with stress, and mean delta RVEF was -0.08 (SD 0.050). There was no significant correlation between delta LVEF and delta RVEF, implying that the right ventricular dysfunction was due to right ventricular ischaemia, rather than secondary to left ventricular dysfunction. Stress induced right ventricular ischaemia can therefore be detected readily by radionuclide ventriculography.

Adult↗
PubMed1987

Choice of therapy in angina.

Ischaemic heart disease is one of the most serious health problems in the Western world. Angina is the commonest symptom and its therapy is still palliative, although complete relief from symptoms can generally be achieved by appropriate drugs or revascularization procedures. The degree of disability caused varies and therapeutic choice depends on patient characteristics and causative factors in the production of angina. This article reviews the management of angina from ischaemic heart disease assuming other causes like valvular disease, congenital anomalies, arteritis and cardiomyopathies have been excluded.

Adrenergic beta-Antagonists↗
PubMed1985

Gated blood-pool emission tomography: a new technique for the investigation of cardiac structure and function.

ECG-gated single-photon emission-computed tomography of the intracardiac blood pool is a new technique that has not previously been widely applied. It involves the acquisition of ECG-gated images of the intracardiac blood pools labelled with sodium pertechnetate Tc 99m in 32 projections around the left-anterior hemithorax using a rotating gamma camera. From these images, tomographic sections are reconstructed orthogonal to the long axis of the left ventricle. The heart is therefore imaged three dimensionally, and more extensive information is obtained than in planar radionuclide ventriculography where imaging is usually restricted to only a single projection. Both structure and function can be studied, and the left-ventricular volume and ejection fraction, and wall motion are obtained. Of 50 patients studied, 7 cases are illustrated in order to show normal findings, examples of wall motion that were not shown by planar-contrast and radionuclide ventriculography, examples of the localisation of ventricular hypertrophy, and a comparison between blood-pool and 201TI myocardial tomography.

Adult↗
PubMed1985

Left ventricular volume and ejection fraction determined by gated blood pool emission tomography.

Electrocardiogram gated single photon emission computed tomography of the intracardiac blood pools is a recent development that involves the acquisition of images in multiple projections after in vivo erythrocyte labelling with technetium-99m and reconstruction of these images into tomographic sections in any desired plane. The technique was used in 25 subjects to measure left ventricular volume, by summing the areas of the ventricle in each of the tomographic sections, and the results compared with those using a counts based (non-geometric) technique from planar radionuclide ventriculography. Endocardium was defined with the aid of a contour at 43% of maximum left ventricular counts, and this contour was validated for a left ventricular phantom. Correlation between tomographic and counts based left ventricular volume was close. Similarly, ejection fraction correlated well. The technique is therefore an accurate method for determining left ventricular volume and ejection fraction, avoiding the assumptions about shape made by other geometric methods.

Cardiac Output↗