Multifunctional catheters combining intracardiac ultrasound imaging and electrophysiology sensing

A family of 3 multifunctional intracardiac imaging and electrophysiology (EP) mapping catheters has been in development to help guide diagnostic and therapeutic intracardiac EP procedures. The catheter tip on the first device includes a 7.5 MHz, 64-element, side-looking phased array for high resolution sector scanning. The second device is a forward-looking catheter with a 24-element 14 MHz phased array. Both of these catheters operate on a commercial imaging system with standard software. Multiple EP mapping sensors were mounted as ring electrodes near the arrays for electrocardiographic synchronization of ultrasound images and used for unique integration with EP mapping technologies. To help establish the catheters' ability for integration with EP interventional procedures, tests were performed in vivo in a porcine animal model to demonstrate both useful intracardiac echocardiographic (ICE) visualization and simultaneous 3-D positional information using integrated electroanatomical mapping techniques. The catheters also performed well in high frame rate imaging, color flow imaging, and strain rate imaging of atrial and ventricular structures. The companion paper of this work discusses the catheter design of the side-looking catheter with special attention to acoustic lens design. The third device in development is a 10 MHz forward-looking ring array that is to be mounted at the distal tip of a 9F catheter to permit use of the available catheter lumen for adjunctive therapy tools.

Gender and racial differences in mathematical performance

The authors examined gender and racial differences in mathematics performance among 5th- and 8th-grade students in the United States. Math performance was assessed by scores on the math-concepts and math-computation sections of the California Achievement Test (CTB/McGraw-Hill, 1986) given at the end of the previous year. There were no significant gender differences, but in both grades, the White students scored significantly higher than the Black students. The racial differences were more pronounced in the scores for concepts than in the scores for computation. Responses to a parent questionnaire showed significant relationships between parents' self-reported math anxiety, parents' most advanced math course, and parents' education level in relation to the child's math performance. Differences in these relationships suggest that, although parents' beliefs and attitudes about math influence their child's math performance, the relationship is complex and may vary with race.

Structural analysis of the Björk-Shiley Delrin heart valve occluder

BACKGROUND AND AIMS OF THE STUDY

Impact wear grooves were evident in some Delrin occluder discs of explanted Björk-Shiley Delrin (BSD) heart valves. This study focuses on the finite element analysis (FEA) method to understand the maximum principal stresses experienced during the peak in vivo loading of valves in the closed position.

MATERIALS AND METHODS

The maximum pressure difference across the valve was measured to be 130 mmHg in a pulse duplicator simulating normal sinus rhythm obtained clinically by cardiac catheterization. The corresponding measured strain was 1.81 x 10(-3). The FEA model incorporated four points of contact between the disc and the orifice ring to estimate the maximum principal stresses in the disc of the BSD heart valve. A linear pressure distribution averaging 130 mmHg was applied so that the finite element results gave a strain of 1.81 x 10(-3) at the gauge location as experimentally observed.

RESULTS

The largest stress in the Delrin disc of the BSD valve occurred when the occluder made four-point contact with the orifice ring struts. The resulting localized compressive stress on the inflow side could be as high as 42 ksi, assuming the Hertzian contact theory. The magnitude of tensile stresses were less, but were highest on the outlet surface opposite the point of contact. The highest tensile stress for an ungrooved disc was found to be 8.35 ksi, which was below the ultimate tensile strength and yield stress in flexure for Delrin. Therefore, it is unlikely that yielding or tensile failure will occur at this level of stress. Maximum tensile stresses were found to be 1.442 and 1.448 ksi for discs with single and multiple grooves respectively.

CONCLUSION

The model predicts that as a wear groove is created, the area of contact between the disc and the inlet strut of the BSD valve will increase, thereby reducing average compressive contact stress and hence, the wear rate.

Magnesium deficiency. Role in arrhythmias complicating acute myocardial infarction?

Magnesium deficiency is likely to occur in certain patients prone to developing acute myocardial infarction, such as hypertensive patients being treated with diuretics, alcoholics, diabetics and patients with ischaemic cardiomyopathy taking diuretics and digitalis. Magnesium deficiency commonly accompanies potassium deficiency, can also cause it, and can prevent correction of potassium deficiency if potassium supplements alone are used. The results of analysis of plasma magnesium and potassium levels in 25 patients presenting with acute myocardial infarction are presented. Three patients were hypomagnesaemic and all exhibited serious ventricular arrhythmias (two patients exhibited early ventricular fibrillation and the third exhibited ventricular trigeminy and multifocal ventricular ectopy). Two of the three hypomagnesaemic patients were hypokalaemic. Two other patients in the series exhibited ventricular tachycardia and both were hypokalaemic. Magnesium therapy should be considered in hypokalaemic patients during the early stages of acute myocardial infarction, as the body distribution kinetics of magnesium and potassium are interlinked and magnesium deficiency may be the crucial factor in hypokalaemia-associated arrhythmias. In addition, consideration should be given to magnesium supplementation in patients prone to acute myocardial infarction if there is a likelihood of magnesium deficiency developing, as magnesium-deficient patients may be more susceptible to developing potentially fatal ventricular tachyarrhythmias during the early stages of infarction.