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Biomedical subjects

R Yee

Publications and source records attributed to R Yee.

At least 37 records · Page 2Linked to original sources
PubMed2001

Intraoperative study of polarization and evoked response signals in different endocardial electrode designs.

Some new generation pacemakers use an algorithm based on evoked response (ER) detection to verify beat-to-beat capture and to enable automatic adjustment of output. This is a prospective acute study of polarization signal (PS) and ER in nine currently available electrodes. Intraoperative testing of ventricular bipolar electrodes used the Autocapture (AC) algorithm. The intrinsic R wave, PS, ER, acceptance of AC function, and stimulation thresholds (STs) were obtained. Ventricular electrodes were categorized as follows: titanium nitride (TiN)-coated passive and active fixation, high impedance (HI), passive fixation (VP), iridium oxide-coated titanium (IROX) (VI), and platinum helix (PH) active fixation. Acute testing was performed in 217 patients with an average age of 74.26 years, 59.6% were men with primary pacing indication-SSS (46.3%). There were no significant differences found with respect to R wave and threshold between the various electrodes. PH active-fixation electrodes had significantly higher ER and PS than other groups including the TiN-coated active-fixation electrodes. TiN-coated electrodes (active and passive fixation) had significantly lower PS than other electrodes. As a result, TiN electrodes had a significantly higher functional rate of AC (91.7%), whereas PH had the lowest rate (0%). In conclusion, (1) polarization characteristics are significantly different for commercially available ventricular electrodes, (2) certain physical features at the tissue to electrode interface like TiN coating appears to be more important in determining PS than electrode tip size and fixation method, and (3) the current algorithm for AC requires electrodes that provide low polarization for satisfactory performance.

Adult↗
PubMed2001

A randomized, double-blind, placebo-controlled evaluation of the efficacy and safety of intravenously administered dofetilide in patients with Wolff-Parkinson-White syndrome.

Pharmacological conversion of arrhythmias in Wolff-Parkinson-White (WPW) syndrome is often frequently undertaken. Current antiarrhythmic drugs used for conversion can be associated with significant side effects and variable efficacy. Fifteen male patients (mean age 34, range 18-63 years) with WPW syndrome and atrial fibrillation or AVRT induced in the electrophysiology laboratory were enrolled in a prospective, randomized, placebo-controlled crossover study. Patients were randomized to one of two doses of intravenous dofetilide or placebo. Patients who failed to respond to this initial infusion received a second higher dose infusion of dofetilide. With the initial infusion, six of ten dofetilide patients converted to sinus rhythm compared to one of five placebo patients. After a second infusion of dofetilide for placebo patients and higher dose dofetilide for low dose dofetilide patients, the overall conversion rate was 71% with dofetilide compared with 20% for placebo (P = 0.046). Atrial fibrillation converted to sinus rhythm in 82% of patients who received dofetilide. Intravenous dofetilide was safe and effective at converting induced atrial fibrillation in patients with WPW syndrome.

Adolescent↗
PubMed2001

QT dispersion: an electrocardiographic derivative of QT prolongation.

BACKGROUND: QT dispersion has been considered a surrogate for heterogeneity of repolarization, leading to ventricular arrhythmias. METHODS: High-resolution 12-lead electrocardiograms were obtained in 15 patients with a history of ventricular tachycardia or ventricular fibrillation, 15 patients with congestive heart failure, 17 patients with a history of previous Q-wave myocardial infarction without heart failure, and 23 healthy control subjects. RESULTS: QTc dispersion was prolonged in all 3 patient groups compared with controls (71+/-22, 68 +/-31, 61+/-27 vs 44+/-17 msec, P =. 003), but no difference was seen between heart disease groups. QTc dispersion was strongly correlated with the QTc max (r = 0.73, P<.0001) but did not correlate with the QTc min (r = 0.04, P =.76). QTc dispersion also strongly correlated with the JTc max (r = 0.54, P<.0001) but did not correlate with JTc min (r = -0.007, P =.95). QTc dispersion correlated inversely with T-wave amplitude (r = -0.35, P =.003). When all 876 electrocardiographic signals were considered, a significant negative correlation was present between QTc duration and T-wave amplitude (r = -0.133, P =.0002). Logistic regression analysis failed to demonstrate any independent risk factors that predicted ventricular arrhythmias, including all measures of dispersion. CONCLUSIONS: The measurement of QT dispersion is strongly influenced by the maximum QT interval, as well as by changes in T-wave amplitude. QT "dispersion" may represent a summary of these changes that reflect the underlying myocardial process but does not represent an accurate quantitative measure of heterogeneity of refractoriness.

Electrocardiography↗
PubMed2001

Predictive value of presyncope in patients monitored for assessment of syncope.

BACKGROUND: The purpose of this study was to assess the diagnostic value of recording the cardiac rhythm during presyncope in patients undergoing monitoring for undiagnosed syncope. METHODS AND RESULTS: Eighty-five patients (age, 59 +/- 18 years; 44 men, 41 women) with recurrent unexplained syncope underwent prolonged monitoring with an implantable loop recorder. Patients were examined for syncope, which was either recurrent or associated with at least 2 presyncopal episodes. Patients had a mean of 5.1 +/- 5.5 syncopal episodes in the previous 12 months, and 70% of patients had symptoms for >2 years. Sixty-two (73%) patients had recurrent symptoms during a 12-month follow-up period. Of 150 recurrent events captured by the implantable loop recorder, there were 38 (25%) episodes of syncope and 112 (75%) episodes of presyncope. Syncope alone recurred in 12 patients, presyncope in 25, and both in 16. An arrhythmia was present in 64% of syncopal events (bradycardia in 16, tachycardia in 2) versus 25% for presyncopal events (bradycardia in 7, tachycardia in 3, P =.001). An arrhythmia was detected in 9 (56%) of the 16 patients with both syncope and presyncope, which was present in all recorded episodes of syncope compared with 6 of 9 presyncopal episodes. Patient-related failure to freeze the device after symptoms occurred in 21 (36%) of 59 syncopal events compared with 15 (12%) of 127 presyncopal events (P =.0001). CONCLUSIONS: Syncope is more likely to be associated with an arrhythmia than is presyncope in patients undergoing extended monitoring. Presyncope is a nonspecific end point that is frequently associated with sinus rhythm. Patients undergoing extended monitoring for syncope should continue to be monitored after an episode of presyncope unless an arrhythmia is detected.

Bradycardia↗
PubMed2001

Safety and feasibility of a novel rate-smoothed ventricular pacing algorithm for atrial fibrillation.

OBJECTIVES: This study was conducted to establish the safety and performance of a new rate-smoothing pacing algorithm for patients with atrial fibrillation (AF). BACKGROUND: Irregularity of the ventricular response is a hallmark of AF. This irregularity may contribute to symptoms and hemodynamic compromise in patients with AF. Interventions designed to reduce irregularity have not previously been evaluated in a long-term, clinical setting. METHODS: We designed a prospective, double-blind study with randomized crossover. Patients with either paroxysmal or chronic AF whose conditions were medically refractory and who were referred for an atrioventricular node ablation procedure all underwent pacemaker implantation. Subjects were then randomly assigned to either DDD mode with the rate-smoothing algorithm (RSA) on, or to OOO mode. After 2 months they were crossed over to the other arm. RESULTS: Fourteen patients (9 with paroxysmal AF and 5 with chronic AF) were enrolled. There were no significant differences between the group randomly assigned to RSA first versus the group assigned to OOO first. The mean left ventricular ejection fraction with the RSA was not significantly different than it was in OOO mode (45.1 +/- 18.6 vs 51.9 +/- 12.3; P =.11), although some individuals with uncontrolled ventricular rates did have a large decrease in ejection fraction with rate smoothing. One developed overt heart failure. One quality-of-life instrument detected a significant improvement in the "physical limitations" domain with the rate-smoothing mode. Eleven of 14 patients preferred the RSA ON arm, and 6 of those 11 elected to defer the ablation procedure. CONCLUSIONS: Long-term rate-smoothed pacing is feasible. Because of concerns about pacing-induced heart failure in some patients with rapid ventricular rates, rate-smoothed pacing should be reserved for those who remain symptomatic despite adequate control of the ventricular rate. The RSA may help to reduce symptoms in patients with medically refractory AF; more study is required to define its efficacy in reducing symptoms and morbidity in this population.

Aged↗
PubMed2000

Cryothermal ablation of the slow pathway for the elimination of atrioventricular nodal reentrant tachycardia.

BACKGROUND: We report the first successful slow pathway ablation using a novel catheter-based cryothermal technology for the elimination of atrioventricular nodal reentrant tachycardia (AVNRT). METHODS AND RESULTS: Eighteen patients with typical AVNRT underwent cryoablation. Reversible loss of slow pathway (SP) conduction during cryothermy (ice mapping) was demonstrated in 11 of 12 patients. Because of time constraints, only 2 sites were ice mapped in 1 patient. Seventeen of 18 patients had successful cryoablation of the SP. One patient had successful ice mapping of the SP, but inability to cool beyond -38 degrees C prevented successful cryoablation. A single radiofrequency lesion at this site eliminated SP conduction. No patient has had recurrent AVNRT over 4.9+/-1.7 months of follow-up. During cryoablation, accelerated junctional tachycardia was not seen and was therefore not available to guide lesion delivery. Adherence of the catheter tip during cryothermy (cryoadherence) allowed atrial pacing to test for SP conduction. Cryoablation in the anterior septum produced inadvertent transient PR prolongation consistent with loss of fast pathway conduction in 1 patient and transient (6.5 seconds) 2:1 AV block in another. On rewarming, the PR interval returned to normal, and the AV nodal effective refractory period was unchanged in both. Accelerated junctional tachycardia was seen on rewarming in both but not during cryothermy. CONCLUSIONS: Cryothermal ablation of the SP was achieved in patients with this novel technique. Successful ice mapping of both the SP and fast pathway was demonstrated. The ability to test the functionality of specific ablation sites before production of a permanent lesion may eliminate inadvertent AV block.

Adult↗
PubMed2000

Randomized crossover comparison of DDDR versus VDD pacing after atrioventricular junction ablation for prevention of atrial fibrillation. The atrial pacing peri-ablation for paroxysmal atrial fibrillation (PA (3)) study investigators.

BACKGROUND: Some clinical data suggest that atrial-based pacing prevents paroxysmal atrial fibrillation (AF). This study tested the hypothesis that DDDR pacing compared with VDD pacing prevents AF after atrioventricular (AV) junction ablation. METHODS AND RESULTS: Patients were randomized to DDDR pacing (n=33) or to VDD pacing (n=34) after AV junction ablation and followed every 2 months for 6 months. Patients then crossed over to the alternate pacing mode and were followed for an additional 6 months. Primary analysis included the time to first recurrence of sustained AF (duration >5 minutes), total AF burden, and the development of permanent AF. The time to first episode of AF was similar in the DDDR group (0.37 days, 95% CI 0.1 to 1.3 days) and the VDD pacing group (0.5 days, 95% CI 0.2 to 1.7 days, P=NS). AF burden increased over time in both groups (P<0.01). At the 6-month follow-up, AF burden was 6.93 h/d (95% CI 4. 37 to 10.96 h/d) in the DDDR group and 6.30 h/d (95% CI 3.99 to 9.94 h/d) in the VDD group (P=NS). Twelve (35%) patients in the DDDR group and 11 (32%) patients in the VDD group had permanent AF within 6 months of ablation. Within 1 year of follow-up, 43% of patients had permanent AF. CONCLUSIONS: DDDR pacing compared with VDD pacing does not prevent paroxysmal AF over the long term in patients in the absence of antiarrhythmic drug therapy after total AV junction ablation. Many patients have permanent AF within the first year after ablation.

Aged↗
PubMed2000

Does endogenous immune response determine the outcome of surgical therapy for metastatic melanoma?

BACKGROUND: Although the presence of tumor cells in the blood of patients with metastatic melanoma suggests widely disseminated disease, many of these patients enjoy prolonged survival or cure after surgical resection. Our previous study of adjuvant vaccine therapy after complete resection of metastatic melanoma revealed a strong correlation between postoperative survival and elevated antibody titers to a 90-kDa tumor-associated antigen (TA90) expressed by melanoma cells of the vaccine. We hypothesized a similar correlation between postoperative survival and endogenous anti-TA90 antibody titers induced by the patient's melanoma in the absence of postoperative adjuvant immunotherapy. METHODS: From 1970 to 1996, 64 patients underwent complete resection of distant melanoma metastases and did not receive postoperative adjuvant immunotherapy. Serum collected within 4 months after surgery was tested in a coded and blinded fashion for anti-TA90 IgG and IgM by enzyme-linked immunosorbent assay, and for total IgG and IgM (controls) by radial immunodiffusion. RESULTS: Median follow-up for the study population was 19 months (range, 3-147 months). There was no significant correlation between anti-TA90 IgG titer and total IgG level (P = .4785), or between anti-TA90 IgM and total IgM (P = .0989). Univariate analysis showed that postoperative anti-TA90 IgM titer as a continuous variable was significantly associated with overall survival (OS); i.e., the higher the anti-TA90 IgM titer, the longer the OS. Using an established cutoff titer of 800, median OS was 42 months for patients with high anti-TA90 IgM titers (n = 28) vs. 9 months for patients with low titers (n = 36) (P = .0001). There was no significant correlation between total IgG/IgM and survival (P = .4107 and .4044, respectively). Multivariate analysis identified anti-TA90 IgM as the most significant independent variable influencing OS after complete resection of distant melanoma metastases (P = .0001). CONCLUSIONS: We conclude that the endogenous immune response to metastatic melanoma determines the outcome after surgical therapy. Enhancement of this specific immune response may prolong the survival of patients with distant melanoma metastases.

Antigens, Neoplasm↗
PubMed2000

Static and dynamic stresses of practical thermowells

A flexible beam model is proposed for calculating the flow induced stresses and application limits of common thermowell designs. It is intended to replace traditional selection methods with one which emphasizes mechanical integrity and process containment.

Journal Article↗
PubMed2000

Recurrent seizure diagnosed by the insertable loop recorder.

INTRODUCTION: The Insertable Loop Recorder (ILR) has emerged as an important new tool in the diagnostic armamentarium for patients with syncope. METHODS AND RESULTS: A case report illustrates how the ILR unexpectedly led to the diagnosis of seizure as the explanation for a man's recurrent, but infrequent episodes of sudden loss of consciousness. CONCLUSIONS: This case raises the possibility that the development of implantable recording devices which monitor physiologic parameters other than cardiac rhythm (eg. brain, nerve or muscle activity) may provide the long-term monitoring capability needed to improve the diagnostic yield for conditions, such as seizures, which occur infrequently.

Aged↗
PubMed2000

A novel mutation in KVLQT1, L122P, found in a family with autosomal dominant long QT syndrome.

BACKGROUND: Linkage and mutation analysis in long QT syndrome kindreds has demonstrated locus heterogeneity, with causative mutations reported in at least 5 different genes, including KVLQT1. METHODS AND RESULTS: A 12-year-old male proband with recurrent syncope and a prolonged QT interval underwent clinical assessment and exercise testing along with 3 affected and 3 unaffected family members. The coding regions of 5 putative transmembrane segments (S2-S6) and a putative pore region of the KVLQT1 gene for the proband were amplified with the polymerase chain reaction. DNA sequencing of the KVLQT1 gene of the proband revealed a T-->C transversion at the second position of codon 122, which predicted a substitution of proline for leucine (L122P). By using restriction analysis, the L122P was found to be co-segregated with the electrocardiographic abnormalities in the nuclear family. Although the patient's mother was heterozygous for L122P, neither maternal grandparent was a carrier, suggesting that the mutation arose spontaneously. In comparison, there was a complete absence of the mutation in 1336 alleles from 668 normal individuals of 6 different ethnic backgrounds. CONCLUSION: The KVLQT1 L122P mutation is a rare novel mutation that probably arose spontaneously in this family, leading to long QT syndrome.

Child↗
PubMed2000

The mode selection trial (MOST) in sinus node dysfunction: design, rationale, and baseline characteristics of the first 1000 patients.

BACKGROUND: More than 200,000 permanent pacemakers will be implanted in the United States in 2000 at a cost of more than $2 billion. Sick sinus syndrome (SSS) will likely account for approximately half of all cases necessitating implantation. Pacemaker technology permits the selection of ventricular (single-chamber) or dual-chamber devices. However, clinical and outcomes data are inadequate to support a clear recommendation that one or the other type of device be used. METHODS: The Mode Selection Trial (MOST) is a single-blind study supported by the National Heart, Lung, and Blood Institute designed to enroll 2000 patients with SSS. All patients will receive a DDDR pacemaker programmed to VVIR or DDDR before implantation. The average time of follow-up will be 3 years. MOST has a >90% power to detect a 25% reduction in the primary end point-nonfatal stroke or total (all cause) mortality-in the DDDR-treated group. Secondary end points will include health-related quality of life and cost effectiveness, atrial fibrillation, and development of pacemaker syndrome. Prespecified subgroups for analysis will include women and the elderly. Enrollment was completed in October 1999, with a total of 2010 patients. RESULTS: The median age of the first 1000 enrolled patients is 74 years, with 25% of patients 80 years or older. Women comprise 49%, and 17% are nonwhite, predominantly black (13%). Before pacemaker implantation, 22% of patients reported a history of congestive heart failure, 11% coronary angioplasty, and 25% coronary bypass surgery. Supraventricular tachycardia including atrial fibrillation was present in 53% of patients. A prior stroke was reported by 12%. Antiarrhythmic therapy was in use in 18% of patients. CONCLUSIONS: MOST will fill the clinical need for carefully designed prospective studies to define the benefits of dual-chamber versus single-chamber ventricular pacing in patients with SSS. The MOST population is typical of the overall pacemaker population in the United States. Thus the final results of MOST should be clinically generalizable.

Aged↗
PubMed2000

Rate-control versus conversion strategy in postoperative atrial fibrillation: a prospective, randomized pilot study.

BACKGROUND: Atrial fibrillation remains a frequent complication after heart surgery. The optimal strategy to treat the condition has not been established. Several retrospective studies have suggested that a primary rate-control strategy may be equivalent to a strategy that restores sinus rhythm. METHODS: Fifty patients with atrial fibrillation after heart surgery were randomly assigned to a strategy of antiarrhythmic therapy with or without electrical cardioversion or ventricular rate control. Both arms received anticoagulation with heparin overlapped with warfarin. The primary end point was time to conversion to sinus rhythm analyzed by the Kaplan-Meier method. Atrial fibrillation relapse after the initial conversion was monitored in the hospital over a 2-month period. RESULTS: There was no significant difference between an antiarrhythmic conversion strategy (n = 27) and a rate-control strategy (n = 23) in time to conversion to sinus rhythm (11.2 +/- 3. 2 vs 11.8 +/- 3.9 hours; P =.8). With the use of Cox multivariate analysis to control for the effects of age, sex, beta-blocker usage, and type of surgery, the antiarrhythmic strategy showed a trend toward reducing the time from treatment to restoration of sinus rhythm (P =.08). The length of hospital stay was reduced in the antiarrhythmic arm compared with the rate-control strategy (9.0 +/- 0.7 vs 13.2 +/- 2.0 days; P =.05). In-hospital relapse rates in the antiarrhythmic arm were 30% compared with 57% in the rate-control strategy (P =.24). There were no significant difference in relapse rates at 1 week (24% vs 28%), 4 weeks (6% vs 12%), and 6 to 8 weeks (4% vs 9%). At the end of the study, 91% of the patients in the rate-control arm were in sinus rhythm compared with 96% in the antiarrhythmic arm (P =.6). CONCLUSIONS: This pilot study shows little difference between a rate-control strategy and a strategy to restore sinus rhythm. Regardless of strategy, most patients will be in sinus rhythm after 2 months. A larger randomized, controlled study is needed to assess the impact of restoration of sinus rhythm on length of stay.

Aged↗
PubMed2000

Unipolar electrogram characteristics predictive of successful radiofrequency catheter ablation of accessory pathways.

INTRODUCTION: The purpose of this study was to determine the characteristics of the unipolar electrogram that are most helpful in predicting successful radiofrequency ablation of accessory pathways. METHODS AND RESULTS: The unipolar electrogram was analyzed at 185 ablation sites in 53 patients; 94 attempts were directed at the site of earliest atrial activation ("atrial group") and 91 at the site of earliest ventricular activation ("ventricular group"). The electrogram was analyzed for several features, including pattern ("QS" or "initial R"). Unipolar pattern: Overall, a "QS" pattern was seen at 55% of unsuccessful, 75% of temporarily successful, and 90% of permanently successful sites. For the atrial group, the respective frequencies were 53%, 77%, and 92%, and for the ventricular group, 57%, 73%, and 86%. The difference in pattern distribution between unsuccessful and permanently successful sites was significant for all groups: overall, P < 0.0001; atrial group, P = 0.0005; ventricular group, P = 0.02. Absence of a "QS" pattern (i.e., "initial R") predicted a 92% chance of unsuccessful ablation. Additional features: Activation times were significantly shorter at permanently successful than at unsuccessful (P < 0.0001) or temporarily successful sites (P = 0.0002). No significant differences were found in atrial or ventricular amplitudes or in A/V ratios. Intrinsic deflection slew was lower at temporarily successful sites (P = 0.03 vs all other sites). CONCLUSION: Ablation at sites revealing an "initial R" pattern (i.e., absent "QS") is very unlikely to be successful. Activation time is shorter at successful sites. These features are equally applicable when mapping the atrial potential as when mapping the ventricular potential.

Adolescent↗
PubMed2000

Impact of a mandatory physician reporting system for cardiac patients potentially unfit to drive.

CONTEXT: Sudden cardiac incapacitation of a driver may lead to the death or serious injury of passengers or bystanders. This has raised public safety concerns and has led to the creation of legislation to protect the public. Some jurisdictions in Canada and the United States have introduced mandatory physician reporting of patients who may be unfit to drive for medical reasons. The impact on motor vehicle accident (MVA)-related morbidity and mortality of mandatory physician reporting for at-risk cardiac patients is unknown. OBJECTIVE: To determine the impact of mandatory physician reporting legislation (for cardiac patients) in Ontario (population 10.3 million) on MVA-related morbidity and mortality. DATA SOURCES: Reporting data were obtained from the Ontario Ministry of Transportation. Incidence and prevalence data were taken from Ontario Ministry of Health sources and from the literature (MEDLINE). Data for modelling were taken from the literature (MEDLINE) and from the Canadian Cardiovascular Society's Consensus Conference document on cardiac illness and fitness to drive. DATA EXTRACTION: Licence suspension data (correlated with medical illness) were taken directly from government documents. These were then applied to a 'risk of harm' formula used to calculate the risk posed to bystanders and passengers by the suspended patients if they had continued to drive. Canadian licence suspension guidelines were then reviewed in conjunction with cardiac disease incidence and prevalence data to arrive at the number of patients who should have been suspended. Physician compliance with the legislation was then calculated, along with the potential impact on MVA-related morbidity and mortality in the scenario of 100% physician compliance. STUDY SELECTION: All Ontario drivers who had licence suspensions in 1996 for reasons of cardiac disease were included in the analysis. DATA SYNTHESIS: Nine hundred and ninety-four licences were suspended for cardiac reasons in 1996, compared with an estimated 72,407 that should have been suspended if Canadian guidelines had been followed (1.4%). Less than one death or serious injury was avoided as a result of the legislation (from the 'risk of harm' formula). If all drivers with cardiac illness had been suspended from driving, up to 29.2 such events could potentially have been avoided. However, only 13 of 929 (1.4%) road fatalities in Ontario in 1996 were attributed to a driver with a medical illness. CONCLUSIONS: Mandatory physician reporting of patients with cardiac illness has a negligible impact on MVA-related morbidity and mortality.

Accidents, Traffic↗