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Biomedical subjects

G J Klein

Publications and source records attributed to G J Klein.

At least 19 recordsLinked to original sources
PubMed2005

Use of medications in Wolff-Parkinson-White syndrome.

The diagnosis of Wolff-Parkinson-White syndrome is generally straightforward; however, the management may not be, and requires an understanding of the competing risks of various treatment options and that of the clinical setting in which the diagnosis is made. The symptomatic patient with Wolff-Parkinson-White has an increased risk of atrial fibrillation and a small but significant risk of sudden cardiac death. Therapy is based on reduction in symptom burden and attenuation of the risk of pre-excited atrial fibrillation. Catheter ablation is the most effective means of achieving this goal with abolition of symptoms and risk of pre-excited atrial fibrillation. Medication is often employed in the acute setting to terminate paroxysms of arrhythmia associated with the accessory pathway and reduce the subsequent burden of symptoms until ablation can be performed. An overview of the agents commonly used is provided together with recommendations.

Anti-Arrhythmia Agents↗
PubMed2003

Use of the implantable loop recorder in patients with unexplained syncope.

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. Conventional testing is often unproductive in patients when initial non-invasive testing is negative, particularly when a paroxysmal ar-rhythmia is suspected. Holter monitoring is often employed initially, with limited utility. Holter monitoring provides a rhythm profile, but rarely achieves the gold standard of a symptom rhythm correlation. The external loop re-corder extends the period of monitoring, enhancing the diagnostic yield to as high as 60% in patients with symptoms likely to recur during a month of device use. Finally, implantable loop recorders further 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 select patients.

Electrocardiography↗
PubMed2001

Randomized assessment of syncope trial: conventional diagnostic testing versus a prolonged monitoring strategy.

BACKGROUND: Establishing a diagnosis in patients with unexplained syncope is complicated by infrequent and unpredictable events. Prolonged monitoring may be an alternative strategy to conventional testing with short-term monitoring and provocative tilt and electrophysiological testing. METHODS AND RESULTS: Sixty patients (aged 66+/-14 years, 33 male) with unexplained syncope were randomized to "conventional" testing with an external loop recorder and tilt and electrophysiological testing or to prolonged monitoring with an implantable loop recorder with 1 year of monitoring. If patients remained undiagnosed after their assigned strategy, they were offered crossover to the alternate strategy. A diagnosis was obtained in 14 of 27 patients randomized to prolonged monitoring compared with 6 of 30 patients undergoing conventional testing (52% versus 20%, P=0.012). Crossover was associated with a diagnosis in 1 of 6 patients undergoing conventional testing compared with 8 of 13 patients who completed monitoring (17% versus 62%, P=0.069). Overall, prolonged monitoring was more likely to result in a diagnosis than was conventional testing (55% versus 19%, P=0.0014). Bradycardia was detected in 14 patients undergoing monitoring compared with 3 patients undergoing conventional testing (40% versus 8%, P=0.005). CONCLUSIONS: A prolonged monitoring strategy is more likely to provide a diagnosis than conventional testing in patients with unexplained syncope. Consideration should be given to earlier implementation of a monitoring strategy.

Aged↗
PubMed2001

Should patients with asymptomatic wolff-parkinson-white pattern undergo a catheter ablation?

Many individuals with the Wolff-Parkinson-White electrocardiographic pattern are asymptomatic. Optimal management of these individuals is still a matter of debate. On the one hand, sudden cardiac death from ventricular fibrillation is a rare yet possible outcome in these individuals. On the other hand, there is a low risk of serious complication from electrophysiologic study and ablation. Given that the risk of these competing strategies is comparable, the decision needs to be individualized with considerable patient input.

Catheter Ablation↗
PubMed2001

Supraventricular tachycardia.

Supraventricular tachycardias (SVT) comprise those tachycardias that originate above the bifurcation of the bundle of His. They can be classified broadly as AV node dependent and AV node independent. The mechanism and clinical manifestation of SVTs, which is essential to their correct diagnosis, is reviewed. The therapeutic management of SVTs, including acute and chronic drug therapy and catheter ablation, is discussed also.

Anti-Arrhythmia Agents↗
PubMed2001

Progression to chronic atrial fibrillation after pacing: the Canadian Trial of Physiologic Pacing. CTOPP Investigators.

OBJECTIVES: This study examined the effect of physiologic pacing on the development of chronic atrial fibrillation (CAF) in the Canadian Trial Of Physiologic Pacing (CTOPP). BACKGROUND: The role of physiologic pacing to prevent CAF remains unclear. Small randomized studies have suggested a benefit for patients with sick sinus syndrome. No data from a large randomized trial are available. METHODS: The CTOPP randomized patients undergoing first pacemaker implant to ventricular-based or physiologic pacing (AAI or DDD). Patients who were prospectively found to have persistent atrial fibrillation (AF) lasting greater than or equal to one week were defined as having CAF. Kaplan-Meier plots for the development of CAF were compared by log-rank test. The effect of baseline variables on the benefit of physiologic pacing was evaluated by Cox proportional hazards modeling. RESULTS: Physiologic pacing reduced the development of CAF by 27.1%, from 3.84% per year to 2.8% per year (p = 0.016). Three clinical factors predicted the development of CAF: age > or =74 years (p = 0.057), sinoatrial (SA) node disease (p < 0.001) and prior AF (p < 0.001). Subgroup analysis demonstrated a trend for patients with no history of myocardial infarction or coronary disease (p = 0.09) as well as apparently normal left ventricular function (p = 0.11) to derive greatest benefit. CONCLUSIONS: Physiologic pacing reduces the annual rate of development of chronic AF in patients undergoing first pacemaker implant. Age > or =74 years, SA node disease and prior AF predicted the development of CAF. Patients with structurally normal hearts appear to derive greatest benefits.

Aged↗
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

Effects of physiologic pacing versus ventricular pacing on the risk of stroke and death due to cardiovascular causes. Canadian Trial of Physiologic Pacing Investigators.

BACKGROUND: Evidence suggests that physiologic pacing (dual-chamber or atrial) may be superior to single-chamber (ventricular) pacing because it is associated with lower risks of atrial fibrillation, stroke, and death. These benefits have not been evaluated in a large, randomized, controlled trial. METHODS: At 32 Canadian centers, patients without chronic atrial fibrillation who were scheduled for a first implantation of a pacemaker to treat symptomatic bradycardia were eligible for enrollment. We randomly assigned patients to receive either a ventricular pacemaker or a physiologic pacemaker and followed them for an average of three years. The primary outcome was stroke or death due to cardiovascular causes. Secondary outcomes were death from any cause, atrial fibrillation, and hospitalization for heart failure. RESULTS: A total of 1474 patients were randomly assigned to receive a ventricular pacemaker and 1094 to receive a physiologic pacemaker. The annual rate of stroke or death due to cardiovascular causes was 5.5 percent with ventricular pacing, as compared with 4.9 percent with physiologic pacing (reduction in relative risk, 9.4 percent; 95 percent confidence interval, -10.5 to 25.7 percent [the negative value indicates an increase in risk]; P=0.33). The annual rate of atrial fibrillation was significantly lower among the patients in the physiologic-pacing group (5.3 percent) than among those in the ventricular-pacing group (6.6 percent), for a reduction in relative risk of 18.0 percent (95 percent confidence interval, 0.3 to 32.6 percent; P=0.05). The effect on the rate of atrial fibrillation was not apparent until two years after implantation. The observed annual rates of death from all causes and of hospitalization for heart failure were lower among the patients with a physiologic pacemaker than among those with a ventricular pacemaker, but not significantly so (annual rates of death, 6.6 percent with ventricular pacing and 6.3 percent with physiologic pacing; annual rates of hospitalization for heart failure, 3.5 percent and 3.1 percent, respectively). There were significantly more perioperative complications with physiologic pacing than with ventricular pacing (9.0 percent vs. 3.8 percent, P<0.001). CONCLUSIONS: Physiologic pacing provides little benefit over ventricular pacing for the prevention of stroke or death due to cardiovascular causes.

Aged↗
PubMed2000

Canadian implantable defibrillator study (CIDS) : a randomized trial of the implantable cardioverter defibrillator against amiodarone.

BACKGROUND: Patients surviving ventricular fibrillation (VF) or sustained ventricular tachycardia (VT) are at a high risk of death due to a recurrence of arrhythmia. The implantable cardioverter defibrillator (ICD) terminates VT or VF, but it is not known whether this device prolongs life in these patients compared with medical therapy with amiodarone. METHODS AND RESULTS: A total of 659 patients with resuscitated VF or VT or with unmonitored syncope were randomly assigned to treatment with the ICD or with amiodarone. The primary outcome measure was all-cause mortality, and the secondary outcome was arrhythmic death. A total of 328 patients were randomized to receive an ICD. A thoracotomy was done in 33, no ICD was implanted in 18, and the rest had a nonthoracotomy ICD. All 331 patients randomized to amiodarone received it initially. At 5 years, 85.4% of patients assigned to amiodarone were still receiving it at a mean dose of 255 mg/day, 28.1% of ICD patients were also receiving amiodarone, and 21.4% of amiodarone patients had received an ICD. A nonsignificant reduction in the risk of death was observed with the ICD, from 10.2% per year to 8.3% per year (19.7% relative risk reduction; 95% confidence interval, -7.7% to 40%; P=0.142). A nonsignificant reduction in the risk of arrhythmic death was observed, from 4.5% per year to 3.0% per year (32.8% relative risk reduction; 95% confidence interval, -7.2% to 57.8%; P=0.094). CONCLUSIONS: A 20% relative risk reduction occurred in all-cause mortality and a 33% reduction occurred in arrhythmic mortality with ICD therapy compared with amiodarone; this reduction did not reach statistical significance.

Aged↗
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↗