Incremental Conduction Research Articles

Incremental Heat Conduction Versus Mass Reduction in Large Corrugated Walls Derived from a Large Plane Wall

Incremental Heat Conduction Versus Mass Reduction in Large Corrugated Walls Derived from a Large Plane Wall

Mounting Evidence That Fibrosis Generates a Major Mechanism for Atrial Fibrillation

See related article, pages 839–847 It is widely known that atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, with the problem magnified by the clinical sequelae; eg, thromboembolic events. It is pertinent that the incidence of AF is expected to increase in the future,1 especially in aging patients. Thus, finding preventive measures for this arrhythmia has become an increasingly important goal. In addition to considering clinical risk factors, focusing on prevention necessitates knowledge of the associated pathophysiology of AF,2 which involves the initiation of AF and the wavefront dynamics that sustain it. In recent years considerable new information has appeared concerning AF mechanisms that occur in different regions of the atria in different cardiac states.3 This point is highlighted by the report of Tanaka et al4 in this issue of Circulation Research . These authors used high-resolution electrophysiological and microstructural techniques, along with computer model simulations, to study wavefront dynamics during acetylcholine (ACh)-induced AF in heart failure sheep hearts. The heart failure hearts had developed prominent fibrotic patches in the posterior left atrium near the pulmonary veins, whereas in the control (normal) hearts patches of fibrosis were smaller, diffusely distributed, and more centrally located with respect to the 4 pulmonary vein ostia. In the heart failure hearts, during AF variable wavefront breakthroughs to the endocardium occurred in the area of fibrotic patches adjacent to the pulmonary veins. The authors concluded that scroll waves within the posterior left atrial wall produced a microreentry source for the endocardial breakthroughs in the region of the larger collagen patches, thus providing the underlying mechanism of AF.4 A myriad of reports provide varied information about substrates and mechanisms of AF as a background for the study of Tanaka et al …

Late Breaking Science Abstracts

### A New Apolipoprotein Influencing Plasma Triglyceride Levels in Humans and Mice Len Pennacchio, Lawrence Berkeley National Laboratory, Berkeley, CA; Michael Olivier, Medical College of Wisconsin, Milwaukee, WI; Jaroslav A Hubacek, Jonathan C Cohen, UT Southwestern Medical Center, Dallas, TX; David R Cox, Stanford Human Genome Center, Palo Alto, CA; Jamilla Fruchart, Pasteur Institute, Lille, France; Ronald M Krauss, Edward M Rubin, Lawrence Berkeley National Laboratory, Berkeley, CA The apolipoprotein gene cluster on human chromosome 11q23 (apoAI/CIII/AIV) represents a well-studied region that influences a variety of plasma lipid parameters and atherosclerosis susceptibility in humans. To facilitate the identification of evolutionarily conserved sequences with potential function near this cluster, we determined the sequence of ∼200 kbp of orthologous mouse DNA and compared the mouse and human sequences. The presence of a stretch of inter-species sequence conservation approximately 30 kbp proximal to the apoAI/CIII/AIV gene cluster, led us to an interval that upon further analysis was shown to encode a new member (apoAV) of the chromosome 11 apolipoprotein gene cluster. ApoAV transcripts were identified predominantly in liver tissue from mice and humans. To assess the function of apoAV, we generated mice over-expressing a human apoAV transgene as well as apoAV knockout mice. We observed dramatic but opposite effects on plasma triglyceride in these two groups of animals; a 3-fold decrease in plasma triglycerides in the apoAV transgenics and a 4-fold increase in the knockout mice. To explore the relationship between apoAV and lipid parameters in humans, several single nucleotide polymorphisms (SNPs) across the apoAV locus were identified and genotyped in two independent patient populations of normo-lipidemics. A common haplotype was found to be significantly associated with increased plasma triglycerides in the two large independent studies each employing different study designs. These findings in humans and mice illustrate the utility of comparative sequence analysis as a means to prioritize regions of the genome for further …

Regional right and left atrial activation patterns during single- and dual-site atrial pacing in patients with atrial fibrillation

We examined the activation of the right atrium and left atrium by pacing from different atrial sites using several single- and dual-site atrial pacing modes in patients with atrial fibrillation or flutter. We also analyzed the effect of these pacing modes on fixed coupled extrastimuli in this population. Patients underwent detailed mapping of regional right atrial (RA) and left atrial (LA) sites. Bipolar pacing was performed individually from the high right atrium, coronary sinus ostium, and the distal coronary sinus, and simultaneously from the high right atrium and coronary sinus ostium (dual-site RA pacing) or high right atrium and distal coronary sinus (biatrial pacing). Extrastimuli were delivered from the high right atrium at fixed coupling intervals of 350 and 250 ms. Twenty patients with atrial fibrillation were studied. P-wave duration during pacing was significantly abbreviated by both dual-site RA and biatrial pacing (p <0.001 vs high RA pacing, respectively) but not by any other single-site atrial pacing method. Both dual-site atrial pacing modes also significantly abbreviated P wave durations for closely coupled high RA premature beats (p <0.001) in contrast to high RA pacing. During the basic pacing drive and for high RA extrastimuli, RA activation at the crista terminalis and atrial septum was comparable in sinus rhythm, high RA pacing, and in both dual-site atrial pacing methods, but was significantly delayed by coronary sinus ostial and distal coronary sinus pacing. In contrast, proximal coronary sinus activation was delayed with high RA pacing compared with all other pacing modes, and high RA extrastimuli encountered reduced conduction delay at this location with dual-site atrial pacing modes. LA activation was advanced superiorly by both single-site coronary sinus pacing methods and both dual-site atrial pacing techniques. Inferior and lateral LA activation was advanced by all pacing modes using a coronary sinus pacing site. However, earlier activation of LA sites occurred for high RA premature beats after both dual-site pacing methods (p <0.05) compared with single-site pacing modes. Incremental conduction delay at different atrial regions for closely coupled high RA extrastimuli ranged from 33% to 120% during high RA pacing and was significantly attenuated at multiple RA and LA sites by dual-site RA and biatrial pacing. Distinct global, as well as regional electrophysiologic effects, may mediate the variable antiarrhythmic effects of different and novel atrial pacing methods.

Electrophysiological studies in mild idiopathic carpal tunnel syndrome

Many techniques have been reported to improve the diagnosis of carpal tunnel syndrome (CTS), but there is no agreement on the diagnostic yield of these different methods. We used an electrophysiological protocol including the assessment of the orthodromic sensory conduction velocity of the median nerve along the carpal tunnel, comparison of median and ulnar sensory conduction between the ring finger and wrist, short segment incremental median sensory nerve conduction across the carpal tunnel recording from the III digit ('inching test'), the study of the refractory period of transmission (RPT) and calculation of the distoproximal ratio obtained by dividing the nerve conduction velocity in the median nerve between the third digit and the palm and between the palm and wrist in 41 patients with mild CTS (75 symptomatic hands) and in 45 control subjects. The distoproximal ratio calculation was the most sensitive technique (81%), but was also the least specific. The 'inching test', even though less sensitive, had the advantage of localising focal abnormalities of the median nerve along the carpal tunnel. RPT was abnormal in patients with recent symptoms. Combining the different techniques, an overall sensitivity of 92% was reached, 11% higher than the yield of the single best test suggesting that a multimodal approach could be useful. The best procedure for electrodiagnosis of mild CTS was to combine the median/ulnar comparison test with calculation of the disto-proximal ratio.

Mechanism of apparent incremental retrograde conduction across left lateral accessory pathways

Mechanism of apparent incremental retrograde conduction across left lateral accessory pathways

High transconductance AllnAs/InGaAs superlattice channel heterojunction fet

We have fabricated a novel AllnAs/InGaAs superlattice channel heterojunction FET, demonstrating very high multiple positive-negative transconductance peaks. The structure is designed in such a way as to provide conduction first from the heterojunction 2DEG channel and then incremental parallel conduction from the superlattice channel by retracting the depletion region of the gate. The characteristics of the transistor showed excellent pinch-off and flat saturation at the high reverse gate bias regime. At the low reverse gate bias (VG < 2V) regime negative differential resistance (NDR) was clearly evident in the IDS -VDS characteristics of the transistor, which was attributed to the tunneling perpendicular to the interface through the states of the superlattice. The heterojunction 2DEG channel had a peak transconductance gmH = 100 – 130mS/mm for the 2 μm gate devices fabricated here. Superlattice conduction parallel to the interface is established for reverse gate biases VG < 2V and small forward biases, where multiple transconductance peaks are observed showing a positive maximum g+mSL as high as 400 mS/mm and a negative minimum g−mSL as low as 50 mS/mm for the main peak that occurs at reverse gate biases close to 0V. The increase in gm is attributed to the rapid incremental increase of IDS with VG when the superlattive is exposed, and the decrease, to the tunneling perpendicular to the interface through the states of the superlattice. Our results demonstrate for the first time the possibility of using doped superlattice conduction to obtain high transconductances.