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Biomedical subjects

N A Estes

Publications and source records attributed to N A Estes.

At least 73 records · Page 4Linked to original sources
PubMed1996

Antiarrhythmic drug therapy for ventricular arrhythmias: current perspectives.

Pharmacologic therapy for ventricular arrhythmias has undergone a remarkable change recently. Recognition of the importance of underlying structural heart disease on prognostic implications of ventricular arrhythmias has resulted in the refinement of the clinical classification of these arrhythmias. With refinement of techniques of risk stratification, it is now possible to identify patients ventricular arrhythmias at high risk for sudden death. Retrospective analyses of prior antiarrhythmic drug trials and new data from prospective randomized trials are now available and can more directly define the risks and benefits of antiarrhythmic therapy. Prevention of sudden death, reduction in total mortality, or improvement in symptoms remain the only benefits of antiarrhythmic drugs. With inclusion of total mortality as the major endpoint for assessment of pharmacologic interventions in high-risk patients, the potential for excess mortality due to antiarrhythmic agents is now recognized. The pharmacologic diversity of newly released antiarrhythmic agents and others under development has resulted in a re-evaluation of the traditional classification of these drugs. Multiple ongoing clinical trials will define the risks and benefits of antiarrhythmic therapy and other nonpharmacologic interventions in patients with ventricular arrhythmias.

Animals↗
PubMed1996

Strategies for managing atrial fibrillation.

The limitations of current therapies for atrial fibrillation are forcing a rethinking of how they should be used. Questions are being raised about the use of antiarrhythmic drugs, and new nonpharmacologic procedures are promising alternatives. Most patients with atrial fibrillation still require warfarin therapy, but some low-risk patients can forego it. Sinus rhythm spontaneously returns within the first 24 hours in almost half of cases of new atrial fibrillation. Patients with hemodynamic instability due to new-onset atrial fibrillation should proceed directly to electrical cardioversion. Warfarin therapy to maintain an International Normalized Ratio (INR) of 2.0 to 3.0 is currently recommended for all patients with atrial fibrillation with no contraindications to it, except for patients younger than 60 years with lone atrial fibrillation, in whom the risk of stroke is low. Certain antiarrhythmic drugs should be avoided in patients with congestive heart failure, in whom the risks may exceed the benefits. The maze procedure is emerging as an option to restore and maintain sinus rhythm. Radiofrequency atrioventricular node ablation and modification hold promise as options to control the ventricular rate without drugs.

Anti-Arrhythmia Agents↗
PubMed1995

Radiofrequency ablation of atrial insertion of left-sided accessory pathways guided by the "W Sign".

INTRODUCTION: The aim of this study was to evaluate the efficacy of radiofrequency (RF) ablation of the atrial insertion of left-sided accessory pathways with guidance by a specific morphologic characteristic of the local electrogram, which we call the "W sign." This represents the shortest local atrioventricular (AV) interval during sinus rhythm in patients with manifest preexcitation or the shortest local VA interval during AV reciprocating tachycardia and/or ventricular pacing in patients with concealed accessory pathways. METHODS AND RESULTS: The transseptal technique was used in 31 patients (18 men, 13 women; aged 32 +/- 13 years), and RF ablation of 33 accessory pathways (26 manifest and 7 concealed) was attempted. Patients presented with palpitations (n = 16), presyncope (n = 10), or syncope (n = 5). The clinical arrhythmia was AV reciprocating tachycardia (n = 24) or atrial fibrillation (n = 7). In 21 patients (68%) electrophysiologic study and RF ablation were performed at a single session. Accessory pathways were left posteroseptal (n = 5) or left free wall (n = 28). The "W sign," formed from merging of the local atrial and ventricular electrograms, was identified at all successful sites prior to ablation. Ablation was successful in all patients. A median of 7 RF lesions were delivered per patient. The fluoroscopy time was 76 +/- 48 minutes; total procedure time was 5.4 +/- 1.9 hours. No significant complications occurred. Early recurrence (< or = 24 hours) occurred in 1 patient; during 6 +/- 4 months, accessory pathway conduction recurred in another patient. CONCLUSION: We conclude that RF ablation of the atrial insertion of left accessory pathways can be very successful when guided by the "W sign."

Adolescent↗
PubMed1994

Radiofrequency catheter ablation for cardiac tachyarrhythmias.

PURPOSE: To review the radiofrequency ablation method, describe the technique, and discuss the indications, results, and limitations of its use in patients with cardiac tachyarrhythmias. DATA SOURCES: Peer-reviewed reports in the literature by clinical investigators who use radiofrequency catheter ablation as identified by a MEDLINE search and our own experience with this intervention in 214 patients with cardiac tachyarrhythmias. STUDY SELECTION: All articles reporting results of radiofrequency ablation for cardiac tachyarrhythmias and articles describing the ablation technique or comparing it with direct-current or surgical methods. RESULTS OF DATA SYNTHESIS: Percutaneous catheter ablation of cardiac arrhythmias using high-voltage, direct current was limited by a high complication rate and a need for general anesthesia. This method was recently replaced by a new safe and efficacious technique using low-voltage, high-frequency (radiofrequency) alternating current. Nonsurgical cure of many supraventricular arrhythmias is now feasible with radio-frequency ablation, especially in patients with accessory pathways or atrioventricular nodal reentrant tachycardia. For these arrhythmias, success rates are greater than 90%. The indications for ablation include preexcitation syndromes, atrioventricular nodal reentrant tachycardia, and other selected atrial and ventricular tachyarrhythmias refractory to antiarrhythmic drug therapy. The efficacy and safety profile of this technique has made it feasible for children as well as adults. CONCLUSIONS: Percutaneous radiofrequency catheter ablation has evolved as a safe and effective method for managing and curing the two most common forms of supraventricular tachycardia: those associated with preexcitation syndromes and atrioventricular nodal reentrant tachycardia. Further studies are needed to determine the efficacy of this method or to evaluate alternative transcatheter techniques in patients with atrial tachycardias and, more importantly, in the large population of patients with ischemic ventricular tachycardia.

Atrioventricular Node↗
PubMed1994

A consensus report on antiarrhythmic drug use.

During the past few years, a number of new antiarrhythmic agents have become available for use in the United States, encainide has been withdrawn from use, and others have had indications for use modified. Therefore, a meeting of arrhythmia specialists was convened in an attempt to develop guidelines for antiarrhythmic therapy. The resultant discussions and guidelines presented in this article address general issues such as the most important antiarrhythmic drug attributes, as well as therapy for particular arrhythmias such as premature ventricular contractions, ventricular tachycardia, ventricular fibrillation, ventricular ectopy, and supraventricular tachyarrhythmias.

Anti-Arrhythmia Agents↗
PubMed1994

Antitachycardia pacing and low-energy cardioversion for ventricular tachycardia termination: a clinical perspective.

When incorporated into tiered therapy implantable cardioverter defibrillators (ICDs), antitachycardia pacing (ATP) techniques have proved useful for termination of sustained monomorphic ventricular tachycardias (VT) and have the advantages of rapid delivery, absence of patient discomfort, and minimal battery drain. The efficacy of low-energy cardioversion (LEC) is similar to that of pacing techniques for VT termination, but LEC has the disadvantages of patient discomfort, atrial proarrhythmia, and greater battery drain compared with ATP. Acceleration of VT occurs with similar frequency with each technique. Neither technique should be used without back-up defibrillation capability in an ICD. VT termination algorithms are currently empiric and require repetitive arrhythmia induction and trials of ATP or LEC. Future studies of the risk and benefits of each technique are likely to define optimal programming strategies in tiered therapy ICDs.

Algorithms↗
PubMed1994

Fully transvenous cardioverter defibrillators: rare need for subcutaneous patch with two newer-generation systems.

In published series of nonthoractomy ICDs, there has invariably been a need for combining transvenous lead(s) with a subcutaneous patch to obtain adequate DFTs. Since the newer generation transvenous lead ICD systems became available for clinical investigation, we have tested and implanted 38 such systems in patients with drug-refractory malignant ventricular arrhythmias who were first seen with aborted sudden death (n = 10), syncope (n = 3), or sustained ventricular tachycardia (n = 25). These patients (mean age 60 +/- 15 years) had coronary artery disease (n = 25), congenital heart disease (n = 1), or cardiomyopathy (n = 12) as the underlying heart disease and a mean left ventricular ejection fraction of 34% +/- 16%. Seventeen (45%) patients had previous cardiac surgery (coronary bypass and/or valve replacement). The transvenous lead system included the Endotak C (single) lead of CPI (n = 27) or the EnGuard double-lead system of Telectronics (n = 11). The integrated pace/sense/defibrillation lead(s) were usually introduced via the left cephalic vein; after endocardiac positioning and testing, the leads were tunneled to the abdominal pocket in which the ICD device was implanted. DFTs were adequate for all patients (100%) and averaged 13.5 +/- 5.4 J (range 2.4 to 25 J). A subcutaneous patch or array was needed in only three patients. Because of protocol requirements, a subcutaneous patch or electrode array was intraoperatively tested in another three patients but was finally not implanted because better DFTs were achieved with the transvenous lead-alone configuration. The leads were combined with second-generation devices in 12 patients and third-generation ICDs in 26 (68%) patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Implantable cardioverter-defibrillator therapy in 300 patients with coronary artery disease presenting exclusively with ventricular fibrillation.

To determine outcomes of implantable cardioverter-defibrillator (ICD) therapy in a uniform population of survivors of sudden cardiac death, we used epicardial defibrillation lead systems to study 300 patients with coronary artery disease (CAD) presenting exclusively with ventricular fibrillation (VF) unassociated with acute myocardial infarction. Operative (30-day) mortality, 2.7% overall, was lower (0.6%) in patients with ejection fractions (EF) > or = 0.30. Over a median follow-up of 1.9 years, cumulative actuarial shock incidence was similar in patients who underwent concomitant coronary artery bypass graft (CABG) surgery (38%) and in those who did not. The 2-year cumulative actuarial incidences of any or appropriate shocks were 65% and 38%, respectively. Sudden death survival at 2 years was 92.5% and 99.3% for patients with EFs < or = 0.30 and > 0.30, respectively. The total mortality rate was similar in shocked and in unshocked patients. Multivariate analysis identified EF and female gender as significant predictors of any and appropriate shock occurrence (all p values < or = 0.05) and EF as a significant predictor of sudden, cardiac, and total mortality (all p values < 0.03). We conclude that in CAD patients presenting exclusively with VF unassociated with acute myocardial infarction and treated with thoracotomy-requiring ICD therapy: (1) operative (30-day) mortality is minimal for patients with an EF > or = 0.30; (2) device use is high and sudden death rates low regardless of concomitant CABG; (3) low EF is a significant predictor of cumulative shock occurrence and mortality (sudden, cardiac, and total); (4) female gender may be a predictor of shock occurrence; and (5) similar mortalities and low sudden-death rates in shocked and nonshocked ICD patients imply that ICD therapy improves survival in shocked patients to a level observed in comparable patients in whom ventricular tachyarrhythmia does not recur.

Actuarial Analysis↗
PubMed1994

Radiofrequency ablation of left-sided accessory pathways: transaortic versus transseptal approach.

The aim of this study was to compare the efficacy of transaortic (n = 54) and transseptal (n = 28) techniques during radiofrequency (RF) ablation of left accessory pathways (n = 75) in both left posteroseptal and free-wall locations in 73 consecutive patients (mean age 32 +/- 15 years). The transseptal approach included transseptal puncture and use of a retained long sheath in the left atrium (n = 24) or direct insertion of the mapping/ablation catheter via a patent foramen ovale (n = 4). Transseptal RF ablation was used as the primary method in 23 patients or at a separate session after the transaortic RF ablation failed in 5 patients. Transaortic RF ablation was used as primary method in 50 patients and after failed transseptal ablation in 4 patients. Transaortic ablation was successful in 47 (87%) of 54 procedures, transseptal ablation in 24 (86%) of 28 procedures, with total RF ablation success in 70 (96%) of 73 patients. The transseptal puncture/long sheath method was successful in 23 (96%) of 24 patients. This latter technique resulted in more stable positioning and easier manipulation of the ablation catheter. Switching from transseptal puncture/long sheath to transaortic technique was needed in 1 of 24 patients, from transseptal/patent foramen ovale approach to the transaortic route in 3 of 4 patients, and from the transaortic to the transseptal approach at a separate session in 5 patients. The age of patients and number of RF lesions were similar in the two groups. Fluoroscopy time was lower for the transseptal group (81 +/- 57 vs 121 +/- 81 min; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Cardiovascular causes of loss of consciousness in patients with presumed epilepsy: a cause of the increased sudden death rate in people with epilepsy?

UNLABELLED: BACKGROUND, METHODS, AND RESULTS: Syncope and seizures are often indistinguishable clinically. We present a series of 12 patients diagnosed as having epilepsy. Despite normal or nonspecific electroencephalographic findings, 11 of 12 patients were treated or offered treatment with long-term anticonvulsant agents. Subsequently, diagnoses of arrhythmic or neurally mediated syncope were made in all patients using Holter monitoring, long-term ambulatory loop electrocardiographic recording, or tilt-table studies. Arrhythmias included torsades de pointes (four patients), atrioventricular nodal reentrant supraventricular tachycardia (one patient), and sinus arrest (two patients). The remaining five patients had neurally mediated syncope with hypotension and bradycardia, including asystole in two patients. Treatment for the documented cardiovascular abnormalities resulted in the alleviation of syncopal symptoms. CONCLUSIONS: Because the observed cardiovascular abnormalities are potentially fatal, this series suggests that undiagnosed cardiac syncope may contribute to the documented increased sudden death rate in patients with presumed epilepsy. Cardiac causes of loss of consciousness should be considered in patients with presumed epilepsy, atypical premonitory symptoms (such as nausea, lightheadedness, or palpitations), nondiagnostic electroencephalograms, and failure to respond to anticonvulsant therapy.

Adolescent↗
PubMed1994

Radiofrequency ablation of slow pathway in patients with atrioventricular nodal reentrant tachycardia. Do arrhythmia recurrences correlate with persistent slow pathway conduction or site of successful ablation?

BACKGROUND: Residual slow pathway conduction in the form of persistent jump in the atrioventricular (AV) conduction time or atrial echo beats is a common finding after successful radiofrequency (RF) ablation of the slow pathway in patients with AV nodal reentrant tachycardia (AVNRT). Sites of successful RF ablation of the slow pathway may be located anteriorly in the tricuspid annulus (cephalad to the coronary sinus os) or posteriorly (at, within, or caudal to the coronary sinus os). The aim of this study was to investigate whether arrhythmia recurrences correlate with persistent slow pathway conduction or site of successful ablation. METHODS AND RESULTS: Among 55 patients with symptomatic AVNRT having RF ablation, 23 patients (42%) (group 1) had evidence of persistent dual AV nodal pathway physiology and/or echo beats, whereas in 32 patients (group 2), slow pathway conduction had been completely eliminated. With regard to ablation sites, 14 patients (25%) (group A) had their slow pathway successfully ablated at an inferoposterior site, whereas in 41 patients (group B), the ablation site was located anteriorly to the coronary sinus os. The study patients included 17 men and 38 women, aged 37 +/- 18 years. The electrophysiological study and RF ablation were performed in a single session in 50 patients (91%). After the first session, the technique was successful in all patients (100%), with elimination of AVNRT and without affecting AV conduction. A mean of 9 +/- 6 lesions were applied. The total procedure time averaged 4 +/- 1 hours. Fluoroscopy time was 41 +/- 25 minutes. Except for transient AV block in 1 patient, no other complications occurred. Over 12 +/- 8 months, a total of 7 patients (13%) had recurrence of AVNRT, and 6 of them underwent successful repeat slow pathway RF ablation. Recurrence rate was 9% (2 patients) for group 1, with persistent jump or echo beats, and 16% (5 patients) for group 2, without residual slow pathway conduction (P = NS). Five of the recurrences (71%) were noted in group A and 2 in group B. Thus, the recurrence rate was 36% for group A (5 of 14 patients), with posterior ablations, and 5% for group B (2 of 41 patients), with anterior sites of successful RF ablation (P < .05). CONCLUSIONS: After successful RF ablation of the slow pathway in patients with AVNRT, residual slow pathway conduction does not correlate with clinical tachycardia recurrences. However, the site of successful RF ablation of the slow pathway does correlate with arrhythmia recurrences. More recurrences are observed when the site is located inferoposteriorly, at or below the os of the coronary sinus, as compared with medial and anterior locations of the ablation site.

Adolescent↗
PubMed1993

Outcome with implantable cardioverter-defibrillator therapy for survivors of ventricular fibrillation secondary to idiopathic dilated cardiomyopathy or coronary artery disease without myocardial infarction.

Patients with idiopathic dilated cardiomyopathy (IDC) constitute a minority among implantable cardioverter-defibrillator (ICD) recipients; how these patients fare versus those with coronary artery disease (CAD) is not well defined, nor is the mechanism of cardiac arrest recurrence, which may involve a more significant role of bradyarrhythmias. A retrospective multicenter study regarding outcome of ICD therapy was conducted in 224 patients with either IDC (n = 69; 31%) or CAD (n = 155; 69%) presenting exclusively with ventricular fibrillation (VF) unassociated with acute myocardial infarction. Patients with IDC were significantly younger (mean age 57 vs 61 years in patients with CAD, p < 0.04) and less male predominant (64 vs 79% in patients with CAD, p < 0.02). There was no significant difference in mean left ventricular ejection fraction (0.27 in IDC patients vs 0.29 in CAD patients), but sustained ventricular tachycardia was induced less often in patients with IDC (21 vs 58% in CAD patients, p < 0.001). Bradycardia pacing, either by an ICD with bradycardia pacing ability or a separate bradycardia pacemaker, was available in only 15% of ICD implantees. During a median follow-up duration of 1.7 years for patients with IDC and 1.9 years for patients with CAD, estimated cumulative event rates were similar for any type shock (2-year incidence of 74% in IDC patients, 69% in CAD patients) as well as for appropriate shock (2-year incidence of 46% in IDC patients, 40% in CAD patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiomyopathy, Dilated↗
PubMed1993

Effects of coronary artery bypass grafting on ventricular arrhythmias: results with electrophysiological testing and long-term follow-up.

Myocardial revascularization was performed in 56 patients with coronary artery disease who presented with ventricular tachycardia (VT) (n = 39) or ventricular fibrillation (n = 17). There were 46 men and 10 women, aged 65 +/- 10 years. Three vessel (n = 42) or left main disease (n = 4) was present in 82%. Left ventricular ejection fraction averaged 36% +/- 11%. Electrophysiological studies were performed preoperatively in all patients; 50 (89%) had inducible ventricular arrhythmias. Sustained monomorphic VT was induced in 40 patients (cycle length 284 +/- 61 msec). Reproducible symptomatic nonsustained VT was induced in four patients and ventricular fibrillation in six patients, while six patients had no inducible arrhythmia. Preoperatively the patients with inducible VT failed 3.3 +/- 1.2 drug trials during electrophysiological studies. In addition to coronary bypass, 22 patients also received an automatic implantable cardioverter defibrillator (ICD), 26 patients received prophylactic ICD patches, and 1 patient had resection of a false aneurysm. There were no perioperative deaths. Postoperative electrophysiological studies were performed in all 56 surgical survivors. Ventricular tachyarrhythmia could not be induced in the six patients who had no inducible VT preoperatively and in 13 of 40 (33%) with preoperatively inducible sustained VT or in 19 of 50 (38%) patients with any previously inducible ventricular arrhythmia, thus a total of 25 patients (45%) had no inducible VT postoperatively. Of the remaining, 11 patients were treated with antiarrhythmic drugs alone, 11 had already received an ICD (combined with drugs in 7), and another 9 received the ICD postoperatively (combined with drugs in 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Cost-effectiveness of radiofrequency ablation compared with other strategies in Wolff-Parkinson-White syndrome.

BACKGROUND: Patients with Wolff-Parkinson-White syndrome fall into four risk groups: those with (1) prior cardiac arrest, (2) paroxysmal supraventricular tachycardia or atrial fibrillation (PSVT/AF) with hemodynamic compromise, (3) PSVT/AF without hemodynamic compromise, and (4) no symptoms. METHODS AND RESULTS: For each group, we developed a cost-effectiveness analysis examining five clinical management strategies: (1) observation, (2) observation until a cardiac arrest dictates the need for therapy, (3) initial drug therapy guided by noninvasive monitoring, (4) initial radiofrequency ablation (RFA), and (5) initial surgical ablation. We used a Markov simulation model to estimate life expectancy and costs for patients whose ages are between 20 and 60 years. The model includes the risks of cardiac arrest, PSVT/AF, drug side effects, procedure-related complications and mortality, the efficacy of drugs and RFA, and costs. Based on literature and expert opinion, we assumed that the annual risks of cardiac arrest are 0.01%, 0.05%, and 0.5%, respectively, in patients who are asymptomatic, who had PSVT/AF without hemodynamic compromise, or who had PSVT/AF with hemodynamic compromise. We also assumed that RFA has an overall efficacy of 92% in preventing cardiac arrest and arrhythmias. Our model predicts that RFA should yield a life expectancy greater than or equal to other strategies. In cardiac arrest survivors and patients who have had PSVT/AF with hemodynamic compromise, our model suggests that RFA should both prolong survival and save resources. For patients with PSVT/AF without hemodynamic compromise, the marginal cost-effectiveness of attempted RFA (followed by conservative treatment if the RFA fails) ranges from $6600 per quality-adjusted life year (QALY) gained for 20-year-old patients to $19,000 per QALY gained for 60-year-old patients. For asymptomatic patients, RFA costs from $174,000 per QALY gained for 20-year-old patients to $540,000 per QALY gained for 60-year-old patients. CONCLUSIONS: Our analysis supports the emerging practice of performing RFA in patients with Wolff-Parkinson-White syndrome who survive cardiac arrest or who experience PSVT/AF but also supports the current practice of observing asymptomatic patients.

Adult↗
PubMed1992

Moricizine.

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Arrhythmias, Cardiac↗