Dynamic Mode Suppression and Frequency Tuning in S-Band GaN/YIG Magnetoelastic HBARs.

This work presents the detailed characterization and analysis of recently reported magnetoelastic high-overtone bulk acoustic resonators (ME-HBARs), which are multimode RF-acoustic (phononic) resonators operating in the S -band. These unique devices are fabricated by microtransfer printing (MTP) piezoelectric GaN transducers onto a ferrimagnetic yttrium iron garnet (YIG) substrate. The YIG substrate also supports spin waves (magnons) when biased with an external magnetic field. The resulting phonon-magnon hybridization can be used to suppress or tune the acoustic modes of the ME-HBAR. The experiment spans 66 distinct acoustic resonance modes from 2.4 to 3 GHz, each of which can be suppressed or tuned as much as ±6 MHz, with a bias magnetic field ≤ 0.21 T. The experimental ME-HBAR data show good agreement with analytical modeling of the magnetoelastic hybridization in YIG. Such ME-HBARs can be used as dynamically tunable or switchable resonators, oscillators, comb filters, or frequency selective limiters in RF signal processing subcomponents. By integrating incompatible materials (YIG, epitaxial GaN) and disparate functionalities (spin waves, acoustic waves) into one hybrid multidomain system, this work also demonstrates the power and broad scope of the MTP technique.

A rare case of echo enhancing agent anaphylaxis complicated by acute coronary syndrome.

Enhancing agents in echocardiography are used frequently to improve endocardial border visualization and assessment of structural heart disease. We present a unique case of anaphylactic shock with acute coronary syndrome following administration of sulfur hexafluoride echo enhancing agent. This case emphasizes the importance of recognizing anaphylaxis to enhancing agents, as well as recognizing the potential relationship between anaphylaxis and acute coronary syndrome with in-stent thrombosis.

Blood pressure changes during routine transthoracic echocardiography.

Background: Increased afterload affects many of the flow dependent metrics assessed during transthoracic echocardiography (TTE) especially in the evaluation valvular disease. A single timepoint blood pressure (BP) may not accurately reflect the afterload present at the time of flow-dependent imaging and quantification. We assessed the magnitude of change in BP at discrete timepoints during routine TTE. Method: We conducted a prospective study where participants underwent automated BP measurement while undergoing a clinically indicated TTE. The first reading was obtained right after the patient lay supine and subsequent readings were taken at 10-min intervals during image acquisition. Result: We included 50 participants (66% were male, with a mean age of 64 years). After 10 min, 40 (80%) participants had a drop in systolic BP of >10 mmHg. Compared to the baseline, there was a significant drop in systolic BP (mean decrease 20.0 ± 12.8 mmHg; P < 0.05), and diastolic BP (mean decrease 15.7 ± 13.2 mmHg; P < 0.05) at 10 min. The systolic BP remained different from the baseline value throughout the duration of the study (average decrease from baseline to study end was 12.4 ± 16.0 mmHg, p < 0.05). Conclusion: BP recorded just prior to TTE does not accurately reflect the afterload present during most of the study. This finding has important implications for valvular heart disease imaging protocols that incorporate flow dependent metrics, where the presence or absence of hypertension may lead to under- or over-estimation of disease severity.

Left ventricular stroke volume index following transcatheter aortic valve replacement is an early predictor of 1-year survival.

BACKGROUND: Adverse cardiac events are common following transcatheter aortic valve replacement (TAVR). Our aim was to investigate the low left ventricular stroke volume index (LVSVI) 30 days after TAVR as an early echocardiographic marker of survival. HYPOTHESIS: Steady-state (30-day) LVSVI after TAVR is associated with 1-year mortality. METHODS: A single-center retrospective analysis of all patients undergoing TAVR from 2017 to 2019. Baseline and 30-day post-TAVR echocardiographic LVSVI were calculated. Patients were stratified by pre-TAVR transaortic gradient, surgical risk, and change in transvalvular flow following TAVR. RESULTS: This analysis focuses on 238 patients treated with TAVR. The 1-year mortality rate was 9% and 124 (52%) patients had normal flow post-TAVR. Of those with pre-TAVR low flow, 67% of patients did not normalize LVSVI at 30 days. The 30-day normal flow was associated with lower 1-year mortality when compared to low flow (4% vs. 14%, p = .007). This association remained significant after adjusting for known predictors of risk (adjusted odds ratio [OR] of 3.45, 95% confidence interval: 1.02-11.63 [per 1 ml/m2 decrease], p = .046). Normalized transvalvular flow following TAVR was associated with reduced mortality (8%) when compared to those with persistent (15%) or new-onset low flow (12%) (p = .01). CONCLUSIONS: LVSVI at 30 days following TAVR is an early echocardiographic predictor of 1-year mortality and identifies patients with worse intermediate outcomes. More work is needed to understand if this short-term imaging marker might represent a novel therapeutic target.

Do Patients With Non-Viable Myocardium From Ischemic Cardiomyopathy Benefit From Revascularization? A Systematic Review And Meta-Analysis.

BACKGROUND: Myocardial viability assessment is used to select patients who will derive the greatest benefit from revascularization. It remains controversial whether revascularization only benefits patients with ischemic cardiomyopathy who have viable myocardium. The objective of this meta-analysis was to compare mortality between patients with ischemic cardiomyopathy and non-viable myocardium who underwent revascularization and those who underwent medical therapy alone. METHODS: The MEDLINE database was searched using PubMed to retrieve studies published up to December 2021. Inclusion criteria were 1. studies that evaluated the impact of revascularization (revascularization group) versus medical therapy alone (control group) following myocardial viability assessment; 2. patients who had coronary artery disease that was amenable to coronary artery bypass grafting or percutaneous coronary intervention; and 3. patients who had non-viable myocardium. The main outcome measure was all-cause mortality. RESULTS: A total of 12 studies were included, evaluating 1363 patients with non-viable myocardium, of whom 501 patients underwent revascularization and 862 patients received medical therapy alone. There was a significant reduction in all-cause mortality (RR 0.76, 95 % CI: 0.62-0.93, I2 = 0) in the revascularization group compared to the control group. There was no association between the type of viability imaging modality and the risk of all-cause mortality (P-interaction = 0.58). CONCLUSIONS: The findings of this meta-analysis suggest a benefit from revascularization compared to medical therapy in patients with ischemic cardiomyopathy despite the lack of myocardial viability.

Bayés syndrome secondary to atrial lipoma.

This case describes a 74-year-old male who presented with rapid atrial flutter in association with large atrial lipoma along the interatrial septum. Conversion to sinus rhythm revealed the electrocardiographic criteria for advanced interatrial block. Interatrial block results from disruption of conduction through Bachmann's bundle, most commonly due to progressive atrial fibrosis. Bayés syndrome is recognized as the association of atrial arrhythmias with underlying interatrial block. This case supports the concept that localized disruption of atrial conduction via Bachmann's bundle from an atrial lipoma can produce the electrophysiologic substrate for atrial arrhythmias and the Bayés syndrome.

Comparison of the Limb-lead Electrocardiogram to the 12-Lead Electrocardiogram for Identifying Conditions Associated with Sudden Cardiac Death in Youth Athletes.

The optimal screening strategy to prevent sudden cardiac death (SCD) in athletes remains unknown. Pre-participation screening with electrocardiogram (ECG) remains controversial. The utility and accuracy of limb-lead (LL) ECG alone in identifying cardiac abnormalities associated with SCD has not been studied. This study was a comparative secondary data analysis, comparing the interpretation accuracy of 4 physicians evaluating publicly available ECGs of the most common cardiac conditions associated with SCD in athletes. Each physician interpreted a total of 100 ECGs: 50 normal ECGs (25 LL and 25 standard 12L) and 50 abnormal ECGs (25 LL and 25 standard 12L). The agreement between LL ECGs and 12L ECGs was assessed by Cohen's kappa coefficient and the accuracy of identifying an abnormal ECG was compared across LL and 12L ECGs using a chi-squared test. Inter-rater reliability was assessed by estimating the Fleiss's kappa coefficient. The sensitivity of LL ECG and 12L ECG was identical at 86%. The specificity of LL ECG was 75% (95% CI = 65% to 83%) and 12L ECG was 82% (95% CI = 73% to 89%). Substantial agreement was seen between LL ECG and 12L ECG interpretation across all readers (k = 0.63; 95% CI = 0.49 to 0.77). Interpretation accuracy was 81% (95% CI = 74% to 86%) and 84% (95% CI 78% to 89%) using LL ECG and 12L ECG, respectively (p = 0.43). In conclusion, the accuracy, sensitivity, and specificity were high and comparable for both LL ECG and 12L ECG in identifying cardiovascular conditions associated with SCD. Agreement between LL ECG and 12L ECG was substantial.

Passive High Power RF Comb Filters Using Epitaxial GaN/NbN/SiC HBARs.

This report presents the first demonstration of passive RF comb filters made using epitaxial GaN/NbN/SiC high overtone bulk acoustic resonators (epi-HBARs). The two-port device is fabricated on electronic-grade GaN, electrically transduced, and acoustically coupled. The multi-mode epi-HBAR comb filter demonstrated here has 158 sharp filter passbands periodically distributed between 1 and 4 GHz (L-S-bands) with a free spectral range (FSR) of 17 MHz. The individual passbands of the epi-HBAR comb filter demonstrate transmission bandwidths (BWs) up to 800 kHz, f × Q values of up to 7×1014 Hz, and an average [Formula: see text] figure of merit of 41.2 at room temperature. The GaN/NbN/SiC epi-HBAR comb filter is capable of operating at high RF power levels, with linear and distortion-free performance seen up to at least 1 W of continuous wave (CW) power and up to at least 10 W of pulsed power. The compact epi-HBAR comb filters can be co-fabricated with GaN-based electronics and could potentially replace larger, off-chip or discrete-component comb filters. They can be used for spectrum sensing and as signal processing elements for remote sensing and pulsed radar.

An all-epitaxial nitride heterostructure with concurrent quantum Hall effect and superconductivity.

Creating seamless heterostructures that exhibit the quantum Hall effect and superconductivity is highly desirable for future electronics based on topological quantum computing. However, the two topologically robust electronic phases are typically incompatible owing to conflicting magnetic field requirements. Combined advances in the epitaxial growth of a nitride superconductor with a high critical temperature and a subsequent nitride semiconductor heterostructure of metal polarity enable the observation of clean integer quantum Hall effect in the polarization-induced two-dimensional (2D) electron gas of the high-electron mobility transistor. Through individual magnetotransport measurements of the spatially separated GaN 2D electron gas and superconducting NbN layers, we find a small window of magnetic fields and temperatures in which the epitaxial layers retain their respective quantum Hall and superconducting properties. Its analysis indicates that in epitaxial nitride superconductor/semiconductor heterostructures, this window can be significantly expanded, creating an industrially viable platform for robust quantum devices that exploit topologically protected transport.

Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics.

Solid-state quantum acoustodynamic (QAD) systems provide a compact platform for quantum information storage and processing by coupling acoustic phonon sources with superconducting or spin qubits. The multi-mode composite high-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source well suited for QAD. However, scattering from defects, grain boundaries, and interfacial/surface roughness in the composite transducer severely limits the phonon relaxation time in sputter-deposited devices. Here, we grow an epitaxial-HBAR, consisting of a metallic NbN bottom electrode and a piezoelectric GaN film on a SiC substrate. The acoustic impedance-matched epi-HBAR has a power injection efficiency >99% from transducer to phonon cavity. The smooth interfaces and low defect density reduce phonon losses, yielding (f × Q) and phonon lifetimes up to 1.36 × 1017 Hz and 500 µs respectively. The GaN/NbN/SiC epi-HBAR is an electrically actuated, multi-mode phonon source that can be directly interfaced with NbN-based superconducting qubits or SiC-based spin qubits.

GaN/NbN epitaxial semiconductor/superconductor heterostructures.

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors-silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor-an electronic gain element-to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance-a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family.

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors.

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm2/V∙sec for devices with a sheet charge density of 1.7 x 1013 cm-2.

Polyvinyl chloride as a multimodal tissue-mimicking material with tuned mechanical and medical imaging properties.

PURPOSE: The mechanical and imaging properties of polyvinyl chloride (PVC) can be adjusted to meet the needs of researchers as a tissue-mimicking material. For instance, the hardness can be adjusted by changing the ratio of softener to PVC polymer, mineral oil can be added for lubrication in needle insertion, and glass beads can be added to scatter acoustic energy similar to biological tissue. Through this research, the authors sought to develop a regression model to design formulations of PVC with targeted mechanical and multimodal medical imaging properties. METHODS: The design of experiment was conducted by varying three factors-(1) the ratio of softener to PVC polymer, (2) the mass fraction of mineral oil, and (3) the mass fraction of glass beads-and measuring the mechanical properties (elastic modulus, hardness, viscoelastic relaxation time constant, and needle insertion friction force) and the medical imaging properties [speed of sound, acoustic attenuation coefficient, magnetic resonance imaging time constants T1 and T2, and the transmittance of the visible light at wavelengths of 695 nm (Tλ695) and 532 nm (Tλ532)] on twelve soft PVC samples. A regression model was built to describe the relationship between the mechanical and medical imaging properties and the values of the three composition factors of PVC. The model was validated by testing the properties of a PVC sample with a formulation distinct from the twelve samples. RESULTS: The tested soft PVC had elastic moduli from 6 to 45 kPa, hardnesses from 5 to 50 Shore OOO-S, viscoelastic stress relaxation time constants from 114.1 to 191.9 s, friction forces of 18 gauge needle insertion from 0.005 to 0.086 N/mm, speeds of sound from 1393 to 1407 m/s, acoustic attenuation coefficients from 0.38 to 0.61 (dB/cm)/MHz, T1 relaxation times from 426.3 to 450.2 ms, T2 relaxation times from 21.5 to 28.4 ms, Tλ695 from 46.8% to 92.6%, and Tλ532 from 41.1% to 86.3%. Statistically significant factors of each property were identified. The regression model relating the mechanical and medical imaging properties and their corresponding significant factors had a good fit. The validation tests showed a small discrepancy between the model predicted values and experimental data (all less than 5% except the needle insertion friction force). CONCLUSIONS: The regression model developed in this paper can be used to design soft PVC with targeted mechanical and medical imaging properties.

The relationship between glycosylated hemoglobin and myocardial perfusion imaging.

BACKGROUND: The relationship between long-term glucose control (measured by glycosylated hemoglobin [HgbA1C]) and myocardial perfusion imaging (MPI) abnormalities in symptomatic diabetic patients has not been studied. HYPOTHESIS: We hypothesized that diabetic patients with poorly controlled HgbA1C would have more abnormal MPI compared to both patients without diabetes and diabetic patients with tighter glycemic control. METHODS: This was a retrospective evaluation of 1037 consecutive patients referred for MPI. All patients completed a 1-day MPI protocol. The electronic medical records were accessed for demographics and relevant medical history. RESULTS: Diabetic patients had a higher risk of abnormal MPI (including ischemia, infarction, and mixed ischemia/infarction) compared to nondiabetic patients (relative risk [RR] = 1.77). The populations with suboptimal (HgbA1C ≥ 7%) and poor (HgbA1C ≥ 8%) glycemic control had significantly higher risk of abnormal MPI (RR = 1.78 and 2.17, respectively) compared to nondiabetic patients. Coronary angiography supported the MPI results; 66% of diabetic patients had coronary artery disease (CAD), which was higher than the 53% of patients without diabetes found to have CAD. CONCLUSIONS: The importance of strict glycemic control to reduce cardiovascular complications in diabetic patients is well known. Our study shows a significantly higher risk of abnormal MPI and CAD in diabetic patients with suboptimal and poor long-term glycemic control, further emphasizing the need for aggressive risk factor modification to minimize vascular complications from DM.

Incidence and significance of pacemaker and implantable cardioverter-defibrillator lead masses discovered during transesophageal echocardiography.

BACKGROUND: Pacemaker and implantable cardioverter-defibrillator device infections are feared complications. The finding of a lead-associated mass on transesophageal echocardiogram (TEE) raises concern for endocarditis. However, the incidence and clinical importance of lead masses is not currently known. METHODS: Consecutive patients with transvenous leads undergoing TEE from July 1, 2003, to June 30, 2005, were identified and assessed for a clinical diagnosis of endocarditis. An echocardiographer blinded to clinical information reviewed all TEEs. RESULTS: Of 177 TEEs performed on 153 patients, a visible mass on a device lead was observed in 25 (14%), including 11 TEEs showing a lead vegetation, 13 TEEs showing lead strands, and one study showing both. Seventeen patients were adjudicated to have endocarditis, of which eight had a mass seen on a lead during TEE. Thus, 72% of patients (18 of 25) with a lead-associated mass did not have evidence of an infection. In TEEs performed for indications other than to rule out endocarditis, lead masses were seen in 13 of 136 studies (10%), with only one patient adjudicated to clinically have an infected device. CONCLUSION: During this 2-year study of consecutive patients with a tranvenous lead undergoing TEE, lead-associated masses were found in 14% of patients. In 72% of patients, the mass did not prove to be secondary to infectious causes. Thus, masses attached to a device lead should be interpreted in the overall clinical context and, in the absence of concomitant evidence of endocarditis, should not mandate device and lead removal.

Low-density lipoprotein cholesterol target achievement in patients at high risk for coronary heart disease.

OBJECTIVES: Although improvement in target lipid achievement has been observed in recent studies, a significant proportion of patients still do not reach their recommended low-density lipoprotein (LDL-C) targets. We conducted a study in high-risk patients to evaluate the success rate in attaining LDL-C goals. METHODS: Medical records of patients referred for cardiac stress testing were reviewed. Demographic data, coronary heart disease (CHD) risk factors, and the most recent lipid profile were recorded. The patients who did not achieve LDL-C target on initial evaluation were reassessed in 12 months. RESULTS: A total of 765 patients were classified as high-risk CHD. The average age was 66 ± 12 years; 62% were men, and 29% had a previous history of CHD. The mean LDL-C was 96 ± 35 mg/dL and the LDL-C goal of less than 100 mg/dL was achieved in 62%. In 217 patients with very high CHD risk, 83% had LDL-C less than 100 mg/dL and 37% had LDL-C less than 70 mg/dL. At month 12, data from 267 patients were reviewed, and 161 patients (60%) reached LDL-C less than 100 mg/dL. The mean LDL-C was 131 ± 27 mg/dL and 100 ± 29 mg/dL (P < .001) at month 0 and 12, respectively. Antihyperlipidemics were initially prescribed in 49% of these patients and 71% at month 12 (P < .001). CONCLUSION: Our study confirms an improving trend in lipid goal attainment in high and very high CHD-risk patients, but despite this, certain high- and very high-risk patients may require more aggressive intervention.

Atypical takotsubo cardiomyopathy: dobutamine-precipitated apical ballooning with left ventricular outflow tract obstruction.

Takotsubo cardiomyopathy, or transient apical ballooning syndrome, is a recently recognized form of transient left ventricular dysfunction that is presumably caused by stress. Takotsubo cardiomyopathy can clinically resemble an acute coronary syndrome. Reported cases have been preceded by emotional stress or medical illness. Herein, we report a fatal case of takotsubo cardiomyopathy that followed a dobutamine stress test. We believe that the dobutamine infusion led to stress-induced cardiomyopathy with a dynamic left ventricular outflow tract obstruction. To our knowledge, there is only 1 other report of an association between dobutamine infusion and the development of takotsubo cardiomyopathy.