Effect of Shock Waveform on Relationship Between Upper Limit of Vulnerability and Defibrillation Threshold

ULV-DFT Waveform. Introduction: The upper limit of vulnerability (ULV) correlates with the defibrillation threshold (DFT). The ULV can he determined with a single episode of ventricular fibrillation and is more reproducible than the single-point DFT. The critical-point hypothesis of defibrillation predicts that the relation between the ULV and the DFT is independent of shock waveform. The principal goal of this study was to test this prediction. Methods and Results: We studied 45 patients at implants of pectoral cardioverter defibrillators. In the monophasic-biphasic group (n = 15), DFT and ULV were determined for monophasic and biphasic pulses from a 120-μF capacitor. In the 60- to 110-μF group (n = 30), DFT and ULV were compared for a clinically used 110-μF waveform and a novel 60-μF waveform with 70% phase 1 tilt and 7-msec phase 2 duration. In the monophasic-biphasic group, all measures of ULV and DFT were greater for monophasic than biphasic waveforms (P < 0.0001). In the 60- to 110-/tF group, the current and voltage at the ULV and DFT were higher for the 60-μF waveform (P < 0.0001), hut stored energy was lower (ULV 17%, P < 0.0001; DFT 19%, P = 0.03). There was a close correlation between ULV and DFT for both the monophasic-biphasic group (monophasic r²= 0.75, P < 0.001; hiphasic r²= 0.82, P < 0.001) and the 60- to 110-μF group (60 μF r²= 0.81 P < 0.001; 110 μF r²= 0.75, P < 0.001). The ratio of ULV to DFT was not significantly different for monophasic versus biphasic pulses (1.17 ± 0.12 vs 1.14 ± 0.19, P = 0.19) or 60-μF versus 110-μF pulses (1.15 ± 0.16 vs 1.11 ± 0.14, P = 0.82). The slopes of the ULV versus DFT regression lines also were not significantly different (monophasic vs biphasic pulses, P = 0.46; 60-μF vs UO-μF pulses, P = 0.99). The sample sizes required to detect the observed differences between experimental conditions (P < 0.05) were 4 for ULV versus 6 for DFT in the monophasic-biphasic group (95% power) and 11 for ULV versus 31 for DFT in the 60- to 110-μF group (75% power). Conclusion: The relation between ULV and DFT is independent of shock waveform. Fewer patients are required to detect a moderate difference in efficacy of defibrillation waveforms by ULV than by DFT. A small-capacitor biphasic waveform with a long second phase defibrillates with lower stored energy than a clinically used waveform.     

Serial Defibrillation Lead Impedance in Patients with Epicardial and Nonthoracotomy Lead Systems

Lead Impedance in ICDs. Introduction: The stability of implantable cardiac defibrillation lead impedance subsequent to implantation has not been reported and may have important clinical implications. The objective was to characterize the incidence and degree of impedance changes occurring after implantation of defibrillation lead systems. Methods and Results: The study cohort consisted of patients who received epicardial or nonthoracotomy lead systems. Defibrillation impedance was recorded at implantation, prior to hospital discharge (predischarge), and during follow-up. For each individual the magnitude of the impedance change relative to implantation was characterized. Among patients with an epicardial system, a significant decrease in impedance was observed at predischarge (mean 9.3 Ω). The magnitude of the decrease was large in 39% and moderate in 31% of individuals. Subsequently, a gradual rise in mean impedance was apparent. At 18–21 months postimplantation, impedance was significantly increased relative to implantation (mean 6.8 ω). At this time, the magnitude of the increase was large in 46% and moderate in 23% of patients. Among patients with a nonthoracotomy lead system including a subcutaneous patch, a significant decrease in mean impedance was observed at predischarge (mean 3.5 ω). The magnitude of the decrease was large in 8% and moderate in 50% of individuals. Subsequently, a gradual rise in impedance was apparent. At 5–6 months, it was significantly increased relative to implantation (mean 2.3 ω). The magnitude of the increase was large in 10% and moderate in 33% of patients. Among the group of patients whose nonthoracotomy lead system did not include a subcutaneous patch, there was no significant change in mean impedance at predischarge relative to implantation. In subsequent intervals, a gradual rise was apparent. At 5–6 months, impedance was significantly increased relative to implantation (mean 4.3 ω). The magnitude of the increase was large in 16% and moderate in 47% of individuals. Conclusion: Significant changes in defibrillation lead impedance occur after implantation of epicardial and nonthoracotomy defibrillation lead systems. These data may serve as a standard for identifying the anticipated maximum change in lead impedance and thus may be useful as a tool for recognizing problems with defibrillation lead integrity.     

ETHANOL-INDUCED GROWTH INHIBITION IN EMBRYONIC CHICK BRAIN IS ASSOCIATED WITH CHANGES IN CYTOPLASMIC CYCLIC AMP-DEPENDENT PROTEIN KINASE REGULATORY SUBUNIT

Several lines of research have suggested that ethanol-inducedchanges in the adenylate cyclase/protein kinase cascade maycontribute to the growth retardation observed in infants exposedto ethanol in utero. Based on studies with an embryonic chickmodel, the data presented here suggest that chronic ethanoltreatment significantly lowered the binding of cyclic AMP byprotein kinase regulatory subunit (R₁₁ and reduced the levelof phosphorylation of R₁₁ by the endogenous cytoplasmic proteinkinase catalytic subunit. Furthermore, ethanol treatment alteredthe phosphorylation of at least one other brain cytosolic protein(molecular weight=62–65 kD).     

Techniques for Management of the Calcified Mitral Annulus

Mitral annulus calcification is most often associated with myxomatous degeneration of the mitral valve. It is characterized by a horseshoe-shaped area of mitral annulus calcification that extends into the ventricular cavity to varying degrees. Standard suture techniques may be associated with fracture of the calcification and subsequent paravalvular leak. Seventeen patients aged 54 to 85 (mean 68.1) had mitral valve replacement using four techniques: suture through calcified annulus (3); decalcification (6); onlay patch (5); and drill technique (3). There were no hospital deaths, and one 81-year-old patient with associated coronary artery disease and ascending aortic calcification succumbed to a cerebrovascular accident three months postoperatively. The remaining patients are living and active with functional improvement. Follow-up has ranged from seven months to seven years with a mean of 4.0 years. One patient has hemodynamically insignificant mitral regurgitation after use of an onlay patch technique. No one technique could be singled out as clearly advantageous over the others from this series of patients.     

Runaway Pacemaker in an Implantable Cardioverter Defibrillator

Runaway Pacemaker in an ICD. Introduction : Runaway pacemaker is a potentially catastrophic complication of any permanent pacing system.
Methods and Results : A 70-year-old man was found to have erratic behavior of his implantable cardioverter defibrillator (ICD) during a routine outpatient interrogation. His device was turned off, and he was hospitalized in preparation for a pulse generator replacement. During his hospitalization, his ICD unexpectedly began pacing rapidly. Despite prompt resuscitation attempts, the patient died. Postmortem examination of the device demonstrated a crystal oscillator failure.
Conclusion : A previously unrecognized component malfunction is a potentially lethal complication of ICDs.     

Abstinent Opiate Abusers Exhibit Conditioned Craving, Conditioned Withdrawal and Reductions in both through Extinction

Abstinent opiate abusers who have just completed a 30-day treatment program in a Therapeutic Community setting experience intense drug craving and may even experience subjective withdrawal signs/symptoms when exposed to drug-related stimuli. The described extinction procedures were effective in virtually eliminating conditioned craving and conditioned withdrawal signs/symptoms to drug-related stimuli within 20 hour-long treatment sessions (a 3-week inpatient stay). These findings are discussed in terms of the need to address conditioned opiate-related responses in the treatment of abstinent opiate abusers, as these responses may make the patient more vulnerable to relapse.     

Antiplaque effects and mode of action of a combination of zinc citrate and a nonionic antimicrobial agent

Abstract – The effect upon plaque growth of adding a nonionic antimicrobial agent, triclosan, to a dentifrice containing zinc citrate was established in short-term in vivo studies. Plaque regrowth was inhibited by brushing with dentifrices which contained either zinc citrate or triclosan. When both were combined in the same dentifrice, the inhibition of overnight plaque regrowth was significantly greater. In two 4-day non-brushing studies, the dentifrices containing both zinc citrate and triclosan were applied either undiluted by the use of a cap splint or as 23% suspensions in water. Both methods resulted in significant reductions in plaque accumulation, with the greater activity being observed for the undiluted application of the dentifrice. Analysis of results of the overnight plaque studies for individual teeth revealed that the two agents had a complementary inhibitory action on plaque regrowth, zinc citrate being more effective on existing plaque whereas triclosan inhibited plaque formation on clean surfaces. The dentifrice containing both agents was effective against both existing plaque and new plaque formation. It is concluded that the addition of triclosan to a dentifrice containing zinc citrate improves its antiplaque potential.