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Biomedical subjects

C Bucknall

Publications and source records attributed to C Bucknall.

15 recordsLinked to original sources
PubMed2005

Simulation of cardiac pathologies using an electromechanical biventricular model and XMR interventional imaging.

Simulating cardiac electromechanical activity is of great interest for a better understanding of pathologies and for therapy planning. Design and validation of such models is difficult due to the lack of clinical data. XMR systems are a new type of interventional facility in which patients can be rapidly transferred between X-ray and MR systems. Our goal is to design and validate an electromechanical model of the myocardium using XMR imaging. The proposed model is computationally fast and uses clinically observable parameters. We present the integration of anatomy, electrophysiology, and motion from patient data. Pathologies are introduced in the model and simulations are compared to measured data. Initial qualitative comparison on the two clinical cases presented is encouraging. Once fully validated, these models will make it possible to simulate different interventional strategies.

Algorithms↗
PubMed2001

Atrial arrhythmia suppression by atrial overdrive pacing: pacemaker Holter assessment.

The purpose of this study was to assess the efficacy of overdrive, single-site right atrial appendage pacing to reduce the burden of atrial fibrillation (AF) when compared with a standard lower rate limit of 60 bpm. This was verified by using the pacemaker's Holter. Eighteen subjects with a pre-implant history of paroxysmal AF and implanted DDDR mode-switching pacemakers were recruited. The pacemaker lower rate limit was programmed in random order to 60, 75 or 90 bpm for three 2-month periods and the amount of AF quantified. In addition, the exercise tolerance (ET), general well being (GWB), functional capacity (FC) and specific symptom prevalence (SSP) were assessed. The main finding of the study was that when ranked according to the amount of AF, there was no significant difference in the amount of AF according to the pacing rate. Six patients failed to tolerate pacing at 90 bpm. There were no differences in the ET, GWB, FC and SSP scores. It is concluded that those clinicians that manage patients with paroxysmal

Adult↗
PubMed2001

Atrial flutter ablation: efficacy and cost-effectiveness of a single decapolar electrode to demonstrate bidirectional isthmus block.

AIMS: To evaluate whether a single decapolar electrode is a reliable and cost-effective substitute for the 'Halo' catheter to map the circuit and detect bidirectional isthmus block during atrial flutter (AFL) ablation. METHODS AND RESULTS: Twenty-four patients underwent AFL ablation by using the decapolar electrode in the infero-lateral wall of right atrium (group A) while a 'Halo' catheter was used in 11 patients (group B). Both groups had similar clinical characteristics. Anti-clockwise rotation (20 patients), clockwise (3 patients) or both forms of AFL (1 patient) were detected in group A. All patients in group B had anti-clockwise AFL. Bidirectional isthmus block was completed in 22 patients of group A and in 9 of group B (P=NS) while incomplete isthmus block was detected in 2 patients in each group (P=NS). Mean fluoroscopy and procedure time was 27 +/- 47 min, 107 +/- 36 min in group A and 14 +/- 19 min, 114 +/- 65 min in group B (P=NS). AFL relapsed in 3 patients of group A (follow-up 7 +/- 4 months) and in 2 of group B (4 +/- 2 months). CONCLUSION: A single decapolar electrode is a reliable method to map the circuit and demonstrate bidirectional isthmus block during AFL ablation. The cost of the decapolar electrode is a quarter of that of the 'Halo' catheter. This represents a significant saving particularly for centres with a substantial number of AFL ablations.

Adult↗
PubMed1999

Alterations in atrial electrophysiology associated with chronic atrial fibrillation in man.

BACKGROUND: The purpose of this study was to determine the changes in atrial electrophysiology associated with chronic persistent atrial fibrillation in man. METHODS AND RESULTS: Atrial monophasic action potential duration at 90% repolarization and the effective refractory period were measured in 13 patients with chronic persistent atrial fibrillation after low-energy endocardial cardioversion, and compared to eight controls without a history of atrial fibrillation. Measurements were made at the right atrial appendage and midlateral right atrial wall at basic, 600 ms and 400 ms drive cycle lengths. In control patients, the effective refractory periods were significantly longer at the atrial appendage than the lateral wall at 600 ms (right atrial appendage 265 ms, midlateral right atrial wall 228 ms, P<0.05), and 400 ms cycle lengths (right atrial appendage 270 ms, midlateral right atrial wall 218 ms, P<0.05), but this was not evident in patients with atrial fibrillation. The monophasic action potentials and effective refractory periods at both atrial sites were shorter in the atrial fibrillation patients compared to controls; however, only the effective refractory periods at atrial appendage at 600 ms (atrial fibrillation 210 ms, controls 265 ms, P<0.001), and 400 ms cycle lengths (atrial fibrillation 200 ms, controls 270 ms, P>0.001) reached statistical significance. Effective refractory period dispersion was significantly greater in controls than in patients with atrial fibrillation (cycle length 600 ms: controls 36, atrial fibrillation 13, P=0.01; cycle length 400 ms: controls 54, atrial fibrillation 18, P<0.01). CONCLUSIONS: In patients without a history of atrial fibrillation, the refractory period at the right atrial appendage is significantly longer than at the midlateral right atrial wall. This 'normal' pattern of atrial refractory dispersion is lost in patients with chronic persistent atrial fibrillation, with marked shortening of the effective refractory period at the right atrial appendage. This may explain the high risk of recurrence of atrial fibrillation following successful electrical cardioversion.

Action Potentials↗
PubMed1997

Ambulatory patient-activated arrhythmia monitoring: comparison of a new wrist-applied monitor with a conventional precordial device.

A wrist-applied transtelephonic device (WrTTD) and a precordial (PrTTD) patient-activated transtelephonic electrocardiographic (ECG) recorder were compared objectively (quality of ECG traces) and subjectively (device preference) in a prospective randomized crossover study of 24 patients. All underwent cardioversion for chronic atrial fibrillation and were then randomized to each device for 1 month. The ECG traces were sent weekly with additional traces if symptomatic. Self-administered questionnaires were completed after 1 month with each device, and the first five telemetered ECG traces for each patient were blindly assessed by two experienced cardiologists. Although the QRS complexes were smaller with the WrTTD (P < .001), the quality of the traces was similar. In particular, there was no significant difference in number of nondiagnostic traces, ability to detect atrial activity, degree of baseline fluctuation, or amount of artifact. Overall, patients preferred the PrTTD (P = .02). Patients found the PrTTD easier to use (P = .007) and were able to apply it more rapidly (P = .02). The quality of ECG traces obtained from the upper limbs by using a wrist-applied transtelephonic device was concluded to be comparable with those obtained by direct precordial application. In order to increase patient acceptability of the former, further improvements to simplify its operation are necessary.

Adolescent↗
PubMed1997

Is mode switching beneficial? A randomized study in patients with paroxysmal atrial tachyarrhythmias.

OBJECTIVES: We sought 1) to compare three pacing modalities-DDDR with mode switching (DM), DDDR with conventional upper rate behavior (DR) and VVIR (VR)-in patients with a history of atrial tachyarrhythmias, and 2) to assess the efficacy of six mode-switching algorithms. BACKGROUND: A history of atrial tachyarrhythmias has been a relative contraindication to dual-chamber pacing. Several mode-switching algorithms have recently been developed to prevent rapid tracking of atrial tachyarrhythmias. METHODS: Forty-eight patients (mean age 64 years, 58% male) with a history of atrial tachyarrhythmias and heart block had a DM pacemaker implanted. Pacemakers were programmed to DM, DR and VR modes for 4 weeks each in a randomized crossover design. All subjects used a patient-activated electrocardiographic (ECG) recorder throughout the study and additionally underwent ambulatory ECG monitoring and a treadmill exercise test in each mode. They completed three symptom questionnaires at the end of each pacing period. At the end of the study, patients chose their preferred pacing period. RESULTS: DM was significantly better than VR mode objectively (exercise time DM 8.1 min, VR 7.0 min, p < 0.01) and subjectively (perceived well-being DM 69, VR 51, p < 0.001; functional class DM 2.2, VR 2.5, p < 0.05; subjective symptom score DM 21.2, VR 26.8, p = 0.01). Patient-perceived well-being was significantly better with DM than with DR mode (DM 69, DR 60, p = 0.02). DM mode was the preferred pacing period (DM 51%, DR 14%, VR 14%). Early termination of pacing because of adverse symptoms was requested by 33% of patients during VR, 19% during DR but only 3% during DM mode. A higher proportion of patients with a fast mode-switching device preferred DM mode (fast 55%, slow 49%), whereas no patients with a fast mode-switching device chose VR as the preferred mode (fast 0%, slow 19%). In the subgroup of patients who had had atrioventricular node ablation, DM was also preferred to VR mode (DM 53%, VR 27%). Overall, there were only two cases of inappropriate mode switching and one case of inappropriate tracking of an atrial tachyarrhythmia. CONCLUSIONS: DM is the pacing mode of choice of patients with paroxysmal atrial tachyarrhythmias. With optimal programming, inappropriate mode switching and tracking of atrial tachyarrhythmias was very uncommon.

Algorithms↗
PubMed1996

Dual sensor VVIR mode pacing: is it worth it?

Dual sensor ventricular demand rate responsive (VVIR mode) pacing was compared with single sensor rate responsive pacing to assess whether this new development should be more widely incorporated in modern pacemaker devices. A within patient randomized, double-blind crossover study involving ten patients, mean age 67.4 years (70% male), had Medtronic Legend Plus dual sensor VVIR pacemakers implanted for high grade AV block and chronic or persistent paroxysmal atrial fibrillation. Performance values were compared to 20 healthy control subjects of a similar age and gender. Patients were both subjectively and objectively assessed after 2 weeks of out-of-hospital activity in VVIR mode (minute ventilation sensing), VVIR mode (activity sensing), VVIR mode (dual sensor), and VVI mode (no rate response). All patients were assessed for subjective preference for, and objective improvement in, any pacing modality as assessed by standardized daily activity protocols and graded exercise treadmill testing. Subjective perception of exercise capacity and functional status was significantly lower in VVI mode (P < 0.05) compared to any of the VVIR modes, which did not differ. After completion of the study 70% of patients chose VVIR as their preferred mode, with 30% expressing no preference. Forty percent preferred activity sensor VVIR mode pacing, 30% preferred dual sensor VVIR mode pacing, and 70% found either dual sensor VVIR mode, minute ventilation sensor VVIR mode, or both modalities least acceptable. No patient found activity sensing VVIR mode least acceptable. Graded treadmill testing revealed significantly lower exercise tolerance during VVI mode pacing (P < 0.01) compared to the VVIR modalities, which did not differ. Overall, chronotropic response was best with dual sensor pacing during standardized daily activity protocols and during the standard car journey. The data from this study suggest that there is no marked clinical advantage obtained from the use of dual sensor devices over current activity sensing ventricular demand rate responsive pacemakers, but with the probable added disadvantages of increased size, complexity, cost, and decreased longevity.

Activities of Daily Living↗
PubMed1996

Evaluation of a new pacing algorithm to prevent rapid tracking of atrial tachyarrhythmias.

The new SMARTracking (SMT) algorithm was evaluated in seven patients with the Intermedics Relay DDDR pacemakers and a history of atrial tachyarrhythmias. The SMT algorithm uses the sensor calculated rate to define a physiological band whose upper limit is defined by the SMT rate. Pacemakers were programmed to DDDR with SMT (DDDRSM), DDDR with Conditional Ventricular Tracking Limit (DDDRC), DDDR with standard upper rate behavior, and VVIR, for a period of one month each. Patients underwent a CAEP exercise test and 24-hour ECG Holter monitoring in each mode. They also had ambulatory ECG monitoring during daily activities including rest, slow and fast walk, stairs ascent and descent. Three patients were in atrial fibrillation during the daily activities protocol. Their ventricular rates were paced and highly irregular, in both DDDRSM and DDDRC modes. The heart rate was lower in DDDRSM than DDDRC at rest and low levels of exercise but not during more strenuous activity. Two patients in DDDRSM and 3 in DDDRC requested early change of their mode due to unacceptable symptoms. Two patients exhibited Wenckebach behavior at atrial rates below the upper rate limit in both DDDRSM and DDDRC modes. In conclusion, CVTL or SMARTracking are not adequate protection against atrial tachyarrythmias in patients with DDDR pacemakers.

Activities of Daily Living↗
PubMed1990

A randomized dose-ranging study of rt-PA in acute myocardial infarction. Effects on coronary patency and fibrinolytic parameters.

This study was designed to examine the relationships between dose of Wellcome two-chain recombinant tissue type-plasminogen activator (BW rt-PA) and coronary patency and fibrinolytic parameters in acute myocardial infarction (AMI). In an open randomized study, patients with AMI (determined by ECG) and symptoms of less than 4 h duration without contraindications for fibrinolytic therapy were treated with rt-PA in nominal doses of 20 (7.7 MU), 50 (14.8-29.6 MU) or 100 mg (29.6-48.2 MU) administered over 90 min followed by intravenous heparin. Coronary patency was determined by coronary arteriography of the infarct-related artery and haematological parameters (fibrinogen, plasminogen, alpha 2-antiplasmin and fibrin(ogen) degradation products) measured at 90 min. Coronary patency increased in a dose-related manner to 53% (95% C.I. 37-69%) in the 100 mg/90 min group. Logistic regression demonstrated a relationship between dose (in MU kg-1) and coronary patency. Fibrinogen at 90 m was reduced to 74 (61.5-86.4%) of the pooled plasma standard in the nominal 100 mg group. Patients with a higher predose fibrinogen had higher reductions of fibrinogen. Serious bleeding occurred in three (3%) patients, and no intracranial bleeds were reported. BW rt-PA produces dose-related patency of the coronary arteries with moderate, dose-related reduction in fibrinogen.

Aged↗
PubMed1990

Quantitative analysis of contribution of rate response in three different ventricular rate responsive pacemakers during out of hospital activity.

The contribution of rate response provided by three different types of rate responsive pacemaker (Sensolog, Meta, and Vitatron TX) was assessed in 25 patients during out of hospital activity. Pacemakers were optimally programmed and full disclosure 24-hour Holter ECG recordings were obtained during everyday activities. Close visual analysis of these tracings revealed that rate response is active for less than 15% of the 24-hour study period with high rate response (paced rate above 100 beats/min) for just 5% of the day showing peak activation between 1600 and 2000 hours. Low rate response (paced rate below 100 beats/min but 5 beats above base rate) was maximal between 0800 hours and midday and comprised 10% of all heart beats during the study period. Thirty percent of study patients were nonpacemaker dependent and rate response in these subjects was significantly (P less than 0.001) less active between 0800 hours and midday than in pacemaker dependent patients though it was equivalent at all other times. Nonpacemaker dependent patients achieved natural sinus response in the morning and tended to rely on pacemaker supplied rate response in the latter part of the day.

Activities of Daily Living↗
PubMed1988

Mianserin and trazodone for cardiac patients with depression.

In a placebo controlled double-blind cross-over study, the cardiovascular and antidepressant effects of three weeks' treatment with mianserin (30-80 mg daily) and trazodone (150-400 mg daily) were studied in depressed patients who had co-existant cardiac disease. In 14 of the 16 patients, no haemodynamic deterioration occurred with either drug. Two patients withdrew from the study. One with coronary artery disease, whose concomitant medication included a calcium-antagonist and a beta-adrenoceptor blocker and who developed severe postural hypotension after his first dose of trazodone while the other had an increased frequency of transient cerebral ischaemic attacks with both mianserin and trazodone, but not with placebo. Mianserin and trazodone are comparable for both antidepressant efficacy and paucity of cardiovascular effects. Although unwanted effects were generally mild, the incidence of dizziness was greater in those patients receiving trazodone. Caution is advised, however, when prescribing either drug to patients with transient cerebral ischaemic attacks or those with coronary artery disease receiving medication.

Adult↗
PubMed1988

Vasculitis complicating treatment with intravenous anisoylated plasminogen streptokinase activator complex in acute myocardial infarction.

Vasculitis developed in six of 253 patients treated with intravenous anisoylated plasminogen streptokinase activator complex (APSAC) after acute myocardial infarction. All patients recovered spontaneously with no evidence of renal impairment and no long term sequelae. Although leucocytoclastic vasculitis and serum sickness have been reported after streptokinase treatment, such allergic reactions have not been described as a complication of other thrombolytic agents.

Aged↗
PubMed1986

Treatment of acute myocardial infarction with anisoylated plasminogen streptokinase activator complex.

A controlled trial in 149 patients admitted to a district hospital with probable myocardial infarction tested the effect of 30 units of anisoylated plasminogen streptokinase activator complex (APSAC) on indices of infarct size. Patients were grouped prospectively according to whether they entered the trial within two and a half hours (early entry) or between two and a half and four hours (late entry) after onset of the symptoms. Sixty seven of 73 patients in the control group showed increased plasma activity of myocardial creatine kinase isoenzyme that was diagnostic of infarction compared with only 60 of 76 who received APSAC. The difference was significant overall but occurred predominantly in the early entry group. The patients who received APSAC had more early ventricular arrhythmias, compatible with reperfusion, and showed greater preservation of R waves during admission to hospital. Unwanted effects were generally minor and more common in the actively managed group than the control group (26% v 3%). After nine to 12 months of follow up 12 patients in the control group had died compared with seven in the actively managed group. The ease of administration and the apparent efficacy of APSAC suggest that it is suitable for use in a district hospital for patients with suspected acute myocardial infarction.

Anistreplase↗
PubMedDate not supplied

Natural language processing and the representation of clinical data.

OBJECTIVE: Develop a representation of clinical observations and actions and a method of processing free-text patient documents to facilitate applications such as quality assurance. DESIGN: The Linguistic String Project (LSP) system of New York University utilizes syntactic analysis, augmented by a sublanguage grammar and an information structure that are specific to the clinical narrative, to map free-text documents into a database for querying. MEASUREMENTS: Information precision (I-P) and information recall (I-R) were measured for queries for the presence of 13 asthma-health-care quality assurance criteria in a database generated from 59 discharge letters. RESULTS: I-P, using counts of major errors only, was 95.7% for the 28-letter training set and 98.6% for the 31-letter test set. I-R, using counts of major omissions only, was 93.9% for the training set and 92.5% for the test set.

Diagnosis, Computer-Assisted↗