Late survival after valve operation in patients with left ventricular dysfunction

BACKGROUND: Left ventricular dysfunction is a predictor of hospital mortality after cardiac valve operation. We evaluated late survival in a large cohort of these patients. METHODS: From 1980 to 1993, 257 patients with a preoperative ejection fraction of 0.40 or less underwent aortic (n = 177), mitral (n = 72), or combined (n = 8) valve operation, with or without concomitant coronary artery bypass grafting. RESULTS: Hospital mortality was 12.5%. Follow-up was 98% complete. Logistic regression analysis showed that an ejection fraction of less than 0.30, mitral regurgitation, concomitant coronary artery bypass grafting, emergency operation, and reoperation were independent correlates of hospital mortality (all at p < 0.05). Kaplan-Meier survival curves of the 220 hospital survivors showed a 65% 5-year survival. Multivariate analysis revealed preoperative use of diuretics, male sex, reoperation, age exceeding 60 years, and aortic regurgitation to be independent predictors of poor late outcome (all at p < 0.05). CONCLUSIONS: The liability of left ventricular dysfunction with regard to diminished long-term survival is not completely reversed by valve operation. If operation is not performed before left ventricular dysfunction develops, postoperative medical treatment of these dilated, remodeled ventricles should be considered.     

Thickness-shear vibrations of a quartz plate under time-dependent biasing deformations

Incremental thickness-shear vibrations of a Y-cut quartz crystal plate under time-harmonic biasing extensional deformations are studied using the two-dimensional equations for small fields superposed on finite biasing fields in an electroelastic plate. It is shown that the incremental thickness-shear vibrations are governed by the well-known Mathieu's equation with a time-dependent coefficient. Both free and electrically forced vibrations are studied. Approximate analytical solutions are obtained when the frequency of the biasing deformation is much lower than that of the incremental thickness-shear vibration. The incremental thickness-shear free vibration mode is shown to be both frequency and amplitude modulated, with the frequency modulation as a first-order effect and the amplitude modulation a second-order effect. The forced vibration solutions show that both the static and motional capacitances become time-dependent due to the time-harmonic biasing deformations.     

Catheter ablation for atrial flutter and fibrillation. An effective alternative to medical therapy

Atrial flutter and atrial fibrillation are common arrhythmias that can be difficult to manage clinically. In many patients, these conditions are refractory to pharmacologic therapy because of drug failure or intolerance. Radiofrequency catheter ablation may be a reasonable alternative in patients with typical atrial flutter. The procedure has a high initial success rate and a low complication rate. However, recurrence after ablation is common, and a second treatment session may be needed. In selected patients with atrial fibrillation, radiofrequency ablation can be useful for rate control. However, its use in curing chronic fibrillation is still experimental. The procedure involves insertion of a pacemaker, anticoagulation therapy is still needed in most patients, and the need for antiarrhythmic medication may not be obviated.     

Theory and design of piezoelectric resonators immune to acceleration: present state of the art

A typical low noise oscillator uses a crystal resonator as the frequency-determining element. An understanding of the fundamental nature of acceleration sensitivity in crystal oscillators resides primarily in understanding the behavior of the crystal resonator. The driving factor behind the acceleration-induced frequency shift is shown to be deformation of the resonator. The deformation drives two effects: an essentially linear change in the frequency-determining dimensions of the resonator and an essentially nonlinear effect of changing the velocity of the propagating wave. In this paper, the fundamental nature of acceleration sensitivity is reviewed and clarified, and attendant design guidance is developed for piezoelectric resonators. The basic properties of acceleration sensitivity and general design guidance are developed through the simple examples of “bulk acoustic wave (BAW) in a box” and “surface transverse wave (STW) in a box.” These examples serve to clarify a number of concepts, including the role of mode shape and the basic difference between the BAW and STW cases. The design equations clarify the functional dependencies of the acceleration sensitivities on the full range of crystal resonator design and fabrication parameters     

An extension of the hard-sphere particle–particle collision model to study agglomeration

When performing Eulerian–Lagrangian simulations of particle–fluid flows collisions between the particles need to be accounted for. One of the methods used for this is the hard-sphere model. This model, however, does not take into account cohesive forces between the particles, and for this reason it is not able to simulate many aspects of real flows, such as the formation of agglomerates. There have been some attempts in literature to treat cohesive forces in simulations of particulate flows but none of these methods were actually implemented directly into the hard-sphere model but rather have been solved separately as a part of the numerical scheme. In this paper we show how the standard hard-sphere model may be extended to include these important interactions in an efficient and proper way. The extended model is presented in detail and some numerical results are shown.