Showing papers by "Masood Akhtar published in 1998"

Atrioverter: An Implantable Device for the Treatment of Atrial Fibrillation

Abstract: Background: During atrial fibrillation, electrophysiological changes occur in atrial tissue that favor the maintenance of the arrhythmia and facilitate recurrence after conversion to sinus rhythm. An implantable defibrillator connected to right atrial and coronary sinus defibrillation leads allows prompt restoration of sinus rhythm by a low-energy shock. The safety and efficacy of this system, called the Atrioverter, were evaluated in a prospective, multicenter study. Methods and results: The study included 51 patients with recurrent atrial fibrillation who had not responded to antiarrhythmic drugs, were in New York Heart Association Heart failure class I or II, and were at low risk for ventricular arrhythmias. The atrial defibrillation threshold had to be ≤ 240 V during preimplant testing. Atrial fibrillation detection, R-wave shock synchronization, and defibrillation threshold were tested at implantation and during follow-up. Shock termination of spontaneous episodes of atrial fibrillation was performed under physician observation. Results are given after a minimum of 3 months of follow-up. During a follow-up of 72 to 613 days (mean, 259 ± 138 days), 96% of 227 spontaneous episodes of atrial fibrillation in 41 patients were successfully converted to sinus rhythm by the Atrioverter. In 27% of episodes, several shocks were required because of early recurrence of atrial fibrillation. Shocks did not induce ventricular arrhythmias. Most patients received antiarrhythmic medication during follow-up. In 4 patients, the Atrioverter was removed: in 1 because of infection, in 1 because of cardiac tamponade, and in 1 because of frequent episodes of atrial fibrillation requiring His bundle ablation. Conclusions: With the Atrioverter, prompt and safe restoration of sinus rhythm is possible in patients with recurrent atrial fibrillation.

Enviromentally friendly technologies for the pulp and paper industry

Abstract: Partial table of contents: The Need for New Technologies in the Pulp and Paper Industry (M Akhtar & R Young) CHEMICAL APPLICATIONS TO PULP AND PAPER PROCESSING Developments in Organosolv Pulping--An Overview (H Hergert) Catalyzed Alcohol Organosolv Pulping (L Paszner) Steam Explosion Pulping (B Kokta & A Ahmed) BIOLOGICAL APPLICATIONS TO PULP AND PAPER PROCESSING Taxonomy of Industrially Important White-Rot Fungi (H Burdsall) Engineering, Scale-Up, and Economic Aspects of Fungal Pretreatment of Wood Chips (G Scott, et al) Fungal Pretreatment for Organosolv Pulping Dissolving Pulp Production (A Ferraz, et al) Biological Approach for Pulping and Bleaching of Nonwoody Plants (H Sabharwal) Bleaching Kraft Pulps with White-Rot Fungi (I Reid) Fungal Treatment of Wood Chips to Remove Extractives (C Breuil, et al) Index

Use of sublingual nitroglycerin during head-up tilt-table testing in patients >60 years of age

Abstract: Previous work had demonstrated a reduced specificity associated with head-up tilt protocols using high-dose isoproterenol in patients between 20 and 50 years of age. We evaluated the specificity of head-up tilt testing using different isoproterenol infusion doses and administration of nitroglycerin in patients aged >60 years. In addition, whether the same protocols have impact on the sensitivity of the test was also assessed. One hundred sixty subjects were included in this study. Seventy-six were volunteers randomized to either head-up tilt test with low-dose, 3- and 5-microg/min of isoproterenol (group I) or to a protocol including 0.4 mg of sublingual nitroglycerin (group II). In addition, after an upright tilt drug-free state, 58 patients with a history of syncope underwent repeat head-up tilt with increasing doses of isoproterenol infusion, followed by sublingual nitroglycerin if the test result remained negative. The remaining 33 patients were subjected to the nitroglycerin protocol after the drug-free state phase. In the control groups, the incidence of false-positive responses was 88% and 95%, respectively. In patients with syncope after a negative test result during 5 microg of isoproterenol infusion, nitroglycerin administration increased the number of positive responses from 45% to 79%. The percentage of positive tilt in patients undergoing nitroglycerin administration after the drug-free state part of the protocol was 78%. Administration of nitroglycerin was the most significant predictor of a positive upright tilt in patients with syncope. In subjects aged >60 years, head-up tilt protocols with high-dose isoproterenol infusion and nitroglycerin maintained an adequate specificity. In this subset of patients, nitroglycerin seemed to provide a better sensitivity than isoproterenol.

Spontaneous reinitiation of atrial fibrillation following transvenous atrial defibrillation.

Abstract: Spontaneous reinitiation of atrial fibrillation (AF) has not been systematically looked at in patients undergoing transvenous AF. This study involved 11 patients, the mean age 60 ± 8 years. 3 male and 8 female, in whom transvenous atrial defibrillation successfully converted AF to sinus rhythm. Eight patients had paroxysmal AF and three patients had chronic persistent AF for 4 weeks or more. Four patients were taking antiarrhythmic medications at the time of testing. Multipolar transvenous catheters were positioned inside the coronary sinus, right atrium, and the right ventricle. Atrial defibrillation testing was performed using the METRIX atrial defibrillation system in nine patients and the Ventritex HVSO2 in the remaining two patients. A total of 64 therapeutic shocks (range 3–11) were delivered in the 11 patients, and 31 of these successfully converted AF to sinus rhythm. In four patients spontaneous AF was reinitiated following 12 successful transvenous atrial defibrillation episodes. The mean time to reinitiation of AF following shock delivery and restoration of sinus rhythm was 8.26 ± 5.25 seconds, range 1.8–19.9 seconds. All 12 episodes of spontaneous AF were preceded by a spontaneous premature atrial complex. The coupling interval of the premature atrial complexes was 443 ± 43 ms, range 390–510 ms. None of the patients taking antiarrhythmic medications or those demonstrating no premature atrial complexes had spontaneous reinitiation of AF. In conclusion, spontaneous reinitiation of AF can occur in a significant proportion of patients with AE undergoing transvenous atrial defibrillation. This phenomenon is preceded by the occurrence of atrial premature complex. Findings of this study may have significant clinical implications.(PACE 1998; 21:1105–1110)

New technology for papermaking : commercializing biopulping

Abstract: Biopulping is defined as the treatment of wood chips with lignin-degrading fungi prior to pulping. Fungal pretreatment prior to mechanical pulping reduces electrical energy requirements during refining or increases mill throughput, improves paper strength, reduces the pitch content, reduces cooking time for sulfite pulping, and reduces the environemntal impact of pulping. Our recent work involved scaling up the biopulping process toward the industrial level, investigating both the engineering and economic feasibility of the technology. We envision the process to be done in either a chip-pile or silo-based system for which several factors need to be considered : the degree of decontamination, a hospitable environment for the fungus, and the overall process economics. Currently, treatment of the chips with low-pressure steam is sufficient for decontamination. Furthermore, a simple, forced ventilation system can be used to maintain the proper temperature, humidity, and moisture content throughout the chip bed, thus promoting uniform growth of the fungus. The pilot-scale trial resulted in the successful treatment of 4 tons of wood chips (dry weight basis), with results comparable to those on a laboratory scale. For mechanical pulping, a 2-week treatment results in approximately 30% energy savings, which, considering the additionai equipment and operating costs, results in an overall savings of US$ 10-20 per ton of pulp in a chip-pile system. Larger, 40-ton trials were also successful, with energy savings and paper properties comparable with the laboratory scale. Application : biopulping technology produces stronger mechanical pulps together with energy savings, resulting in substantial economic savings.

Engineering, scale-up, and economic aspects of fungal pretreatment of wood chips

Abstract: Biopulping is the treatment of wood chips with lignin-degrading fungi prior to pulping. Two sequential biopulping consortia at the USDA Forest Service. Forest Products Laboratory (FPL). Madison, Wisconsin, established the technical feasibility of biomechanical pulping on a laboratory-scale basis. Through the use of a proper lignin-degrading fungus, at least 30% electrical energy is saved in mechanical pulping amd paper strength properties are improved. Past work and an overview of fungal and pulp and paper research conducted during the consortia are summarized in Chapter 10 of this book and elsewhere in the literature (Akhtar et al., 1997; Blanchette et al., 1991; Kirk et al., 1994; Lawson and Still, 1957; Scott et al., 1995a.b; Sykes, 1994). Current research is aimed at determining the engineering and commercial feasibility of biopulping, which is the subject of this chapter. Our recent work has focused on Ceriporiopsis subvermispora (the best biopulping fungus to date) and loblolly pine (the most commonly used wood species for papermaking in the United States), with greater attention to those factors most likely to affect the engineering and economics of this technology. These factors are attainment of the necessary degree of asepsis, reducing the cost of fungal inoculum, maintaining a hospitable environment in the chip pile, and optimizing overall process economics. Chip piles, silo-based systems, and indoor or covered piles are all being considered for opera tion of the solid-state fermentation. A new biopulping fungus, Phlebia subserialis, is also being investigated (Akhtar et al., 1996b). As discussed in this chapter, this fungus has several advantages over the C. subvermispora, especially when the aforementioned factors are considered.

Sinus tachycardia with atrioventricular block: an unusual presentation during neurocardiogenic (vasovagal) syncope.

Abstract: Sinus Tachycardia with AV Block During VVS. Introduction: Neurocardiogenic (vasovagal) syncope is characterized by hypotension and bradycardia. The presence of sinus tachycardia along with AV block during syncope in patients with neurocardiogenic syncope has not been described previously. Methods and Results: Two female patients (18 and 16 years old) with recurrent syncope and documented sinus tachycardia at the time of syncope are described. Patient 1 had recurrent episodes of syncope. During one of these episodes, which occurred while she was being monitored, sinus tachycardia along with high-grade AV block was seen at the time of syncope and hypotension. Patient 2 had a history of recurrent syncope and seizure. During one of these episodes, she was documented to have ventricular asystole lasting for about 39 seconds. The sinus rate was 480 msec at the beginning, before slowing down to 960 msec prior to restoration of sinus rhythm with 1:1 AV conduction. The same scenario was repeated during head-up tilt testing. Both patients were treated successfully with oral disopyramide and, during a follow-up of 28 months and 9 months, have remained symptom-free. Conclusion: Sinus acceleration along with high-grade AV block during syncope and hypotension can occur in some patients with neurocardiogenic syncope. The exact mechanism of this phenomenon is unclear.

Atrioventricular nodal modification and atrioventricular junctional ablation for control of ventricular rate in atrial fibrillation.

Abstract: Atrial fibrillation results in several structural and functional changes in the heart that lead to worsening ventricular function. Although restoration of sinus rhythm is the ideal goal, it is not always feasible. Pharmacologic therapy is associated with adverse effects and is not always effective. We have reviewed the current status of nonpharmacologic therapy in the management of rapid ventricular response due to atrial fibrillation. Electrophysiologic studies have confirmed that the posterior inputs to the AV node have a shorter refractory period and are mainly responsible for maintaining rapid ventricular response in atrial fibrillation. AV nodal modification involves ablation of these posterior inputs in a sequential fashion until a significant reduction of ventricular response is achieved. This procedure has been reported to be successful in maintaining the controlled ventricular response in about 70% of the patients over long-term follow-up. Ablation of the AV node with implantation of a permanent pacemaker is a more definitive procedure and simpler to perform. Reduction in ventricular response achieved with this procedure results in improvement of the patient's clinical symptoms as well as the underlying left ventricular function. Nonpharmacologic therapy for control of ventricular rate should be considered for patients with atrial fibrillation, in whom pharmacologic therapy for rate control is ineffective or poorly tolerated.

Optimization of shocking lead configuration for transvenous atrial defibrillation

Abstract: Optimum Electrodes for Atrial Defibrillation. Introduction: High atrial defibrillation energy requirements (ADER) in patients with chronic atrial fibrillation (AF) may limit the acceptance of transvenous atrial defibrillation. We evaluated an optimized defibrillation electrode configuration that could help to reduce the ADKR in patients with AF. Methods and Results: We tested ten different configurations in nine dogs with AF (3.33 ± 2.92 days) induced by rapid atrial pacing. The configurations were: right atrial (RA) appendage as anode und coronary sinus (CS) as cathode; RA and innominate vein (I) as anode to CS (cathode); RA-CS (anode) to I (cathode); I-CS (anode) to RA (cathode); RA and left lateral subcutaneous patch (P) as anode to CS (cathode); RA-CS (anode) to P (cathode); P-CS (anode) to RA (cathode); superior vena cava (SVC) and CS (anode) to RA (cathode); RA-CS (anode) to SVC (cathode); and RA-SVC (anode) to CS (cathode). ADER was defined as the voltage needed to defibrillate the atria in 10% to 90% of 20 consecutive shocks. Three lead systems had ADER lower than the RA (anode) to CS (cathode) configuration, which required a mean of 143 ± 58 volts. These three were: RA-SVC (anode) to CS (cathode) 103 ± 29 V; I-CS (anode) to RA (cathode) 129 ± 39 V; and P-CS (anode) to RA (cathode) 130 ± 38 V. The remaining configurations had ADER higher than the RA (anode) to CS (cathode) configuration. Conclusion: Adding an additional shocking electrode may reduce ADER when compared with the RA (anode) to CS (cathode) configuration. This concept could he incorporated into future implantable atrial defibrillators or used for refractory patients undergoing temporary transvenous cardioversion.

Catheter ablation of atrial flutter using radiofrequency current: cumulative experience in 61 patients.

Abstract: UNLABELLED We present our experience with radiofrequency catheter ablation of common atrial flutter. METHODS Radiofrequency ablation of atrial flutter was performed utilizing percutaneous techniques and the anatomic approach under conscious sedation or general anesthesia. RESULTS Sixty-one consecutive patients (51 men, and 10 women) aged 59 +/- 12 years with medically refractory atrial flutter underwent catheter ablation. Thirty-eight patients (62%) had structural heart disease, including complex congenital anomalies in one patient. Atrial flutter ablation was successfully accomplished in 55 patients (90%) in one session. There were no complications, and all patients were discharged within 24-hours of the procedure. During a mean follow-up of 10 +/- 9 months, recurrent atrial flutter occurred in 11 patients (18%), eight of which successfully underwent repeat atrial flutter ablation. CONCLUSIONS Catheter ablation of atrial flutter using radiofrequency current is safe and has a high success rate. This nonpharmacologic approach should be considered as the first line of therapy for common atrial flutter prior to the institution of antiarrhythmic drugs.

An Overview of Biopulping Research : Discovery and Engineering

Abstract: Biopulping is defined as the treatment of wood chips with lignin-degrading fungi prior to pulping. Fungal pretreatment prior to mechanical pulping reduces electrical energy requirements during refining or increases mill throughput, improves paper strength, reduces the pitch content, and reduces the environmental impact of pulping. Our recent work involved scaling up the biopulping process towards the industrial level, investigating both the engineering and economic feasibility. We envision the process to be done in either a chip-pile or silo-based system for which several factors need to be considered: the degree of decontamination, a hospitable environment for the fungus, and the overall process economics. Currently, treatment of the chips with low-pressure steam is sufficient for decontamination and a simple, forced ventilation system maintains the proper temperature, humidity, and moisture conditions, thus promoting uniform growth of the fungus. The pilot-scale trial resulted in the successful treatment of 4 tons of wood chips (dry weight basis) with results comparable to those on a laboratory. Larger, 40-ton trials were also successful, with energy savings and paper properties comparable with the laboratory scale. The overall economics of the process also look very favorable and can result in significant annual savings to the mill. Although the current research has focused on biopulping for mechanical pulping, it is also beneficial for sulfite chemical pulping and some applications to recycled fiber have been investigated.

Implantable atrial defibrillator for atrial fibrillation.

Abstract: Atrial fibrillation is a common problem. Pharmacological and nonpharmacological approaches have limited therapeutic efficacy in many patients. Low energy transvenous atrial defibrillation using catheters positioned inside the right atrium and cornonary sinus has been shown to be efficacious in converting atrial fibrillation to sinus rhythm. We report the successful use of this technology in an implantable form in a patient with symptomatic atrial fibrillation. The patient could be kept in sinus rhythm using an implanted atrial defibrillator.

Incorporating biopulping technology into wood yard operations

Abstract: Biopulping is the treatment of wood chips and other lignocellulosic materials with lignin-degrading fungi prior to pulping. Ten years of industry-sponsored research has demonstrated the technical feasibility of the technology for mechanical pulping at a laboratory scale. Two 50-ton outdoor chip pile trials recently conducted at the USDA Forest Service, Forest Products Laboratory (FPL) in Madison, Wisconsin have established the engineering and economical feasibility of the technology. After refining the control and the fungus-treated chips through a thermomechanical pulp (TMP) mill, the resulting pulps were made into papers on the pilot-scale paper machine at FPL. In addition to the 30% savings in electrical energy consumption during refining, improvements in the strength of the resulting paper were seen due to fungal pretreatment. Because of the stronger paper, we were able to substitute at least 5% kraft pulp in a blend of mechanical and kraft pulps. This recent work has clearly demonstrated that economic benefits can be achieved with biopulping technology through both the energy savings and substitution of the stronger biopulped TMP for more expensive kraft, while maintaining the paper quality.