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Biomedical subjects

A Dhala

Publications and source records attributed to A Dhala.

At least 73 records · Page 4Linked to original sources
PubMed1994

Efficacy and safety of atrioventricular nodal modification for atrioventricular nodal reentrant tachycardia in the pediatric population.

The safety and efficacy of radiofrequency catheter modification of the atrioventricular node for atrioventricular nodal reentrant tachycardia in the pediatric population is described. Twenty-one patients with a mean age of 14.9 +/- 3.6 years underwent slow-pathway atrioventricular nodal modification with a stepwise anatomic approach. The average cumulative fluoroscopy exposure time (22 procedures in 21 patients) inclusive of the electrophysiologic study was 36.1 +/- 22 minutes. Noninducibility of tachycardia was achieved in all patients with one procedural complication (hemothorax). During a mean follow-up of 15 +/- 9.06 months, tachycardia recurred in one patient. Patient and family acceptance and satisfaction with the procedure was high. Because of the curative potential of radiofrequency catheter modification with low associated short- and long-term risks, it may be considered as a primary treatment option in pediatric patients with symptomatic atrioventricular nodal reentrant tachycardia.

Adolescent↗
PubMed1994

Preliminary experience with a hybrid nonthoracotomy defibrillating system that includes a biphasic device: comparison with a standard monophasic device using the same lead system.

OBJECTIVES: This study analyzed the advantage of combining a biphasic device with a transvenous system and compared the results with those obtained with a standard monophasic device. BACKGROUND: Available lead systems use monophasic pulses and may require lengthy intraoperative testing to achieve adequate defibrillation threshold in a conspicuous number of patients. The option of biphasic waveform may provide further benefits. However, clinical experience with a permanent implant is lacking. METHODS: Fifty-five patients underwent testing and received a permanent implant using the Endotak lead system associated with a CPI monophasic device. The remaining 36 patients received a permanent implant with the Endotak lead system connected to a biphasic device. In both groups a subcutaneous patch was combined when needed to obtain acceptable defibrillation thresholds. RESULTS: Biphasic pulses resulted in lower mean (+/- SD) defibrillation thresholds (monophasic 15 +/- 4.7 J vs. biphasic 12 +/- 5 J, p = 0.03) and a better implantation rate (100% biphasic vs. 89% monophasic, p = 0.07). Biphasic pulses allowed implantation with less ventricular fibrillation induction (7.4 +/- 3.2 vs. 3.5 +/- 1.8, p < 0.01) and a mean shorter procedure time (168 +/- 39 vs. 111 +/- 30 min, p < 0.01). With the biphasic waveform a greater proportion of patients met the implantation criteria with the lead system alone (83% vs. 45%, p < 0.01). When needed, the left prepectoral location of the patch electrode was always sufficient in left subscapular position was required in 15 patients in the monophasic group. Implantation of the biphasic device was associated with a shorter mean hospital stay (3.8 +/- 0.8 vs. 5.4 +/- 2.2 days, p < 0.01). CONCLUSIONS: Incorporation of a biphasic device in a transvenous implantable cardioverter-defibrillator uniformly increases the efficacy of the system and the ease of implantation.

Adult↗
PubMed1994

The anatomical determinants for the design of intracardiac mapping and ablation catheters.

An important factor in the efficient and successful completion of the ablation procedure is the design characteristics of the mapping/ablation catheters. These procedures are often hampered by the inability to maneuver the catheter to the desired location, in part because the catheters only have a single plane deflection capability and are not designed for the specific cardiac anatomical structures that contain the arrhythmogenic substrate. Single and Biplane Deflectable Catheters: Using measurements taken from six normal human cadaver hearts, ablation catheter design characteristics are presented for posterior, posterior septal, lateral, and posterior lateral pathways for retrograde and transseptal approaches. Three catheter designs based on anatomical characteristics were also evaluated. Pigtail Catheter: This catheter adapts to the atrial side of the mitral ring and improves positioning and stability for mapping and ablation of left-sided accessory pathways. Loop Catheter: This catheter is positioned at the perivalvular tricuspid ring and provides simultaneous mapping and ablation capabilities without the need to move the catheter or the need for additional catheters. Rotating Tip Catheter: The tip of this catheter is made up of three elongated teeth, which were curved 120 degrees apart into the rotating tip electrode. This electrode was designed to negotiate the surfaces of the atrial and intraventricular chambers. It is capable of discrete movements and has a large electrode-tissue contact area for the ablation of atrial and ventricular arrhythmias. Catheter designs presented in this article are based on the ability of the catheter to adapt to the anatomical location of the arrhythmogenic tissue as well as the maneuverability of the catheter's mapping and ablation electrodes. An anatomical approach to the design of ablation catheter technology is likely to reduce the x-ray radiation exposure for patient and operator, and may further increase the success rate of the procedure.

Animals↗
PubMed1994

Experience with two different nonthoracotomy systems for implantable defibrillator in 170 patients.

Implantation of a nonthoracotomy system (Medtronic PCD or CPI Endotak) was attempted in 170 patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) not requiring concomitant cardiac surgery. A nonthoracotomy system could be successfully implanted in 95 of the 115 patients with the PCD system and 49 of 55 patients receiving the Endotak lead system. In 26 patients with failed nonthoracotomy system because of defibrillation threshold (DFT) > 25 joules (J), an epicardial system was implanted at the same setting. Patients receiving the two lead systems were comparable with regard to age, sex, and ejection fraction. However, since the PCD system offers tiered therapy multiprogrammable options, all attempts were made to implant this lead system in patients with VT that could be pace terminated. Mean DFT (15 +/- 4.7 vs 17 +/- 4.6 J; P = 0.03) and implant time (2.5 +/- 0.6 vs 3.3 +/- 0.7 hours; P = 0.02) were less with the Endotak lead system. There was no perioperative mortality. During a mean follow-up of 20 +/- 4 months, there were eight instances of lead dislodgment in patients receiving the PCD system. There were four nonsudden cardiac deaths and one sudden death in the Endotak group and three nonsudden deaths in the PCD group. Sudden cardiac death and total survival using the intention-to-treat analysis during this follow-up period were 99% and 95%, respectively. In conclusion, successful implantation, perioperative mortality, and survival rate are comparable with both lead systems; however, incorporating two defibrillating electrodes in one lead minimizes lead dislodgment and reduces implant time.

Anti-Arrhythmia Agents↗
PubMed1994

Ventricular fibrillation and polymorphic ventricular tachycardia with critical coronary artery stenosis: does bypass surgery suffice?

INTRODUCTION: Previous studies have suggested that coronary artery bypass surgery is sufficient to prevent recurrence of sudden death in patients with critical coronary artery stenosis presenting with ventricular fibrillation or polymorphic ventricular tachycardia. We present our experience in patients with one or more episodes of sudden death associated with documented ventricular fibrillation or polymorphic ventricular tachycardia and severe operable coronary artery disease who underwent defibrillator implant at the time of bypass surgery. METHODS AND RESULTS: Fifty-eight consecutive patients (age 63 +/- 8 years) were included in this study. Eighteen of the 58 patients had no evidence of previous myocardial infarction. The mean ejection fraction was 37 +/- 13%. All patients underwent electrophysiologic study before and after revascularization. At the time of first defibrillator discharge, each patient was reevaluated to exclude the presence of ischemia. The benefits of defibrillator implant were estimated comparing the projected survival based upon defibrillator discharge preceded by syncope or presyncope with survival curves generated including total death and sudden plus cardiac death. After a mean follow-up of 4.6 +/- 2 years, 22 patients received appropriate shocks preceded by syncope or presyncope, and an additional 19 patients received asymptomatic shocks. At 4 years, survival free of total death was 71.2%, and the projected survival was 58.8% (P < 0.05). Multivariate analysis showed that ejection fraction lower than 30% and induction of arrhythmia with one or two extrastimuli (S2, S3) were independent predictors for defibrillator discharge. None of the remaining variables including age, gender, number of bypasses, history of myocardial infarction, and type of arrhythmias induced were predictive for death and occurrence of shocks. CONCLUSIONS: In patients with ventricular fibrillation and polymorphic ventricular tachycardia, bypass surgery does not protect from recurrence of life-threatening arrhythmias, and, as in our population, defibrillator implant may have significant impact on survival.

Adult↗
PubMed1993

Bundle branch reentry: a mechanism of ventricular tachycardia in the absence of myocardial or valvular dysfunction.

OBJECTIVES: The aim of this study was to present bundle branch reentry as the mechanism of sustained ventricular tachycardia in the absence of myocardial or valvular dysfunction. BACKGROUND: Previous reports have documented the relation between structural heart disease and bundle branch reentrant ventricular tachycardia. Myocardial or valvular dysfunction has thus far been recognized as the only anatomic substrate for the development of this tachycardia. METHODS: Three patients with a wide QRS complex tachycardia underwent noninvasive and invasive cardiac evaluation and electrophysiologic studies to identify the substrate and mechanism of tachycardia. Catheter ablation of the right bundle branch using radiofrequency current was performed in each patient. RESULTS: The patients were all men (aged 54, 34 and 72 years) who presented with presyncope, palpitation and cardiac arrest, respectively. Electrocardiography during sinus rhythm revealed nonspecific intraventricular conduction delay in all three patients. Cardiac evaluation revealed no evidence of myocardial or valvular dysfunction in any patient. The baseline HV interval was prolonged in each patient (90, 100 and 75 ms, respectively). Programmed right ventricular stimulation initiated bundle branch reentrant tachycardia with typical left (three patients) and right (one patient) bundle branch block pattern. Catheter ablation of the right bundle branch using radiofrequency current abolished bundle branch reentry in all three patients. After 26-, 13- and 8-month follow-up periods, complete right bundle branch block persisted, and all three patients remained asymptomatic without antiarrhythmic drugs. CONCLUSIONS: Sustained bundle branch reentry can be a clinical arrhythmia in patients with no identifiable myocardial or valvular dysfunction except for isolated conduction abnormalities in the His-Purkinje system. This mechanism of tachycardia should be recognized during electrophysiologic evaluation, given the seriousness of this arrhythmia and the availability of the effective treatment.

Adult↗
PubMed1993

Comparison of cardiac pacing with drug therapy in the treatment of neurocardiogenic (vasovagal) syncope with bradycardia or asystole.

BACKGROUND: The efficacy of permanent cardiac pacing in patients with neurocardiogenic (or vasovagal) syncope associated with bradycardia or asystole is not clear. We compared the efficacy of cardiac pacing with that of oral drug therapy in the prevention of hypotension and syncope during head-up tilt testing. METHODS: Among 70 patients with a history of syncope in whom hypotension and syncope could be provoked during head-up tilt testing, 22 had bradycardia (a heart rate < 60 beats per minute, with a decline in the rate by at least 20 beats per minute) or asystole along with hypotension during testing. There were 9 men and 13 women, with a mean (+/- SD) age of 41 +/- 17 years. Head-up tilt testing was repeated during atrioventricular sequential pacing (in 20 patients with sinus rhythm) or ventricular pacing (in 2 patients with atrial fibrillation). Regardless of the results obtained during artificial pacing, all the patients subsequently had upright-tilt testing repeated during therapy with oral metoprolol, theophylline, or disopyramide. RESULTS: During the initial tilt test, 6 patients had asystole and 16 had bradycardia along with hypotension. Despite artificial pacing, the mean arterial pressure during head-up tilt testing still fell significantly, from 97 +/- 19 to 57 +/- 19 mm Hg (P < 0.001); 5 patients had syncope, and 15 had presyncope. By contrast, 19 patients who later received only medical therapy (metoprolol in 10, theophylline in 3, and disopyramide in 6), 2 patients who received both metoprolol and atrioventricular sequential pacing, and 1 patient who received only atrioventricular sequential pacing had negative head-up tilt tests. After a median follow-up of 16 months, 18 of the 19 patients who were treated with drugs alone (94 percent) remained free of recurrent syncope or presyncope, whereas the patient treated only with permanent dual-chamber pacemaker had recurrent syncope. CONCLUSIONS: In patients with neurocardiogenic syncope associated with bradycardia or asystole, drug therapy is often effective in preventing syncope, whereas artificial pacing is not.

Adolescent↗
PubMed1993

Physics and engineering of transcatheter cardiac tissue ablation.

Ablation of arrhythmogenic cardiac tissues has emerged as one of the most important advances in cardiac electrophysiology. With the introduction of transcatheter ablation, the treatment of ventricular tachycardia, Wolff-Parkinson-White syndrome and other cardiac arrhythmias has progressed from an expensive and painful surgical therapy accompanied by a long recovery period to the less expensive, less traumatic transcatheter approach. The feasibility of cardiac ablation, along with the increasing number of physicians using the technique, requires understanding of the anatomic and electrophysiologic bases of transcatheter ablation as well as the different technologies, their limitations and complications. This report provides an overview of the physical, scientific and technical aspects of cardiac ablation performed with the methods currently available and a summary of the limitations of each method and expected future technologic developments in this growing field. Emphasis is placed on radiofrequency and direct current energies, the primary methods now used. Methods such as cryoablation and laser, and microwave and chemical ablation are discussed with less detail because the method of delivering energy for these ablative procedures has not been fully developed.

Animals↗
PubMed1993

Cardioversion, defibrillation, and overdrive pacing of ventricular arrhythmias: the effect of moricizine in dogs with sustained monomorphic ventricular tachycardia.

The purpose of this investigation is to define whether the antiarrhythmic drug moricizine has beneficial or adverse effects on currently used antitachycardia and antifibrillatory devices. These studies were performed in a dog model of sustained monomorphic ventricular tachycardia (VT). In 11 dogs, the left anterior descending artery and all surrounding epicardial collateral feeder vessels were ligated. Defibrillator patches were implanted and the dogs were allowed to recover. After a 7-day recovery period, effective refractory period (ERP), end diastolic threshold (EDT), VT induction, and VT and ventricular fibrillation (VF) termination data were collected before and after moricizine infusion (2 mg/kg). In this experimental model, moricizine caused the following electrophysiological changes: a prolongation of the ERP from 173 +/- 14 to 182 +/- 15 (P < 0.02) with no significant effect on the EDT for pacing; a prolongation of the VT cycle length from 175 +/- 18 to 201 +/- 23 msec (P < 0.003); an increased cycle length required for overdrive pacing from 136 +/- 20 to 157 +/- 22 msec (P < 0.01); no effect on the energy required to cardiovert VT; an increase in the defibrillation threshold from 7.5 +/- 4 to 9.4 +/- 4 joules (P < 0.006) and; in 5 of the 8 dogs with VT, the VT could be initiated with somewhat less aggressive stimulation. Significant beneficial electrophysiological physiological effects were noted on the VT cycle length, including a proportionately prolonged overdrive pacing cycle length for VT termination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Implantable cardioverter defibrillator for prevention of sudden cardiac death in patients with ventricular tachycardia and ventricular fibrillation: ICD therapy in sudden cardiac death.

Among the various therapy options for survivors of ventricular tachycardia-ventricular fibrillation (VT-VF), the implantable cardioverter defibrillator (ICD) seems most promising. It reliably terminates VT-VF and thus significantly impacts sudden cardiac death (SCD) survival. It is more effective than any of the known antiarrhythmic drugs in prevention of SCD, particularly among survivors of cardiac arrest. Compared to VT surgery, the ICD therapy can be offered to a larger pool of patients and can be placed at a lower surgical risk. With proper patient selection, ICD therapy is of major benefits to its recipients since it markedly reduces the chances of VT-VF related mortality; the main cause of premature death in this population. The ICD therapy is cost effective when compared to other medical interventions and could be more so if the implant is carried out early in the course of VT-VF management.

Death, Sudden, Cardiac↗
PubMed1993

Bundle branch reentrant ventricular tachycardia: cumulative experience in 48 patients.

INTRODUCTION: The clinical, electrophysiologic features and follow-up of 48 patients with inducible bundle branch reentrant (BBR) tachycardia are presented. METHODS AND RESULTS: Forty-eight patients were identified in whom a diagnosis of BBR tachycardia was made during electrophysiologic evaluation. The clinical presentation was syncope or sudden death in 38 patients, and sustained palpitations during wide QRS complex tachycardia in 5 patients. Electrophysiologic studies were performed in 5 additional patients for various other reasons. Structural heart disease was present in 45 patients. Idiopathic dilated cardiomyopathy and coronary artery disease were the anatomical substrates in 19 (39%) and 24 (50%) patients, respectively, severe aortic regurgitation was present in 2 patients, and no organic heart disease was identified in 3. All 48 patients had evidence of His-Purkinje system disease. BBR tachycardia with left and right bundle branch block morphologies was induced in 46 and 5 patients, respectively, and interfascicular BBR tachycardia was initiated in 2 patients. Ventricular tachycardia of a myocardial origin was induced in 11 patients. Management of BBR tachycardia included transcatheter bundle branch ablation in 28 patients, and antiarrhythmic drug therapy in 16 patients. Four patients were treated with implantable defibrillators. After a mean follow-up of 15.8 months in 42 patients, there were 13 deaths due to congestive heart failure, 4 sudden cardiac deaths, 3 nonsudden cardiac deaths, and 3 noncardiac related deaths. CONCLUSION: Sustained BBR, a form of monomorphic ventricular tachycardia, is a highly malignant arrhythmia usually seen in patients with structural heart disease. Three different types of BBR tachycardia are described. If distinguished from ventricular tachycardia of a myocardial origin, catheter ablation of the right bundle branch can be easily performed and effectively eliminates BBR. During follow-up, congestive heart failure is the most common cause of death in this population.

Adult↗
PubMed1993

Atrioventricular nodal reentry. Clinical, electrophysiological, and therapeutic considerations.

BACKGROUND: Atrioventricular (AV) nodal reentry is a relatively common cause of regular, narrow QRS tachycardia. The underlying basis for this arrhythmia is functional (and anatomic) duality of pathways in the region of the AV node, although the exact boundaries of the reentrant circuit have not been convincingly defined. During the more common type of AV nodal reentry (seen in approximately 90% of cases), a slow conducting pathway is used in the anterograde direction, and a fast pathway is operative in the retrograde direction. In the uncommon form, the direction of impulse propagation within the reentrant circuit is reversed. In this article, the clinical, ECG, and electrophysiological features of AV nodal reentry as well as approaches to therapy are discussed. METHODS AND RESULTS: Clinical diagnosis may be made from the surface ECG. In the common type of AV nodal reentry, the P wave is obscured by the QRS or may be present in its terminal portion. The P wave in the uncommon form occurs late (i.e., in or after the T wave), producing a pattern of long RP and short PR. Both forms of AV nodal reentry are controllable with various therapeutic modalities. For acute termination, adenosine is probably the ideal agent. Prevention of recurrences can be achieved with several pharmacological agents, including beta-blockers, calcium channel blockers, and class Ia, Ic, and III antiarrhythmic agents. Curative therapy is now available with a variety of nonpharmacological methods. However, the most promising therapy at the present time is catheter modification of the AV node by ablation of either the fast or slow pathway, using radiofrequency energy. Ablation of the fast pathway carries a higher risk of second- or third-degree AV block. Slow pathway ablation, by providing a high rate of success and minimal risk of AV block, seems to be a more acceptable initial approach. CONCLUSIONS: AV nodal reentry is a common cause of paroxysmal supraventricular tachycardia, and a precise diagnosis can be made with intracardiac electrophysiological evaluation. Although the arrhythmia responds to a variety of antiarrhythmic agents, curative therapy can now be offered with catheter modification of the AV node using radiofrequency energy. At the time of this writing, it seems that catheter modification of the AV node is rapidly becoming the therapy of initial choice in patients with symptomatic AV nodal reentrant tachycardia requiring treatment.

Adult↗
PubMed1993

Control of supraventricular tachycardia with transcatheter ablative technique using radio frequency as the energy source.

Supraventricular tachycardia constitutes a significant clinical problem, frequently requiring medical intervention. We analyzed data in 413 consecutive patients with supraventricular tachycardia treated at our center with the catheter ablative technique and found the following outcome. Among 272 patients who had regular narrow QRS tachycardia without ventricular pre-excitation during sinus rhythm (Group I), control was achieved in all but one case (success rate 99.6%). Patients in Group II had ventricular pre-excitation during sinus rhythm and narrow or wide QRS tachycardia. Elimination of ventricular pre-excitation and control of the tachycardia was achieved in 104 of the 106 cases in this group (a success rate of 98%). Group III patients had atrial flutter-fibrillation as the predominate arrhythmia and control of rapid ventricular response was successfully achieved with atrioventricular junctional ablation in all 35 cases. Serious complications were related to anticoagulation and were seen in less than 2% of the cases. There were no instances of thromboembolic phenomena or death related to these procedures. It is concluded that the catheter ablative technique with radio frequency as the energy source is a highly effective means for control of supraventricular tachycardia with minimal associated risk of serious complications.

Adult↗
PubMed1993

Neurocardiogenic syncope. Diagnosis, mechanisms, and treatment.

Neurocardiogenic syncope is a common medical problem that can be identified easily by history and the findings of the head-up tilt test. Depressor reflexes from the heart causing sympathetic withdrawal that, in turn, lead to peripheral vasodilatation and hypotension may have an important role in the pathogenesis of neurocardiogenic dysfunction. Once a diagnosis of neurocardiogenic syncope has been made, specific therapeutic strategies can usually prevent recurrent syncope. However, the natural history of neurocardiogenic syncope has not been studied. Double-blind placebo-controlled studies or drug withdrawal trials are needed to assess whether all patients with neurocardiogenic syncope need lifelong therapy.

Autonomic Nervous System↗
PubMed1993

Implantable cardioverter-defibrillator therapy for prevention of sudden cardiac death.

Patients with known symptomatic VT or VF are at high risk for sudden cardiac death. Various therapeutic choices can be used to reduce the incidence of arrhythmic sudden cardiac death. These include beta-blockers, class I and III antiarrhythmic agents, VT focal ablations, and ICD therapy. The overall incidence of sudden cardiac death in ICD recipients is less than 2% per year, a rate of survival not achieved with any of the available antiarrhythmic agents. VT surgical therapy can produce comparable survival results, but the minimal operative mortality is higher than that with ICD therapy. In patients with noninducible VT/VF or inducible polymorphic VT, and in those refractory to or intolerant of antiarrhythmic agents and poor left ventricular function, ICD therapy may be the only realistic option.

Death, Sudden, Cardiac↗
PubMedDate not supplied

Implantable cardioverter defibrillator therapy in children with long QT syndrome.

We report our experience with implantable cardioverter defibrillator (ICD) implantation and follow-up in high-risk patients with congenital long QT syndrome (LQTS). Congenital LQTS is associated with significant risk of malignant ventricular arrhythmias and sudden cardiac death (SCD). ICD implant is recommended for prevention of SCD in this patient population, but there are few published data regarding the efficacy and side effects of such therapy. We report our experience with 12 patients who underwent ICD implant for high-risk LQTS at our center in the past 5 years with respect to implant complications, appropriate and inappropriate therapies, device follow-up, and the impact on lifestyle. During a follow-up of 34.7+/-16.6 months, appropriate therapies were noted in 5, inappropriate therapies in 4, and no therapies in 3 patients. Clusters of appropriate therapies were seen in 3 patients, 1 of whom subsequently died. Female sex and congenital deafness appear to be associated with a higher risk of appropriate therapies. One patient experienced two complications at implant that were successfully treated. ICD implantation in LQTS patients presenting with SCD or recurrent syncope despite beta-blocker therapy appears to be justified in preventing SCD risk. In asymptomatic siblings of SCD patients, the benefits of ICD implant are not clear from our data.

Adolescent↗