The accurate calculation of left ventricular (LV) wall motion from two-dimensional echocardiographs will require the accurate registration of the position from which each two-dimensional (2-D) view was obtained. This paper describes a mechanical arm with five degrees of freedom that was developed so that the position and orientation of 2-D echo sections could be calculated in three-dimensional space. High precision potentiometers, direct or gear driven, permit calibration and measurement of each of the five movements. Using the length of the arm and the angles measured by these potentiometers, the position of a 2-D section can be calculated with respect to a fixed reference point outside the body. The measurement arm was extensively retested after six months of clinical use. In patient studies, 95% confidence interval for positioning a cross-section of the long axis is +/- 6 mm. This error is similar to the cross-plane resolution to most contemporary two-dimensional transducers. On the basis of an extensive analysis of variance, recommendations are made to improve the accuracy of the arm.
1) Angiography demonstrated recanalization in all five arteries treated with the "hot tip" and three of the five arteries treated with the bare fiber. 2) Only one perforation occurred with the "hot tip," whereas three perforations occurred with the bare fiber. 3) The larger metal cap was capable of creating a wider channel in the occluded arterial segment. Although the trend favored the heated metal cap in terms of recanalization and less perforation than the bare fiber, the total number of experiments were not adequate to demonstrate statistical significance. Microscopic examination of the vessels recanalized by either technique was similar. Characteristic charring at the recanalization site was seen regardless of the technique used. These observations suggest that the effect of direct laser radiation on plaques is predominantly a thermal effect. Although these results would suggest utilization of a metal-capped fiber for vascular recanalization, more studies need to be done to confirm these preliminary findings.
In the operative correction of tetralogy of Fallot with a severely narrowed right ventricular outflow tract, widening of the pulmonic annulus is frequently necessary to prevent a high residual pressure gradient and to reduce right ventricular pressure overload. This can be accomplished by incising the pulmonic annulus and inserting a patch graft across the valve, but this usually results in pulmonary valvular insufficiency. Of 426 patients who underwent total correction of Fallot's tetralogy between 1959 and 1970, 63 required a patch across the pulmonic annulus. The mortality rate for this group was 30.1%, compared with a total mortality among the 426 patients of 18%. The high mortality rate is influenced by the fact that the majority were corrected in the early years of the series. Fifteen patients were restudied by cardiac catheterization and cineangiography an average of 9.1 years after total correction. Twelve patients were asymptomatic and three patients had only mild symptoms on exertion in spite of angiographically significant pulmonic regurgitation. The average right ventricular systolic pressure was 40 mm Hg; right ventricular end-diastolic pressure was 7 mm Hg; and the right ventricular/pulmonary arterial peak systolic pressure gradient was 14.9 mm Hg. This experience suggests that after a more difficult immediate postoperative period, patients who have right ventricular outflow reconstruction with patches across the pulmonic ic annulus tolerate their chronic pulmonic regurgitation very well.
Between the extremes of those who have no coronary disease and those limited by it are those with documented ischemia but no symptoms. Treating these patients in the "murky middle" generates some important questions. Should we treat patients with no symptoms solely on the basis of test abnormalities? Can we make the asymptomatic person better? What interventions would we use to treat such a disorder? How do we justify the risk, inconvenience, and cost of these interventions? How do we measure the efficacy of our intervention? Treating the asymptomatic person can only be justified if we prevent future events through our intervention. The management of silent ischemia can serve as a model for handling other preventative measures. The following article describes the issues around silent cardiac ischemia and some of the insights obtained in the Asymptomatic Cardiac Ischemia Pilot (ACIP) Study.
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