Xylella taiwanensis sp. nov., causing pear leaf scorch disease.

A Gram-stain-negative, nutritionally fastidious bacterium (PLS229T) causing pear leaf scorch was identified in Taiwan and previously grouped into Xylella fastidiosa. Yet, significant variations between PLS229T and Xylellafastidiosa were noted. In this study, PLS229T was evaluated phenotypically and genotypically against representative strains of Xylellafastidiosa, including strains of the currently known subspecies of Xylellafastidiosa, Xylella fastidiosa subsp. multiplex and 'Xylella fastidiosasubsp.pauca'. Because of the difficulty of in vitro culture characterization, emphases were made to utilize the available whole-genome sequence information. The average nucleotide identity (ANI) values, an alternative for DNA-DNA hybridization relatedness, between PLS229T and Xylellafastidiosa were 83.4-83.9 %, significantly lower than the bacterial species threshold of 95 %. In contrast, sequence similarity of 16S rRNA genes was greater than 98 %, higher than the 97 % threshold to justify if two bacterial strains belong to different species. The uniqueness of PLS229T was also evident by observing only about 87 % similarity in the sequence of the 16S-23S internal transcribed spacer (ITS) between PLS229T and strains of Xylellafastidiosa, discovering significant single nucleotide polymorphisms at 18 randomly selected housekeeping gene loci, observing a distinct fatty acid profile for PLS229T compared with Xylellafastidiosa, and PLS229T having different observable phenotypes, such as different susceptibility to antibiotics. A phylogenetic tree derived from 16S rRNA gene sequences showed a distinct PLS229T phyletic lineage positioning it between Xylellafastidiosa and members of the genus Xanthomonas. On the basis of these data, a novel species, Xylella taiwanensis sp. nov. is proposed. The type strain is PLS229T (=BCRC 80915T=JCM 31187T).

Manifestation of work function difference in high order Gundlach oscillation.

Gundlach oscillation (or the standing-wave state) is a general phenomenon manifesting in the tunneling spectrum acquired from a metal surface using scanning tunneling spectroscopy. Previous studies relate the energy shift between peaks of the lowest-order Gundlach oscillation observed on the thin film and the metal substrate to the difference in their work functions. By observing Gundlach oscillations on Ag/Au(111), Ag/Cu(111), and Co/Cu(111) systems, we demonstrate that the work function difference is not the energy shift of the lowest order but the ones of higher order where a constant energy shift exhibits. Higher order Gundlach oscillations can thus be applied to determine the work function of thin metal films precisely.

Patients at lower risk of arrhythmia recurrence: a subgroup in whom implantable defibrillators may not offer benefit. Antiarrhythmics Versus Implantable Defibrillator (AVID) Trial Investigators.

OBJECTIVES: The goal of this study was to identify subgroups of arrhythmia patients who do not benefit from use of the implantable cardiac defibrillator (ICD). BACKGROUND: Treatment of serious ventricular arrhythmias has evolved toward more common use of the ICD. Since estimates of the cost per year of life saved by ICD therapy vary from $25,000 to perhaps $125,000, it is important to identify patient subgroups that do not benefit from the ICD. METHODS: Data for 491 ICD patients enrolled in the Antiarrhythmics Versus Implantable Defibrillators Study were used to create a hazards model relating baseline factors to time to first recurrent arrhythmia. The model was used to predict the hazard for recurrent arrhythmia among all trial patients. A priori cut points provided lower and higher recurrent arrhythmia risk strata. For each stratum the incremental years of life due to ICD versus antiarrhythmic drug therapy were calculated. RESULTS: Factors that predicted recurrent arrhythmia were: ventricular tachycardia as the index arrhythmia, history of cerebrovascular disease, lower left ventricular ejection fraction, a history of any tachyarrhythmia before the index event and the absence of revascularization after the index event. Survival times (over a follow-up of three years) were identical in each arm of the lowest risk sextile (survival advantage 0.03 +/- 0.12 [se] years), while the survival advantage for patients above the first sextile was 0.27 +/- 0.07 (se) years (two-sided p = 0.05). CONCLUSIONS: Patients presenting with an isolated episode of ventricular fibrillation in the absence of cerebrovascular disease or history of prior arrhythmia who have undergone revascularization or who have moderately preserved left ventricular function (left ventricular ejection fraction > 0.27) are not likely to benefit from ICD therapy compared with amiodarone therapy.

Synthesis of biaryls via unusual deoxygenative dimerization of 1,4-epoxy-1,4-dihydroarenes catalyzed by palladium complexes.

Treatment of various 1,4-epoxy-1,4-dihydroarenes with trichlorosilane in toluene in the presence of a palladium complex affords the corresponding biaryls in good to excellent yields. The process appears to occur via a novel palladium-catalyzed hydrosilylative dimerization of 1,4-epoxy-1,4-dihydroarenes and subsequent elimination of HOSiCl(3) and H(2)O.

Catheter ablation for the treatment of paroxysmal supraventricular tachycardia.

Radiofrequency catheter ablation has evolved into a front-line curative therapy for patients who have paroxysmal supraventricular tachycardia secondary to Wolff-Parkinson-White syndrome. AV nodal reentrant tachycardia, and atrial tachycardia. In patients with accessory pathways, cure rates exceed 90% in almost all anatomic locations. Equally high success rates are noted in patients with atriofascicular pathways and the permanent form of junctional reciprocating tachycardia. Complications secondary to catheter ablation of accessory pathways occur in 1% to 3% of patients and include cardiac perforation, tamponade, AV block, and stroke. In patients with AV modal reentrant tachycardia, selective slow pathway ablation is curative in over 95% of patients with a very low risk of AV block. Atrial tachycardias originating in both the left and right atria can be successfully ablated in over 80% of patients. Given the overall effectiveness of this procedure, radiofrequency catheter ablation should be considered as front-line therapy in patients with recurrent or drug-refractory paroxysmal supraventricular tachycardia. Although an effective therapy, the risks and benefits of this procedure need to be assessed in all patients who are candidates for this procedure.

Multiple accessory pathways in the permanent form of junctional reciprocating tachycardia.

The permanent form of junctional reciprocating tachycardia (PJRT) has been successfully eliminated by ablation of the accessory pathway responsible for the tachycardia. The coexistence of multiple accessory pathways responsible for different, long RP-interval tachycardias was not documented previously. Five patients with PJRT underwent radiofrequency catheter ablation of accessory pathways. Three of 5 patients had 2 accessory pathways each: 1 had 2 left free wall accessory pathways, another had a right posterior free wall and right posteroseptal pathway, whereas the third had 2 right posteroseptal pathways approximately 1 cm apart. The remaining 2 patients each had 1 right posteroseptal accessory pathway. Seven of 8 pathways were successfully ablated with a median of 3 radiofrequency pulses. No patient developed complications. Peak serum creatine kinase ranged from 131 to 311 IU/liter, with peak MB fraction 7 to 17 IU/liter, or 5 to 11%. Follow-up electrophysiologic study, 29 to 70 days after ablation, revealed no inducible tachycardia and no evidence of accessory pathway conduction, except for the 1 pathway not ablated. All patients remained asymptomatic 17 to 29 months after ablation. Thus, patients with PJRT can have several accessory pathways that can be safely and effectively eliminated with radiofrequency catheter ablation.

Anatomy of the action potential in the heart.

The surface electrocardiogram can be simply described as the P, QRS, and T (and U) waves, together with PR and ST segments. However, it is actually the summation of the action potential from the sinoatrial node, the atria, the atrioventricular node, the His-Purkinje system, and the ventricles. Although the action potential can be divided grossly into 5 phases, its characteristics vary in different cardiac tissue. This is because the action potential is the end-result of multiple ion channels, pumps, and exchangers opening and closing in concert, and the properties and distribution of these components can be different from one tissue to another. The ion channels can be activated by changes in the membrane voltage and specific ligands, and can be modulated by factors such as neurotransmitters (e.g., through the G-protein system), the G-proteins directly, or other ions. Only in the last 10 years have investigators been able to use molecular biology techniques to peek into the primary structure of ion channels and to develop more workable models of the channel functions. The primary structure and the putative secondary structure of the ion channels show resemblance among the groups, suggesting that, except for IsK, the development of ion channels started with IK1 and IK(ACh), followed by Ito and IK, and then by INa and ICa. However, limitations still exist in our knowledge of the ion channels and hence of the action potential. This is demonstrated by the lack of effective pharmacologic treatment of cardiac arrhythmias to this date. It is to be hoped that advances in cell electrophysiology, genetic engineering, and molecular imaging techniques will soon end the dark days of antiarrhythmic therapy.

Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease.

BACKGROUND: Radiofrequency energy has been used safely and successfully to eliminate accessory pathways in patients with the Wolff-Parkinson-White syndrome and the substrate for atrioventricular nodal reentrant tachycardia. However, this form of ablation has had only limited success in eliminating ventricular tachycardia in patients with structural heart disease. In contrast, direct-current catheter ablation has been used successfully to eliminate ventricular tachycardia in patients with and without structural heart disease. The purpose of this study was to test whether radiofrequency energy can safely and effectively ablate ventricular tachycardia in patients without structural heart disease. METHODS AND RESULTS: Sixteen patients (nine women and seven men; mean age, 38 years; range, 18-55 years) without structural heart disease who had ventricular tachycardia underwent radiofrequency catheter ablation to eliminate the ventricular tachycardia. Two patients presented with syncope, nine with presyncope, and five with palpitations only. Mean duration of symptoms was 6.7 years (range, 0.5-20 years). Radiofrequency catheter ablation successfully eliminated ventricular tachycardia in 15 of 16 patients (94%). Sites of ventricular tachycardia origin included the high right ventricular outflow tract (12 patients), the right ventricular septum near the tricuspid valve (three patients), and the left ventricular septum (one patient). The only ablation failure was in a patient whose ventricular tachycardia arose from a region near the His bundle. An accurate pace map, early local endocardial activation, and firm catheter contact with endocardium were associated with successful ablation. Radiofrequency ablation did not cause arrhythmias, produced minimal cardiac enzyme rise, and resulted in no detectable change in cardiac function by Doppler echocardiography. CONCLUSIONS: Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease is effective and safe and may be considered as early therapy in these patients.

Dihydropyridine receptor gene expression is regulated by inhibitors of myogenesis and is relatively insensitive to denervation.

To evaluate developmental and physiological signals that may influence expression of the dihydropyridine-sensitive "slow" Ca2+ channel, we analyzed dihydropyridine receptor (DHPR) mRNA abundance in mouse skeletal muscle. Using synthetic oligonucleotide probes corresponding to the rabbit skeletal muscle DHPR, a 6.5 kb DHPR transcript was identified in postnatal skeletal muscle and differentiated C2 or BC3H1 myocytes, but not cardiac muscle or brain. DHPR gene expression was reversibly suppressed by 0.4 nM transforming growth factor beta-1 or by transfection with a mutant c-H-ras allele, nominal inhibitors of myogenesis that block the appearance of slow channels and DHPR. In contrast, both BC3H1 and C2 myocytes containing the activated ras vector expressed the gene encoding the nicotinic acetylcholine receptor delta subunit, demonstrating that not all muscle-specific genes are extinguished by ras. Denervation stimulated DHPR gene expression less than 0.6-fold, despite 8-fold upregulation of delta-subunit mRNA and reciprocal effects on the skeletal and cardiac alpha-actin genes. Thus, DHPR gene induction is prevented by inhibitors of other muscle-specific genes, whereas, at most, relatively small changes in DHPR mRNA abundance occur during adaptation to denervation.

Frequency and significance of cardiac arrhythmias in chronic obstructive lung disease.

Ambulatory electrocardiograms obtained in 69 patients enrolled in the nocturnal oxygen therapy trial group were examined for frequency and significance of arrhythmias in patients with stable chronic obstructive lung disease. Ventricular premature beats occurred in 83 percent, ventricular bigeminy in 68 percent, paired ventricular premature beats in 61 percent, and nonsustained ventricular tachycardia in 22 percent of the patients. Supraventricular tachycardia occurred in 69 percent. Repetitive ventricular arrhythmia occurred in 64 percent of the patients, and was significantly more frequent in men and in patients with edema or elevated PCO2. Ventricular premature beats greater or equal to 25 per hour occurred in 35 percent of the patients. Univariate and multivariate Cox proportional hazards analysis showed that a history of coronary heart disease, increased sinus heart rate and decreased maximum work load (measured by maximal treadmill exercise test)--but not arrhythmias--were predictors of death.