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Biomedical subjects

David Birnie

Publications and source records attributed to David Birnie.

11 recordsLinked to original sources
PubMed2006

Reasons for escalating pacemaker implants.

Surveys of pacing practice have shown a steady increase in pacemaker implantation rates in the past 15 years, despite no major changes in United States guidelines for permanent pacing. There are no data to explain why this is occurring. In this study, records were extracted from the National Hospital Discharge Survey to investigate this. There were 3 major findings. First, age-adjusted implantation rates increased progressively over the study period from 370 per million in 1990 to 612 per million in 2002. Second, it was found that the escalating implantation rate is attributable to increasing implantation for isolated sinus node dysfunction (SND). Implantation for SND increased significantly over the study period (by 102%), whereas implantation for all other indications did not. The increasing implantation for SND is due primarily to the increasing prevalence of SND, with a lesser increase in implantation rate relative to prevalence rate. The third major finding of this study is that there has been a progressive relative and absolute increase in the dual-chamber implantation rate. In 2002, 82.8% of all initial pacemaker implantations were dual-chamber devices. Furthermore, the National Hospital Discharge Survey data indicate that the major randomized pacing trials seem to have had no impact on pacing practice in the United States. In conclusion, age-adjusted implantation rates increased progressively over the study period. This escalating implantation rate is primarily attributable to increasing implantation for SND.

Age Factors↗
PubMed2006

Feasibility study of endocardial mapping of ganglionated plexuses during catheter ablation of atrial fibrillation.

BACKGROUND: Numerous reports have demonstrated an association between autonomic tone and atrial fibrillation (AF). Pulmonary vein (PV) denervation during catheter ablation of AF has been shown to significantly reduce recurrence of AF. OBJECTIVES: The purpose of this study was to assess the safety and efficacy of high-frequency stimulation at mapping cardiac ganglionated plexuses in patients undergoing catheter ablation of AF. METHODS: Fourteen patients with a history of symptomatic AF underwent a single transseptal approach and electroanatomic mapping of the left atrium, right atrium, and coronary sinus. Using high-frequency stimulation with patients under general anesthesia (20-50 Hz, 5-15 V, pulse width 10 ms), mapping of ganglionated plexuses was performed. Radiofrequency (RF) ablation was performed during AF guided by complex fractionated atrial electrograms. Lesions were mostly delivered circumferentially in the antral area of the PVs, predominantly over and adjacent to regions of ganglionated plexuses. RESULTS: There was a mean of 4 +/- 1 (range 2-6) ganglionated plexuses per patient, and a mean total of 3 +/- 1 RF applications were delivered over positive vagal sites. Although a vagal response occurred infrequently during ablation (0.9%), postablation high-frequency stimulation failed to provoke a vagal response in 30 (88%) of 34 previously positive vagal sites that underwent ablation. CONCLUSION: Ganglionated plexuses can be precisely mapped using high-frequency stimulation and are located predominantly in the path of lesions delivered during ablation of AF. Objective documentation of modification of autonomic tone can be documented in the majority of patients. Future studies are required to determine the specific role of mapping and targeting of ganglionated plexuses in patients undergoing catheter ablation of AF.

Adult↗
PubMed2006

Is septal glucose metabolism altered in patients with left bundle branch block and ischemic cardiomyopathy?

UNLABELLED: Left bundle branch block (LBBB) is common in patients with heart failure (HF) and contributes to left ventricular (LV) dysfunction. The abnormal septal motion may alter septal metabolic demand but this has not been well characterized in patients with ischemic cardiomyopathy (ICM) and LV dysfunction. The aim of this study was to determine the effect of LBBB on septal metabolism in patients with ICM, LV dysfunction, and LBBB. METHODS: Fifty-three patients with LV dysfunction and ICM were identified: 34 with LBBB, 19 with normal QRS (</=100, control patients). PET using (18)F-FDG and (82)Rb was used to measure myocardial glucose metabolism and perfusion, respectively. Perfusion-metabolism differences were determined. Scar scores (matched decreases in (18)F-FDG and (82)Rb), mismatch scores (hibernating myocardium with decreased (82)Rb relative to (18)F-FDG), and reverse-mismatch (R-MM) scores (reduced (18)F-FDG relative to (82)Rb) were assessed in the septum and lateral wall. RESULTS: (18)F-FDG uptake in the septum was reduced in patients with LBBB (64.0% +/- 15.4%) compared with control patients (74.9% +/- 14.3%; P < 0.05). Mean septal R-MM was greater in patients with LBBB (19.1% +/- 15.3%) versus control patients (4.7% +/- 10.6%; P < 0.05). However, 32% (11/34) of patients with LBBB did not demonstrate septal R-MM, 91% (10/11) of whom demonstrated lateral wall perfusion defects. Of the 68% (23/34) of patients with LBBB and septal R-MM, 52% (12/23) demonstrated lateral wall perfusion defects (P < 0.05). There was a significant difference in the percentage of the lateral wall with scar between those with septal R-MM (9.3% +/- 10.5%) and those without (19.9% +/- 14.3%; P < 0.05). CONCLUSION: Previously, LBBB was believed to be characterized by reduced glucose metabolism relative to perfusion in the septum; however, this is not always the case in ICM. LBBB is not associated with septal R-MM in >30% of this patient population. Absence of this finding was often associated with lateral wall perfusion defects, suggesting an alteration in the metabolic demand on the septum. This may have implications for HF therapies such as resynchronization and requires further study.

Aged↗
PubMed2005

Comparison of induced and spontaneous atrial tachyarrhythmias in patients with a history of spontaneous atrial tachyarrhythmias.

INTRODUCTION: This retrospective study investigated whether induced episodes could be used to predict the morphology of future spontaneous atrial episodes. METHODS: Eighty-two patients (64 +/- 12 years; 77% male; CAD in 60%; left ventricular ejection fraction 45 +/- 16%) with a history of atrial tachycardia or atrial fibrillation (AT/AF) were implanted with a dual-chamber implantable cardioverter defibrillator (ICD) and followed for 6 months. A total of 224 episodes of induced and spontaneous AT/AF were classified into type I, II, and III according to the method of Israel et al. and then compared based on average cycle length (CL) and atrial amplitude. Episodes were also grouped as "pace-terminable" or "nonpace-terminable" based on the CL definition of Gillis et al. RESULTS: The analysis of 121 induced episodes (from 80 patients) and 103 spontaneous episodes (from 43 patients) showed that within each arrhythmia type, there were no significant differences in CL or mean amplitude between induced and spontaneous episodes. Additional analysis of patients that had both induced and spontaneous episodes (n = 41) showed 78% had at least one spontaneous episode that matched the induced episode. Fifty-seven percent of spontaneous episodes were considered to be pace-terminable based on CL. CONCLUSIONS: Our data suggest that there is no significant difference between induced and spontaneous episodes of AT/AF of the same type. The majority of patients had at least one spontaneous episode of the same type as the induced episode, showing that induced atrial arrhythmias may be useful in predicting the morphology of future spontaneous episodes and in identifying patients potentially benefiting from atrial antitachycardia pacing.

Adult↗
PubMed2004

Use of implantable cardioverter defibrillators after out-of-hospital cardiac arrest: a prospective follow-up study.

BACKGROUND: Survivors of out-of-hospital cardiac arrest are at high risk of recurrent arrests, many of which could be prevented with implantable cardioverter defibrillators (ICDs). We sought to determine the ICD insertion rate among survivors of out-of-hospital cardiac arrest and to determine factors associated with ICD implantation. METHODS: The Ontario Prehospital Advanced Life Support (OPALS) study is a prospective, multiphase, before-after study assessing the effectiveness of prehospital interventions for people experiencing cardiac arrest, trauma or respiratory arrest in 19 Ontario communities. We linked OPALS data describing survivors of cardiac arrest with data from all defibrillator implantation centres in Ontario. RESULTS: From January 1997 to April 2002, 454 patients in the OPALS study survived to hospital discharge after experiencing an out-of-hospital cardiac arrest. The mean age was 65 (standard deviation 14) years, 122 (26.9%) were women, 398 (87.7%) had a witnessed arrest, 372 (81.9%) had an initial rhythm of ventricular tachycardia or ventricular fibrillation (VT/VF), and 76 (16.7%) had asystole or another arrhythmia. The median cerebral performance category at discharge (range 1-5, 1 = normal) was 1. Only 58 (12.8%) of the 454 patients received an ICD. Patients with an initial rhythm of VT/VF were more likely than those with an initial rhythm of asystole or another rhythm to undergo device insertion (adjusted odds ratio [OR] 9.63, 95% confidence interval [CI] 1.31-71.50). Similarly, patients with a normal cerebral performance score were more likely than those with abnormal scores to undergo ICD insertion (adjusted OR 12.52, 95% CI 1.74-92.12). INTERPRETATION: A minority of patients who survived cardiac arrest underwent ICD insertion. It is unclear whether this low usage rate reflects referral bias, selection bias by electrophysiologists, supply constraint or patient preference.

Age Distribution↗
PubMed2004

Left atrial vein pacing: a technique of biatrial pacing for the prevention of atrial fibrillation.

Biatrial pacing is a promising new therapy for drug refractory AF. This article reports two studies. First, an initial 14-patient experience with a novel technique for biatrial pacing. The authors attempted to pace from the LA vein branches of the proximal CS for LA stimulation. LA vein pacing would potentially offer the advantages of greater interatrial synchronization and possibly greater reduction in AF burden and also of lesser far-field R wave sensing and greater lead stability. Second, a postmortem series examining the number, size, and site of LA veins draining into the proximal CS is described. LA vein pacing was successful in 9 of 14 patients. LA vein electrode parameters have been stable during a median follow-up of 580 days. There were three early lead dislodgments but no other complications. In the second study, a postmortem analysis of 43 human hearts was performed. The study found that 38 (88.4%) of 43 hearts had at least one LA vein draining into the proximal 5 cm of the CS. In addition, 81.2% (33/43) had at least one vein greater than 4 Fr caliber. Thus, pacing in a greater proportion of patients might be achieved by the development and use of smaller (3, 4, and 5 Fr) electrodes. Furthermore, these smaller leads would obviously allow deeper advancement into the LA veins with the potential advantages of greater interatrial synchronization and lead stability and lesser far-field R wave sensing.

Aged↗
PubMed2003

Effectiveness of treatment for Class II malocclusion with the Herbst or twin-block appliances: a randomized, controlled trial.

The aim of this study was to evaluate the effectiveness of Herbst and Twin-block appliances for established Class II Division I malocclusion. The study was a multicenter, randomized clinical trial carried out in orthodontic departments in the United Kingdom. A total of 215 patients (aged 11-14 years) were randomized to receive treatment with either the Herbst or the Twin-block appliance. Treatment with the Herbst appliance resulted in a lower failure-to-complete rate for the functional appliance phase of treatment (12.9%) than did treatment with Twin-block (33.6%). There were no differences in treatment time between appliances, but significantly more appointments (3) were needed for repair of the Herbst appliance than for the Twin-block. There were no differences in skeletal and dental changes between the appliances; however, the final occlusal result and skeletal discrepancy were better for girls than for boys. Because of the high cooperation rates of patients using it, the Herbst appliance could be the appliance of choice for treating adolescents with Class II Division 1 malocclusion. The trade-off for use of the Herbst is more appointments for appliance repair.

Adolescent↗
PubMed2003

Effectiveness of early orthodontic treatment with the Twin-block appliance: a multicenter, randomized, controlled trial. Part 1: Dental and skeletal effects.

This study evaluated the effectiveness of early orthodontic treatment with the Twin-block appliance for the developing Class II Division 1 malocclusion. This multicenter trial was carried out in the United Kingdom. A total of 174 children, aged 8 to 10 years old, with Class II Division 1 malocclusion were randomly allocated to receive treatment with a Twin-block appliance or to an untreated, control group. Data were collected at the start of the study and 15 months later. Results showed that early treatment with Twin-block appliances resulted in reduction of overjet, correction of molar relationships, and reduction in severity of malocclusion. Most of this correction was due to dentoalveolar change, but some was due to favorable skeletal change. Early treatment with the Twin-block appliance is effective in reducing overjet and severity of malocclusion. The small change in the skeletal relationship might not be considered clinically significant.

Age Factors↗
PubMed2003

Effectiveness of early orthodontic treatment with the Twin-block appliance: a multicenter, randomized, controlled trial. Part 2: Psychosocial effects.

The aims of this project were to evaluate whether early orthodontic treatment with the Twin-block appliance for the developing Class II Division 1 malocclusion resulted in any psychosocial benefits. This multicenter trial was carried out in the United Kingdom, with 174 children aged 8 to 10 years with Class II Division 1 malocclusions randomly allocated to receive treatment with Twin-block appliances or to an untreated control group. Data were collected at the start of the study and 15 months later. Results showed that early treatment with Twin-block appliances resulted in an increase in self-concept and a reduction of negative social experiences. The subjects also reported treatment benefits that could be related to improved self-esteem. Further research is needed to determine the extent to which these effects translate into social behavior and experiences.

Child↗