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Biomedical subjects

P Taggart

Publications and source records attributed to P Taggart.

At least 73 records · Page 4Linked to original sources
PubMed1983

The role of nitrates on regional subendocardial ischaemia--studies with endocardial monophasic action potentials during pacing-induced angina.

Intracavitary recording of monophasic action potentials (MAP) is a sensitive means of detecting the electrophysiological effects of early or subendocardial ischaemia. The effect of nitroglycerin on the MAP was evaluated during pacing-induced angina in seven patients with localized, reversible ischaemia. Recordings from the ischaemic zone demonstrated a decrease in MAP amplitude and an abnormal rate-corrected shortening of MAP repolarization. The "control" right ventricular MAP showed only the expected rate-dependent decrease in duration throughout the pacing stress test. The ischaemic MAP were unchanged following the intracoronary administration of 100 micrograms nitroglycerin. In contrast, 200-300 micrograms intravenous nitroglycerin produced a normalization of MAP amplitude and duration in spite of continuous pacing at the angina-provoking rate. These changes were preceded by a fall in aortic pressure (from mean 123/84 to 96/62) and subsequent lowering of the rate-pressure product. The major beneficial effects of nitroglycerin on the early electrical changes of pacing-induced ischaemia are thus related to decreased oxygen demand due to cardiac unloading.

Action Potentials↗
PubMed1980

Exercise testing after beta-blockade: improved specificity and predictive value in detecting coronary heart disease.

The value of exercise testing in detecting myocardial ischaemia resulting from coronary atheroma remains controversial. In order to increase the reliability of exercise testing, all its components (asymptomatic, haemodynamic, and electrocardiographic) have been scrutinised. In this study, concerned only with the electrocardiographic response to exercise, the incorporation of beta-blockade into the standard exercise procedure has improved specificity and predictive value without affecting sensitivity. Fifty patients with anginal pain and 50 asymptomatic subjects with an abnormal electrocardiogram were investigated by exercise testing before and after beta-blockade (oxprenolol). All subjects had coronary arteriograms and left ventriculograms, and the results of exercise testing were related to the presence or absence of obstructive coronary artery disease. Possible causes of false positive exercise tests were eliminated by echocardiography. Though beta-blockade was unreliable in distinguishing ischaemic from non-ischaemic resting electrocardiograms, it eliminated all the false positive electrocardiographic responses to exercise in both groups and did not abolish any of the true positive electrocardiographic responses. Thus, specificity and predictive value were improved without reduction in sensitivity. This technique may not necessarily be applicable to other groups of patients or to a random population, but the results of this study suggest it will be a useful additional routine procedure in the investigation of coronary heart disease.

Adolescent↗
PubMed1979

Electrocardiographic changes resembling myocardial ischaemia in asymptomatic men with normal coronary arteriograms.

T wave and ST segment abnormalities in 20 asymptomatic men aged 18 to 55 were investigated because they were identical with myocardial ischaemic changes, and the professional livelihood of the subjects was jeopardised. Coronary arteriograms showed unobstructed arteries in all except one in whom a 50 per cent lesion of the left anterior descending artery was present. Left ventricular angiograms showed a normal contraction pattern, Ejection fractions were normal in 12 and increased in 8. Three characteristic electrocardiographic patterns were observed: flat or inverted T waves in leads II, III, aVF, and V4 to 6 designated type 1; deep T inversion particularly evident in leads V2 to 5 designated type 2, and minor ST segment depression in the inferior and lateral leads without T changes designated type 3. Characteristically, type 1 changes were temporarily suppressed by either beta-blockade or an overnight rest and were more abnormal in the standing position. Type 2 and 3 changes were relatively uninfluenced by these manoeuvres. Maximal treadmill exercise tests were positive in 6 and borderline or negative in 14. When repeated after oxprenolol all tests were negative. Echocardiograms showed asymmetric septal hypertrophy in 3 subjects (ratio of greater than 1.5 between ventricular septum and posterior left ventricular wall). After normalisation by an overnight rest, type 1 T wave abnormalities were reproduced by intravenous adrenaline infusion (0.024 to 0.18 microgram/kg/min) but not by noradrenaline or by adrenaline after prior administration of oxprenolol. When the T waves had remained deeply inverted before infusion despite rest (type 2) adrenaline infusion normalised them and again noradrenaline was without effect. This effect was also prevented by oxprenolol. Type 3 changes were uninfluenced by catecholamine infusion. Plasma catecholamine estimations suggest that catecholamine hypersecretion and hypersensitivity may both be relevant, particularly the latter. The apparent bimodal response of the ventricular myocardium to adrenaline infusion is not surprising since in vitro experiments suggest that reversal of T wave polarity in either direction may result from summation of changes in action potential duration in different parts of the heart. Such changes may be unimodal, that is both areas involved show lengthening or shortening of action potential duration, but by occurring at different rates may lead to a bimodal change in the differences in duration which generate the T wave.

Adolescent↗
PubMed1978

Rock climbing: observations on heart rate and plasma catecholamine concentrations and the influence of oxprenolol.

Observations are presented on the electrocardiogram and plasma catecholamine concentrations of 11 healthy men monitored during two rock climbing ascents. A placebo was administered prior to the first climb and an oral dose of the beta blocking agent oxprenolol ("Trasicor") prior to the second. Mean heart rates were 166 (+/- 20.4 SD) and 120 (+/- 10.2) respectively. Median plasma adrenaline concentrations were 0.05 microgram/1 and 0.33 microgram/1 before and after the climbs following the placebo. No significant difference was observed in the adrenaline concentrations before and after climbing following oxprenolol, or of noradrenaline concentrations on either occasion. These results are interpreted as suggesting that this popular sport represents more an anxiety-type of psychological stress than a physical stress and as such is likely to increase moral fibre rather than muscle fibre.

Adult↗
PubMed1976

Observations on electrocardiogram and plasma catecholamines during dental procedures: the forgotten vagus.

Emotional stress is conventionally considered to be associated with tachycardia and enhanced sympathetic activity. The electrocardiogram and plasma catecholamine and lipid concentrations were observed in 21 young healthy women undergoing dental procedures. Ten of these received premedication with the beta-blocking agent oxprenolol and 11 with a placebo, administered on a double-blind randomised basis. Mild tachycardia occurred in the placebo group a few minutes before and a few minutes after dentistry, but there was a reduction in heart rate immediately before and during the procedure. The pattern was similar in the group who received oxprenolol, though the heart rates at each stage were lower. Plasma adrenaline concentrations were much higher in the samples taken during the procedure than in those taken shortly before and after it. Plasma noradrenaline and lipid concentrations remained unchanged. A decrease in heart rate in the face of intense emotional arousal and an increased plasma adrenaline concentration suggest that the expectation or experience of pain may be associated with parasympathetic dominance despite greatly enhanced sympathetic activity.

Adult↗
PubMed1973

Vagotonicity of violence: biochemical and cardiac responses to violent films and television programmes.

In a search for a reproducible means of evoking different types of emotional stress it was found that in spite of increased adrenaline secretion slowing of the heart occurred when watching violent television programmes. Further evidence of increased vagal tone was provided by the "sinus arrhythmia" effect, a widening of the gap between the maximum and minimum heart rates during the respiratory cycle in parts of the humour, violence, and suspense sections of the television programme.Groups of people taken to see two particularly violent films showed similar evidence suggesting vagal overactivity, together with increases in plasma free fatty acids and decreases in triglycerides. As these changes occurred even with beta-blockade it is suggested that they might be caused by non-sympathetically mediated changes in the levels of hormones, such as growth hormone, producing lipolysis.The ability to assess objectively an individual's reaction to viewing violence might make it possible to judge the likely social impact of violent films and television programmes.

Blood Glucose↗
PubMed1972

Cardiac responses to thermal, physical, and emotional stress.

We have studied the effect of a short period of exposure to the intense heat of a sauna bath on the electrocardiogram and plasma catecholamine, free fatty acid, and triglyceride concentrations in 17 subjects with apparently normal hearts and 18 persons with coronary heart disease. Similar observations were made on 11 of the 17 normal subjects and on 7 of the persons with coronary heart disease in response to exercise.Exposure to heat was associated with an increase in plasma adrenaline with no change in noradrenaline, free fatty acid, or triglyceride concentrations. Exercise was associated with the expected increase in both plasma noradrenaline and adrenaline concentrations. A heart rate up to 180 beats/min was observed in response to both heat and exercise. Apart from the ST-T changes inherent to sinus tachycardia, ST-T segment abnormalities were frequent in response to heat in both the subjects with normal and abnormal hearts, but little change occurred in the ST-T configuration when the subjects were exercised to produce comparable heart rates. Ectopic beats, sometimes numerous and multifocal, were observed in some subjects of both groups in response to heat, but not to exercise. It seems likely that the net unbalanced adrenaline component of the increased plasma catecholamine concentrations (which is also seen in certain emotional stress situations) is predominantly responsible for ischaemic-like manifestations of the electrocardiogram in susceptible subjects. The observations provide further validation for previously reported studies that it is the increased plasma noradrenaline in response to emotional stress that is associated with the release of free fatty acids and ultimate hypertriglyceridaemia, of probable importance in the aetiology of atheroma.

Adult↗
PubMed1971

Significance of potassium in genesis of arrhythmias in induced cardiac ischaemia.

Paired biopsy specimens from the right or left atrial appendage have been taken from patients undergoing cardiopulmonary bypass surgery after various periods of intermittent coronary artery occlusion and analysed for potassium, sodium, and chloride content, total tissue water, and extracellular fluid volume.Tissue potassium content is reduced after coronary artery occlusion, and potassium loss bears an apparently linear relationship to the duration of occlusion. After 150 minutes of occlusion the potassium content had decreased by nearly 50%.For the first 50 minutes of occlusion the myocardial cells swelled at the expense of the extracellular fluid volume. Thereafter there was movement of water in the opposite direction, with subsequent cell shrinkage.The loss of potassium and the alteration in cellular hydration exert profound effects on the calculated gradient of potassium across the cell membrane. This is discussed in relation to the arrhythmias and low cardiac output after myocardial ischaemia. An attempt to rationalize treatment is made.

Adult↗