The Automatic Implantable Cardioverter Defibrillator: T Wave Sensing in the Newest Generation

The AICD uses an automatic gain control amplifier for detecting the small electrograms during ventricular fibrillation. The latest generation of the AICD appears to have a more sensitive lock on gain amplifier, as 6 of 76 patients implanted with the new AICD had double counting of the QHS-T wave complex resulting in asymptomatic discharges. Solutions to the problem of limiting these asymptomatic discharges are difficult and include slowing of the heart rate with beta blockers, changing the lead system, or replacement of the device. One of the six patients was treated with beta blockers. Three patients had their device changed, two patients requested the inactivation of their device until a rate programmable unit was available. The potential for T wave sensing in a lock on gain amplifier represents the unique dilemma between detecting small electrograms of ventricular fibrillation, and detecting diastolic events which occur shortly after the QRS complex.     

Transseptal Defibrillation Is Superior for Transvenous Defibrillation

The conventional electrode configuration of current internal defibrillation systems most commonly use superior vena caval (SVC) or combined SVC and subcutaneous (SC) electrodes as anode, and right ventricular apex (HVA) electrode as cathode. We have demonstrated earlier that the septal mass is important for defibrillation. The purpose of the present study was to compare a transseptal to a conventional electrode arrangement in the canine model. Three endocardial electrodes, 5 French EnGuard™ were positioned in RVA, SVC, and the right ventricular outflow (RVO) in eight dogs. A 5 French SC electrode was positioned in the fifth left intercostal space. RVA-RVO^-/SC⁺ (configuration 2) was compared to SVC-SC⁺/RVA^-(configuration 1). Defibrillation threshold testing was performed using asymmetrical biphasic shock, 6 msec⁺/2 msec^-. Probit fit was used to compare the results at 40%, 50%, 60%, and 90% probabilities, and the logistic regression analysis to estimate the impact of variables. Electrode configuration had the strongest predictive value. Configuration 2 was superior to configuration 1 (P = 0.0016). At any voltage settings the probability of success for configuration 2 was greater, and current less (P < 0.00005). The energy requirements were reduced by approximately 33% for configuration 2. There were no significant differences in impedance between the two configurations. We conclude that transseptal defibrillation is more effective because of the improved lead geometry and voltage gradient.     

MRI-based morphometric topographic parcellation of human neocortex in trichotillomania

Abstract  The purpose of the present study was to test specific hypotheses regarding volumetric changes ot the neocortex between 10 female trichotillomania (TTM) subjects and 10 female normal controls. A standard three-dimensional (3-D) brain coordinate system was imposed over each newly acquired native magnetic resonance imaging (MRI) scan for positional normalization and 3-D shape/geometric localization analyses were based on the midpoints of anterior and posterior commissures, and the longitudinal fissure. The brain segmentation method, using well-characterized semiautomated intensity and differential contour algorithms by signal intensity-frequency histograms, was used blind to segment the principal gray and white matter structures. The segmented neocortical ribbon was subdivided into 48 regions (i.e. parcellation units) per hemisphere via a new method of morphometric topographic parcellation. There were no significant volumetric changes of the precentral gyrus, postcentral gyrus, supplementary motor cortex or opercular cortex in TTM patients compared with control subjects. A broader analysis as a hypothesis-generating post-hoc effort showed that TTM subjects exhibited significantly reduced left inferior frontal gyrus volume of 27% (t = 2.21, d.f. = 18, P = 0.04) and enlarged right cuneal cortex volume of 40% (f = -2.30, d.f. = 18, P = 0.03) compared to normal controls. This is the first report of a structural neocortex abnormality in TTM. Results are discussed in terms of the behavioral specialization of these two brain neocortical regions and the complex interractions between visual and sensorimotor cortices. The results also showed the feasibility of the MRI-based morphometric topographic parcellation for investigation of the human neocortex in neuroscience research.     

Electrode Surface Area Is An Important Variable for Defibrillation

Previous studies have established efficacy of transseptal defibrillation. The purpose of the present study was to evaluate the role of transvenous electrode surface area for defibrillation. Sixteen dogs were randomized to 8 French and 5 French EnGuard™ electrodes; 8 dogs in each group. The length of the defibrillation coils was identical for both, but the surface area was different due to differences in the electrode diameters. Defibrillation threshold (DFT) testing was performed using a biphasic shock waveform, 6 msec⁺/2 msec^-. Logistic regression analysis was used to determine if the probability of defibrillation adjusted for voltage, current, and energy was different for 8 French electrodes. Logistic regression analysis found significant differences between 8 French and 5 French electrodes, with less voltage (P < 0.005), current (P < 0.03), and energy (P < 0.001) required at any level of probability to defibrillate for 8 French electrodes. These results support the conclusion that the surface area for endocardial electrodes is a significant factor for defibrillation. Therefore, when designing endocardial electrodes a desirable objective of reducing the electrode size should be weighed against the need to minimize DFTs.     

Development and Validation of a Risk Scoring Model to Predict Net Adverse Cardiovascular Outcomes after Primary Percutaneous Coronary Intervention in Patients Pretreated with 600 mg Clopidogrel: Rationale and Design of the RISK-PCI Study

Background: No comprehensive primary PCI (pPCI) risk model to predict net adverse cardiovascular events (NACE) has been reported with the use of clopidogrel 600 mg, which is now considered the standard loading dose. The primary hypothesis of the RISK-PCI trial is that an accurate risk prediction may be achieved by using clinical, angiographic, and procedural variables available at the time of intervention.
Methods: The present single-center, longitudinal, cohort study will include 1,750 consecutive patients with ST-elevation myocardial infarction (STEMI), undergoing pPCI after pretreatment with 300 mg aspirin and 600 mg clopidogrel. The primary end-points of the trial (NACE) include major adverse cardiovascular events (MACE) and major bleeding. A logistic regression model will be developed to predict 30-day and 1-year NACE after pPCI. A risk score derived from study set data will be validated using validation set data.
Results: Until June 1, 2008, 1,166 patients have been enrolled. Thirty-day follow-up is available in 1,007 patients.
Conclusions: The RISK-PCI study is designed to develop an accurate risk scoring system, using variables available at the time of intervention, to predict long-term adverse outcomes after pPCI.
Trial Registration: Current Controlled Trials Register—ISRCTN83474650— http://www.controlled-trials.com/ISRCTN83474650) .     

Analysis of Putative Interactions Between Potyviral Replication Proteins and Plant Retinoblastoma Proteins

Sequence comparisons suggest that the RNA-dependent RNA polymerase (NIb) of potyviruses and bymoviruses, as well as the viral polymerase of potexviruses may contain a putative retinoblastoma protein (pRb) binding motif. The possibility that the potyviral NIb may function in the nucleus through interactions with plant pRb-related (RBR) proteins, and the modifications of the cell cycle was investigated by a combination of mutagenesis of the NIb and yeast two-hybrid system (YTHS). Mutation of a highly conserved glutamic acid residue in the putative pRb-binding motif of the NIb had no detectable phenotypic effect on replication of Potato virus A (PVA). Furthermore, the NIb proteins from Potato virus V and PVA failed to interact with maize or tobacco RBR proteins in yeast. Although the conservation of the motif for pRb interaction in plant RNA viruses is intriguing, these proteins from plant RNA viruses appear not to interact with plant RBR proteins.     

The Effect of Chronic Fluvoxamine Treatment on Overnight Melatonin Secretion in Medicated Chronic Schizophrenic Patients

Overnight melatonin levels were measured in five male schizophrenic patients on steady antipsychotic treatment following the addition of fluvoxamine. Melatonin secretion increased in the first week of treatment and progressively decreased after 3 weeks. The findings are consistent with the development of tolerance in the processes underlying melatonin secretion. © 1997 John Wiley & Sons, Ltd.     

T-Wave Variability as a Risk Stratifier in Patients with Dilated Cardiomyopathy

Background: T-wave alternans is an important identifier of patients at risk of sudden cardiac death (SCD), but the procedure usually requires stress testing. In this study, the variability of T-wave amplitude (TVAR) was evaluated at rest, as a risk stratifier for SCD.
Methods: This study included 57 patients in sinus rhythm and with a left ventricular ejection fraction ≤40%, of whom 34 (60%) received an implantable cardioverter-defibrillator (ICD) after surviving SCD, and 23 (40%) presented with ischemic or nonischemic cardiomyopathy and no history of SCD. A 20-minute high-resolution electrocardiographic recording for TVAR assessment was performed during supine rest. The vector magnitude was used as a primary lead for TVAR analysis.
Results: The mean, median, and maximum (max) values of TVAR were measured. The patients with ICD had a lower max TVAR than the patients without ICD (67 vs 95 μV; P = 0.045), though the mean and median TVAR values were similar. By multivariate logistic analysis, max TVAR remained a predictor of SCD, after adjustments for potentially confounding factors (P = 0.044).
Conclusion: Max TVAR was a predictor of arrhythmic events in patients with dilated cardiomyopathy at rest.