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Biomedical subjects

B Olshansky

Publications and source records attributed to B Olshansky.

At least 19 recordsLinked to original sources
PubMed1999

Catheter ablation of accessory pathways, atrioventricular nodal reentrant tachycardia, and the atrioventricular junction: final results of a prospective, multicenter clinical trial. The Atakr Multicenter Investigators Group.

BACKGROUND: The purpose of this study was to evaluate the safety and efficacy of a temperature-controlled radiofrequency catheter ablation system. METHODS AND RESULTS: The patient population included 1050 patients who had undergone ablation of atrioventricular nodal reentrant tachycardia (AVNRT), an accessory pathway (AP), or the atrioventricular junction (AVJ). Ablation was successful in 996 patients. The probability of success was highest among patients who had undergone ablation of the AVJ, lowest in patients who had undergone ablation of an AP, and in between for patients who had undergone ablation of AVNRT. A major complication occurred in 32 patients. Four variables predicted ablation success (AVJ, AVNRT, or left free wall AP ablation and an experienced center). Four factors predicted arrhythmia recurrence (right free wall, posteroseptal, septal, and multiple APs). Two variables predicted development of a complication (structural heart disease and the presence of multiple targets), and 3 variables predicted an increased risk of death (heart disease, lower ejection fraction, and AVJ ablation). CONCLUSIONS: These findings may serve as a guide to clinicians considering therapeutic options in patients who are candidates for ablation.

Adolescent↗
PubMed1999

Clinical significance of syncope in the electrophysiologic study versus electrocardiographic monitoring (ESVEM) trial. The ESVEM Investigators.

BACKGROUND: Syncope may portend risk of death, but which patients with syncope are at high risk remains unclear. OBJECTIVE: The ESVEM trial, a multicenter randomized prospective trial, provided the opportunity to compare mortality rates of patients enrolled with syncope to those enrolled with spontaneous ventricular arrhythmias. METHODS: Patients enrolled in the ESVEM trial presenting with syncope alone (25 patients) or in combination with ventricular tachycardia (24 patients) were compared with patients with spontaneous ventricular tachycardia alone (332 patients) or ventricular fibrillation (105 patients). All patients had ventricular tachyarrhythmias induced at electrophysiology testing of >/=10 premature ventricular complexes per hour on Holter monitor. RESULTS: Of all patients randomly assigned, arrhythmic death and total mortality rates were the same for those with syncope alone, with ventricular tachycardia and syncope, with ventricular tachycardia alone, or with ventricular fibrillation. At 1 year, arrhythmic and total mortality rate for all patients was 21% and 24%, respectively; for patients with syncope alone, 30% and 29%, respectively (P = NS). At 4 years, arrhythmic death and total mortality rate for all patients was 33% and 42%, respectively; for patients with syncope alone, 37% and 42%, respectively (P = NS). CONCLUSION: Syncope, associated with induced ventricular tachyarrhythmias at electrophysiologic testing, indicates high risk for death, similar to that of patients with documented spontaneous ventricular tachyarrhythmias.

Aged↗
PubMed1999

Cardiac arrhythmias and the athlete.

Athletes, although the healthiest segment of society, can develop cardiac arrhythmias. Benign bradycardias and atrial and ventricular premature contractions are common and seldom require treatment. Supraventricular tachycardias are less common and are usually not life-threatening, but do require treatment. Ventricular arrhythmias, although uncommon, are life-threatening and require treatment. Most athletes with ventricular arrhythmias have structural cardiac abnormalities, and further competitive play is usually prohibited. Commotio cordis, which is a recently described syndrome of sudden death caused by low-energy chest wall impact, may account for a significant percentage of the sudden deaths in athletes.

Arrhythmias, Cardiac↗
PubMed1997

Thromboembolism in chronic atrial flutter: is the risk underestimated?

OBJECTIVES: We sought to evaluate the risk of thromboembolic events in the presence of chronic atrial flutter and to determine the impact of anticoagulation therapy, if any, on this risk. BACKGROUND: Thromboembolic events are thought to be rare after cardioversion of atrial flutter. METHODS: This study was a retrospective analysis of 110 consecutive patients referred to the electrophysiology laboratory for cardioversion of chronic atrial flutter from 1986 to 1996. Atrial flutter was present for at least 6 months. Of the 110 patients reviewed, 100 had adequate information available regarding the effectiveness of anticoagulation (mean age 64 years, range 27 to 86; 75 men, 25 women; mean left ventricular ejection fraction 42%). RESULTS: Thirteen patients (13%) had a thromboembolic event. Of these, seven were attributable to causes other than atrial flutter. In the remaining six patients (6%), thromboembolic events occurred during a rhythm of atrial flutter or after cardioversion to sinus rhythm. Other causes of thromboembolism were excluded. Effective anticoagulation was associated with a decreased risk of thromboembolism (p = 0.026). CONCLUSIONS: Patients with chronic atrial flutter are at an increased risk of thromboembolic events. Effective anticoagulation may decrease this risk.

Adult↗
PubMed1997

Autonomic influences in atrial ischemia: vagally mediated atrial conduction improvement.

To investigate the effects of autonomic nerve activation on electrophysiological properties of ischemic atrial myocardium, experiments were performed in 10 open chest adult dogs anesthetized with xylazine and alpha-chloralose. Ischemia was created in the right atrial free wall by ligation of one or more branches of the right coronary artery. Bipolar electrograms were recorded from multiple sites in the ischemic and non-ischemic zones. The atria were paced at 400 ms and 180 ms to assess conduction properties. One hour after ligation, delayed activation, electrogram fractionation, and electrogram alternans were observed in the ischemic zone. All local conduction abnormalities were heart rate dependent in that they were only observed at a pacing cycle length of 180 ms. The average duration of ischemic zone electrograms was significantly prolonged from 17.7+/-1.6 ms to 26.4+/-1.6 ms (P<0.001). Right and left vagal stimulation significantly shortened the electrogram duration in the ischemic zone from 26.4+/-1.6 ms to 19.7+/-1.1 ms (P<0.01) and 20.0+/-1.1 ms (P<0.01), respectively. Ischemia-induced electrogram alternans was eliminated completely. During right and left stellate stimulation, electrogram duration was not altered and alternans was still present. In conclusion, vagal stimulation in this canine model improves local conduction in ischemic myocardium in the right atrium. This effect may be mediated by a reversal of the ischemia-induced membrane depolarization and a shortening of refractoriness in the atrium during vagal activation.

Animals↗
PubMed1997

Teletronics 330-801 atrial lead extraction via the subclavian approach.

BACKGROUND: The Telectronics 330-801 atrial J (801) lead was recalled after reports implicated lead fracture/retention wire protrusion in patient mortality and morbidity. Recent reports suggest that 801 lead extraction may be associated with substantial morbidity and, possibly, excess mortality. We hypothesized that the 801 lead could be extracted using the subclavian approach with a high success rate and acceptable morbidity. METHODS: We analyzed the clinical outcomes in 60 consecutive patients who underwent 801 lead extraction. RESULTS: Sixty patients (34 women) with a mean age of 67 +/- 14.8 years had 18 class I, 13 class II, and 29 class III fractures. The lead age was 39 +/- 17 months. The subclavian approach was successful in 58 of 60 patients (96%). Complications, three major and eight minor, occurred in 10 of 60 patients (16%). All complications were successfully treated. There were no deaths. Only concurrent ventricular lead extraction was associated with complications (p = 0.008 by Fisher's exact test). CONCLUSIONS: Telectronics 801 leads can be successfully extracted using the subclavian approach with acceptable short-term morbidity, low mortality, and excellent long-term results.

Adult↗
PubMed1997

Symptomatic atrioventricular block in an atriofascicular pathway inserting into the left bundle branch without apparent atrioventricular node function.

We report a patient with symptomatic AV block associated with conduction solely through an atriofascicular pathway that inserted into the left bundle branch. There was no apparent conduction present through the AV node. There was, however, passive activation through the His-Purkinje system. His-bundle pacing demonstrated normal conduction through both right and left bundles. This is the first report of such a case.

Atrioventricular Node↗
PubMed1996

Current-based transthoracic defibrillation.

This study examines in a prospective, multicenter trial the feasibility and advantage of current-based, transthoracic defibrillation. Current-based, damped, sinusoidal waveform shocks of 18, 25, 30, 35, or 40 amperes (A) were administered beginning with 25 A for polymorphic ventricular tachycardia (VT) and ventricular fibrillation (VF) or 18 A for monomorphic VT; success rates were compared with those of energy-based shocks beginning at 200 J for VF/polymorphic VT and 100 J for VT. The current-based shocks were delivered from custom-modified defibrillators that determined impedance in advance of any shock using a "test-pulse" technique; the capacitor then charged to the exact energy necessary to deliver the operator-selected current against the impedance determined by the defibrillator. Three hundred sixty-two patients received > 1 shock for VF, polymorphic VT, or monomorphic VT: 569 current- based shocks and 420 energy-based shocks. Current-based shocks of 35/40 A achieved success rates of up to 74% for VF/polymorphic VT; 30 A shocks terminated 88% of monomorphic VT episodes. Energy-based shocks of 300 J terminated 72% of VF/polymorphic VT; 200-J shocks terminated 89% of monomorphic VT. We could not demonstrate a significant increase in the success rate of current-based shocks over energy-based shocks for patients with high transthoracic impedance; this may be due to inadequate sample size. Thus, current-based defibrillation is clinically feasible and effective. A larger study will be needed to test whether current-based defibrillation is superior to energy-based defibrillation.

Electric Countershock↗
PubMed1996

Management of atrial fibrillation after coronary artery bypass graft.

More than 400,000 patients undergo coronary artery bypass graft surgery (CABG) each year in the United States. At least 20-30% of these patients have atrial fibrillation (Afib), making this arrhythmia one of the most common postoperative problems. This generally benign problem can increase surgical morbidity and the cost and length of hospital stay. If not treated promptly and effectively, Afib can delay a full and rapid recovery. Afib usually occurs in paroxysms between the second and fifth postoperative day and appears directly related to effects of surgery (pericarditis, changes in autonomic tone, cardioplegia, myocardial damage, fluid shifts, etc.). Although similar to Afib in other settings, beta-adrenergic blockade is more effective in preventing and terminating Afib in the postoperative setting. The unique circumstances that precipitate postoperative Afib may explain the favorable therapeutic and prophylactic actions of beta-adrenergic blockade. Other therapies such as amiodarone, sotalol, and digoxin are surprisingly ineffective for postoperative Afib, while intravenous diltiazem is not well tested in this setting. Despite the lack of proven benefit for some of these therapies, they are still frequently used in current clinical practice. Management of postoperative Afib is initially directed at ventricular rate control, but the ultimate goal is return to sinus rhythm. The approach to therapy depends on several clinical variables, including the time course of the arrhythmia, but hemodynamic stability of the patient is the key issue. Return to sinus rhythm may be difficult to achieve early after surgery, so opting for rate control is the best initial approach. If tolerated, beta-adrenergic blockade and calcium antagonism are the best first options. Class IA and III antiarrhythmic drugs should be reserved for persistent or poorly tolerated and prolonged episodes of Afib. Elective cardioversion, either by direct current or with drugs, should be delayed for as long as possible after surgery. Anticoagulation for post-CABG Afib remains controversial. More prudent use of presently available drugs to treat Afib could reduce morbidity, cost, and duration of hospital stay after CABG. More rapid-acting and reliably effective antiarrhythmic therapies with minimal adverse effects would greatly improve management of post-CABG Afib.

Adrenergic beta-Antagonists↗
PubMed1996

Dofetilide versus quinidine for atrial flutter: viva la difference!?

Dofetilide is more effective than quinidine to terminate atrial flutter in this animal model. It is also more capable of lengthening refractoriness more uniformly than quinidine. While the investigators describe local changes in refractoriness and dispersion of refractoriness and wavelength meticulously, it is not clear which, if any, of these properties cause flutter termination or influence reinduction. This report provides new insight into the electrophysiologic mechanisms of antiarrhythmic drugs used to treat atrial arrhythmias. Related investigations are needed to expand our knowledge of the actions of antiarrhythmic drugs, how these drugs affect critical portions of the reentrant circuit, and how to identify potential adverse effects of these agents. Application of these data may help guide the use of antiarrhythmic drugs and allow development of safer, and yet more potent, compounds. At least, it will give us pause about using more toxic and less effective drugs. While Class III drugs, specifically dofetilide, may be more potent and beneficial than quinidine in this model, it is uncertain that these results pertain to human reentrant atrial arrhythmias, particularly, atrial flutter. Perhaps dofetilide will be effective for certain types of atrial flutter requiring an anatomical center defined by an area of injury or surgical scar in the right atrium. The fact that these, and previous, data indicate a specific beneficial effect of dofetilide, particularly on atrial flutter, is interesting. Even if dofetilide proves highly effective for human atrial flutter, its safety will need to be proven in large clinical trials. The most obvious concern about dofetilide is development of serious side effects such as torsades de pointes. Clinical trials of this drug for atrial arrhythmias are presently ongoing. Ultimately, the long-term use of such a drug is dependent on the emergence of other highly effective therapies such as radiofrequency ablation.

Animals↗
PubMed1996

Reflex vagal control of atrial repolarization.

The reflex vagal control of atrial repolarization was investigated in eight open-chest, anesthetized dogs. A monophasic action potential was recorded from the right atrium, and the action potential duration to 90% repolarization (APD90) was determined every cardiac cycle. beta-Adrenergic receptors were blocked with timolol (0.1 mg/kg). Under baseline conditions, sinus slowing during sinus arrhythmia was accompanied by a significant shortening of APD90 (24 +/- 4.0 ms). Transient occlusion (30 s) of the descending thoracic aorta increased systolic aortic pressure from 138 +/- 2.8 to 181 +/- 3.3 mmHg (P < 0.01). Heart rate decreased from 99 +/- 3.6 to 42.5 +/- 3.4 beats/min (P < 0.01), and APD90 shortened from 168 +/- 5.1 to 94 +/- 3.3 ms (P < 0.01). Release of the occlusion caused arterial hypotension (95 +/- 2.8 mmHg) and an overshoot in both rate (126 +/- 5.2 beats/min) and APD90 (189 +/- 2.3 ms). Aortic occlusion during atrial pacing (130-160 beats/min) decreased APD90 from 147 +/- 7.0 to 78 +/- 3.4 ms (P < 0.01). Cervical vagotomy or atropine eliminated changes in rate and APD90 evoked by aortic occlusion. The results indicate that there is parallel central vagal control of both sinus rate and atrial repolarization. Sinus bradycardia during reflex vagal activation does not prevent the acceleration of atrial repolarization.

Action Potentials↗
PubMed1996

Sympathetic influences on electrical and mechanical alternans in the canine heart.

OBJECTIVE: The aim was to investigate the influence of the sympathetic nervous system on the induction of mechanical and electrical alternans in the intact canine heart. METHODS: Experiments were performed on 8 open-chest dogs anesthetized with sodium pentobarbital. A micromanometer-tipped catheter was used to measure left ventricular pressure, dp/dt and the time constant of isovolumic relaxation. Rapid atrial pacing was used to induce alternans and the left stellate ganglion was stimulated electrically to alter sympathetic tone. The longest pacing cycle length that showed a significant alternation in peak systolic pressure was defined as the alternans threshold. Electrical alternans was detected by comparing the ST-T area in the surface ECG (lead II) on alternate beats. RESULTS: The alternans threshold was 305(s.e.m. 10.4) ms under control conditions and decreased to 271(12.1), 225(33.4), and 177(6.2)ms, as the frequency of left stellate stimulation was increased to 1, 2, and 5 Hz, respectively (P < 0.001). Tau and peak -dp/dt began to alternate at the same pacing cycle length as peak +dp/dt and peak systolic pressure. Electrical alternans was only observed during mechanical alternans and the ST-T area of the strong beat was 243(143)% greater than the ST-T area of the weak beat (P < 0.001). Timolol (1 mg.kg-1) blocked the effect of left stellate stimulation (1 and 2 Hz) on mechanical and electrical alternans. CONCLUSIONS: Left sympathetic activation causes a frequency-dependent reduction in the threshold cycle length for global mechanical and electrical alternans. Alternation in relaxation occurs at the same pacing cycle length as does alternation in contraction. Repolarization alternans in the surface ECG appears to reflect underlying mechanical events.

Animals↗
PubMed1995

Predictors of defibrillation energy requirements with nonepicardial lead systems.

The determinants of high defibrillation energy requirements (DER) using nonepicardial lead systems (NELS) have not been well characterized. The goal of this study was to examine prospectively the influence of clinical, radiographic, echocardiographic, and procedural variables on DER during NELS placement. Data from 100 consecutive patients undergoing attempted NELS implantation were analyzed. Transvenous leads, subcutaneous patches, and monophasic shock devices from two manufacturers were used. Leads were successfully positioned for testing in 95% of patients. An adequate DER (< or = 25 J) was obtained in 73 of 95 (77%) of patients. Univariate analysis identified amiodarone therapy and left ventricular mass as predictors of high DER. With multivariate analysis, amiodarone therapy was the sole significant predictor of high DER (P = 0.002, odds ratio 5.46). The 22 patients with high NELS DER also had high epicardial DER (mean 24 +/- 9 J). The two patch epicardial DER was > 25 joules in 12 of 22 patients. Thus, adequate DER with monophasic shock waveforms can be obtained in most patients undergoing NELS testing. However, amiodarone therapy significantly increases the probability of obtaining high DER.

Amiodarone↗
PubMed1995

Adenosine-sensitive atrial tachycardia.

Limited data suggest that adenosine termination of atrial tachycardia is uncommon. To investigate further the effect of adenosine on atrial tachycardia, adenosine (6-12 mg) was administered during sustained atrial tachycardia in 17 patients. All patients underwent electrophysiological study to exclude other mechanisms of supraventricular tachycardia. Mean patient age was 51 +/- 20 years (range 18-82 years). Seven patients had no structural heart disease. The mean atrial tachycardia cycle length was 390 +/- 80 msecs (range 260-580). Sustained atrial tachycardia was induced with atrial extrastimuli in 8 patients, and was either incessant at baseline or developed spontaneously during isoproterenol infusion in 9 patients. Adenosine terminated atrial tachycardia in 3 patients (18%), transiently suppressed atrial tachycardia in 4 patients (23%), and produced AV block without affecting tachycardia cycle length in the remaining 10 patients. Adenosine sensitivity was observed in 3 of 8 patients with tachycardias initiated and terminated by atrial extrastimuli, and in 4 of 9 patients with spontaneous, but not inducible tachycardias including 3 of 4 patients with isoproterenol facilitated tachycardias. Of multiple clinical and electrophysiological variables examined as potential predictors of adenosine sensitivity, only isoproterenol facilitation of spontaneous or inducible sustained tachycardia predicted adenosine sensitivity (P = 0.02). These observations suggest that adenosine-sensitive atrial tachycardia may be more common than previously recognized. Adenosine sensitivity does not appear to be specific for tachycardia mechanism and cannot be predicted by response to pacing. Atrial tachycardias dependent on beta-adrenergic stimulation are most likely to be terminated by adenosine.

Adenosine↗