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Biomedical subjects

A M Tonkin

Publications and source records attributed to A M Tonkin.

At least 19 recordsLinked to original sources
PubMed1992

Haematological profile of healthy elderly Australians.

OBJECTIVE: To determine normal values for haematological parameters in healthy elderly persons, and document any changes in these over a 12 month period. DESIGN: The study was conducted as part of a randomised controlled trial of low-dose aspirin for primary prevention of cardiovascular disease in the elderly. All participants (380) had a full blood examination performed at entry, which was repeated after 12 months. The baseline results for all patients and the 12 month findings in a cohort of 162 persons allocated placebo were used in the present study. SETTING: Community-based (general practices and residential retirement villages). SUBJECTS: Persons aged 70 years and over (53% females) who were ambulatory, living independently, and volunteered to participate. None had significant vascular disease, peptic ulceration, haemorrhagic symptoms or were currently taking non-steroidal anti-inflammatory drugs. MAIN OUTCOME MEASURES: Full blood examination (excluding white cell differential counts) performed with a Technicon H1 analyser. RESULTS: The mean haemoglobin level +/- standard deviation (SD) was 14.69 +/- 1.10 g/dL (for men) and 13.72 +/- 1.05 g/dL (for women). Significant differences (P less than 0.001) in packed cell volume, red cell and platelet counts were observed between the two sexes. No clinically significant change was observed in any of the parameters over a 12 month period. CONCLUSIONS: Haematological reference values for healthy elderly Australians are consistent with normal values reported in younger populations for both sexes. As a result recommendations are provided for normal reference values among this group in an Australian setting.

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PubMed1992

Treatment of ventricular arrhythmias after CAST.

OBJECTIVE: The primary objective of this article is to review the management of ventricular arrythmias in the light of the unfavourable results reported in the Cardiac Arrhythmia Suppression Trial (CAST). STUDY SELECTION, DATA EXTRACTION AND SYNTHESIS: CAST tested the hypothesis that suppression of ventricular arrhythmias recorded on a Holter monitor in patients with myocardial infarction would lead to a decrease in subsequent mortality, presumably by preventing sudden death. In the trial, patients with a myocardial infarction which occurred six days to two years previously and with asymptomatic ventricular premature beats which could be suppressed by one of the antiarrhythmic agents flecainide, encainide or moricizine, were randomised to treatment with one of these agents or placebo. Over a mean follow-up period of 10 months, mortality was significantly higher in those patients receiving flecainide or encainide than in those receiving placebo. On the recommendation of the Data and Safety Monitoring Board the trial in these groups was terminated. More recently CAST II in which moricizine was compared to placebo was also terminated, again because of a higher mortality in the patients receiving active treatment. It is likely that much of the excess mortality can be attributed to proarrhythmic effects of the agents. CONCLUSION: Current management of ventricular arrhythmias are considered in the light of these findings. CAST suggests that specific treatment should be dictated by the presence of associated symptoms and as much by associated structural heart disease as the arrhythmia per se. In particular, specific treatment of ventricular premature beats alone should be avoided. In those with potentially lethal ventricular arrhythmias, referral for appropriate investigation and consideration of non-pharmacological measures is necessary.

Anti-Arrhythmia Agents↗
PubMed1992

Development and validation of echocardiographic methods for estimating left ventricular mass in rats.

1. The aim of this study was to develop non-invasive echocardiographic methods of measuring left ventricular mass (LVM) in rats, and to determine their usefulness in detecting left ventricular hypertrophy. 2. After initial studies to identify the optimum transducer and to ascertain the resolution limits of echocardiography, the repeatability of LVM estimates was studied. The average difference between two independent estimates in 86 male rats (average LVM = 674.7 mg) was 5.4 mg, and the standard deviation of the difference was 107.6 mg. 3. To determine agreement between direct and indirect methods, LVM was measured in 38 male rats by echocardiography and compared with direct measurement of the left ventricular weight at sacrifice. The mean difference between the two methods was 9.14 +/- 56.6 mg. The limits of agreement were from -122.4 to +104.1 mg. 4. Echocardiography was then used to measure LVM in eight male spontaneously hypertensive rats and eight male normotensive Donryu rats at 9 weeks of age. The mean LVM of SHR was 768.2 mg +/- 152.6, which was significantly (2P less than 0.001) greater than the LVM of DRY (435.4 mg +/- 32.2). 5. We conclude that echocardiography provides a non-invasive, repeatable and relatively accurate estimate of LVM in rats. The method is a potentially useful tool for studying the development or regression of cardiac hypertrophy in longitudinal experiments.

Animals↗
PubMed1992

Prevention of sudden cardiac death: the ICD, or an electrical end-point with preceding opportunities for intervention?

Sudden cardiac death (SCD) is usually due to monomorphic ventricular tachycardia and/or ventricular fibrillation. However, in the vast majority of patients these arrhythmias are associated with advanced structural disease. In our society, this is usually due to coronary artery disease (CAD). The implantable cardioverter--defibrillator is the logical approach to management in survivors of SCD. Its rational use must be guided by electrophysiology study. However, a realistic and cost-effective approach to the prevention of a first cardiac arrest must be multifaceted and take cognisance of other aspects including primary prevention. Limitation of the size of myocardial infarction (MI) is vital. Trials already suggests that effective thrombolysis may impinge long-term on arrhythmic end-points. Following infarction, ventricular arrhythmias and sudden death may also be decreased by aspirin, beta-blockers, and possibly angiotensin converting enzyme inhibitors and amiodarone. Many post-infarction studies employ a combined end-point of death and clinical arrhythmias. However, death is usually confined to those with an ejection fraction < 35%. In them, treatment of associated heart failure is often a consideration and if the ejection fraction < 15-20%, depending on donor availability, transplantation may even be the preferred therapeutic option to the cardioverter-defibrillator.

Australia↗
PubMed1992

Atrial fibrillation: epidemiology and the risk and prevention of stroke.

Atrial fibrillation is a common disorder and the incidence increases with each decade of life. Previously, rheumatic mitral valve disease has been the condition most highly associated with atrial fibrillation. However, with the decreasing incidence of rheumatic heart disease, other conditions have assumed greater importance and now congestive cardiac failure, coronary artery disease, and hypertension are the most commonly associated conditions. Nonrheumatic atrial fibrillation is associated with an approximately five-fold increase in the risk of ischemic stroke and a 5% to 7% yearly risk that increases with age. In addition, atrial fibrillation is associated with an increased incidence of silent cerebral infarction and increased mortality. However, whether atrial fibrillation is independently associated with the risk of stroke or is a marker of underlying cardiac disease is contentious. Until recently, the use of preventive therapy has been controversial. However, data from four recently published, prospective randomized studies clearly support the use of warfarin prophylaxis in nonrheumatic atrial fibrillation. Within the diverse group of patients with nonrheumatic atrial fibrillation there are high and low risk subgroups and identification of these may influence decisions regarding antithrombotic prophylaxis. With a few exceptions, however, this remains an area in which there are contradictory findings in the literature. The role of aspirin for prophylaxis in nonrheumatic atrial fibrillation remains unclear and further evaluation awaits the publication of ongoing studies.

Atrial Fibrillation↗
PubMed1991

Comparison of recruitment strategies for a large-scale clinical trial in the elderly.

Formal evaluation of recruitment strategies for clinical trials conducted in the community setting, rather than in hospitals, is limited despite recruitment rates and costs having significant implications for the planning of large trials. As part of the development of a large-scale primary prevention trial of low-dose aspirin in 15,000 elderly persons (aged 70 years and above) to be undertaken in a community setting, a pilot study involving 400 participants was carried out to evaluate different recruitment strategies. Three techniques were compared: recruiting from the electoral roll (by individual invitation using direct mail), local community approach (through retirement villages, local media, elderly community groups), and using general/family practice (identifying persons over 70 within a practice and direct mail invitation to participate). Screening of potential participants was carried out by a trained trial nurse with limited involvement only of medical practitioners. The target recruitment figure was achieved in 4 months using the equivalent of 1.5 full-time nurses. General practice was the most effective method utilized, with a yield of one participant recruited per six approached at an estimated cost of A$48.36 per recruited participant. This compares with yield rates of 1 per 29 (for the local community approach) and 1 per 17 for the electoral roll, and costs per participant of A$42.54 and A$59.37 respectively. Other less tangible benefits of general practice include the greater cooperation of primary care practitioners in patient follow-up and end-point ascertainment.

Aged↗
PubMed1991

Rationale for a primary prevention study using low-dose aspirin to prevent coronary and cerebrovascular disease in the elderly.

The benefits of prophylactic aspirin therapy to prevent cardiovascular and cerebrovascular disease in asymptomatic individuals remains unclear. The rationale for developing a multicentered, double-blind, placebo-controlled clinical trial to determine whether low-dose aspirin (100 mg daily) prevents cardiovascular and cerebrovascular morbidity and mortality in persons aged 70 years and over with no evidence of pre-existing cardiovascular or cerebrovascular disease is described. Sample size calculations have indicated that 15,000 subjects would be required over a 4-year follow-up period in order to demonstrate a 20% reduction in overall cardiovascular mortality at the 0.01 level with a power of 0.8. Such a large-scale community-based clinical trial has never been conducted in Australia in this age group. Therefore the PACE (prevention by low-dose aspirin of cardiovascular disease in the elderly) pilot study has been developed to test recruitment strategies and methods and ascertaining disease end-points.

Adult↗
PubMed1991

A randomized comparison of intravenous heparin with oral aspirin and dipyridamole 24 hours after recombinant tissue-type plasminogen activator for acute myocardial infarction. National Heart Foundation of Australia Coronary Thrombolysis Group.

BACKGROUND: This study addressed the need for heparin administration to be continued for more than 24 hours after coronary thrombolysis with recombinant tissue-type plasminogen activator (rt-PA). METHODS AND RESULTS: A total of 241 patients with acute myocardial infarction were treated with 100 mg rt-PA and a bolus of 5,000 units i.v. heparin followed by 1,000 units/hr i.v. heparin for 24 hours. At 24 hours, 202 patients were randomized to continue intravenous heparin therapy (n = 99) in full dosage or to discontinue heparin therapy and begin an oral antiplatelet regimen of aspirin (300 mg/day) and dipyridamole (300 mg/day) (n = 103). On prospective recording, there were no differences in the pattern of chest pain, reinfarction, or bleeding complications. Coronary angiography on cardiac catheterization at 7-10 days showed no differences in patency of the infarct-related artery. The proportion of patients with total occlusion (TIMI grade 0-1) of the infarct-related artery was 18.9% in the heparin group and 19.8% in the aspirin and dipyridamole group. In the patients with an incompletely occluded infarct-related artery, the lumen was reduced by 69 +/- 2% of normal in the heparin group and 67 +/- 2% in the aspirin and dipyridamole group. Left ventricular function assessed on cardiac catheterization and radionuclide study at day 2 and at 1 month showed no differences between the two groups. Left ventricular ejection fraction on radionuclide ventriculography at 1 month was 52.4 +/- 1.2% in the heparin group and 51.9 +/- 1.2% in the aspirin and dipyridamole group. CONCLUSIONS: We conclude that heparin therapy can be discontinued 24 hours after rt-PA therapy and replaced with an oral antiplatelet regimen without any adverse effects on chest pain, reinfarction, coronary patency, or left ventricular function.

Administration, Oral↗
PubMed1990

Concentrations of plasma atrial natriuretic factor during and after reversion of ventricular tachycardia.

Plasma concentrations of immunoreactive atrial natriuretic factor were considerably increased (mean 745 (376) pg/ml) in 15 patients during spontaneous ventricular tachycardia. There was no significant relation, however, between concentrations of plasma atrial natriuretic factor and systolic arterial blood pressure during tachycardia. Samples taken 30 minutes and 24 hours after reversion of ventricular tachycardia to sinus rhythm showed that, although plasma concentrations of atrial natriuretic factor had fallen significantly, they were still raised after 24 hours. Raised concentrations of atrial natriuretic factor during ventricular tachycardia did not seem to contribute significantly to the hypotension that is often associated with the arrhythmia.

Aged↗
PubMed1990

Atrial fibrillation: the questions and controversies.

Atrial fibrillation is one of the commonest arrhythmias. It was first recognized over 100 years ago. However, many aspects including its mechanism, the role of autonomic as well as structural influences, and appropriate management including prevention of embolic events and indications for cardioversion have continued to provide questions for clinicians. This article is not intended to be all-embracing but to deal with some of these more perplexing and controversial areas.

Atrial Fibrillation↗
PubMed1989

Echocardiographic study of U wave inversion in the electrocardiograms of hypertensive patients.

The prevalence of U wave inversion was evaluated in 58 adult patients with hypertension, and a possible mechanism for it was examined using M-mode echocardiographic indices. U wave inversion was the most common electrocardiographic abnormality, occurring in 34% of patients; voltage criteria for left ventricular hypertrophy were present in only 14% of patients, and ventricular strain pattern was not detected in any patient. Nonetheless, on echocardiography left ventricular posterior wall thickness was increased in 58% of patients. However, neither U wave inversion nor conventional voltage criteria for left ventricular hypertrophy was strongly predictive for this finding. The authors conclude that U wave inversion is a frequent finding in patients with hypertension, often occurring alone. Although it does not appear to be closely linked to the presence of left ventricular hypertrophy, it may relate to other, perhaps subtle, abnormalities of diastolic ventricular relaxation.

Adult↗
PubMed1989

Hemorrhagic myocardial infarction complicated by free wall-rupture: a case associated with unusual clinical features following intravenous thrombolytic therapy.

A patient is described who developed a systolic murmur soon after she was administered intravenous thrombolytic therapy for acute myocardial infarction. She died and autopsy revealed extensive hemorrhagic myocardial infarction and a free-wall rupture. A review of the literature suggests that this may be an unusual complication of thrombolytic therapy.

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PubMed1989

Transesophageal electrocardiography and atrial pacing in acute cardiac care: diagnostic and therapeutic value.

The utility of transesophageal electrocardiography using a bipolar 'pill electrode' was assessed in 17 consecutive patients with tachycardia presenting to our casualty department. Standard 12-lead electrocardiography showed regular narrow QRS tachycardia in 12 patients, and five patients had wide QRS tachycardia. Esophageal atrial electrogram recordings were obtained in 14 patients (82%), and these were helpful in determining the mechanism of tachycardia in 11 patients (78%). Of these 11, seven patients fulfilled criteria for atrioventricular junctional (AVJ) tachycardia based on measurement of the minimum interval between the onset of ventricular depolarisation and earliest atrial (esophageal) activity. One of these patients had presented with a wide QRS tachycardia. The other four patients were diagnosed as having ventricular tachycardia (VT) following diagnosis of AV dissociation. Atrial overdrive pacing, via the pill electrode, successfully reverted four of the nine patients (44%) with narrow QRS tachycardia but no patient with VT. Esophageal recording during tachycardia is a simple, relatively non-invasive technique which is helpful in suggesting the mechanism of tachycardia both in patients with narrow and wide QRS tachycardia, and may have a therapeutic role in patients with AVJ tachycardia.

Adolescent↗
PubMed1988

Clinical implications of electrophysiology study findings in patients with chronic bifascicular block and syncope.

Electrophysiology study was performed in 93 patients with bifascicular block and unexplained syncope. Clinical evidence of organic heart disease was present in 33 (35%). Electrophysiological abnormalities were detected in 45 patients (48%). Of these, 36 had distal conduction disease, including 28 with an HV interval greater than 55 ms (mean 76.4 ms), and eight who developed infraHisian block following either intravenous procainamide (four) or atrial pacing (four). Sick sinus syndrome was evident in six patients and a further two had carotid sinus hypersensitivity. Sustained monomorphic ventricular tachycardia (VT) was induced in only three patients, two of whom also had prolonged HV interval. Among the 93 patients, 45 had therapy which was guided by positive findings at electrophysiology study (Group 1). Of these, 42 received permanent pacemakers, two were treated with combined permanent pacing and antiarrhythmic drug therapy, and one was treated with antiarrhythmic drug alone. In addition, eight patients without electrophysiologic abnormalities were treated empirically by pacing (Group 2). Finally, 40 patients without electrophysiologic abnormalities received no specific therapy (group 3). At a mean follow-up of 39 months (range two-125 months), recurrence of syncope had occurred in 4% of Group 1 patients, and 25% of Group 3 patients (p less than 0.05). No patient in Group 2 had had recurrence. Total mortality was 40%, including 47% of patients in Group 1, 25% of Group 2, and 35% of Group 3. Death was sudden in seven patients. We concluded that among patients with bifascicular block and syncope, therapy directed by findings at electrophysiology study was associated with symptomatic improvement, but mortality was not significantly influenced.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗