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Biomedical subjects

G J Klein

Publications and source records attributed to G J Klein.

At least 37 records · Page 2Linked to original sources
PubMed2000

Diagnostic assessment of recurrent unexplained syncope with a new subcutaneously implantable loop recorder. Reveal-Investigators.

AIM: Patients with recurrent syncope undiagnosed after extensive non-invasive and invasive testing pose a diagnostic and therapeutic dilemma. Holter monitoring is nondiagnostic in 90% of cases. Recent developments in loop recorder technology permit long-term ECG monitoring in patients with recurrent unexplained syncope. The aim of this study was to report the worldwide experience with a new subcutaneously implantable loop recorder, implanted in 133 patients with unexplained syncope and negative laboratory investigations. METHODS AND RESULTS: The implantable loop recorder monitors continuously a single lead electrogram using two sensing electrodes on the device shell. The device was implanted in 133 patients, 67 male and 66 female with recurrent syncope. During a mean follow-up of 10.8 +/- 4.3 months after device implantation, 83 patients (62%) experienced syncope or pre-syncope. In the remaining 50 patients no diagnosis could be made because either no events occurred, the patients were lost to follow-up, had adverse events, or died prior to diagnosis. In 72 of the 83 patients with syncope during follow-up (87%), loop recording definitively determined whether an arrhythmia was the cause of symptoms or not. Diagnosis included bradycardia in 21 patients, pacemaker dysfunction in one patient, and tachycardia in 10 patients. One patient experienced multiple rhythm disturbances. Syncope was non-arrhythmic in 40 patients. The remaining 11 patients failed to press the activator. Therapy was instituted in all patients, in whom an arrhythmic cause was found. Severe anticipated device related complications occurred in three patients. CONCLUSION: An implantable loop recorder is useful for establishing a diagnosis when symptoms are recurrent but too infrequent for conventional monitoring techniques.

Equipment Design↗
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

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

List-mode maximum-likelihood reconstruction applied to positron emission mammography (PEM) with irregular sampling.

We present a preliminary study of list-mode likelihood reconstruction of images for a rectangular positron emission tomograph (PET) specifically designed to image the human breast. The prospective device consists of small arrays of scintillation crystals for which depth of interaction is estimated. Except in very rare instances, the number of annihilation events detected is expected to be far less than the number of distinguishable events. If one were to histogram the acquired data, most histogram bins would remain vacant. Therefore, it seems natural to investigate the efficacy of processing events one at a time rather than processing the data in histogram format. From a reconstruction perspective, the new tomograph presents a challenge in that the rectangular geometry leads to irregular radial and angular sampling, and the field of view extends completely to the detector faces. Simulations are presented that indicate that the proposed tomograph can detect 8-mm-diameter spherical tumors with a tumor-to-background tracer density ratio of 3:1 using realistic image acquisition parameters. Spherical tumors of 4-mm diameter are near the limit of detectability with the image acquisition parameters used. Expressions are presented to estimate the loss of image contrast due to Compton scattering.

Algorithms↗
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

Pacing in right ventricular dysplasia after disconnection surgery.

This report describes a 33-year-old patient with arrhythmogenic right ventricular (RV) dysplasia who had a dual chamber pacemaker implanted at age 23 years for drug-induced bradycardia. Pacing was continued after right ventricular free-wall disconnection (RVFWD) at age 24 years. Her pacemaker was not replaced after battery depletion 7 years later. She presented the following year in severe right-sided heart failure. Her old pacemaker generator was replaced. This was followed by rapid resolution of her clinical failure and return to a full, active, physical lifestyle. This observation suggests the potential benefit of dual chamber pacing in patients with RV dysplasia after RVFWD.

Adult↗
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↗
PubMed1999

Use of an extended monitoring strategy in patients with problematic syncope. Reveal Investigators.

BACKGROUND: The conventional investigation of patients who present with syncope involves short-term ECG monitoring or provocative testing with head-up tilt and electrophysiological testing. A symptom-rhythm correlation is often difficult to obtain during spontaneous syncope because of its sporadic, infrequent, and unpredictable nature. METHODS AND RESULTS: We used a prolonged monitoring strategy to determine the cause of syncope in 85 patients (age, 59+/-18 years; 44 men) with recurrent undiagnosed syncope with an implantable loop recorder capable of cardiac monitoring for up to 18 months. During a mean of 10.5+/-4.0 months of follow-up, symptoms recurred in 58 patients (68%) 71+/-79 days (2.3+/-2.6 months) after implantable loop recorder insertion. An arrhythmia was detected in 42% of patients who recorded a rhythm during recurrent symptoms, with bradycardia present in 18 and tachycardia in 3. Five of the 18 bradycardic patients and 2 additional sinus rhythm patients received a clinical diagnosis of neurally mediated syncope. Patients who experienced presyncope were much less likely to record an arrhythmia during symptoms compared with recurrence of syncope (24% versus 70%, P=0.0005). There were no adverse events associated with recurrent symptoms, and there were no sudden deaths. Inability to freeze after an event occurred in 8 patients, and pocket infection occurred in 3. CONCLUSIONS: The strategy of prolonged monitoring is effective and safe in patients with problematic syncope.

Adult↗
PubMed1999

The high cost of syncope: cost implications of a new insertable loop recorder in the investigation of recurrent syncope.

BACKGROUND: Patients with recurrent syncope frequently undergo extensive investigations that consume significant health care resources. Recent advances in long-term monitoring techniques have enhanced diagnostic yield in patients with infrequent symptoms. There is little information on the relative cost-effective profile of the investigative tools used in patients with syncope. METHODS: Two methods to determine health care costs in patients with syncope were used. In the first, health care resource utilization was determined in 24 patients with recurrent unexplained syncope and negative investigations who underwent insertion of the implantable loop recorder (ILR) during a pilot study of the feasibility of the device. The costs of investigations before, during, and after ILR implantation in each patient were calculated on the basis of median charges for an index investigation and a regression analysis of 1018 US Medicare hospital claims for syncope from 1993. Charges were converted to costs using a cost-to-charge ratio of 0.64. The second method was based on estimated costs per diagnosis and published diagnostic yields of 6 commonly applied tests in patients with syncope. A cohort simulation using theoretic models of 100 patients undergoing investigation for syncope was created to compare the diagnostic yield and cost per diagnosis of various diagnostic cascades. RESULTS: In the pilot study, the cost of investigation of syncope in the 2 years before ILR insertion was $7584 per patient. After the ILR was inserted, a diagnosis was obtained in 21 of 24 patients (diagnostic yield 88%). The cost of therapy was $2452, followed by a reduction in cost of care to $596 over 30 +/- 10 months of follow-up. In the second method, the diagnostic yield of individual tests ranged from 3% for echocardiography to 88% for the ILR. The cost per diagnosis obtained ranged from $529 for the external loop recorder to $73,260 for electrophysiologic testing in patients without structural heart disease. An approach to syncope similar to that of the ILR pilot study resulted in a cost per diagnosis of $3193 and a diagnostic yield of 98%. Performance of echocardiography in half of the patients and electrophysiologic testing only in the presence of structural heart disease reduced the cost to $2494 and retained a diagnostic yield of 98%. CONCLUSIONS: The cost of investigation of syncope is high. The ILR may reduce health care resource utilization by providing a diagnosis permitting definitive therapy. The cost per diagnosis profile of current diagnostic tests commonly used in patients with syncope is highly variable. A cost-effective approach to diagnosing this disorder can retain a high diagnostic yield with a reduction in resource utilization compared with a conventional approach.

Cost of Illness↗
PubMed1999

Sevoflurane has no effect on sinoatrial node function or on normal atrioventricular and accessory pathway conduction in Wolff-Parkinson-White syndrome during alfentanil/midazolam anesthesia.

BACKGROUND: The effects of sevoflurane on the electrophysiologic properties of the human heart are unknown. This study evaluated the effects of sevoflurane on the electrophysiologic properties of the normal atrioventricular conduction system, and on the accessory pathways in patients with Wolff-Parkinson-White syndrome, to determine its suitability as an anesthetic agent for patients undergoing ablative procedures. METHODS: Fifteen patients with Wolff-Parkinson-White syndrome undergoing elective radiofrequency catheter ablation were studied. Anesthesia was induced with alfentanil (20-50 microg/kg) and midazolam (0.15 mg/kg), and vecuronium (20 mg) and maintained with alfentanil (0.5 to 2 microg x kg(-1) x min(-1)) and midazolam (1 or 2 mg every 10-15 min, as required). An electrophysiologic study measured the effective refractory period of the right atrium, atrioventricular node, and accessory pathway; the shortest conducted cycle length of the atrioventricular node and accessory pathway during atrial pacing; the effective refractory period of the right ventricle and accessory pathway; and the shortest retrograde conducted cycle length of the accessory pathway during ventricular pacing. Parameters of sinoatrial node function included sinus node recovery time, corrected sinus node recovery time, and sinoatrial conduction time. Intraatrial conduction time and the atrial-His interval were also measured. Characteristics of induced reciprocating tachycardia, including cycle length, atrial-His, His-ventricular, and ventriculoatrial intervals, also were measured. Sevoflurane was administered to achieve an end-tidal concentration of 2% (1 minimum alveolar concentration), and the study measurements were repeated. RESULTS: Sevoflurane had no effect on the electrophysiologic parameters of conduction in the normal atrioventricular conduction system or accessory pathway, or during reciprocating tachycardia. However, sevoflurane caused a statistically significant reduction in the sinoatrial conduction time and atrial-His interval but these changes were not clinically important. All accessory pathways were successfully identified and ablated. CONCLUSIONS: Sevoflurane had no effect on the electrophysiologic nature of the normal atrioventricular or accessory pathway and no clinically important effect on sinoatrial node activity. It is therefore a suitable anesthetic agent for patients undergoing ablative procedures.

Adult↗
PubMed1999

Acute testing of the rate-smoothed pacing algorithm for ventricular rate stabilization.

We evaluated the capability of a new pacemaker-based rate-smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 +/- 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 +/- 299 vs 855 +/- 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 +/- 55 vs 393 +/- 74 ms, P = 0.292). A small shortening of the mean RR interval (634 +/- 153 vs 594 +/- 135 ms, P = 0.007) was seen with no change in the median RR interval (609 +/- 153 vs 595 +/- 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 +/- 52 vs 82 +/- 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 +/- 64 vs 77 +/- 34, P = 0.0005) and MAD/mean RR ratio (0.23 +/- 0.05 vs 0.13 +/- 0.04, P = 0.0005). We conclude that rate-smoothed pacing effectively reduces RR variability of AF in the acute setting.

Adult↗
PubMed1999

A cost effective approach to the investigation of syncope: relative merit of different diagnostic strategies.

OBJECTIVE: To compare the cost effectiveness of a conventional diagnostic work-up with that of several different diagnostic cascades for the investigation of undifferentiated syncope. DESIGN: A MEDLINE search established a weighted estimate of diagnostic yield for several diagnostic investigations. 'High-end' and 'low-end' cost estimates were calculated for these investigations based on figures from four representative Canadian tertiary care centres in four different provinces. Several diagnostic models were applied to a hypothetical cohort of 100 patients with undifferentiated syncope. RESULTS: The conventional diagnostic cascade resulted in a diagnosis in 85% of patients, at a cost per diagnosis of $467 to $959. The optimal model increased the diagnostic yield to 98.9%, at a cost of $460 to $1043 per diagnosed patient. CONCLUSION: A combination of new technology and selective use of investigations has the potential to raise diagnostic yield without appreciably increasing cost per diagnosis.

Algorithms↗
PubMed1998

Final results from a pilot study with an implantable loop recorder to determine the etiology of syncope in patients with negative noninvasive and invasive testing.

Twenty-four patients with recurrent unexplained syncope and negative tilt and electrophysiologic testing underwent implantation of the implantable loop recorder, with recurrence of syncope in 21 patients 5.1+/-4.8 months after device implantation. Eighteen of the 21 had a treatable diagnosis, with arrhythmias in 11. Treatment resulted in resolution of syncope in most patients during long-term follow-up.

Adult↗
PubMed1998

Correlation of waiting time with adverse events in patients admitted for nonelective permanent pacemaker implantation.

OBJECTIVE: To determine the effect of a dedicated permanent pacemaker implantation procedure room on waiting time and waiting time-related morbidity. DESIGN: Retrospective chart review. SETTING: Two tertiary care teaching hospitals in southern Ontario; one with a dedicated procedure room (centre B) and one without (centre A). PATIENTS: Two hundred and fourteen consecutive patients who required permanent pacing urgently or emergently. METHODS: Charts were examined retrospectively at centre A (131 patients) and centre B (83 patients) to determine the waiting time for and the number of preoperative adverse events in nonelective permanent pacemaker implantation. RESULTS: Patients in centre A waited a mean of 4.5 +/- 3.0 days while patients in centre B waited a mean of 1.9 +/- 1.6 days (P = 0.0001). Centre A patients experienced a total of 57 adverse events that were likely or possibly related to the waiting period, while patients at centre B experienced eight such events (P < 0.0001). Thirty-three per cent of the centre A patients experienced at least one adverse event, while 8% of centre B patients experienced at least one adverse event (P < 0.00001). Of the centre A patients who waited for more than six days (26 patients), 58% had at least one adverse event, compared with 26% of those who waited less than six days (105 patients, P = 0.0009). CONCLUSIONS: Delays in implanting nonelective permanent pacemakers are strongly associated with an increase in adverse events. Measures to shorten the waiting time are likely to result in a reduction in morbidity in conjunction with a beneficial impact on health care resource utilization.

Humans↗