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Raymond Yee

Publications and source records attributed to Raymond Yee.

At least 19 recordsLinked to original sources
PubMed2007

The expectation effect and cardiac pacing for refractory vasovagal syncope.

BACKGROUND: Clinical trials of pacing for vasovagal syncope have shown conflicting results. We performed a meta-analysis to determine whether permanent pacemaker therapy prevents refractory vasovagal syncope. METHODS: Randomized trials comparing pacemaker therapy with medical therapy, usual care, placebo, or different pacing algorithms in the prevention of recurrent vasovagal syncope were considered. The primary endpoint was first recurrence of syncope. RESULTS: Nine randomized trials (2 double blind, 7 open label or single blind) were included. There was significant heterogeneity when all 9 trials were pooled (P=.0009 and I(2)=69.6%), reflecting methodological diversity in blinding and the nature of the control therapy. When pooled by trial methodology, heterogeneity was no longer apparent. Permanent pacing reduced the risk of recurrent syncope in unblinded studies (odds ratio [OR] 0.09, 95% confidence interval [CI], 0.04 to 0.22) and in studies comparing pacemaker algorithms (OR 0.04, 95% CI, 0.0 to 0.23). No effect was seen in double-blinded trials (OR 0.83, 95% CI, 0.41 to 1.70). Awareness that a permanent pacemaker was implanted and functional was associated with a significant 'expectation' effect, which itself reduced the risk of recurrent syncope (OR 0.16, 95% CI, 0.06 to 0.40, P=.0001). Results were similar when restricted to patients with a marked cardioinhibitory response on baseline tilt table testing. CONCLUSION: The results of small, preliminary trials have overestimated the treatment effect of pacemakers due to a lack of blinding of physicians and patients. Blinded trials suggest that the apparent response is due to a strong expectation response to pacing.

Cardiac Pacing, Artificial↗
PubMed2007

Right ventricular apical pacing: a necessary evil?

PURPOSE OF REVIEW: Clinical trial evidence suggests that traditional right ventricular apical pacing may be harmful. This review summarizes the existing evidence and outlines the major avenues of ongoing research in this field. RECENT FINDINGS: Despite theoretical advantages of dual-chamber pacing, large randomized trials found only a small advantage over single-chamber ventricular pacing. Subsequent analysis of one of these trials suggested that this was due to the tendency for dual-chamber pacemakers to produce frequent, unnecessary right ventricular pacing. This hypothesis is supported by a prospective study among defibrillator recipients, showing that dual-chamber pacing results in a very high frequency of ventricular pacing and worse clinical outcomes, compared with backup ventricular pacing. These observations have led to a renewed interest in single-chamber atrial pacing for sinus node dysfunction, the development of new dual-chamber pacemaker algorithms designed to minimize right ventricular pacing, and the search for better ways to pace the ventricles in patients who require ventricular pacing. SUMMARY: Conventional right ventricular apical pacing should be avoided whenever possible. In patients who require ventricular pacing, ongoing research will determine if selected-site pacing or multisite pacing improves clinical outcomes compared with traditional right ventricular apical pacing.

Arrhythmias, Cardiac↗
PubMed2006

A novel pacing maneuver to localize focal atrial tachycardia.

BACKGROUND: Although focal atrial tachycardias cannot be entrained, we hypothesized that atrial overdrive pacing (AOP) can be an effective adjunct to localize the focus of these tachycardias at the site where the post-pacing interval (PPI) is closest to the tachycardia cycle length (TCL). METHODS: Overdrive pacing was performed in nine patients during atrial tachycardia, and in a comparison group of 15 patients during sinus rhythm. Pacing at a rate slightly faster than atrial tachycardia in group 1 and sinus rhythm in group 2 was performed from five standardized sites in the right atrium and coronary sinus. The difference between the PPI and tachycardia or sinus cycle length (SCL) was recorded at each site. The tachycardia focus was then located and ablated in group 1, and the atrial site with earliest activation was mapped in group 2. RESULTS: In both groups the PPI-TCL at the five pacing sites reflected the distance from the AT focus or sinus node. In group 1, PPI-TCL at the successful ablation site was 11 +/- 8 msec. In group 2, PPI-SCL at the site of earliest atrial activation was 131 +/- 37 msec (P < 0.001 for comparison). In groups 1 and 2, calculated values at the five pacing sites were proportional to the distance from the AT focus or sinus node, respectively. CONCLUSIONS: The PPI-TCL after-AOP of focal atrial tachycardia has a direct relationship to proximity of the pacing site to the focus, and may be clinically useful in finding a successful ablation site.

Cardiac Pacing, Artificial↗
PubMed2006

Delayed enhancement magnetic resonance imaging predicts response to cardiac resynchronization therapy in patients with intraventricular dyssynchrony.

OBJECTIVES: We evaluated the ability of delayed enhancement magnetic resonance imaging (DE-MRI) to predict clinical response to cardiac resynchronization therapy (CRT). BACKGROUND: Cardiac resynchronization therapy reduces morbidity and mortality in selected heart failure patients. However, up to 30% of patients do not have a response. We hypothesized that scar burden on DE-MRI predicts response to CRT. METHODS: The DE-MRI was performed on 28 heart failure patients undergoing CRT. Patients with QRS > or =120 ms, left ventricular ejection fraction < or =35%, New York Heart Association functional class II to IV, and dyssynchrony > or =60 ms were studied. Baseline and 3-month clinical follow-up, wall motion, 6-min walk, and quality of life assessment were performed. The DE-MRI was performed 10 min after 0.20 mmol/kg intravenous gadolinium. Scar measured by planimetry was correlated with response criteria. RESULTS: Twenty-three patients completed the protocol (mean age 64.9 +/- 11.7 years), with 12 (52%) having a history of myocardial infarction. Thirteen (57%) patients met response criteria. Percent total scar was significantly higher in the nonresponse versus response group (median and interquartile range of 24.7% [18.1 to 48.7] vs. 1.0% [0.0 to 8.7], p = 0.0022) and predicted nonresponse by receiver-operating characteristic analysis (area = 0.94). At a cutoff value of 15%, percent total scar provided a sensitivity and specificity of 85% and 90%, respectively, for clinical response to CRT. Similarly, septal scar < or =40% provided a 100% sensitivity and specificity for response. Regression analysis showed linear correlations between percent total scar and change in each of the individual response criteria. CONCLUSIONS: The DE-MRI accurately predicted clinical response to CRT. This technique offers unique information in the assessment of patients referred for CRT.

Aged↗
PubMed2006

Utility and cost effectiveness of temporary pacing using active fixation leads and an externally placed reusable permanent pacemaker.

Active-fixation leads and externally placed permanent pacemakers for temporary pacing may be beneficial because they allow for greater patient mobility and comfort and increased reliability of lead placement. The relative cost of this form of pacing may be prohibitive unless markedly prolonged pacing is required. Twenty patients (63 +/- 15 years of age, 15 men) underwent external "temporary permanent" pacing. Pacing duration and associated complications were recorded. Cost models were then constructed using data from the London Health Sciences Center business unit to compare the cost of traditional temporary pacing and this technique using a Medtronic KSR903 pacemaker and 5,076 leads. Direct costs were calculated based on the 2005 Ontario Health Insurance Plan fee schedule, combined with calculation of labor and materials. Pacing was undertaken for a median of 2 days (range 2 to 83). There were no complications during implantation or pacing or after system removal. Sensing was lost in only 1 instance, which was reprogrammed uneventfully. Cost comparison showed that, although active-fixation lead placement was initially more costly ($798.71 vs $471.91), the added reliability of the permanent system allowed ward telemetry instead of cardiac care unit monitoring. This resulted in cost equivalence after only 18 hours and conferred a cost savings of $456 per 24-hour period thereafter. As a result, a savings of $585.20 is projected for a modeled patient after 48 hours of temporary pacing. In conclusion, temporary pacing using this technique is a reliable and comfortable alternative to traditional temporary pacing and appears to be a cost-effective temporary pacing option after 18 hours.

Adult↗
PubMed2006

Somatic mutations in the connexin 40 gene (GJA5) in atrial fibrillation.

BACKGROUND: Atrial fibrillation is the most common type of cardiac arrhythmia and a leading cause of cardiovascular morbidity, particularly stroke. The cardiac gap-junction protein connexin 40 is expressed selectively in atrial myocytes and mediates the coordinated electrical activation of the atria. We hypothesized that idiopathic atrial fibrillation has a genetic basis and that tissue-specific mutations in GJA5, the gene encoding connexin 40, may predispose the atria to fibrillation. METHODS: We sequenced GJA5 from genomic DNA isolated from resected cardiac tissue and peripheral lymphocytes from 15 patients with idiopathic atrial fibrillation. Identified GJA5 mutations were transfected into a gap-junction-deficient cell line to assess their functional effects on protein transport and intercellular electrical coupling. RESULTS: Four novel heterozygous missense mutations were identified in 4 of the 15 patients. In three patients, the mutations were found in the cardiac-tissue specimens but not in the lymphocytes, indicating a somatic source of the genetic defects. In the fourth patient, the sequence variant was detected in both cardiac tissue and lymphocytes, suggesting a germ-line origin. Analysis of the expression of mutant proteins revealed impaired intracellular transport or reduced intercellular electrical coupling. CONCLUSIONS: Mutations in GJA5 may predispose patients to idiopathic atrial fibrillation by impairing gap-junction assembly or electrical coupling. Our data suggest that common diseases traditionally considered to be idiopathic may have a genetic basis, with mutations confined to the diseased tissue.

Adult↗
PubMed2006

Effect of defibrillation testing on management during implantable cardioverter-defibrillator implantation.

BACKGROUND: Verification of defibrillation efficacy by defibrillation threshold (DFT) testing during implantable cardioverter-defibrillator implantation is the current standard. Generally, defibrillation of ventricular fibrillation at 10 J below the maximum output of a device is felt to establish an adequate safety margin. Nonetheless, DFT testing adds to cost and carries some potential for morbidity, whereas its impact on outcomes in the modern era of defibrillator technology is unclear. We aimed to determine the frequency that DFT testing resulted in a change at device implant and to identify clinical and echocardiographic predictors of the need for DFT testing. METHODS: We reviewed all implantable cardioverter-defibrillators that were implanted at the London Health Sciences Centre (Ontario, Canada) from June 1999 to August 2003 and used multivariate analysis to determine variables associated with DFT test failures and elevated DFT values. When a defibrillation failure was not observed, a lowest energy to defibrillate (LED) was recorded. RESULTS: Among 168 implants, DFT testing was successful with a minimum 10-J safety margin in 152 (90%), whereas the remaining 16 required changes at device implant. In a multivariate analysis, use of amiodarone was independently associated with DFT failure (odds ratio, 4.6; 95% confidence interval, 1.2-17.0). Significantly higher mean DFT/LED values were observed among patients on amiodarone (1.36 J; P = .0041). Those with nonischemic cardiomyopathy had a higher mean DFT/LED compared with those with ischemic cardiomyopathy (1.44 J; P = .028). CONCLUSIONS: Use of amiodarone is associated with a 4-fold increase in risk of DFT failure and subsequent need for changes at implant to achieve a safe threshold. Defibrillation threshold testing appears to be most useful for patients taking amiodarone.

Amiodarone↗
PubMed2006

Differentiating arrhythmogenic right ventricular cardiomyopathy from right ventricular outflow tract ventricular tachycardia using multilead QRS duration and axis.

BACKGROUND: Ventricular tachycardia (VT) resulting from arrhythmogenic right ventricular cardiomyopathy (ARVC) may be difficult to differentiate from idiopathic right ventricular outflow tract (RVOT) VT. OBJECTIVES: The purpose of this study was to investigate the hypothesis that QRS characteristics would be different in ARVC because of altered conduction through abnormal myocardium. METHODS: In 24 RVOT VT patients (18 women and 6 men; age 42 +/- 10 years) and 20 ARVC patients (12 women and 8 men; age 38 +/- 14 years), mean QRS duration, frontal plane axis, and precordial R-wave transition were measured in 12-lead ECGs recorded during VT. RESULTS: Mean QRS duration was longer in all 12 leads in ARVC patients. A significant difference was noted in leads I, III, aVL, aVF, V(1), V(2), and V(3) (P <.05). Leads I and aVL had the largest mean difference between ARVC and RVOT VT patients of 17.6 +/- 4.7 ms and 15.8 +/- 7.5 ms, respectively (P <.0001). Lead I QRS duration > or =120 ms had a sensitivity of 100%, specificity 46%, positive predictive value 61%, and negative predictive value 100% for ARVC. The area under the receiver operating characteristic (ROC) curve was 0.89. The addition of mean QRS axis <30 degrees (R<S in lead III) to the above criterion increased specificity for ARVC to 100%. QRS duration remained sensitive and specific in the subgroup of nine ARVC ECGs with an inferior axis (ROC area 0.82). R-wave transition was not different between groups. CONCLUSION: QRS duration is longer in ARVC compared with RVOT VT. An algorithm combining lead I QRS duration for sensitivity and axis for specificity is useful for differentiating the two tachycardia substrates.

Adult↗
PubMed2006

Universal access -- but when? Treating the right patient at the right time: access to electrophysiology services in Canada.

The Canadian Cardiovascular Society Access to Care Working Group has published a series of commentaries on access to cardiovascular care in Canada. The present article reviews the evidence for timely access to electrophysiology services. Using the best available evidence along with expert consensus by the Canadian Heart Rhythm Society, the panel proposed a series of benchmarks for access to the full scope of electrophysiology services, from initial consultation through to operative procedures. The proposed benchmarks are presented herein.

Canada↗
PubMed2006

Investigating syncope: a review.

PURPOSE OF REVIEW: This review focuses on recent literature on the cardiovascular investigation of syncope. RECENT FINDINGS: Syncope is a common and complex clinical entity with many varied etiologies, the diagnosis of which can often be elusive. Recent advances in the area of investigation in syncope include improvements in technologies for arrhythmia event monitoring and an increase in applicability and efficacy of traditional investigations. These advances have increased our ability to manage syncope. SUMMARY: A better understanding of the etiology of syncope in certain cohorts has allowed tailoring of investigations and management of syncope. This is evident when syncope occurs in the presence of structural heart disease, which is associated with a higher incidence of arrhythmias and an increased 1-year mortality. Patients with left-ventricular dysfunction should be considered candidates for an implantable cardioverter defibrillator based on heart function and syncopal presentation. In the absence of significant heart disease, investigations need to be tailored to diagnose neurally mediated causes for syncope and detection of intermittent bradycardia. The improved understanding of syncope has arisen from studies using improved investigational tools for syncope, in particular loop recorders, which are able to monitor cardiac rhythm over long periods. In those without structural heart disease and undifferentiated syncope, neurally mediated causes should be pursed initially. Tilt testing and loop recorders are employed most often in this cohort. Electrophysiological studies have largely been supplanted by implantable cardioverter defibrillator use in structural heart disease, with a low yield in patients with preserved heart function.

Cardiac Pacing, Artificial↗
PubMed2006

Pacing delivered rate and rhythm control for atrial fibrillation.

PURPOSE OF REVIEW: Device therapy for atrial fibrillation remains contentious despite the recognized benefit of atrial pacing in sinus node dysfunction. There are various new specialized pacing algorithms that aim to provide rhythm or rate control in atrial fibrillation. We review the various options for device therapy and the evidence available concerning their effectiveness. RECENT FINDINGS: Randomized trials on preventative algorithms for atrial fibrillation have not shown consistent benefit. Anti-tachycardia pacing for atrial fibrillation has inherent problems illustrated in this review and has failed to demonstrate objective improvement except in the case of atrial flutter. Several large randomized trials have demonstrated an adverse outcome with right ventricular apical pacing. These studies have shown an increase in atrial fibrillation with ventricular pacing. Recent studies have emphasised the importance of right ventricular apical pacing in burden of atrial fibrillation and therefore we discuss the likely confounding effect on previous trials and speculate on future directions. SUMMARY: The use of a device with atrial fibrillation prevention algorithms in a patient with a bradycardia indication for pacing is not unreasonable but there is no hard evidence of benefit. Patients with sinus node dysfunction should be paced in the atrium alone. There is no indication for use of a device for atrial fibrillation without a conventional indication for pacing.

Algorithms↗
PubMed2006

Multi-center clinical experience with a lumenless, catheter-delivered, bipolar, permanent pacemaker lead: implant safety and electrical performance.

PURPOSE: Reduced lead diameter and reliability can be designed into transvenous permanent pacing leads through use of redundant insulation and removal of the stylet lumen. The model 3830 lead (Medtronic Inc., Minneapolis, MN, USA) is a bipolar, fixed-screw, steroid-eluting, lumenless, 4.1-Fr pacing lead. Implantation can be performed in a variety of right heart sites using a deflectable catheter (Model 10600, Medtronic). Lead performance and safety were studied. METHODS: Two prospective trials of 338 implanted subjects from 56 global sites were conducted. Electrical and safety data were obtained at implant, pre-discharge, and up to 18 months post-implant. Leads were implanted at traditional and alternate right heart sites. RESULTS: The study enrolled 338 subjects (204 males, 70.6 +/- 11.6 years) followed-up for a mean of 10.2 months (range, 0-21.6). Mean P-wave amplitudes ranged from 3.2 mV at 3 months to 2.9 mV at 18 months, while mean atrial pulse width thresholds at 2.5 V ranged from 0.07 ms at 3 months to 0.09 ms at 18 months. Mean R-wave amplitudes ranged from 11.3 mV to 11.1 mV and mean ventricular pulse width thresholds at 2.5 V ranged from 0.10 ms to 0.14 ms. There were 22 ventricular and 12 atrial lead complications within 3 months post-implant. Survival from lead-related complications improved to a clinically acceptable rate in the cohort of patients when revised implant techniques were employed. CONCLUSIONS: With the use of recommended implant techniques, the study results support the electrical efficacy and safety of a catheter-delivered, lumenless lead in traditional or alternate right atrium or right ventricle sites through 18 months post-implant.

Aged↗
PubMed2006

The garden path.

Explore the source record for details and available documents.

Atrial Flutter↗
PubMed2006

Characteristics of slow pathway conduction after successful AVNRT ablation.

BACKGROUND: AV node slow pathway conduction can persist following successful ablation for AV node reentrant tachycardia (AVNRT). We hypothesized that careful examination of AV nodal conduction curves before and after effective AVNRT ablation in patients with persistent slow pathway conduction could shed light on this apparent paradox. METHODS AND RESULTS: Thirty patients (age 40.9 +/- 14.3; 8 male) were included. AV node function curves were created based on pre- and postablation atrial extrastimulus testing. Analysis of slow pathway function curves demonstrated significant decrease in AH for any given coupling interval after ablation (mean difference -68.1 [-94.5, -41.7] P < 0.001), graphically indicated by downward displacement of the curve. In addition, mean slow pathway effective refractory period (ERP) increased from 247.9 +/- 36.1 msec to 288.6 +/- 56.0 msec (P < 0.001); mean maximum AH interval decreased from 361.3 +/- 114.2 msec to 306.9 +/- 65.2 msec (P = 0.013); mean difference in minimum and maximum AH interval during slow pathway conduction decreased (from 94.5 +/- 75.8 msec to 59.6 +/- 46.2 msec (P = 0.016). Finally, mean difference between the fast and slow pathway effective refractory periods, the span of coupling intervals over which slow pathway conduction occurred, decreased (from 113.9 +/- 61.4 msec to 63.2 +/- 41.5 msec, P = 0.001). CONCLUSIONS: Ablation, which successfully eliminates inducible and spontaneous AVNRT in the presence of persistent slow pathway conduction, is associated with significantly altered slow pathway conduction characteristics, indicating the presence of a damaged or different slow pathway after ablation, incapable of sustaining tachycardia.

Adult↗