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Biomedical subjects

R W Campbell

Publications and source records attributed to R W Campbell.

At least 19 recordsLinked to original sources
PubMed1996

Digoxin therapy and survival in heart failure in sinus rhythm.

The effect of digoxin therapy on the survival of heart failure patients in sinus rhythm was assessed using a retrospective case control study. Patients with an acute exacerbation of chronic heart failure secondary to ischemic heart disease were selected. All were in sinus rhythm and all were treated with digoxin. Case-matched controls were identified for all digoxin-treated patients. Long-term survival was ascertained for all 18 digoxin-treated patients and 18 controls who formed the study population. The relative risk of death was 6.4 for digoxin-treated patients (95% confidence interval 0-36) during the period of hospitalization. Te increased risk of death among digoxin-treated patients persisted up to 1 year following discharge from hospital. The results raise further concern regarding the safety of digoxin therapy in managing heart failure exacerbation, when the patients are in sinus rhythm.

Administration, Oral↗
PubMed1996

Quinacrine-resistant Giardia duodenalis.

Quinacrine resistance has been induced in 3 Giardia duodenalis laboratory stocks and 4 lines resistant to other drugs. The quinacrine-resistant lines were maintained in normally lethal levels of 5 microM quinacrine and some lines are viable in 20 microM levels of the drug. Fluorescence studies indicated that quinacrine was taken up by sensitive cells but was actively excluded from resistant trophozoites. The nuclei were not a site of drug accumulation and no specific fluorescence in the trophozoite could be attributed to any structure. Blebs of concentrated drug appeared prior to disintegration of the membrane of drug-sensitive trophozoites exposed to drug overnight. Parasite lines already resistant to furazolidone adapted more readily to quinacrine exposure than drug-sensitive stocks. This multiple drug resistant phenotype was not as marked with metronidazole-resistant lines.

Adult↗
PubMed1996

Supraventricular tachycardia. Occasional nuisance or frequent threat?

Supraventricular tachycardias (SVTs) are common and are widely regarded as a nuisance. They are often repetitive and persistent, and cause more upset than is currently acknowledged although only rarely do they threaten life. Surprisingly, they are ill-defined. A modern approach to SVT requires an accurate diagnosis and a readiness to abandon obsolete therapies in favour of effective new strategies, whether pharmacological or ablative.

Electrocardiography↗
PubMed1996

Pharmacologic therapy of atrial flutter.

Atrial flutter is a relatively rare but nonetheless important arrhythmia. Its mechanism and anatomy have been defined as right atrial macroreentry. It responds to treatment with a variety of antiarrhythmic agents but, in general, drug efficacy for acute termination is low. The addition of pacing to drug therapy markedly improves the success rate for restoration of sinus rhythm. Useful antiarrhythmic agents include amiodarone, sotalol, disopyramide, flecainide, and propafenone, but definitive efficacy studies have not been performed. The risk of provoking 1:1 AV conduction and a marked increase in ventricular response rate is always present. AV nodal blocking drugs (digoxin and verapamil) probably offer protection from this unwanted effect, but the prevalence of 1:1 conduction and the efficacy of AV nodal blockade remain to be established. When drug management fails, there is a place for radiofrequency ablation. Little is known about the thromboembolic risk of atrial flutter. As a consequence, the role of prophylactic anticoagulation is uncertain. Current interest in atrial flutter will ensure that these and other clinical questions are answered in the near future.

Animals↗
PubMed1996

Accuracy of four automatic QT measurement techniques in cardiac patients and healthy subjects.

OBJECTIVE: To assess differences in the accuracy of automatic QT measurement in three subject groups, and to determine the influence of T wave amplitude on these measurements. SUBJECTS: Standard simultaneous 12 lead electrocardiograms were acquired from 25 patients post myocardial infarction, 25 with arrhythmias, and 25 controls. DESIGN: Because there is not yet a standard automatic method for QT analysis, four different techniques were used. Manual QT measurements were used as the reference. QT was measured in two complexes by each technique in each lead, subject, and group. MAIN OUTCOME MEASURE: The differences between reference and automatic QT measurements from the three subject groups were compared independently for the four techniques. The T wave amplitudes for each of the groups were also compared. RESULTS: Variability of the automatic QT measurements, relative to the manual reference, in the cardiac patients was 2.1 times that in the controls (P < 0.005). Mean T wave amplitude was lower (by a factor of two) for the cardiac patients compared with the controls (P < 0.01). No simple relation between T wave amplitude and the difference between automatic and manual QT measurements was found, although the difference was 2.2 times greater for absolute T wave amplitudes of less than 0.25 mV (P < 0.001). CONCLUSIONS: Automatic QT measurement techniques are less accurate in cardiac patients than in controls. Measurements from T waves with amplitudes less than 0.25 mV are less reliable.

Arrhythmias, Cardiac↗
PubMed1996

Post-infarction sustained ventricular tachycardias. The role of drugs and methods for assessing antiarrhythmic efficacy.

Sustained monomorphic ventricular tachycardia is the most important tachyarrhythmia post-infarction. It is re-entrant and is amenable to examination by programmed stimulation. Despite several shortcomings, this technique remains an important method for predicting the long term efficacy of antiarrhythmic drugs. Ventricular ectopic beat suppression and indirect tools for evaluating the electrophysiological conditions of the myocardium (signal averaging, heart rate variability, QT dispersion, etc.) have a useful but limited role for selecting and assessing therapy. Implantable cardioverter defibrillators, surgery and catheter ablation are important treatment options but antiarrhythmic drugs are the first line approach. Their efficacy is not high but for those in whom they work, they offer acceptable levels of reliability and safety.

Anti-Arrhythmia Agents↗
PubMed1995

Electrophysiologic profile and efficacy of intravenous dofetilide (UK-68,798), a new class III antiarrhythmic drug, in patients with sustained monomorphic ventricular tachycardia. Dofetilide Arrhythmia Study Group.

There is increasing evidence that class III antiarrhythmic agents may be superior to class I agents for the long-term treatment of life-threatening ventricular tachyarrhythmias. This open study evaluated the acute electrophysiologic effects, antiarrhythmic efficacy, and safety of different doses of intravenous dofetilide, a new class III drug, in 50 patients with sustained monomorphic ventricular tachycardia inducible by programmed electrical stimulation who had previously been unsuccessfully treated with 0 to 7 (median 3) other drugs. Intravenous dofetilide was administered over 60 minutes at the following dose levels: 1.5, 3.0, 6.0, 9.0, and 15.0 micrograms/kg. Significant class III activity was apparent at doses of 3.0 to 15.0 micrograms/kg, as evidenced by dose-related prolongation of the QTc interval by 13.4% to 14.2%, ventricular effective refractory period by 7.9% to 20.6%, and ventricular functional refractory period by 7.3% to 25.0%. The corresponding mean +/- SD plasma dofetilide concentrations ranged from 1.45 +/- 0.52 to 6.48 +/- 1.31 ng/ml. There was no evidence of reverse use-dependence. At these electrophysiologically active dose levels, intravenous dofetilide suppressed (complete response) or slowed (partial response) inducible ventricular tachycardia in 17 of 41 patients (41%) compared with 0 of 9 patients receiving only 1.5 micrograms/kg. The response rate was fairly uniform among the groups receiving 3.0, 6.0, 9.0, and 15.0 micrograms/kg. Intravenous dofetilide was hemodynamically well tolerated. Torsades de pointes (which was self-limiting) developed in only 1 patient, who was allocated to receive 15.0 micrograms/kg. There were no other proarrhythmic episodes or serious adverse effects. Further evaluation of the therapeutic potential of dofetilide in the management of life-threatening ventricular arrhythmias is justified.

Aged↗
PubMed1995

Coadministration of calcium antagonists and ACE inhibitors--is a skeptic convinced?: a personal view.

The pathological chain of events that stretches from the earliest atheromatous lesion to end-stage myocardial failure and death is amenable to attack in many places. It may well prove that a multifaceted intervention offers the best therapeutic option. Two important cardiovascular therapies, the calcium entry blockers and ACE inhibitors, may offer more than their effects on vascular tone and remodeling. Both have actions on the basic process of atheroma. Individually, or more challengingly in combination, they may strike at the basic pathogenesis of atherosclerosis yet still provide their more general beneficial effect on vasomotor tone. Whilst clinical data are yet scant, there is a plausible biological basis for their coprescription.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Biological and genetic analysis of a longitudinal collection of Giardia samples derived from humans.

Duodenal aspirates from children investigated for diarrhoea have been examined for the presence of Giardia over an eleven year period, and where possible, in vitro or in vivo Giardia cultures in mice were established. Based on biochemical characteristics of electrophoretic karyotype, RFLP analysis and rDNA hybridization studies of 40 stocks at least two major varieties, or demes, of Giardia have infected the population of South East Queensland and environs during this period. These demes carried different rDNA repeat units and differed markedly in both the electrophoretic karyotype pattern and the molar representation of chromosome bands. From 1983 to 1991 only one deme was documented. The first evidence of a new deme seen in local children occurred in 1991 and was followed by a predominance of this deme in 1993. These 40 stocks do not represent all positive samples. Other stocks established in vivo were not able to be cultured in vitro, and these probably represent other demes. Since all of the stocks established in vivo were not able to be cultured in vitro, and these probably represent other demes. Since all of the stocks were derived from children with similar chronic symptoms it appears that at least two demes of Giardia are pathogenic.

Animals↗
PubMed1995

Assessment of the ventricular fibrillation detection algorithm in the semi-automatic Cardio-Aid defibrillator.

The sensitivity and specificity of ventricular fibrillation (VF) detection in the semi-automatic Cardio-Aid defibrillator was assessed with 25 ECG recordings, each of length 40 s. Of the 25 ECG recordings, 12 contained VF requiring defibrillation, 3 contained a tachyarrhythmia with a waveform similar to VF but which self-terminated, and 10 were selected from abnormal rhythms and artefacts which contained some features similar to VF. Sensitivity was assessed from the VF data. Specificity was assessed from both the rhythm preceding VF or the tachyarrhythmias, and from the VF-like data. The response to a changing rhythm was assessed from the self-terminating tachyarrhythmias. Each recording was replayed to the defibrillators at 3 signal amplitudes (normal, half and double). Request to analyse the ECG because of possible VF and advice to shock were noted separately. The sensitivity for recommending a shock when a shock was required was 92%. The sensitivity for drawing attention to VF, through requesting analysis was 97%. There were no false detections in the rhythms preceding VF or the tachyarrhythmias (specificity with good quality signals 100%). The specificity with the VF-like data ws 90%. There was significant difference between this defibrillator and other semi-automated defibrillators previously assessed.

Algorithms↗
PubMed1995

Objective features of the surface electrocardiogram during ventricular tachyarrhythmias.

The aim of this study was to quantify the electrocardiographic signal characteristics of three types of ventricular arrhythmia; monomorphic ventricular tachycardia, polymorphic ventricular tachycardia and ventricular fibrillation. Patients in a coronary care unit were monitored using a single bipolar ECG lead. Thirty episodes of ventricular tachyarrhythmia (ten from each group) were recorded automatically by computer. Frequency analysis of ten consecutive 1 s epochs from each recording gave 100 spectra for each tachyarrhythmia group. Each spectrum was characterised by the frequency, there were significant differences in all characteristics between the tachyarrhythmia groups (P<0.025). Ventricular fibrillation had a higher mean dominant frequency (4.8 Hz) than polymorphic ventricular tachycardia (3.7 Hz) and monomorphic ventricular tachycardia (3.8 Hz). The dominant frequency of ventricular fibrillation was also more variable than that of monomorphic ventricular tachycardia (P<0.01). Mean peak size was largest for monomorphic ventricular tachycardia (0.78) and smallest for ventricular fibrillation (0.64). The single spectral peaks seen throughout this study indicate that all three tachyarrhythmias have an underlying periodic mechanism. The differences in spectral characteristics show that varying degrees of myocardial electrical organisation can be quantified from surface ECG features.

Electrocardiography↗
PubMed1995

Use of 24 h ambulatory ECG recordings in the assessment of new chemical entities in healthy volunteers.

1. Ambulatory (24 h) cardiac monitoring (ACM) is frequently used to screen healthy volunteers before inclusion in trials of new chemical entities in man. We analysed 156 consecutive ACM recordings in 'healthy' volunteers (on no medication). 2. Only 20 (13%) of the recordings showed normal sinus rhythm throughout. 3. Supraventricular ectopics were the commonest abnormality (83%). Ventricular ectopics occurred in 11%; ventricular tachycardia (unsustained) in 2% and sinus pauses in 6.5%. One volunteer was found to be in atrial fibrillation throughout. 4. The data indicate that when ACM recordings are performed in the assessment of the effects of experimental drugs, guidelines are needed to assess 'normality' to suggest when cardiological investigation is needed and to assign causality of the arrhythmia to the new chemical entity. 5. Proposed guidelines are presented.

Adolescent↗
PubMed1995

Analysis of the body surface ECG measured in independent leads during ventricular fibrillation in humans.

The degree of myocardial electrical organization during ventricular fibrillation remains unknown. The aim of this study was to compare the characteristics of the surface ECG on three independent and approximately orthogonal leads. Ten recordings of ventricular fibrillation, each induced at electrophysiology study and successfully terminated by direct current shock, were analyzed. Each recording was divided into 1-second epochs for analysis. Frequency analysis using the Fast Fourier Transform showed that the frequency of the dominant spectral peak increased significantly from a mean of 4.1 +/- 0.8 Hz to 5.2 +/- 0.7 Hz during the first 5 seconds of ventricular fibrillation. In 95% of the epochs analyzed, a similar dominant frequency was observed on either two or three ECG leads. Frequency agreement tended to increase as ventricular fibrillation evolved. This study shows that the rate of ventricular fibrillation increases rapidly during the first 5 seconds but only gradually thereafter, and that similar signal characteristics are observed on independent ECG leads. These findings are not compatible with the traditional view of incoherent myocardial activity during ventricular fibrillation.

Body Surface Potential Mapping↗
PubMed1995

Evidence for electrical organization during ventricular fibrillation in the human heart.

INTRODUCTION: Ventricular fibrillation is a most dangerous cardiac arrhythmia that has received considerable attention, yet its pattern of electrical activation remains controversial. The aim of this study was to investigate the degree of organization during the clinical arrhythmia and to examine the phase relationship between deflections in independent ECG leads. METHODS AND RESULTS: Ten recordings of ventricular fibrillation were examined. Each had been provoked during routine electrophysiological study. The mean duration of ventricular fibrillation was 21 seconds (range 11 to 34). Independent and approximately orthogonal ECG leads I, aVF, and V2 were recorded to computer at a sampling rate of 250 Hz. The phase relationship of each ECG lead pair was measured from the lag of peaks in their cross-correlation function (CCF). In 61% of the 1-second ECG epochs analyzed, CCF peak lag changed by < 20 msec compared to the previous epoch. Thus, the overall phase relationship was stable most of the time. Changes in CCF peak lag tended to be either gradual or to punctuate periods of stability. CONCLUSIONS: This study provides evidence of organized myocardial activation during human ventricular fibrillation.

Electrocardiography↗