PubMed Health⌕ Search

Biomedical subjects

J Sra

Publications and source records attributed to J Sra.

At least 55 records · Page 3Linked to original sources
PubMed1996

Distribution of atrial electrogram types during atrial fibrillation: effect of rapid atrial pacing and intercaval junction ablation.

OBJECTIVES: This study examined the anatomic distribution types and possible determinant of atrial electrogram types during atrial fibrillation. BACKGROUND: Different types of atrial electrograms during atrial fibrillation have been observed and classified, but their anatomic distribution patterns, determinants and potential usefulness in guiding future catheter ablation are unknown. METHODS: Two animal models of atrial fibrillation were used: the sterile pericarditis model (n = 10) and the rapid atrial pacing model (400 beats/min for 6 weeks, n = 6). The atrial electrogram of atrial fibrillation and the atrial effective refractory period were obtained from multiple sites of the right and left atrium. In addition, decremental rapid atrial stimulation was applied to the site of shortest and longest atrial effective refractory periods until atrial fibrillation induction in a subgroup of nine dogs. Ablation of the intercaval junction was performed using the radiofrequency catheter technique in dogs with atrial fibrillation duration > 1 min. RESULTS: In both models, organized atrial electrograms (type I) were predominantly observed at the left atrial sites and the right atrial appendage, whereas disorganized atrial electrograms (type III) were mainly observed at the right posterolateral atrium. The distribution of the atrial electrogram types closely followed that of the atrial effective refractory period, with the shortest atrial effective refractory period corresponding to organized atrial electrograms (type I) and the longest atrial effective refractory period corresponding to disorganized atrial electrograms (type III). The correlation of atrial electrogram type with the atrial effective refractory period was further demonstrated by the effect of rapid atrial stimulation. When rapid atrial stimulation was applied to the site with the shortest atrial effective refractory period, disorganized atrial electrograms were observed at sites with the longest atrial effective refractory period, whereas 1:1 atrial capture was still present at the stimulation site. Ablation of the intercaval junction made atrial fibrillation noninducible or tended to shorten the atrial fibrillation duration (from 26.4 +/- 24.2 to 8.8 +/- 22.6 min in the pericarditis group, p = 0.02, and from 33.7 +/- 29.2 to 12.1 +/- 23.8 min in the rapid pacing group, p = 0.09) but did not change the atrial electrogram types during atrial fibrillation. CONCLUSIONS: Various types of atrial electrograms are present at different locations during atrial fibrillation. The atrial electrogram characteristics of atrial fibrillation at a specific location are related to the atrial effective refractory period, with short effective refractory periods associated with organized atrial electrograms and long effective refractory periods associated with disorganized electrograms.

Animals↗
PubMed1996

Sudden death in patients with implantable cardioverter-defibrillators.

UNLABELLED: Of the 733 patients with implantable cardioverter-defibrillators (ICDs) from 1982 to 1995 in our center, 20 died suddenly while the ICD was activated. This number included 16 men and four women with a mean age of 60 +/- 8 years and ejection fractions of 24.2% +/- 8.6%. ICDs were implanted for drug refractory ventricular tachycardia (VT) in 13 patients and for resucitated cardiac arrest in seven patients. The clinical VT was associated with syncope in 7 of 13 patients. VT was induced in 18 patients and was hemodynamically unstable in 12 patients. Shock therapies associated with syncope were delivered in 7 of 15 patients during the follow-up. This subgroup of patients survived a median of only 18 months after ICD implant. Ventricular fibrillation-defibrillation was found to surround death in nine patients. CONCLUSIONS: (1) Sudden death victims of the ICD population are characterized by poor left ventricular function and hemodynamically unstable ventricular tachyarrhythmias. (2) Ventricular tachyarrhythmias are the major cause of sudden death in ICD patients.

Aged↗
PubMed1996

Relative efficacy of different tilts with biphasic defibrillation in humans.

OBJECTIVE: The goal of this study was to assess if tilt bears any impact on defibrillation efficacy of biphasic shocks. BACKGROUND: Although it has been shown that biphasic waveform may increase the defibrillation efficacy, this pulsing method has not been as extensively studied in patients, and information regarding the effect of different tilts is lacking. METHODS: This study consisted of two similar but distinct protocols including 33 patients undergoing transvenous defibrillator implant. In 17 patients (Part I) defibrillation threshold was obtained delivering biphasic waveforms with 50%, 65%, and 80% tilt in random fashion. Similarly, in 16 patients (Part II) testing of biphasic waveform with 40%, 50%, and 65% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a subcutaneous patch in all 33 patients. RESULTS: In Part I, tilt of 50% demonstrated a defibrillation threshold significantly lower than 65% tilt (7.5 +/- 4.3 J vs 9.7 +/- 5.0 J; P = 0.04) and 80% tilt (7.5 +/- 4.3 J vs 11.7 +/- 5.9 J; P < 0.01). Similarly, 65% tilt provided a lower defibrillation threshold than 80% tilt (9.7 +/- 5.0 J vs 11.7 +/- 5.9 J; P = 0.02). In Part II, no significant difference was observed in terms of defibrillation threshold between 40% tilt and the two tilts of 50% and 65%. However, as in Part I, 50% tilt provided a significant reduction of the energy to defibrillate as compared to 65% tilt (6.3 +/- 3.6 J vs 9.0 +/- 4.8 J; P < 0.01). The 50% tilt resulted in better defibrillation efficacy than 65% tilt independent of the lead system used for testing (Medtronic Transvene and CPI Endotak-C). CONCLUSIONS: Biphasic shocks with 50% tilt required less energy for defibrillation than 40%, 65%, and 80% tilts. However, in the clinical setting a programmable tilt may be preferable to account for some patient-to-patient variability.

Adult↗
PubMed1996

Response to beta blockers in patients with neurocardiogenic syncope: how to predict beneficial effects.

UNLABELLED: No definitive data are available about the possibility of predicting improvement in patients with neurocardiogenic syncope treated with beta blockers. Among 112 patients with syncope and a positive head-up tilt test (HUT), independent predictors for prevention of symptoms with beta blockers were determined using the Cox proportional hazards model. Each patient underwent HUT at 70 degrees for 20 minutes both in the drug-free state and during isoproterenol infusion given to increase the heart rate by at least 25%. Fifty-nine patients had a positive HUT during isoproterenol infusion and 53 in the drug-free state. All patients were then given esmolol infusion at 500 micrograms/kg per minute for 3 minutes followed by 300 micrograms/kg per minute maintenance dose. HUT was then repeated as previously described with or without isoproterenol, depending upon the initial positive response. Regardless of the response during esmolol, all patients were treated with metoprolol 50 to 100 mg twice daily. At follow-up, 36 patients experienced symptom relapse. Four of them had negative HUT on esmolol, whereas the remaining 32 did not respond to the acute infusion of esmolol. Only four patients with positive HUT on esmolol had a favorable response to metoprolol. Patients responding to metoprolol were older (55 +/- 12 years vs 42 +/- 15 years, P < 0.05). Response to metoprolol was predicted by a negative test on esmolol (P < 0.0001) and a positive HUT on isoproterenol (P < 0.001). Age older than 42 years was also associated with a higher likelihood of metoprolol success (P < 0.02). CONCLUSION: Acute challenge with esmolol infusion appears to be an accurate predictor of response to chronic beta blockers, together with age and a positive HUT during low-dose isoproterenol infusion.

Adrenergic beta-Agonists↗
PubMed1995

Characterization of atrioventricular nodal behavior and ventricular response during atrial fibrillation before and after a selective slow-pathway ablation.

BACKGROUND: The presence of atrioventricular nodal dual-pathway physiology in patients with atrioventricular nodal reentrant tachycardia (AVNRT) provides an opportunity to characterize the effect of a selective slow-pathway ablation on the ventricular rate during atrial fibrillation (AF). This may have important clinical implications for the nonpharmacological management of AF with a rapid ventricular rate. METHODS AND RESULTS: Selective radiofrequency catheter ablation of the atrioventricular nodal slow pathway was performed with a stepwise approach in patients with documented sustained AVNRT. The AV nodal conduction properties and refractoriness and the ventricular rate during induced AF were assessed at baseline and under autonomic blockade before and after a selective slow-pathway ablation in 18 patients (mean age, 34 +/- 8 years). Sustained AVNRT was induced with a mean cycle length of 339 +/- 58 ms. A slow-pathway ablation was successfully achieved with 5 +/- 4 applications of radiofrequency energy. The shortest cycle length of 1:1 AV conduction and the AV nodal effective refractory period significantly prolonged after ablation (367 +/- 53 versus 403 +/- 55 ms, P < .0001, and 258 +/- 55 versus 292 +/- 74 ms, P < .05, respectively). Selective slow-pathway ablation significantly prolonged the mean (526 +/- 93 versus 612 +/- 107 ms, P < .0001), the shortest (378 +/- 59 versus 423 +/- 73 ms, P < .0001), and the longest (826 +/- 150 versus 969 +/- 226 ms, P < .01) cycle lengths of the ventricular response to AF. Significant slowing of the ventricular rate during AF occurred in 13 patients (72%), including all eight patients in whom AV nodal dual-pathway physiology was abolished. Five patients did not have a significant change in the ventricular rate during AF; a persistent dual AV nodal pathway physiology was demonstrable in four of these patients. Loss of dual-pathway physiology after ablation had a sensitivity of 77%, specificity of 80%, and positive predictive value of 91% for slowing the ventricular rate during AF. CONCLUSIONS: In patients undergoing a slow-pathway ablation for control of AVNRT, selective slow-pathway ablation may cause a significant decrease in the ventricular rate during AF. These effects are primarily due to the prolongation of AV nodal conduction properties and refractory period of the residual AV nodal transmission system. These findings may have important therapeutic implications for the nonpharmacological treatment of AF, particularly in patients with underlying dual AV nodal physiology.

Adult↗
PubMed1995

Termination of atrioventricular nodal reentrant tachycardia by premature stimulation from ablating catheter. A reliable guide to identify site for slow-pathway ablation.

BACKGROUND: Slow-pathway ablation is currently used more frequently to control atrioventricular nodal reentrant tachycardia (AVNRT). However, in patients with the common type of AVNRT, successful ablation of the slow pathway can be difficult and time-consuming. We tested a simple method to predict a site for slow-pathway ablation in patients with AVNRT of the common variety. METHODS AND RESULTS: Twenty patients with symptomatic common AVNRT (13 women and 7 men; mean age, 41 +/- 21 years) were included in the study. Once the AVNRT had a stable cycle length (+/- 10 ms) for at least 20 cycles, single extrastimuli were delivered from the ablating catheter tip beginning with 20 ms less than the tachycardia cycle length and decrementing by 10 ms until tachycardia terminated or loss of capture occurred at the pacing site. The pacing protcol was performed systematically in a stepwise fashion at four adjacent sites starting from the posterior/inferior interatrial septum near the tricuspid annulus and moving progressively more anteriorly. The pacing protocol was then repeated in the same sequence, followed by delivery of radiofrequency current at each site to determine its effect at sites where AVNRT could not be terminated with a pacing protocol. AVNRT could be terminated in the anterograde direction from at least one site in 19 patients. Tachycardia could be terminated at two or more adjacent sites in 5 patients. The longest atrial coupling interval at the site of tachycardia termination was 67 +/- 27 ms (range, 30 to 130 ms) less than the AVNRT cycle length. Resetting of subsequent His bundle depolarization (H2), producing an H-H2 interval prolongation of 26 +/- 24 ms (range, 10 to 80 ms), occurred in 17 patients before termination of the tachycardia. In 18 of the 19 patients, the slow pathway was successfully ablated at the site at which AVNRT was terminated at the longest atrial coupling interval. CONCLUSIONS: Termination of tachycardia in the anterograde direction at the longest atrial coupling interval by extrastimuli delivered from the ablating catheter can be helpful for identification of an optimal site for slow-pathway ablation in patients with the common variety of AVNRT.

Adult↗
PubMed1995

Relevance of asystole during head-up tilt testing.

The prognosis of patients manifesting prolonged asystole during head-up tilt testing is unclear. In 209 consecutive patients with a history of syncope and positive head-up tilt tests, 19 had asystole lasting > 5 seconds (mean duration 15 +/- 10) (group 1a). When compared with patients without asystole (group 1b), group 1a patients were younger (32 +/- 12 vs 47 +/- 21 years, p < 0.005), but clinical manifestations were not any more dramatic (the number of episodes of syncope [7 +/- 5 vs 8 +/- 6 episodes, p = NS] and injury during syncope [2 vs 13 patients, p = NS] were similar). During follow-up (mean 2 +/- 1 year), with the patient taking pharmacologic therapy such as beta blockers, ephedrine, theophylline, or disopyramide, the recurrence rate was 11% and 8% in groups 1a and 1b (p = NS). No patient in the asystole group underwent pacemaker implantation. Additionally, of 75 normal volunteers (group 2) with no history of syncope undergoing tilt tests to define its specificity, 3 had asystole (mean duration 10 seconds). During > 1 year of follow-up, despite no treatment, all 3 are symptom free. Thus, asystole during head-up tilt testing does not predict either a more malignant outcome or a poor response to pharmacologic therapy. Moreover, an asystolic response does not enhance the specificity of the head-up tilt test because it may be present in asymptomatic "normal" volunteers.

Adolescent↗
PubMed1995

Comparison of biphasic and monophasic pulses: does the advantage of biphasic shocks depend on the waveshape?

With present implantable defibrillators, the ability to vary the defibrillation technique has been shown to increase the number of patients suitable for transvenous system. As newer waveforms become available, the need for a flexible device may change. In addition, although it has been shown that the option of biphasic waveform may increase the defibrillation efficacy, this may depend upon the shape of the biphasic waveform used. Thirty patients undergoing transvenous defibrillator implant were included in the study. In 20 patients (group I), defibrillation efficacy of simultaneous monophasic, sequential monophasic, and biphasic waveform with 50% tilt was determined randomly. Similarly, in ten patients (group II) testing of simultaneous monophasic shocks and biphasic waveforms with 65% and 80% tilt was performed in random order. The electrode system used consisted of two transvenous leads and a subcutaneous patch in all 30 patients. In group I, 50% tilt biphasic waveform consistently provided similar or better defibrillation efficacy compared to monophasic waveforms (biphasic 7.5 +/- 5.1 joules vs simultaneous 17 +/- 7.8 joules, P < 0.01; and vs sequential 17 +/- 8.4 joules, P < 0.01). In group II, 65% tilt biphasic pulse required less energy for defibrillation as compared with simultaneous monophasic shocks (9.6 +/- 4.5 joules vs 15.6 +/- 5.1 joules, P = 0.04). No significant difference was observed in terms of defibrillation threshold between 80% tilt biphasic shocks and simultaneous monophasic pulses (11.8 +/- 6 joules vs 15.6 +/- 5.1 joules, P = NS). Biphasic shocks with smaller tilt delivered using a triple lead system more uniformly improved defibrillation threshold over standard monophasic waveforms.

Defibrillators, Implantable↗
PubMed1995

Effects of initial polarity on defibrillation threshold with biphasic pulses.

BACKGROUND: Previous studies have shown that the polarity of epicardial patches significantly affects the defibrillation efficacy of monophasic shocks. However, whether this improvement can be extended to different pulsing methods and lead systems, such as biphasic shocks using endocardial defibrillating electrodes, is unknown. METHODS: Twenty consecutive patients undergoing testing and permanent implant using an Endotak lead system with a biphasic device were included in the study. In each patient the defibrillation threshold was determined delivering biphasic pulses with the distal coil as the cathode and the proximal coil as the anode during the positive phase and with the polarity reversed. The initial electrode polarity tested was chosen randomly. The defibrillation threshold was defined as the lowest pulse amplitude that effectively terminated ventricular fibrillation induced with 60-Hz alternating current. For each biphasic pulse peak voltage, pulse duration, resistance, and stored energy were recorded. RESULTS: Of the 20 patients, 12 (60%) had lower defibrillation threshold when the proximal coil was negative, whereas only 2 patients had a lower defibrillation threshold when the distal coil was negative. In four patients a subcutaneous patch would have been required if only the biphasic pulse with the distal coil as negative had been tested. The mean stored defibrillation threshold energy was lower with the configuration using the proximal coil as cathode (16.3 +/- 8.8 J vs 21.5 +/- 11 J; P < 0.01). CONCLUSION: Change in the initial polarity of biphasic shocks may influence defibrillation efficacy and should, therefore, be assessed in each patient to achieve a more satisfactory safety margin and minimize the use of more invasive lead configurations.

Defibrillators, Implantable↗
PubMed1995

Efficacy of different treatment strategies for neurocardiogenic syncope.

OBJECTIVES: The purpose of this study was to evaluate the efficacy of different therapeutic approaches for patients with a history of syncope and positive head-up tilt testing. BACKGROUND: Head-up tilt testing has gained broad acceptance as a reliable diagnostic method for the assessment of patients with recurrent unexplained syncope. However, once the diagnosis is established, there is no consensus on the most appropriate treatment. In this respect, efficacy of drug therapy in preventing recurrence of symptoms in such patients is not entirely clear, and controversies exist regarding the need to confirm the effects of pharmacological interventions. METHODS: Clinical follow-up was obtained in 303 patients with a history of syncope and positive head-up tilt testing. After the diagnostic head-up tilt, patients were assigned to different therapeutic approaches according to their preference or logistic impediments. Of 303 patients, 44 received empiric therapy, 210 were treated with medications proven effective during repeated head-up tilt testing, and 49 refused or discontinued medical therapy. The three groups were similar with regard to age, sex, and clinical presentation. The mean follow-up was 2.8 +/- 1.8 years. Among the patients treated according to head-up tilt guided therapy, 130 were on beta blockers, 35 on theophylline, 10 on ephedrine, 31 on disopyramide, and 4 on miscellaneous regimens. Empiric treatment consisted of beta blockers in 37 of 44 patients and other drugs in the remaining patients. RESULTS: During the follow-up, recurrence of symptoms was experienced in 12 (6%) of the 210 patients receiving the head-up tilt guided therapy, 16 (36%) of 44 in the empiric therapy group, and 33 (67%) of 49 in the no therapy group. Recurrence of symptoms in patients on empiric or no therapy was significantly more frequent as compared to the head-up tilt guided therapy group (P < 0.01). CONCLUSIONS: In patients with unexplained syncope and positive upright tilt testing, therapeutic strategies identified on the basis of response during head-up tilt have a more positive impact on the recurrence of symptoms during follow-up.

Adolescent↗
PubMed1995

Posteroseptal accessory pathways: an overview of anatomical characteristics, electrocardiographic patterns, electrophysiological features, and ablative therapy.

First, the posteroseptal region of the heart is probably the most complex area among those that harbor AV accessory fibers and a firm grasp of the anatomical characteristics of this region may facilitate achieving a successful AP ablation. Second, there is no sharp demarcation between the posteroseptal area and its surrounding regions including mid-septal, left posterior paraseptal, and right posterior paraseptal locations. Therefore, there are some inevitable overlaps between the electrocardiographic and electrophysiological features of APs located in the posteroseptal region and those areas immediately adjacent to it. Third, in the vast majority of cases, successful ablation can be achieved using a right atrial approach. Therefore, dividing posteroseptal APs into right- or left-sided pathways may only be useful for describing their ECG or electrophysiological characteristics with little or no value in predicting the site of successful ablation. Fourth, it seems advisable to attempt efforts to induce functional bundle branch block during orthodromic tachycardia and assess its effect on the VA interval. Ventriculoatrial interval prolongation due to right bundle branch block strongly favors a right free-wall or anteroseptal AP location. Prolongation of the VA interval by 30 msec or less in response to left bundle branch block is compatible with a posteroseptal location. In this situation, the mapping and ablative efforts should primarily be focused on the right atrial approach, including the terminal coronary sinus. If left bundle branch block causes VA interval lengthening of 30 msec or greater, the AP is most likely in the left free-wall region, including the posterior paraseptal area. Finally, the presence of APs having an intimate relationship with the middle cardiac (posterior interventricular) vein or the coronary sinus pouch, although exceedingly uncommon, should be considered in difficult cases in which radiofrequency applications to the conventional posteroseptal locations are unsuccessful. Such cases may require coronary sinus venography for better visualization and precise mapping of the terminal sinus complex.

Arrhythmias, Cardiac↗
PubMed1995

Catheter ablation in supraventricular tachycardia.

The evolution of catheter ablation for the treatment of supraventricular tachycardias represents a major advance in the management of cardiac arrhythmias. Excellent results in the majority of patients undergoing the procedure, together with a low rate of early complications and a brief hospitalization, make catheter ablation a highly cost-effective permanent cure. At present, however, its place in relation to alternate therapies in the management of supraventricular tachycardias has not been clearly established owing to unresolved risk-benefit issues. Continuing technical advances will likely enable catheter ablation to be successfully applied to a broader range of cardiac arrhythmias.

Anti-Arrhythmia Agents↗
PubMed1994

Feasibility of concomitant implantation of permanent transvenous pacemaker and defibrillator systems.

In 17 patients (14 men and 3 women aged 69 +/- 10 years), a transvenous pacemaker was implanted before (8 patients), following (7 patients), or simultaneously (2 patients) with the insertion of a transvenous defibrillator. Indications included malignant ventricular arrhythmias and symptomatic bradycardia in all patients. All patients had structural heart disease. All pacemakers were non-programmable bipolar, either single chamber (n = 7) or dual chamber (n = 10). Eleven pacemakers were rate responsive. The Transvene system was implanted in 7 patients (Pacer-Cardioverter-Defibrillator in 6 patients and the Cadence defibrillator in 1). The Endotak lead system was implanted in 10 patients (Ventak in 7 patients and the Cadence in 3). The mean defibrillation threshold was 16 +/- 5 J. Repositioning of the pacemaker leads eliminated undersensing of ventricular fibrillation by the defibrillator, which occurred during asynchronous pacing in 2 patients. During a mean follow-up of 11 +/- 6 months, 2 patients died because of pump failure and 7 patients received defibrillator therapy for ventricular arrhythmias. No significant complications were noted. Successful concomitant implantation of transvenous pacemakers and defibrillators was thus accomplished in 17 patients, which suggests that insertion of a second transvenous device can be safely accomplished.

Adult↗
PubMed1994

Catheter ablation of ventricular tachycardia.

The role and success rate of catheter ablation for monomorphic ventricular tachycardia (VT) depend on the mechanism and origin of the tachycardia (i.e., myocardial versus His-Purkinje system) and whether it occurs in the presence or absence of structural heart diseases. For sustained bundle-branch reentry, a form of VT associated with structural heart disease, radiofrequency catheter ablation of the right bundle-branch can be performed readily and is highly successful in eliminating this arrhythmia. Because of modest success rates of catheter ablation of VT associated with a prior infarction (between 17% and 75%), this treatment modality is usually considered for cases refractory to drug therapy and should be viewed as adjunctive therapy. The target for ablation is a critical area of slow conduction, which is selected based on earliest endocardial activation, mid-diastolic potentials, concealed entrainment, or pace mapping. Radiofrequency catheter ablation may be the treatment of choice in patients with VT and no apparent structural heart disease; this is especially true for young patients who would otherwise require long-life antiarrhythmic therapy. Success rates between 75% and 100% have been reported, especially when the origin is in the right ventricular outflow tract.

Bundle-Branch Block↗
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↗