Hill number as a bacterial diversity measure framework with high-throughput sequence data.

Bacterial diversity is an important parameter for measuring bacterial contributions to the global ecosystem. However, even the task of describing bacterial diversity is challenging due to biological and technological difficulties. One of the challenges in bacterial diversity estimation is the appropriate measure of rare taxa, but the uncertainty of the size of rare biosphere is yet to be experimentally determined. One approach is using the generalized diversity, Hill number (Na), to control the variability associated with rare taxa by differentially weighing them. Here, we investigated Hill number as a framework for microbial diversity measure using a taxa-accmulation curve (TAC) with soil bacterial community data from two distinct studies by 454 pyrosequencing. The reliable biodiversity estimation was obtained when an increase in Hill number arose as the coverage became stable in TACs for a ≥ 1. In silico analysis also indicated that a certain level of sampling depth was desirable for reliable biodiversity estimation. Thus, in order to attain bacterial diversity from second generation sequencing, Hill number can be a good diversity framework with given sequencing depth, that is, until technology is further advanced and able to overcome the under- and random-sampling issues of the current sequencing approaches.

Reentrant ventricular tachycardia originating from the periaortic region in the absence of overt structural heart disease.

BACKGROUND: In the absence of overt structural heart disease, most left ventricular outflow tract ventricular tachycardias (VTs) have a focal origin and are benign. We hypothesized that multiple morphologies (MMs) of inducible left ventricular outflow tract VT may indicate a scar-related VT that can mimic idiopathic VT. METHODS AND RESULTS: Of 54 consecutive patients referred for ablation of sustained outflow tract VT without overt structural heart disease, 24 had left ventricular outflow tract VT, 10 had MM VT, and 14 had a single VT (SM). The MM group were older (70.3±4.3 versus 53.9±15.9 years; P=0.004), had more hypertension (100% versus 29%; P=0.0006), and had longer PR intervals and QRS durations compared with the SM group. In contrast to the SM group, the MM group VTs had features consistent with reentry, including induction by programmed stimulation without isoproterenol, entrainment in some, and abnormal electrograms in the periaortic area. Periaortic region voltages suggested scar in the MM group, but not in the SM group. MRI in 2 MM patients was consistent with scar, but not in 10 SM patients. Longer radiofrequency applications were required in the MM group than in the SM group. At a median follow-up of 9.7 (3.0-32.0) months, recurrences tended to be more frequent in the MM group than in the SM group (70% versus 22%; P=0.07). CONCLUSIONS: VTs from small regions of periaortic scar can mimic idiopathic VT but are suggested by multiple VT morphologies and are more difficult to ablate. Whether these patients are at greater risk, as feared for other scar-related VTs, warrants further study.