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Biomedical subjects

Raymond Yee

Publications and source records attributed to Raymond Yee.

At least 19 recordsLinked to original sources
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

Prognostic differences between atrial fibrillation and atrial flutter.

This report presents the outcome of a cohort of 94 patients with atrial fibrillation from the Canadian Registry of Atrial Fibrillation, in which we paid particular attention to the probability of stroke and death. We also evaluated warfarin use over time and compared left atrial dimensions in patients with atrial flutter with those with atrial fibrillation.

Aged↗
PubMed2004

The use of monitoring strategies in patients with unexplained syncope--role of the external and implantable loop recorder.

Syncope is a complex clinical syndrome with multiple etiologies that can be very difficult to diagnose. The major obstacles to diagnosis are the periodic and unpredictable nature of events and the high spontaneous remission rate. Short-term electrocardiographic monitoring is often unproductive in patients when initial non-invasive testing is negative, particularly when a paroxysmal arrhythmia is suspected. The external and implantable loop recorders extend the ability to monitor cardiac patients, enhancing the diagnostic yield to as high as 85% in difficult to diagnose syncope. Several recent studies suggest that prolonged monitoring with an implantable loop recorder has a role in patients with syncope and conduction disturbances, negative tilt testing, unexplained seizures and may be superior to conventional testing with tilt and electrophysiologic studies in selected patients.

Electrocardiography, Ambulatory↗
PubMed2004

External loop recorders: determinants of diagnostic yield in patients with syncope.

OBJECTIVES: The purpose of the current study was to determine the optimal duration of external loop recorder (ELR) monitoring in patients with presyncope or syncope and to identify factors that predict failure to activate the device effectively. DESIGN: A multivariate analysis was performed using data from the Comparison Of Loop Recorders Against Holter in Patients with Syncope (COLAPS) trial, a prospective study comparing diagnostic utility of ELRs and Holter monitors for assessment of syncope. METHODS: Patients with failure to effectively activate ELRs were compared to those who were successful. This analysis was performed separately for failure of test transmission and for failure to successfully record and transmit data from symptomatic episodes. Patient characteristics were compared among the groups to determine risk factors for device failure. RESULTS: Among 78 patients who received ELRs, a test transmission was successfully performed by 84.5% of patients. Twenty-one percent of diagnoses were made within 48 hours, 50% at 15 days, and 90% at 33 days. Patients performing a successful test transmission were more familiar with technology, with ability to use a bank automatic teller machine being a significant independent predictor. Patients with a successful test transmission were, in turn, significantly more likely to record and transmit data from symptomatic episodes. Patients living alone were much less likely to use the loop recorder effectively. The presence of factors that may influence motivation to reach a diagnosis (degree of worry/fear of symptoms and impact on daily life) were associated with successful use of the device in a univariate analysis. CONCLUSION: ELRs should be worn for at least 30 days to maximize their diagnostic yield. Patients who are unfamiliar with technology, live alone, or have low motivation to reach a diagnosis have a lower diagnostic yield from ELRs for assessment of syncope.

Electrocardiography, Ambulatory↗
PubMed2004

Detection of asymptomatic arrhythmias in unexplained syncope.

BACKGROUND: Although electrocardiographic monitoring during syncope is the most unambiguous method of diagnosing or excluding an arrhythmia, it requires recurrence of syncope with potential morbidity. We hypothesized that long-term monitoring of patients with syncope would yield significant asymptomatic abnormalities that might preclude waiting for recurrence of actual syncope. METHODS: Sixty patients (age, 67+/-16 years; 27 men) with recurrent unexplained syncope, aged >or=30 years, with a left ventricular ejection fraction >or=35% and negative results on conventional monitoring were enrolled in a prospective study involving long-term automatic arrhythmia detection monitoring with an implantable loop recorder. Pre-specified significant asymptomatic arrhythmias were a pause >5 seconds, 3 degrees atrioventricular block >10 seconds, heart rate (HR) <30 beats/min for >10 seconds while awake, wide complex tachycardia >10 beats, and narrow complex tachycardia >180 beats/min for >30 beats. Borderline asymptomatic arrhythmias included 3- to 5-second pauses, HR <30 beats/min for <10 seconds while awake, HR <30 beats/min for >10 seconds while asleep, and nonsustained wide complex tachycardia or narrow complex tachycardia. RESULTS: Recurrent symptoms developed in 30 patients during the 1-year follow-up period (47%), with arrhythmias detected in 14 patients (23%). Pre-specified significant asymptomatic arrhythmias developed in 9 patients (15%), with bradycardia in 7 patients who underwent pacemaker implantation. Twenty patients (33%) had borderline asymptomatic arrhythmias. Five of these patients (25%) went on to have more pronounced diagnostic arrhythmias of the same mechanism during further follow-up, including pauses of 6 to 17 seconds duration in 3 patients. CONCLUSION: Long-term monitoring of patients with unexplained syncope with automatic arrhythmia detection demonstrated that significant asymptomatic arrhythmias were seen more frequently than anticipated, leading to a change in patient treatment. Automatic arrhythmia detection provides incremental diagnostic usefulness in long-term monitoring of patients with syncope.

Aged↗
PubMed2004

Prospective randomized study of mode switching in a clinical trial of pacemaker therapy for sinus node dysfunction.

INTRODUCTION: Atrial fibrillation (AF) is common in pacemaker patients with sinus node dysfunction (SND) and may result in rapid ventricular pacing (RVP) in the DDDR mode. Mode switching (MS) reduces RVP, but its clinical benefit in patients with SND is unknown. METHODS AND RESULTS: Two hundred two patients in the Mode Selection Trial (MOST; 2,010-patient, 6-year trial of DDDR vs VVIR pacing in SND) randomized to DDDR pacemakers with atrial high-rate episode (AHRE) storage capabilities were subrandomized to MS ON (N = 96) or MS OFF (N = 106). Cardiovascular symptoms, quality of life (QOL), reprogramming due to RVP, death, stroke, and heart failure hospitalization (HFH) were compared between groups. The treatment groups were similar with regard to AF history (59% MS ON vs 57% MS OFF). AHREs occurred in 49% patients during median follow-up of 2.2 years. Median AHRE duration (in min; MS ON 116 vs MS OFF 58, P = 0.29), frequency AHREs/week (MS ON 3.5 vs MS OFF 6.4, P = 0.23), and time spent in AHRE (min/week) (MS ON 450, MS OFF 268) were similar. Reprogramming due to any RVP during AHREs occurred more in MS OFF vs MS ON (13.2% vs 3.1%, P = 0.011) and marginally more for symptomatic RVP (8.5% vs 2.1%, P = 0.062). Cardiovascular symptoms occurred in 93.6% MS ON vs 90.2% MS OFF (P = 0.38). Median number of symptoms reported per visit was similar (MS ON 1.3 vs MS OFF 1.5, P = 0.62). Median symptom frequency/severity, summed and averaged over visits, was similar (MS ON 4.3 vs MS OFF 4.5, P = 0.74). QOL was not different between groups. Death, stroke, and HFH were not different between groups. CONCLUSION: MS reduces pacemaker reprogramming due to RVP during AHREs in a small number of patients but does not improve QOL or cardiovascular symptoms overall among patients with SND.

Aged↗
PubMed2004

Cryoablation: potentials and pitfalls.

The use of cryoablation in the electrophysiology lab provides some distinct advantages not seen with conventional radiofrequency ablation. Ice mapping allows a functional assessment of a putative ablation site prior to the formation of a permanent lesion. This provides a distinct advantage adjacent to the AV node for para-hisian pathways and difficult cases of AVNRT. Cryoablation also produces minimal endothelial disruption and thrombus formation and causes no collagen shrinkage. This is likely advantageous when ablation is required within venous structures. There is also mounting experimental evidence that cryoablation is safe adjacent to the arterial system, especially within the middle cardiac vein or distal coronary sinus. As the technology evolves and further iterations of the catheter proceed, the role for this new but well-established technology is likely to grow.

Animals↗
PubMed2004

Optimal pacing for symptomatic AV block: a comparison of VDD and DDD pacing.

VDD pacing provides the physiological benefits of atrioventricular synchronous pacing with the convenience of a single lead system, but is hampered by uncertainty regarding long term atrial sensing and potential development of sinus node disease. To examine the long-term reliability and complication rates of VDD pacing, we compared the outcome of 112 consecutive patients (age 70 +/- 13 years, 59% men) with symptomatic AV block who received a single pass bipolar VDD system, to 80 patients (age 63 +/- 16 years, 70% men) who received DDD pacing for the same indication. All patients were judged to have intact sinus node function based on submitted ECGs and monitoring results at the time of implant. Implant time was reduced in VDD patients compared to DDD patients (63 +/- 20 vs 97 +/- 36 minutes, P < 0.0001). Implant complications occurred in 5 (6%) DDD patients compared to 3 (3%) VDD patients (P = 0.15). The implant P wave was lower with VDD pacing compared to DDD patients (2.91 +/- 1.48 vs 4.0 +/- 1.7 mv, P < 0.0001), but remained stable during long-term follow-up in both groups. During 17.7 +/- 10.0 months of follow-up in the VDD group, only two VDD patients were reprogrammed to VVIR mode, compared to three DDD patients. Physiological atrioventricular activation was maintained in 94%-99% of beats throughout the follow-up period in the VDD group. VDD pacing is an excellent strategy for treatment of patients with symptomatic AV block. The lower cost, high reliability, and abbreviated implantation time suggest that VDD pacing is a viable alternative to DDD pacing in patients with high degree AV block and normal sinus node function.

Aged↗
PubMed2004

Insertable loop recorder use for detection of intermittent arrhythmias.

The advent of prolonged monitoring with the implanted loop recorders has revolutionized the quest for detection of elusive infrequent arrhythmias in patients with unexplained syncope. The capability of prolonged monitoring has permitted us to obtain symptom rhythm correlation in the majority of patients suspected to have underlying infrequent arrhythmia. The implanted loop recorder is easily implanted in the left pectoral region with a minimally invasive procedure, providing at least 14 months of continuous monitoring that is both patient and automatically activated. Several recent studies suggest that it plays a major role in patients with infrequent symptoms and suspected arrhythmia, including patients with syncope and conduction disturbances, mild to moderate underlying heart disease, and atypical epilepsy. In a randomized trial, the device was found to be cost-effective and improved diagnostic yield compared to conventional tilt and electrophysiological testing. Wider application of prolonged monitoring is ongoing, including assessment of ventricular arrhythmias, atrial fibrillation, and conduction disturbances. The implantable loop recorder is most useful in patients with infrequent unexplained syncope when noninvasive testing is negative.

Arrhythmias, Cardiac↗
PubMed2004

Selective site pacing: tools and training.

Current tools and techniques for pacemaker and ICD lead insertion have been optimized for implantation of leads at traditional sites but may be ill-suited for achieving alternate or selective site placement. If clinical studies confirm that optimal pacing is achieved from locations other than the right atrial appendage and right ventricular apex, new tools for reliably, easily and safely implanting leads at these sites will need to be created and methods for identifying these optimal pacing site(s) in each patient will be needed. Implant centers will need to understand the benefits of selective site pacing and make the transition to using these new tools. The various factors affecting the change from traditional to selective site pacing lead placement are discussed.

Cardiac Pacing, Artificial↗
PubMed2004

Sudden intense exercise increases QT heart rate slope and T wave complexity in long QT syndrome and normal subjects.

Sudden intense physical activity is a trigger for ventricular arrhythmias in long QT syndrome (LQTS), and beta-blockers (B) reduce the risk of ventricular arrhythmias in LQTS. We compared the effect of graded (gradual intensity) versus burst (sudden intensity) exercise on QT-rate adaptation and T wave complexity in LQTS + B (n = 21), LQTS - B (n = 5), and normal controls (n = 20). Graded exercise consisted of symptom-limited bicycle ergometry (30 W, increment 20 W/min). Burst exercise involved a fixed 200 W load for 1.0 minute. ECGs were digitally recorded every 10 seconds during exercise and a 10 minute recovery period. QT-rate adaptation was quantified using the slope of the QT cycle length relationship fit to a quadratic function. Principle component analysis (PCA) was used to quantify T wave complexity. The QT-rate slope was two-fold greater with burst exercise than graded exercise for LQTS + B (-82E +/- 40E vs -36E +/- 40E, P = 0.0016), LQTS - B (-85E +/- 60E vs -30E +/- 50E, P = 0.011) and controls (-100E +/- 60E vs -48E +/- 100E, P = 0.0011) (E = x10(-5)). For each exercise protocol, there was no difference in QT-rate slope between the three groups. In contrast, the QT-rate slope during the 10 minute recovery period was similar between the burst and graded protocol for LQTS + B (25E +/- 40E vs 30E +/- 50E), LQTS - B (81E +/- 80E vs 85E +/- 70E) and controls (90E +/- 80E vs 82E +/- 80E). The coefficient of variability of PCA (T wave complexity variability) during burst exercise was greater than that during graded exercise for LQTS + B (41 +/- 15 vs 30 +/- 10, P = 0.017), LQTS - B (47 +/- 25 vs 26 +/- 4, P = 0.016), and control (46 +/- 14 vs 33 +/- 19, P = 0.012). For each exercise protocol, no difference in T wave complexity variability was seen between the three groups. In conclusion, QT heart rate slope and T wave complexity variability are greater during sudden intense exercise than graded exercise in LQTS patients (on and off beta-blockers) and normal subjects, with similar findings among the three groups of patients.

Adaptation, Physiological↗
PubMed2004

Utility of a simplified lidocaine and potassium infusion in diagnosing long QT syndrome among patients with borderline QTc interval prolongation.

BACKGROUND: Congenital long QT syndrome (LQTS) is caused by mutations in the cardiac Na+ or K+ channels that result in a prolonged QTc interval and increased QT dispersion. Na+ channel blockers and K+ can reverse the repolarization abnormalities in the Na+ channel variant (LQT3) and K+ channel variant (LQT1, LQT2), respectively. The phenotype of LQTS can be difficult to recognize, especially when the QTc interval is mildly prolonged. Additional noninvasive testing methods are needed to enhance the diagnosis of LQTS. This study compared the response of the QTc interval and QT dispersion to a sequential lidocaine/K+ infusion in LQTS patients with borderline QTc interval prolongation and control patients as a means of diagnosing LQTS. METHODS: In this study, eight LQTS patients with borderline QTc, defined as QTc < 470 ms, and 10 healthy controls received sequential lidocaine/K+ infusion. RESULTS: At baseline, LQTS patients had a longer QTc (446 +/- 29 vs 416 +/- 28 ms, P < 0.05) but similar QT dispersion (43 +/- 14 vs 29 +/- 10 ms) compared to controls. After lidocaine administration, baseline QTc and QT dispersion did not change in either LQTS or controls. One LQTS patient had a 54 ms (12%) reduction in his QTc but no change in QT dispersion. Following K+ infusion, baseline QTc and QT dispersion decreased by 9% (P < 0.005) and 45% (P < 0.005), respectively in LQTS. No effect was seen in control patients, where QTc and QT dispersion shortened by 1% (5 +/- 14 ms) and 20% (6 +/- 7 ms), respectively, compared to baseline. The combined lidocaine/K+ infusion had a sensitivity, specificity, and accuracy of 88%, 100%, and 94%, respectively, in diagnosing LQTS. CONCLUSIONS: A simplified sequential lidocaine/K+ challenge is accurate in diagnosing LQTS among patients with borderline QTc prolongation.

Adult↗
PubMed2003

Role of the posterior left atrium and pulmonary veins in human lone atrial fibrillation: electrophysiological and pathological data from patients undergoing atrial fibrillation surgery.

BACKGROUND: Surgery can eliminate atrial fibrillation (AF), but data confirming the rationale for specific lesion sets are lacking. We used postoperative electrophysiological studies to test the rationale and effects of operative pulmonary venous isolation. METHODS AND RESULTS: Fourteen patients undergoing surgical pulmonary venous isolation for drug-refractory lone AF were studied. Successful isolation was confirmed postoperatively in 13 of 14 patients. Spontaneous sustained AF was recorded from the isolated pulmonary venous region (PVR) in 4 and was induced by extrastimulus testing in another. The remaining atrial region (RAR) was in sinus rhythm in 13 patients and nonsustained AF in 1. Atrial extrastimulus testing and burst pacing in the RAR failed to induce sustained AF. In follow-up, 1 patient developed paroxysmal AF, and electrical continuity between the PVR and RAR was confirmed. Isolation was achieved with radiofrequency ablation with no further AF. Another patient developed typical atrial flutter that required ablation. AF has not recurred in any patient at 25.1+/-11.9 months (range, 6 to 56 months) after surgery. Atrial histopathology was consistent with tachycardia-induced changes. CONCLUSIONS: Total electrical isolation of the PVR controlled AF with excellent clinical outcome and appeared necessary for success. The isolated PVR can sustain spontaneous or induced AF, whereas the considerably larger RAR does not. These data provide a sound rationale for PVR in eliminating AF.

Adult↗
PubMed2003

Optimal duration of monitoring in patients with unexplained syncope.

The optimal duration of monitoring of patients with recurrent unexplained syncope who undergo prolonged monitoring with an implantable loop recorder is unknown. We examined the probability of syncope in a group of 167 patients with this condition who underwent prolonged monitoring with an implantable loop recorder. A 12-month monitoring period appears to capture >90% of episodes. Syncope is most likely to occur in younger patients with less heart disease and more frequent syncope. There is a low risk of syncope after 1 year of monitoring without an event.

Adult↗
PubMed2003

Cost implications of testing strategy in patients with syncope: randomized assessment of syncope trial.

OBJECTIVES: We sought to assess the cost implications of two investigation strategies in patients with unexplained syncope. BACKGROUND: Establishing a diagnosis in patients with unexplained syncope is complicated by infrequent and unpredictable events. The cost-effectiveness of immediate, prolonged monitoring as an alternative to conventional diagnostic strategies has not been studied. METHODS: Sixty patients (age 66 +/- 14 years; 33 males) with unexplained syncope and LV ejection fraction >35% were randomized to conventional testing with an external loop recorder, tilt and electrophysiologic (EP) testing, or prolonged monitoring with an implantable loop recorder with one-year monitoring. If patients remained undiagnosed after their assigned strategy, they were offered a crossover to the alternate strategy. Cost analysis of the two testing strategies was performed. RESULTS: Fourteen of 30 patients who were being monitored were diagnosed at a cost of 2,731 Canadian dollars +/- 285 Canadian dollars per patient and 5,852 Canadian dollars +/- 610 Canadian dollars per diagnosis. In contrast, only six of 30 conventional patients were diagnosed (20% vs. 47%, p = 0.029), at a cost of 1,683 Canadian dollars +/- 505 Canadian dollars per patient (p < 0.0001) and 8,414 Canadian dollars +/- 2,527 Canadian dollars per diagnosis (p < 0.0001). After crossover, a diagnosis was obtained in 1 of 5 patients undergoing conventional testing, compared with 8 of 21 patients who completed monitoring (20% vs. 38%, p = 0.44). Overall, a strategy of monitoring followed by tilt and EP testing was associated with a diagnostic yield of 50%, at a cost of 2,937 Canadian dollars +/- 579 Canadian dollars per patient and 5,875 Canadian dollars +/- 1,159 Canadian dollars per diagnosis. Conventional testing followed by monitoring was associated with a diagnostic yield of 47%, at a greater cost of 3,683 Canadian dollars +/- 1,490 Canadian dollars per patient (p = 0.013) and a greater cost per diagnosis (7,891 Canadian dollars +/- 3,193 Canadian dollars, p = 0.002). CONCLUSIONS: A strategy of primary monitoring is more cost-effective than conventional testing in establishing a diagnosis in recurrent unexplained syncope.

Aged↗
PubMed2003

Atrial high rate episodes detected by pacemaker diagnostics predict death and stroke: report of the Atrial Diagnostics Ancillary Study of the MOde Selection Trial (MOST).

BACKGROUND: Some current pacing systems can automatically detect and record atrial tachyarrhythmias that may be asymptomatic. We prospectively studied a 312-patient (pt) subgroup of MOST (MOde Selection Trial), a 2010-patient, 6-year randomized trial of DDDR versus VVIR pacing in sinus node dysfunction (SND). The purpose of the study was to correlate atrial high rate events (AHREs) detected by pacemaker diagnostics with clinical outcomes. METHODS AND RESULTS: Pacemakers were programmed to log an AHRE when the atrial rate was >220 bpm for 10 consecutive beats. Analysis was confined to patients with at least 1 AHRE duration exceeding 5 minutes. The 312 patients were median age 74 years, 55% female, and 60% had a history of SVT. 160 of 312 (51.3%) patients enrolled had at least 1 AHRE >5 minutes duration over median follow-up of 27 months. Cox proportional hazards analysis assessed the relationship of AHREs with clinical events, adjusting for prognostic variables and baseline covariates. The presence of any AHRE was an independent predictor of the following: total mortality (hazard ratio AHRE versus no AHRE and 95% confidence intervals=2.48 [1.25, 4.91], P=0.0092); death or nonfatal stroke (2.79 [1.51, 5.15], P=0.0011); and atrial fibrillation (5.93 [2.88, 12.2], P=0.0001). There was no significant effect of pacing mode on the presence or absence of AHREs. CONCLUSIONS: AHRE detected by pacemakers in patients with SND identify patients that are more than twice as likely to die or have a stroke, and 6 times as likely to develop atrial fibrillation as similar patients without AHRE.

Adult↗