Triode for Magnetic Flux Quanta.

In an electronic triode, the electron current emanating from the cathode is regulated by the electric potential on a grid between the cathode and the anode. Here we demonstrate a triode for single quantum magnetic field carriers, where the flow of individual magnetic vortices in a superconducting film is regulated by the magnetic potential of striae of soft magnetic strips deposited on the film surface. By rotating an applied in-plane field, the magnetic strip potential can be varied due to changes in the magnetic charges at the strip edges, allowing accelerated or retarded motion of magnetic vortices inside the superconductor. Scaling down our design and reducing the gap width between the magnetic stripes will enable controlled manipulation of individual vortices and creation of single flux quantum circuitry for novel high-speed low-power superconducting electronics.

Elemental and magnetic sensitive imaging using x-ray excited luminescence microscopy.

We demonstrate the potential of x-ray excited luminescence microscopy for full-field elemental and magnetic sensitive imaging using a commercially available optical microscope, mounted on preexisting synchrotron radiation (SR) beamline end stations. The principal components of the instrument will be described. Bench top measurements indicate that a resolution of 1 µm or better is possible; this value was degraded in practice due to vibrations and/or drift in the end station and associated manipulator. X-ray energy dependent measurements performed on model solar cell materials and lithographically patterned magnetic thin film structures reveal clear elemental and magnetic signatures. The merits of the apparatus will be discussed in terms of conventional SR imaging techniques.

The local effect of magnetic impurities on superconductivity in CoxNbSe2 and MnxNbSe2 single crystals.

We investigate the effect of individual atomic impurities on the superconducting state that they are embedded in. Using low temperature scanning tunneling microscopy and spectroscopy we could identify Co and Mn atoms in the Co(x)NbSe(2) and Mn(x)NbSe(2) single crystals and observe the influence on the local electronic density of states (LDOS) at 0.4 K. We find that Co is in the weak scattering limit. In this case the LDOS is quite homogeneous on the sample surface, despite the number of defects, and retains sharp coherent superconducting peaks. This is in strong contrast to the effects of Mn impurities, which locally destroy superconductivity. In this case the LDOS shows a strong enhancement of spectral weight inside the superconducting gap even far from the Mn atoms. Moreover, two impurity bound states are found within the superconducting gap at E/Δ(0) = 0.18 and 0.36 at locations close to defects.

Direct observation of geometrical phase transitions in mesoscopic superconductors by scanning tunneling microscopy.

Using scanning tunneling microscopy, we mapped the distribution of the local density of states in a single crystal superconductor heterostructure with an array of submicron normal metal islands. We observe the coexistence of strongly interacting multiquanta vortex lattice with interstitial Abrikosov vortices. The newly formed composite magnetic flux structure undergoes a series of phase transitions between different topological configuration states. The vortex configuration states are strongly dependent on the number of flux quanta and the nanoscale confinement architecture of the mesoscopic superconductor. Here, we present images of vortex phase transitions due to confinement effects when the number of magnetic flux quanta in the system changes. The vortex dynamics in these systems could serve as a model for behavior of confined many-body systems when the number of particles changes.

[Surgical repair of myxomatous mitral valve].

Myxomatous mitral valve disease is now the most common cause of mitral regurgitation in the western world. Repair of the leaking valve has become standard surgical procedure during the past 2 decades. Between 1993-1999 we performed 113 repairs of the mitral valve. In 25 patients the etiology was myxomatous degeneration (no mortality). Long-term clinical results depend on patients' functional class at surgery. Based on this fact, and the good surgical results, it is recommended to refer such patients even with severe mitral incompetence for surgery at an early stage, even if symptoms are minimal.

Effect of surgical repair of secundum-type atrial septal defect on right atrial, right ventricular, and left ventricular volumes in adults.

Surgical repair of atrial septal defect in adults reduces right ventricular and right atrial diameters and volumes, and improves left ventricular filling.

Prevalence and significance of left ventricular outflow gradient during dobutamine echocardiography.

AIMS: This study investigated the clinical and physiological significance of the dynamic left ventricle outflow gradient observed in some patients during dobutamine stress echocardiography. METHODS: Three hundred and ninety-four consecutive patients completed dobutamine stress echocardiography using Doppler echocardiography to assess the presence of myocardial ischaemia and left ventricular outflow gradient. The prevalence of left ventricular outflow gradient was evaluated and correlated with echocardiographic and clinical findings. Fifteen patients with left ventricular outflow gradient during dobutamine infusion underwent exercise echocardiography for appearance of left ventricular outflow gradient. RESULTS: Sixty-nine of 394 (17.5%) patients developed a left ventricular outflow gradient of more than 36 mmHg. In nine of them (13%) the anterior mitral valve leaflet had a systolic anterior motion. In 60 of the 69 patients (87%) there was a dynamic obstruction at the level of the papillary muscles. The mean intracavitary gradient was 75.4 (range 36-175) mmHg. There was no correlation between the presence or absence of a dobutamine stress echocardiography-induced left ventricle outflow gradient and chest pain or shortness of breath. In patients who developed a left ventricular outflow gradient ischaemic wall motion abnormalities occurred at a significantly lower frequency during dobutamine stress echocardiography (2.9 vs 16.4% P<0.001). None of the 15 patients who underwent exercise echocardiography developed significant left ventricular outflow gradient. CONCLUSION: Left ventricular outflow gradient occurs occasionally during dobutamine stress echocardiography examination. Its presence is of no physiological or clinical significance.

Diagnostic value of 12-lead electrocardiogram during dobutamine echocardiographic studies.

BACKGROUND: The diagnostic value of 12-lead electrocardiography during dobutamine stress echocardiography (DSE) is not well documented. METHODS AND RESULTS: We reviewed the records of 116 patients referred for DSE and coronary angiography, 52 of whom were excluded because of abnormal ST segment or inadequate DSE. Of the analyzed 65 patients, 42 had angiographic evidence of significant coronary disease, 41 had evidence of ischemia according to the echocardiographic criteria, and 30 had ST changes during the study. DSE had sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 88%, 81%, 90%, and 78%, respectively. Twelve-lead electrocardiography had sensitivity, specificity, PPV, and NPV of 52%, 64%, 72%, and 41%, respectively. NPV increased to 92% in patients with negative DSE and negative ST changes. PPV increased to 95% if both DSE and 12-lead electrocardiographic ischemic changes were observed. CONCLUSIONS: Twelve-lead electrocardiography has an incremental diagnostic value when used during DSE.

Comparison of exercise hemodynamics among nonstented aortic bioprostheses, mechanical valves, and normal native aortic valves.

BACKGROUND: While aortic valve prostheses are known to perform well at rest, few studies have examined them under stress. We compared stress hemodynamics of mechanical valves and nonstented porcine valves in the aortic position to that of normal native aortic valves. METHODS: Dobutamine echocardiography was used to assess mean and peak gradients and effective orifice area index (EOAI) at rest and exercise in patients with the Toronto Stentless Porcine Valve (SPV) (n = 13, mean implant size 25.7 mm), Sorin Bicarbon mechanical valve (SOR) (n = 11, mean implant size 24.5 mm), and patients with normal native aortic valves (NOR) (n = 10). Dobutamine infusion was started at 5 micron/kg per minute, and increased by increments of 5 micron/kg per minute until the target heart rate was achieved or until a maximal dose of 40 micron/kg per minute. RESULTS: At rest and exercise, respectively, cardiac output (L/min) was 5.2 and 10.4 for Toronto SPV; 7.4 and 13.5 for SOR; and 4.6 and 11.2 for NOR. Measured EOAI (cm2) was 1.1+/-0.2 and 1.15+/-0.2 for TORONTO SPV; 1.60+/-0.3 and 1.58+/-0.3 for SOR; and 1.45+/-0.2 and 1.46+/-0.2 for NOR. Mean gradients (mmHg) were 5.48+/-1.1 and 5.83+/-0.9 for TORONTO SPV; 5.26+/-0.8 and 11.3+/-1.8 for SOR; and 1.54+/-0.4 and 2.18+/-0.7 for NOR. Peak gradients (mmHg) were 11.9+/-2.0 and 21.0+/-3.7 for TORONTO SPV; 10.79+/-1.7 and 25.9+/-3.4 for SOR; and 2.38+/-0.9 and 6.1+/-2.3 for NOR. CONCLUSIONS: Although the mechanical group (SOR) had larger measured EOAI, the greater increase in gradients with exercise in this group suggests that the TORONTO SPV is less obstructive to flow.

Valvular dysfunction in antiphospholipid syndrome: prevalence, clinical features, and treatment.

Valvular abnormalities develop in 36% and 35% of patients with primary antiphospholipid syndrome (PAPS) and with systemic lupus erythematosus (SLE) respectively, and in 48% of patients with SLE and antiphospholipid antibodies (aPL). Valvulopathy includes leaflet thickening, vegetations, regurgitation, and stenosis. A literature survey shows that significant morbidity from valvular dysfunction, mostly mitral regurgitation leading to congestive heart failure, occurs in 4% and 6% of SLE and PAPS patients, respectively. The pathogenesis of valvulopathy may involve interaction of aPL with antigens on the valve surface, resulting in valvulitis. Current therapy includes symptomatic measures and valve replacement. A novel approach for symptomatic antiphospholipid syndrome (APS) related valvulopathy involves treatment with systemic corticosteroid. We describe four such patients and their dramatic clinical and hemodynamic response to treatment with prednisone when symptomatic measures failed.

Severe hypotension induced by combination of dobutamine and dipyridamole.

Pharmacologic testing with dobutamine or dipyridamole in conjunction with echocardiography has become an accepted method for diagnosis of coronary artery disease (CAD). The sensitivity of dobutamine echo ranges from 68 to 86%, and of dipyridamole from 53 to 69% for diagnosis of CAD. Our purpose was to investigate whether the addition of dipyridamole to dobutamine, which may improve the test sensitivity, is safe. Ten patients with low probability of CAD underwent dobutamine echo; 5 were control patients and 5 patients had low dose dipyridamole added at the maximal dose of dobutamine. Four of the latter patients had severe hypotension, while no hypotension was observed in control patients. Our findings suggest that this combination of dobutamine and dipyridamole can be hazardous and should not be used in patients with suspected CAD.

A prospective randomized trial of intravenous magnesium versus intravenous propranolol in acute myocardial infarction.

A total of 266 patients entered into a study comparing the effect of intravenous magnesium and propranolol following acute myocardial infarction. Of these, 97 were able to receive either drug and were therefore randomized into the magnesium (n = 51) or propranolol group (n = 46). 88 patients were unable to receive propranolol and formed a third group (NR) while a further 81 patients could not receive either drug and formed a fourth group (N). The study showed that intravenous magnesium was as effective in preventing potentially lethal arrhythmias as propranolol and could be given to some 70 per cent of such patients whereas propranolol could only be given to 36 per cent.

Long-term follow-up after acute myocardial infarction in patients randomized to treatment with intravenous magnesium or intravenous propranolol in the acute phase.

Ninety-five patients with acute myocardial infarction were followed up for 6 months to 3 years (mean 25.4 months) in a preliminary study to compare the effects of intravenous magnesium (49 patients) with that of intravenous propranolol (44 patients) given immediately after admission to the intensive care unit. There were four cardiac deaths in the propranolol group and no deaths in the magnesium group (P < 0.046) and 27 per cent of patients who received propranolol subsequently developed cardiac failure as opposed to 12 per cent of those who had received magnesium (P < 0.04). Intravenous magnesium given in the early stages of myocardial infarction reduces the subsequent cardiac death rate possibly by reducing infarct size.

Progression and regression of coronary artery disease in one year. Quantitative angiographic assessment in patients with stable angina pectoris.

The rate of progression of coronary artery stenoses (CAS) is not clear. Spontaneous regression may also occur. Seventy-one CAS in 25 patients who were enrolled in a study of the effects of chromium on CAS were analysed. Coronary angiography was performed in multiple views and patients randomised to chromium or placebo treatment. Videodensitometric quantitative analysis was performed using a Vanguard XR70 Analyzer. After 1 year all patients were recatheterised. Corresponding frames from identical views were analysed. CAS were assessed with the observers blinded to the initial study results. No differences were found between chromium or placebo and the results have been combined. There was no overall progression of CAS as assessed by % area stenosis (p = 0.65), % diameter stenosis (p = 0.19), stenotic area (p = 0.87), or stenotic diameter (p = 0.99). However, 20% of individual lesions progressed, while 10% regressed, and 70% remained the same. These changes must be taken into account in studies of interventions which may modify the course of coronary atherosclerosis, and if coronary by-pass surgery is to be performed with a 1 year delay after angiography.

Reproducibility of measurements of coronary narrowings by videodensitometry and by digital calipers.

Computer-assisted videodensitometry has been shown to be a reliable and reproducible method of measuring absolute and relative coronary narrowings. Using a commercially available analyzer (Vanguard XR70) we confirmed intra- and interobserver reproducibilities in 34 narrowings in 9 patients. Analyses were performed on normal area and diameter, stenotic area and diameter, percent area stenosis and percent diameter stenosis. For all 6 analyses, excellent intra- and interobserver correlations were found (r = 0.93-0.98), with slopes close to 1 and intercepts close to zero. Caliper measurements (Mitutoyo Digimatic) of the same lesions by the same observers showed good inter- and intraobserver reproducibility for percent diameter stenosis (r = 0.90 and 0.86), with mean interobserver difference of 1.67 +/- (SD) 6.4% and intraobserver difference of 2.97 +/- (SD) 7.9%. However, less good correlations were found between caliper and videodensitometric measurements of percent diameter stenosis; r = 0.61 and 0.76 for the two observers. These data suggest that videodensitometry is a highly reproducible quantitative angiographic method, suitable for documenting changes in the severity of coronary artery lesions, both spontaneous or related to interventions. Caliper measurements do not provide the same degree of accuracy, but they have acceptable reproducibility in measuring diameter stenosis. As such, they are also suitable for assessing changes in severity of coronary artery lesions in individual patients.

Use of pulmonary artery catheters in patients with acute myocardial infarction. Analysis of experience in 5,841 patients in the SPRINT Registry. SPRINT Study Group.

This study analyzes the use of PAC in a registry comprising 5,841 hospitalized patients with AMI. A total of 371 patients received PAC. In-hospital mortality was higher in patients with CHF who received PAC, while there was no difference in patients with cardiogenic shock or persistent hypotension. Mortality in patients receiving PAC was higher irrespective of the presence or absence of "pump failure." A separate analysis of discharge summaries of 364 patients with CHF showed that PAC was used more frequently in sicker patients and that when severity of CHF was assessed, no difference in mortality was found in patients with mild or moderate CHF. We conclude that while a higher in-hospital mortality is found in patients receiving PAC, this excess is likely related to difference in severity of CHF, which had not been assessed in every individual. It is unlikely that PAC increases mortality.

Continuous intravenous infusion of magnesium sulfate after acute myocardial infarction.

Two hundred and fifty patients admitted with acute myocardial infarction were treated with a continuous infusion of magnesium sulfate for 24 h (a total of 46 mmol of elemental magnesium). Only 1 patient had ventricular fibrillation; no patient had sustained ventricular tachycardia requiring cardioversion. Twenty-five patients had short runs of non-sustained ventricular tachycardia and did not need cardioversion. In 6 further patients, the infusion had to be discontinued because of a drop in blood pressure. The in-hospital mortality for the group was 3.4%.

Reproducibility of measurements of coronary narrowings by videodensitometry: unreliability of single view measurements.

Computer-assisted videodensitometry has been shown to be a reliable and reproducible method of measuring absolute and relative coronary narrowings. Using a commercially available analyzer (Vanguard XR70) we confirmed the intra- and interobserver reproducibilities in 34 narrowings in 9 patients. Analyses were performed on normal area and diameter, stenotic area and diameter, percent area stenosis and percent diameter stenosis. For all 6 analyses, excellent intra- and interobserver correlations were found (r = 0.93-0.98), with slopes close to 1 and intercepts close to zero. In a separate study of 16 lesions in 11 patients, each lesion was analyzed in both the RAO and LAO planes. Correlation between the measurements was reasonable with r = 0.76 for the stenotic area and r = 0.75 for the absolute diameter stenosis. However, with suboptimal slopes (0.54 and 0.63 respectively), actual differences between measurements in the two planes were often unacceptably large. These data suggest that videodensitometry is a highly reproducible quantitative angiographic method; however, single view analyses are inadequate for comparative studies.