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Biomedical subjects

S L Brownstein

Publications and source records attributed to S L Brownstein.

9 recordsLinked to original sources
PubMed1991

Improved patient surveillance and data acquisition with a third generation implantable cardioverter defibrillator.

Thirteen patients were implanted with the Telectronics 4210 ATP implantable cardioverter defibrillator (ICD) for ventricular tachycardia or ventricular fibrillation. This device has multiprogrammable antitachycardia pacing, bradycardia pacing, and shock therapies. In addition, there is extensive data logging and ECG snapshot capability for arrhythmia confirmation and response to therapy. These features permit easy retrieval of all detected and treated events, whatever the eventual outcome. In this study, the data logged at predischarge electrophysiological testing was compared to the data recorded in a standard manner. The bulk of the data, however, was derived from long-term follow-up of spontaneous events over a mean period of 203 days (range 154-257). During this period, a total of 6,193 arrhythmia detections were made: 20 were classified as ventricular fibrillation, and 6,173 as ventricular tachycardia. The vast majority of these (93%) terminated spontaneously without ICD intervention (5,738), underscoring the benefit of a standard second confirmation prior to therapy delivery (noncommitted system). There were 394 arrhythmia episodes treated with antitachycardia pacing; of these a total of 8.3% accelerated to either more rapid ventricular tachycardia or ventricular fibrillation (4.3% and 4.0%, respectively). Events were reported in an "episode log" format, listing all arrhythmia detections with time/date annotation; or in a "sense history" format, detailing each episode from start to conclusion. These data demonstrate that this advanced, "tiered" ICD with data recall contributes to better patient management, and permits a more tailored termination prescription for the individual patient.

Cardiac Pacing, Artificial↗
PubMed1990

Cumulative effects of cycle length on ventricular refractoriness in man.

This study examined the time course of changes of ventricular effective refractory period (VERP) following an abrupt change of cycle length (CL) in man. Stimulation at the right ventricular apex consisted of 19 cycles of an initial CL, followed by a variable number of cycles (0 to 50 cycles) of a new CL, and an extrastimulus to test for VERP. Fifteen patients were enrolled in each part of the study. In part A, initial CLs were long (mean +/- standard error, 650 +/- 20 msec) and new CLs were short (325 +/- 10 msec). VERPs were 259 +/- 6 msec after the long cycles, 238 +/- 6 msec after one short cycle (p less than 0.05), 224 +/- 5 msec after 10 short cycles, and 210 +/- 6 msec after 50 short cycles (p less than 0.05 versus 1 or 10 short cycles). Thus 43% of total shortening of VERP occurred in the first short cycle and 57% occurred in subsequent short cycles. In part B, initial CLs were short and new CLs were long. VERPs were 212 +/- 7 msec after the short cycles, 237 +/- 7 msec after one long cycle (p less than 0.05), 239 +/- 7 msec after 10 long cycles, and 247 +/- 7 msec after 50 long cycles (p less than 0.05 versus 1 or 10 long cycles). Thus 71% of total lengthening of VERP occurred in the first long cycle and 29% occurred in subsequent long cycles. In conclusion, following an abrupt change of CL in man, VERP changes markedly in the first new cycle (immediate effect) and then undergoes further, more gradual change over a large number of subsequent cycles (cumulative effects). Cumulative effects appear to be greater following shortening of CL than following lengthening of CL.

Adult↗
PubMed1990

PR interval behavior during exercise: implications for physiological pacemakers.

The relationship between heart rate response and the dynamic changes in the PR interval was assessed in 631 patients undergoing routine cardiac exercise tests for a variety of clinical indications. Patients were stratified into four subsets: nonmedicated normals (n = 437), patients on beta-antagonist agents (n = 118), those on antiarrhythmic agents alone (n = 61) and those with a clinical diagnosis of advanced (New York Heart Association [NYHA] Class III or IV) congestive heart failure. All patients were in stable sinus rhythm throughout the test. PR intervals were measured at rest, at mid-exercise and at peak exercise. Mean PR intervals shortened to a statistically significant degree in most subgroups. This effect was predominantly observed in the earlier stages of exercise. In patients with advanced heart failure, there was no statistically significant shortening of exercise PR intervals later in exercise, demonstrating a parallel with their relatively blunted heart rate response. These changes in exercise PR intervals suggest that implanted pacemaker algorithms may be constructed to maximize hemodynamic benefit in patients requiring physiological pacemakers.

Adolescent↗
PubMed1989

Induced sustained ventricular tachycardia in nonischemic dilated cardiomyopathy: dependence on clinical presentation and response to antiarrhythmic agents.

Thirty-one patients with nonischemic dilated cardiomyopathy either idiopathic or due to regurgitant valvular disease were studied in the cardiac electrophysiology lab. The indications for study were sustained ventricular tachycardia (VT) in 16, ventricular fibrillation (VF) in 11, and syncope of unknown etiology in 4. Sustained VT was reproducibly induced in 17 patients, including 12 with a history of sustained VT, 2 with VF and 3 with syncope. Of 15 patients undergoing serial antiarrhythmic drug studies, sustained VT was rendered noninducible or nonsustained in 13. Three had recurrent arrhythmic events while on therapy predicted to be effective. One of 2 patients discharged on a regimen predicted to be ineffective had a recurrence of sustained VT that resulted in cardiac arrest. Of 14 patients in whom sustained VT could not be reproducibly induced, 2 subsequently had spontaneous occurrences of sustained VT, and 2 experienced aborted sudden death. These results suggest the following: (1) the induction of sustained VT in the setting of nonischemic dilated cardiomyopathy is dependent on the clinical presentation; (2) antiarrhythmic drugs frequently render sustained VT noninducible or nonsustained; (3) antiarrhythmic drug suppression of inducible sustained VT predicts long-term prevention of spontaneous recurrences; and (4) noninducibility of sustained VT in the baseline state does not predict freedom from subsequent episodes of VT or sudden death.

Adult↗
PubMed1988

Usefulness of isoproterenol in facilitating atrioventricular nodal reentry tachycardia during electrophysiologic testing.

In some patients with documented atrioventricular (AV) nodal supraventricular tachycardia (SVT), the arrhythmia is not inducible during a standard stimulation protocol. In these patients the level of sympathetic activity may be an important factor. This study evaluates the influence of isoproterenol on anterograde and retrograde pathway properties in patients with AV nodal SVT and the mechanism by which this SVT is facilitated. Group 1 consisted of 8 consecutive patients, ages 23 to 85 years (mean +/- standard error, 57 +/- 8) who had no inducible AV nodal SVT during electrophysiologic testing until isoproterenol (0.5 to 3.0 micrograms/min) was infused. These patients were compared with 6 patients in the same age range (45 to 78 years, mean +/- standard error, 64 +/- 5) who had inducible AV nodal SVT without isoproterenol and who comprised group 2. In comparing group 1 (before isoproterenol) with group 2, there was no significant difference in the refractory periods of the anterograde slow and fast pathways, although the anterograde block cycle length was longer in group 1 patients (421 +/- 18 vs 362 +/- 14 ms, p less than 0.05). The retrograde block cycle length was also longer in 7 of the 8 group 1 (before isoproterenol) patients in whom it could be measured versus those in group 2 (411 +/- 14 vs 318 +/- 27 ms, p less than 0.05). During isoproterenol, the anterograde and retrograde block cycle lengths in group 1 were not different from group 2. Therefore, AV nodal SVT may not be inducible in some patients during routine electrophysiologic testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗
PubMed1988

Possible proarrhythmic effects of tocainide in dilated cardiomyopathy.

A patient with a dilated cardiomyopathy experienced a cardiac arrest when taking tocainide for asymptomatic nonsustained ventricular tachycardia. After successful resuscitation from ventricular fibrillation and exclusion of a myocardial infarction, an electrophysiological evaluation was performed. Drug-free study #1 revealed no induction of ventricular tachycardia. A tocainide study revealed induction of sustained monomorphic ventricular tachycardia. Drug-free study #2 revealed induction of nonsustained ventricular tachycardia. This report illustrates a possible proarrhythmic effect of tocainide.

Cardiomyopathy, Dilated↗
PubMed1988

Mechanism of death in patients with the automatic implantable cardioverter defibrillator.

Fifty patients underwent primary implantation of an automatic implantable cardioverter defibrillator between August 1983 and April 1988 and were entered into a long-term surveillance program. There were a total of 14 deaths (28%) in the entire group occurring at a mean of 8.7 months postimplantation. Eleven deaths were cardiac and three were noncardiac (two pneumonia, one leukemia). The group of deceased patients were similar to the survivors in all respects except for a statistically lower ejection fraction (23% vs 32%) at the time of implantation. In addition, 13/14 (93%) of the deceased patients experienced at least one appropriate AICD discharge at a mean of 4.5 months post implantation. Recorded ECGs at the time of death revealed that most of the sudden deaths were due to electromechanical dissociation and not to AICD-treatable arrhythmias. These data suggest therefore that death in AICD patients is usually cardiac, due primarily to low ejection fraction and occurs in patients who have previously received AICD discharges.

Adult↗
PubMed1986

Distal atrioventricular conduction system function.

This article addresses electrophysiologic evaluation of the distal AV conduction system in patients with chronic bifascicular block. It was formerly thought that progression to complete AV block was a common cause of morbidity and even sudden death in this condition, and it was hoped that electrophysiologic evaluation, including measurement of the H-V interval, would facilitate prospective identification and prophylactic treatment of patients prone to these complications. However, a decade of clinical investigation has revealed that progression to complete AV block is rare and that although cardiovascular mortality, including sudden death, is substantial, this mortality usually relates to underlying organic heart disease. The current role for electrophysiologic studies in chronic bifascicular block is limited to delineation of the site of electrocardiographically documented second- or third-degree AV block and to the evaluation of unexplained syncope.

Atrioventricular Node↗