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Biomedical subjects

K Ellenbogen

Publications and source records attributed to K Ellenbogen.

9 recordsLinked to original sources
PubMed2001

Critical analysis of dual-chamber implantable cardioverter-defibrillator arrhythmia detection : results and technical considerations.

BACKGROUND: One of the perceived benefits of dual-chamber implantable cardioverter-defibrillators (ICDs) is the reduction in inappropriate therapy due to new detection algorithms. It was the purpose of the present investigation to propose methods to minimize bias during such comparisons and to report the arrhythmia detection clinical results of the PR Logic dual-chamber detection algorithm in the GEM DR ICD in the context of these methods. METHODS AND RESULTS: Between November 1997 and October 1998, 933 patients received the GEM DR ICD in this prospective multicenter study. A total of 4856 sustained arrhythmia episodes (n=311) with stored electrogram and marker channel were classified by the investigators; 3488 episodes (n=232) were ventricular tachycardia (VT)/ventricular fibrillation (VF), and 1368 episodes (n=149) were supraventricular tachycardia (SVT). The overall detection results were corrected for multiple episodes within a patient with the generalized estimating equations (GEE) method with an exchangeable correlation structure between episodes. The relative sensitivity for detection of sustained VT and/or VF was 100.0% (3488 of 3488, n=232; 95% CI 98.3% to 100%), the VT/VF positive predictivity was 88.4% uncorrected (3488 of 3945, n=278) and 78.1% corrected (95% CI 73.3% to 82.3%) with the GEE method, and the SVT positive predictivity was 100.0% (911 of 911, n=101; 95% CI 96% to 100%). CONCLUSIONS: A structured approach to analysis limits the bias inherent in the evaluation of tachycardia discrimination algorithms through the use of relative VT/VF sensitivity, VT/VF positive predictivity, and SVT positive predictivity along with corrections for multiple tachycardia episodes in a single patient.

Algorithms↗
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.

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PubMed2000

A cardiac evoked response algorithm providing threshold tracking: a North American multicenter study. Clinical Investigators of the Microny-Regency Clinical Evaluation Study.

The purpose of this study was to evaluate a pacing system using the recognition of cardiac evoked response for the automatic adjustment of pacing output. Patients were prospectively followed after primary implantation of VVIR pacemakers using AutoCapture (St. Jude Medical CRMD). Sensing and pacing thresholds, polarization signal, evoked response, and AutoCapture performance were evaluated with serial visits and 24-hour Holter monitoring. Three hundred ninety-eight patients (mean age 71 +/- 15 years) were followed for an average duration of 1 year (3 days-1.75 years) with the algorithm functional in > 90% of patients. Backup pacing in the event of exit block was confirmed in all patients. Pacing thresholds remained stable at 0.89 +/- 0.34 V with a pulse width of 0.31 ms (with chronic output autoset at 0.3 V above the actual threshold). Evoked response exhibited a small but statistically significant increase with time (8.92 mV at implant, 9.60 mV at 12 months), however, this finding did not result in any change in AutoCapture function during our follow-up period. The polarization signal remained stable with minimal variation (1.12 mV at implant, 1.18 at 12 months). No clinical adverse events were observed using the AutoCapture algorithm. In this initial experience with the AutoCapture algorithm the evoked response and polarization measurements remained adequate, allowing the system to function in the majority of patients with safe, low output pacing. High energy backup pacing provided an added safety feature over fixed output devices in cases of unexpected threshold rises. Longer follow-up is required for continued long-term validation of the algorithm.

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PubMed1999

A new system for catheter ablation of atrial fibrillation.

Increased attention is now being focused on developing new technologies to cure atrial fibrillation using catheter ablation techniques. The performance of a MAZE-type procedure using standard catheter ablation technologies is arduous and is associated with an unacceptable risk of complications. The Guidant Heart Rhythm Technologies Linear Ablation System was developed to create long transmural linear lesions. Unique features of this system include the availability of different preshaped multi-electrode steerable ablation catheters, the use of phased radiofrequency (RF) energy, and the control of RF output by varying the duty cycle. A prospective multicenter clinical trial to evaluate the safety and efficacy of a right atrial ablation procedure using this technology to treat atrial fibrillation is currently underway. To date, 15 patients have been enrolled and the procedure was acutely effective in 14 of 15 patients with no complications. Atrial fibrillation has recurred during short-term follow-up in 12 of 15 patients, a not surprising result, because this initial phase of testing involved only right-sided ablation. The early results of the phase I clinical trial confirm the findings of others that successful ablation of chronic atrial fibrillation is likely to require a left atrial approach. This clinical trial, as well as others that are currently underway, will be invaluable in the continuing development of catheter ablation of atrial fibrillation and, ultimately, in determining if the routine use of this therapeutic tool can become a reality.

Atrial Fibrillation↗
PubMed1998

Spontaneous conversion and maintenance of sinus rhythm by amiodarone in patients with heart failure and atrial fibrillation: observations from the veterans affairs congestive heart failure survival trial of antiarrhythmic therapy (CHF-STAT). The Department of Veterans Affairs CHF-STAT Investigators.

BACKGROUND: In a multicenter, double-blind, placebo-controlled study, the long-term effects of amiodarone on morbidity and mortality in patients with congestive heart failure (CHF) and atrial fibrillation (AF) were evaluated during a 4-year period. METHODS AND RESULTS: Of 667 patients with CHF, 103 (15%) had AF at baseline. Of these, 51 were randomized to amiodarone and 52 to placebo. The group with sinus rhythm and the group in AF were comparable except for a higher proportion of AF in patients with nonischemic versus ischemic cardiomyopathy (41% versus 27%, P<0.005). The mean ventricular response (VR) during AF over 24 hours was reduced by amiodarone at 2 weeks (20%, P=0.001), at 6 months (18%, P=0.001), and at 12 months (16%, P=0.006). Maximal VR was reduced 22% (P=0.001) at 2 weeks, 19% (P=0.001) at 6 months, and 14% (P=0.001) at 12 months. Sixteen of 51 patients on amiodarone and 4 of 52 on placebo converted to sinus rhythm during the study (chi2=9.23, P=0.002). During follow-up, 11 of 268 patients in sinus rhythm on amiodarone at baseline and 22 of the 263 in sinus rhythm on placebo developed AF; the difference was significant (chi2=12.88, P=0.005). Analysis of total mortality during follow-up showed a significantly lower mortality rate (P=0. 04) in patients in AF at baseline who subsequently converted to sinus rhythm on amiodarone than in those who did not convert to sinus rhythm on the drug. CONCLUSIONS: In patients with CHF, amiodarone has a significant potential to spontaneously convert patients in AF to sinus rhythm, with patients who convert having a lower mortality rate than those who do not. The drug prevented the development of new-onset AF and significantly reduced the VR in those with persistent AF.

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PubMed1994

Recent insights in programmed electrical stimulation for the management of sustained ventricular arrhythmias.

After more than 20 years of clinical use, programmed electrical stimulation for induction of cardiac arrhythmias remains an important clinical and research tool. The procedure continues to undergo refinement but is not without controversy regarding its accuracy in predicting drug efficacy as determined by serial testing for suppression of ventricular tachyarrhythmias. Recent work has streamlined technical aspects of the procedure itself and promises to improve the selection of patients likely to benefit from such studies. Despite these advances, however, recent publications from the Electrophysiologic Study Versus Electrocardiographic Monitoring trial raise fundamental questions about the ability of any current strategy to predict the efficacy of antiarrhythmic drugs for the prevention of ventricular arrhythmias.

Anti-Arrhythmia Agents↗
PubMed1993

Radiofrequency catheter ablation for the management of cardiac tachyarrhythmias.

Radiofrequency catheter ablation techniques allow for safe and highly effective curative therapy of a variety of cardiac dysrhythmias. The technique involves the delivery of a high-frequency, alternating electrical current through an intravascular catheter to sites of arrhythmogenic myocardium. This current induces resistive electrical heating of the tissue, resulting in discrete areas of myocardial destruction through coagulation and desiccation. Dysrhythmias most commonly treated with these techniques are atrioventricular nodal reentry and tachycardias related to accessory atrioventricular bypass tracts. For these dysrhythmias, success rates of 90% to 95% are achievable with a low (2% to 4%) risk of complications. Radiofrequency catheter ablation techniques also have been used to treat ventricular tachycardias, atrial flutter, ectopic atrial tachycardia, and sinus node reentry, albeit with lower success rates. These techniques are still evolving, alternate energy sources (such as microwave and laser) and improved catheter technology should enhance the technique's safety and efficacy for a wider range of dysrhythmias.

Atrial Flutter↗
PubMed1985

Ultrasound diagnosis of pseudoaneurysm and contiguous ventricular septal defect complicating inferior myocardial infarction.

Two patients with recent inferior myocardial infarction were found by two-dimensional and Doppler echocardiography to have both an inferior wall pseudoaneurysm and a contiguous rupture of the posterior ventricular septum. The pseudoaneurysm was not suspected clinically in either patient. In one patient, a complex or dissecting septal rupture was visualized in detail. To our knowledge, the combined defect has not previously been diagnosed during life by noninvasive methods.

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