Efficacy and safety of left atrial appendage closure in patients with atrial fibrillation and high thromboembolic and bleeding risk

Aim. To compare the incidence of thromboembolic and hemorrhagic events after left atrial appendage occlusion (LAAO) or without prevention of thromboembolic events (TEEs) during prospective follow-up of patients with atrial fibrillation (AF) and a high risk of ischemic stroke (IS) who have contraindications to long-term anticoagulant therapy.Material and methods. The study included 134 patients with AF, a high risk of IS, and contraindications to long-term anticoagulation. Patients were divided into 2 groups as follows: the first group included patients who underwent LAAO (n=74), while the second one — those who did not undergo any TEE prevention (n=60). The follow-up period was 3 years. The cumulative rate of all-cause mortality, IS, transient ischemic attacks (TIA), and systemic embolism (SE) was taken as the primary efficacy endpoint. The primary safety endpoint included major bleeding according to GARFIELD registry criteria.Results.  The rate of composite efficacy endpoint in the LAAO group was significantly lower than in the group without thromboembolic prophylaxis (5,2 vs 17,4 per 100 patient-years; adjusted odds ratio (OR), 4,08; 95% confidence interval (CI): 1,7-9,5; p=0,001). The rate of major bleeding was comparable in both groups (2,4 in the LAAO group vs 1,3 per 100 patient-years in the group without thromboembolic prophylaxis; adjusted OR, 0,55; 95% CI: 0,1-3,09; p=0,509). In addition, the event rate of net clinical benefit (all-cause mortality + ischemic stroke/TIA/SE + major bleeding) in the LAAO group was also significantly lower (5,9 vs 18,2 per 100 patient-years; adjusted OR, 3,0; 95% CI: 1,47-6,36; p=0,003).Conclusion. Among patients with AF and contraindications to long-term anticoagulation after 3 years of follow-up, LAAO demonstrated the significant reduction of cumulative rate of all-cause mortality and non-fatal thromboembolic events. At the same time, the frequency of major bleeding was comparable between the groups, even taking into account access-site bleeding and postoperative antithrombotic therapy (ATT)-associated bleeding in the LAAO group. Further randomized clinical trials are required to confirm these data

Серопревалентность сотрудников первичного звена здравоохранения Санкт-Петербурга в период эпидемического неблагополучия по кори

The measles situation is still unstable — there are imported cases, the formation of nosocomial foci with the involvement of medical personnel, patients and visitors of medical institutions.Objective of the study: to assess the level of seroprevalence of primary health care workers in St. Petersburg during the period of epidemic trouble with measles.Materials and methods: An open retrospective randomized uncontrolled study of the intensity of specific immunity to measles in 980 employees aged 18 to 78 years, examined in July-September 2018, was carried out. The level of anti-measles IgG antibodies was determined by the method of enzyme-linked immunosorbent assay (810 people) and passive hemagglutination reactions (170 people). The results are presented with the indication of the shares (%) and the calculation of the 95% confidence interval according to Clopper — Pearson. Differences between groups were assessed using Pearson's chi-square test (%2). Differences in the groups were considered statistically significant when the criterion level was p < 0.05.Results: It was found that 8.2% of personnel are not protected against measles infection. At the same time, the number of seronegative persons among doctors (8.1 %), nurses (7.7%) and non-medical workers (9.6%) differed statistically. Age-related differences in the immune layer were revealed — the greatest susceptibility was observed in persons under 30 years of age (1 8.3%). Anti-measles antibodies in those who had been ill persisted for a long time and at a high level. At the same time, the intensity of post-vaccination immunity decreased over time, and 20 years after immunization, the number of seronegative individuals increased significantly. Only 64.1 % of those surveyed had two vaccinations, more than a third were immunized once. Nevertheless, the proportion of people unprotected from measles exceeded the criterion of epidemic well-being with the same frequency in both groups (9.2% and 1 0.4%, respectively).The results of a serological study showed that the presence of a record of two vaccinations in the certificate in 9.2% of cases does not guarantee protection in case of contact with a patient with measles. Only a serological examination is evidence of specific immunity to measles infection.Ситуация по кори до настоящего времени остается нестабильной — отмечаются завозные случаи, формирование внутрибольничных очагов с вовлечением медицинского персонала, пациентов и посетителей лечебных учреждений.Цель исследования: оценить уровень серопревалентности сотрудников первичного звена здравоохранения Санкт-Петербурга в период эпидемического неблагополучия по кори.Материалы и методы: Проведено открытое ретроспективное рандомизированное неконтролируемое исследование напряженности специфического иммунитета к кори у 980 сотрудников в возрасте от 18 до 78 лет, обследованных в июле-сентябре 2018 г. Уровень противокоревых антител класса IgG определялся методом иммуноферментного анализа (810 чел.) и реакции пассивной гемагглютинации (170 чел.). Результаты представлены с указанием долей (%) и расчетом 95% доверительного интервала по Клопперу-Пирсону. Различия между группами оценивали с помощью критерия %2 Пирсона. Различия в группах считались статистически значимыми при уровне критерия p < 0,05.Результаты: Установлено, что 8,2% персонала не защищены против коревой инфекции. При этом количество серонегативных лиц среди врачей (8,1%), среднего медицинского персонала (7,7%) и немедицинских работников (9,6%) статистически не различалось. Выявлены возрастные различия в иммунной прослойке — наибольшая восприимчивость отмечена у лиц моложе 30 лет (18,3%). Противокоревые антитела у переболевших сохранялись длительно и на высоком уровне. В то же время напряженность поствакцинального иммунитета с течением времени снижалась и через 20 лет после иммунизации значительно возросло количество серонегативных лиц. Две прививки имели только 64,1 % обследованных, более трети оказались иммунизированы однократно. Тем не менее доля незащищенных от кори лиц превышала критерий эпидемического благополучия с одинаковой частотой в обеих группах (9,2% и 1 0,4% соответственно).Результаты серологического исследования показали, что наличие в сертификате записи о двух прививках в 9,2% случаях не гарантирует защиту при контакте с больным корью. Только серологическое обследование является доказательством наличия специфического иммунитета к коревой инфекции

Readout of a quantum processor with high dynamic range Josephson parametric amplifiers

We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 $\Omega$ environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250-300 MHz, with input saturation powers up to -95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimate of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.Comment: 9 pages, 8 figure

Phase transition in Random Circuit Sampling

Quantum computers hold the promise of executing tasks beyond the capability of classical computers. Noise competes with coherent evolution and destroys long-range correlations, making it an outstanding challenge to fully leverage the computation power of near-term quantum processors. We report Random Circuit Sampling (RCS) experiments where we identify distinct phases driven by the interplay between quantum dynamics and noise. Using cross-entropy benchmarking, we observe phase boundaries which can define the computational complexity of noisy quantum evolution. We conclude by presenting an RCS experiment with 70 qubits at 24 cycles. We estimate the computational cost against improved classical methods and demonstrate that our experiment is beyond the capabilities of existing classical supercomputers

Measurement-Induced State Transitions in a Superconducting Qubit: Within the Rotating Wave Approximation

Superconducting qubits typically use a dispersive readout scheme, where a resonator is coupled to a qubit such that its frequency is qubit-state dependent. Measurement is performed by driving the resonator, where the transmitted resonator field yields information about the resonator frequency and thus the qubit state. Ideally, we could use arbitrarily strong resonator drives to achieve a target signal-to-noise ratio in the shortest possible time. However, experiments have shown that when the average resonator photon number exceeds a certain threshold, the qubit is excited out of its computational subspace, which we refer to as a measurement-induced state transition. These transitions degrade readout fidelity, and constitute leakage which precludes further operation of the qubit in, for example, error correction. Here we study these transitions using a transmon qubit by experimentally measuring their dependence on qubit frequency, average photon number, and qubit state, in the regime where the resonator frequency is lower than the qubit frequency. We observe signatures of resonant transitions between levels in the coupled qubit-resonator system that exhibit noisy behavior when measured repeatedly in time. We provide a semi-classical model of these transitions based on the rotating wave approximation and use it to predict the onset of state transitions in our experiments. Our results suggest the transmon is excited to levels near the top of its cosine potential following a state transition, where the charge dispersion of higher transmon levels explains the observed noisy behavior of state transitions. Moreover, occupation in these higher energy levels poses a major challenge for fast qubit reset

Overcoming leakage in scalable quantum error correction

Leakage of quantum information out of computational states into higher energy states represents a major challenge in the pursuit of quantum error correction (QEC). In a QEC circuit, leakage builds over time and spreads through multi-qubit interactions. This leads to correlated errors that degrade the exponential suppression of logical error with scale, challenging the feasibility of QEC as a path towards fault-tolerant quantum computation. Here, we demonstrate the execution of a distance-3 surface code and distance-21 bit-flip code on a Sycamore quantum processor where leakage is removed from all qubits in each cycle. This shortens the lifetime of leakage and curtails its ability to spread and induce correlated errors. We report a ten-fold reduction in steady-state leakage population on the data qubits encoding the logical state and an average leakage population of less than $1 \times 10^{-3}$ throughout the entire device. The leakage removal process itself efficiently returns leakage population back to the computational basis, and adding it to a code circuit prevents leakage from inducing correlated error across cycles, restoring a fundamental assumption of QEC. With this demonstration that leakage can be contained, we resolve a key challenge for practical QEC at scale.Comment: Main text: 7 pages, 5 figure

Suppressing quantum errors by scaling a surface code logical qubit

Practical quantum computing will require error rates that are well below what is achievable with physical qubits. Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. Here, we report the measurement of logical qubit performance scaling across multiple code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle ($2.914\%\pm 0.016\%$ compared to $3.028\%\pm 0.023\%$). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a $1.7\times10^{-6}$ logical error per round floor set by a single high-energy event ($1.6\times10^{-7}$ when excluding this event). We are able to accurately model our experiment, and from this model we can extract error budgets that highlight the biggest challenges for future systems. These results mark the first experimental demonstration where quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references, Fig. S12, Table I