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Biomedical subjects

I Wiener

Publications and source records attributed to I Wiener.

At least 19 recordsLinked to original sources
PubMed1995

Implantable defibrillators for high-risk patients with heart failure who are awaiting cardiac transplantation.

The objective of this study was to assess the operative risk and efficacy of implantable defibrillators for preventing sudden death in patients with heart failure awaiting transplantation. The average waiting time for elective cardiac transplantation is 6 months to 1 year. Sudden cardiac death is the major source of mortality in outpatients in stable condition awaiting cardiac transplantation. The efficacy of implantable defibrillator therapy in this population is not established. We analyzed the operative risk, time to appropriate shock, and sudden death in 15 patients determined to be at high risk of sudden death who were accepted onto the outpatient cardiac transplant waiting list. Nonfatal postoperative complications occurred in two (13%) subjects with epicardial defibrillating lead systems and in none with transvenous lead systems. Defibrillation energies were 16 +/- 2 J versus 24 +/- 2 J with epicardial and transvenous lead systems, respectively. Sudden death free survival until transplantation was 93%. Most of the patients (60%) had an appropriate shock during a mean follow-up of 11 +/- 12 months. The mean time to an appropriate shock was 3 +/- 3 months. Hospital readmission was required in three (20%) subjects to await transplantation on an urgent basis. However, two of these subjects had received appropriate shocks before readmission. In selected patients at high risk for sudden death while on the outpatient cardiac transplant waiting list, the operative risk is low and adequate defibrillation energies can be obtained to allow implantable defibrillator placement. Most subjects will have an appropriate shock as outpatients before transplantation, and sudden death free survival is excellent.(ABSTRACT TRUNCATED AT 250 WORDS)

Actuarial Analysis↗
PubMed1995

Relation of pace mapping QRS configuration and conduction delay to ventricular tachycardia reentry circuits in human infarct scars.

OBJECTIVES: This study sought to determine the relation of the paced QRS configuration and conduction delay during pace mapping to reentry circuit sites in patients with ventricular tachycardia late after myocardial infarction. BACKGROUND: The QRS configuration produced by ventricular pacing during sinus rhythm (pace mapping) can locate focal idiopathic ventricular tachycardias during catheter mapping, but postinfarction reentry circuits may be relatively large and contain regions of slow conduction. We hypothesized that for postinfarction ventricular tachycardia, 1) pacing during sinus rhythm at reentry circuit sites distant from the exit from the scar would produce a QRS configuration different from the tachycardia; and 2) a stimulus to QRS delay during pace mapping may be a useful guide to reentry circuit slow conduction zones. METHODS: Catheter mapping and ablation were performed in 18 consecutive patients with ventricular tachycardia after myocardial infarction. At 85 endocardial sites in 13 patients, 12-lead electrocardiograms (ECGs) were recorded during pace mapping, and participation of each site in a reentry circuit was then evaluated by entrainment techniques during induced ventricular tachycardia or by application of radiofrequency current. RESULTS: Pace maps resembled tachycardia at < 30% of likely reentry circuit sites identified by entrainment criteria and at only 1 (9%) of 11 sites where radiofrequency current terminated tachycardia. Analysis of the stimulus to QRS interval during entrainment with concealed fusion showed that the conduction time from the pacing site to the exit from the scar was longer at sites where the pace map did not resemble tachycardia. Evidence of slow conduction during pace mapping, with a stimulus to QRS interval > 40 ms was observed at > or = 70% of reentry circuit sites. CONCLUSIONS: At many sites in postinfarction ventricular reentry circuits, the QRS configuration during pace mapping does not resemble the ventricular tachycardia QRS complex, consistent with relatively large reentry circuits or regions of functional conduction block during ventricular tachycardia. A stimulus to QRS delay during pace mapping is consistent with slow conduction and may aid in targeting endocardial sites for further evaluation during tachycardia.

Aged↗
PubMed1993

Low-dose amiodarone for atrial fibrillation.

Concerns about proarrhythmia risk and inefficacy associated with class I antiarrhythmic drugs have revived interest in low-dose amiodarone (maintenance dose 200-400 mg/day) for suppression of atrial fibrillation. In nonrandomized trials of amiodarone for atrial fibrillation refractory to conventional agents, amiodarone has been successful in maintaining sinus rhythm in 53-79% of patients during a mean follow-up of 15-27 months. Intolerable side effects, including pulmonary toxicity, are in the range of 1-12% per year and resolve following amiodarone withdrawal in the majority of cases. Proarrhythmia risk associated with amiodarone, even in the setting of left ventricular dysfunction, is extremely low. In patients with congestive heart failure, in whom other pharmacologic options are limited by proarrhythmia risk and negative inotropism, preliminary experience with amiodarone is especially promising. Randomized trials are needed, directly comparing amiodarone to conventional antiarrhythmic therapy for atrial fibrillation suppression and comparing amiodarone to warfarin for thromboembolism prevention in patients with atrial fibrillation refractory to conventional antiarrhythmic drugs.

Amiodarone↗
PubMed1993

Identification of reentry circuit sites during catheter mapping and radiofrequency ablation of ventricular tachycardia late after myocardial infarction.

BACKGROUND: Ventricular tachycardia reentry circuits in chronic infarct scars can contain slow conduction zones, which are difficult to distinguish from bystander areas adjacent to the circuit during catheter mapping. This study developed criteria for identifying reentry circuit sites using computer simulations. These criteria then were tested during catheter mapping in humans to predict sites at which radiofrequency current application terminated ventricular tachycardia. METHODS AND RESULTS: In computer simulations, effects of single stimuli and stimulus trains at sites in and adjacent to reentry circuits were analyzed. Entrainment with concealed fusion, defined as ventricular tachycardia entrainment with no change in QRS morphology, could occur during stimulation in reentry circuit common pathways and adjacent bystander sites. Pacing at reentry circuit common pathway sites, the stimulus to QRS (S-QRS) interval equals the electrogram to QRS interval (EG-QRS) during tachycardia. The postpacing interval from the last stimulus to the following electrogram equals the tachycardia cycle length. Pacing at bystander sites the S-QRS exceeds the EG-QRS interval when the conduction time from the bystander site to the circuit is short but may be less than or equal to the EG-QRS interval when the conduction time to the circuit is long. The postpacing interval, however, always exceeds the tachycardia cycle length. When conduction in the circuit slows during pacing, the S-QRS and postpacing intervals increase and the slowest stimulus train most closely reflects conduction times during tachycardia. Endocardial catheter mapping and radiofrequency ablation were performed during 31 monomorphic ventricular tachycardias in 15 patients with drug refractory ventricular tachycardia late after myocardial infarction. During ventricular tachycardia, trains of electrical stimuli or scanning single stimuli were evaluated before application of radiofrequency current at the same site. Radiofrequency current terminated ventricular tachycardia at 24 of 241 sites (10%) in 12 of 15 patients (80%). Ventricular tachycardia termination occurred more frequently at sites with entrainment with concealed fusion (odds ratio, 3.4; 95% confidence interval [CI], 1.4 to 8.3), a postpacing interval approximating the ventricular tachycardia cycle length (odds ratio, 4.6; 95% CI, 1.6 to 12.9) and an S-QRS interval during entrainment of more than 60 milliseconds and less than 70% of the ventricular tachycardia cycle length (odds ratio, 4.9; 95% CI, 1.4 to 17.1). Ventricular tachycardia termination was also predicted by the presence of isolated diastolic potentials or continuous electrical activity (odds ratio, 5.2; 95% CI, 1.8 to 15.5), but these electrograms were infrequent (8% of all sites). Combinations of entrainment with concealed fusion, postpacing interval, S-QRS intervals, and isolated diastolic potentials or continuous electrical activity predicted a more than 35% incidence of ventricular tachycardia termination during radiofrequency current application versus a 4% incidence when none suggested that the site was in the reentry circuit. Analysis of the postpacing interval and S-QRS interval suggested that 25% of the sites with entrainment with concealed fusion were in bystander areas not within the reentry circuit. At restudy 5 to 7 days later, 6 patients had no monomorphic ventricular tachycardia inducible, and inducible ventricular tachycardias were modified in 4 patients. None of these 10 patients have suffered arrhythmia recurrences during a follow-up of 316 +/- 199 days, although 4 continue to receive previously ineffective medications. CONCLUSIONS: Regions giving rise to reentry after myocardial infarction are complex and can include bystander areas, slow conduction zones, and isthmuses for impulse propagation at which radiofrequency current lesions can interrupt reentry.

Aged↗
PubMed1992

Low-dose amiodarone for atrial fibrillation: time for a prospective study?

Because atrial fibrillation is associated with substantial morbidity, restoration of sinus rhythm is desirable. Long-term maintenance of sinus rhythm often requires chronic antiarrhythmic therapy. Class I antiarrhythmic drugs such as quinidine or propafenone maintain sinus rhythm in approximately 50% of patients at 1 year and have risks for proarrhythmia and noncardiac toxicity. Studies of low-dose amiodarone for atrial fibrillation have reported sinus rhythm maintenance in 53% to 79% of patients during a mean follow-up of 27 months. Amiodarone has a lower incidence of proarrhythmia and heart failure exacerbation compared with class I drugs. Most noncardiac side effects are dose related, and low-dose amiodarone (less than 300 mg/d) is well tolerated. The time has come for a large-scale prospective evaluation of low-dose amiodarone treatment early in the course of atrial fibrillation.

Amiodarone↗
PubMed1992

Ventricular tachycardia after infarction: sources of coronary blood flow to the infarct zone.

The purpose of this study was to determine the sources of coronary blood flow to infarct scars in patients with sustained ventricular tachycardia occurring late after myocardial infarction, which is necessary for transcoronary sclerosis or embolization. Angiograms of 32 consecutive patients (age 63 +/- 8 years, ejection fraction 0.30 +/- 0.10) were reviewed. Sources of blood flow to the infarct zone were identified as coming from a recanalized infarct-related artery, side branch, collateral, or coronary bypass graft. Eighty-four percent of patients in the study had an identifiable blood supply to the area of previous infarction. More than one source of blood flow to anterior infarct locations were observed more often than to inferior infarct locations (53% vs 17%, p = 0.03). Transcoronary mapping for possible chemical ablation should be technically feasible in the majority of patients with ventricular tachycardia. Infarct zone blood flow arises from any of several sources and varies somewhat depending on infarct location.

Collateral Circulation↗
PubMed1992

Cholelithiasis associated with medroxyprogesterone acetate therapy in men.

Five out of forty-five adult men, 50 years of age or less, who had received, for at least six months, medroxyprogesterone acetate (MPA, Depo Provera) IM, 200-400 mg/week, for prevention of sex-offending or genital-mutilating behavior developed symptomatic cholelithiasis. Thirty of these men were studied with gallbladder ultrasound prospectively off MPA and at six-month intervals while taking the medication and then six months off MPA. Gallstones recovered from two patients were found to have very high cholesterol content, suggesting they were formed in cholesterol supersaturated bile. These findings are consistent with the increased incidence of gallbladder disease related to high-progesterone states and suggest that MPA may be a causative agent in cholelithiasis. The physiologic studies on gallbladder contraction and cholecystokinin release in a subset of the patients failed to provide information on a mechanism for the possible increased incidence of gallbladder disease.

Adult↗
PubMed1992

Identifying sites for catheter ablation of ventricular tachycardia.

The approach to localizing sites for catheter ablation of ventricular tachycardia foci depends on the type of tachycardia. In large reentry circuits such as those arising from infarct scars, areas of slow conduction in and around the scar should be targeted. During sinus rhythm, these can be suspected from the presence of fractionated electrograms and, at some sites, long stimulus to QRS delays during pacing. Slow conduction areas can be classified as: 1. central slow conduction zone sites, 2. exits from the slow conduction zone, 3. entrances to the slow conduction zone, and 4. bystander areas which are not involved in the tachycardia circuit. In the central slow conduction zone stimulation entrains or resets tachycardia with a long stimulus to QRS (S-QRS) delay (40 to greater than 300 ms) without altering the QRS morphology (entrainment with concealed fusion). At slow conduction zone exits, presystolic electrograms are recorded during VT, the pacemap matches the VT QRS morphology, and with pacing during VT the S-QRS interval is relatively short and VT may or may not be entrained. At entrances to the slow conduction zone electrogram timing is variable but early diastolic electrograms are expected and the pace-map QRS may differ from the VT QRS morphology. Relatively late stimuli or slow trains of stimuli entrain VT with concealed fusion with a relatively longer S-QRS interval than observed in the central slow conduction zone. Early stimuli may entrain VT while altering the QRS morphology due to propagation of the stimulated antidromic wavefront out of the scar from a site other than the tachycardia exit. At bystander sites electrogram timing, pace-mapping, and the effects of programmed stimulation are variable but may occasionally mimic reentry circuit sites. Relatively late stimuli are likely to capture the site without altering the VT. If discrete electrograms are present, analysis of these during pacing may provide further evidence that the site is not in the reentry circuit. Catheter ablation will probably be most effective at central slow conduction zone sites. When VT originates from a small focus surrounded by normal myocardium, such as is likely for idiopathic RV outflow tract and some idiopathic left ventricular tachycardias, presystolic electrical activity and pacemapping are likely to identify the tachycardia focus. For macroreentry involving the bundle branches, the right bundle branch can be easily targeted.

Animals↗
PubMed1990

Coronary artery spasm and myocardial infarction in a patient with normal coronary arteries: temporal relationship to pseudoephedrine ingestion.

A 28 yr-old male presented with chest pain and acute ST elevation following ingestion of pseudoephedrine. The pain and electrocardiographic changes disappeared after the administration of sublingual Nitroglycerin. Myocardial enzymes did show some evidence for myocardial necrosis. A subsequent coronary arteriogram showed no occlusive lesions. Pseudoephedrine, a sympathomimetic agent, may be implicated in the initiation of coronary spasm and myocardial infarction in some patients.

Adult↗
PubMed1990

Treatment of catecholamine-sensitive right ventricular tachycardia by endocardial catheter ablation.

Endocardial catheter ablation with direct current high voltage shocks was performed in a patient with recurrent syncope due to a catecholamine-sensitive ventricular tachycardia that was drug refractory and occurred in the absence of identifiable heart disease. Pace mapping and catheter activation mapping of the spontaneous and isoproterenol-induced ventricular tachycardia located the tachycardia origin in the right ventricular outflow tract. Ablation dramatically reduced spontaneous ventricular tachycardia and ectopic activity (from 50,000 to less than 100 ectopic beats/24 h). The patient has remained symptom free and without ventricular tachycardia recurrence for 3 years. These observations and review of previous studies suggest that catheter mapping can easily locate the arrhythmia focus in the right ventricular outflow tract and that catheter ablation can be performed at low risk. Catheter ablation is a viable option for the treatment of right ventricular catecholamine-sensitive tachycardias that are unresponsive to antiarrhythmic drugs.

Adult↗
PubMed1989

Fractionated endocardial electrograms are associated with slow conduction in humans: evidence from pace-mapping.

Fractionated ventricular electrograms recorded during catheter mapping may arise from areas of asynchronous depolarization associated with slow conduction, the substrate for reentrant ventricular tachycardia, but can also be a nonspecific abnormality or even artifact. To determine whether fractionated sinus rhythm electrograms are associated with slow conduction in humans, the results of endocardial catheter mapping and pacing at 133 endocardial sites in 13 patients were analyzed. Eleven patients had sustained monomorphic ventricular tachycardia and two patients had old myocardial infarction without ventricular tachycardia. Functional evidence of slow conduction at the recording site was assessed by pacing at that site and measuring the interval between the stimulus artifact (S) and the onset of the QRS complex in the 12 lead electrocardiogram (ECG). During pacing at 89 of 90 sites without fractionated sinus rhythm electrograms, the S-QRS interval was less than 40 ms, a value consistent with rapid propagation of the stimulated wave front away from the pacing site. During pacing at 21 (49%) of 43 sites with fractionated sinus rhythm electrograms, the S-QRS interval was greater than 40 ms (range 40 to 140), consistent with slow conduction at the pacing site (p less than 0.001 versus nonfractionated sites). In 9 of the 11 patients with ventricular tachycardia analysis of the paced QRS configuration, electrograms during induced ventricular tachycardia or programmed stimulation during tachycardia suggested that a site with a long S-QRS interval during pacing was located at or near a ventricular tachycardia circuit. Therefore, fractionated sinus rhythm electrograms are often associated with slow conduction, which may be the substrate for reentrant ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Programmed electrical stimulation at potential ventricular reentry circuit sites. Comparison of observations in humans with predictions from computer simulations.

The purpose of this study was to define specific types of resetting responses to programmed electrical stimulation during human ventricular tachycardia and to use computer simulations of reentry circuits to assess the possible mechanisms and pacing site location relative to the reentry circuit for each type of response. The effects of scanning single stimuli at 35 left ventricular endocardial sites during sustained monomorphic ventricular tachycardia in 12 patients were studied. In considering alterations in QRS configuration and the delay between the stimulus and the advanced QRS, we identified three types of resetting responses to scanning stimuli consistent with stimulation at sites in or near the reentry circuit at 12 abnormal endocardial sites in eight patients. Type 1: all capturing stimuli were followed after a delay by early QRS complexes that had the same configuration as the tachycardia complexes. Type 2: late stimuli reset tachycardia as in type 1 but early stimuli reset the tachycardia after altering the QRS configuration. Type 3: late stimuli reset tachycardia as in type 1, but early stimuli advanced tachycardia with a short stimulus to QRS delay without altering the QRS configuration. In the simulations, premature depolarization of sites in the circuit produced orthodromic and antidromic wavefronts. The orthodromic wavefront propagated through the circuit and exited the circuit at the same site as did the previous tachycardia wavefronts and advanced the tachycardia without altering the configuration of the advanced QRS. The antidromic wavefront of relatively late stimuli was confined within or near the circuit by collision with the orthodromic wavefront of the preceding tachycardia beat and failed to alter ventricular activation distant from the circuit. Therefore, the QRS configuration after the stimulus was unchanged. A type 1 response occurred when all capturing stimuli produced this effect. However, with increasing stimulus prematurity, the antidromic wavefront propagated farther before colliding with an orthodromic wavefront, and under some conditions, it exited the circuit from a site other than the original circuit "exit," and altered the ventricular activation sequence distant from the circuit and, therefore, the QRS configuration, producing a type 2 pattern. The type 3 pattern occurred when the antidromic wavefront of early premature beats captured the original circuit exit. The effect of a stimulus was dependent on the stimulus prematurity, the relative conduction times from the stimulation site to the potential sites of "exit" from the circuit, and the timing of the excitable gap at the stimulation site.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac Pacing, Artificial↗