Morphology of the Cardiac Conduction System in Patientswith Electrophysiologically Proven Dual Atrioventricular Nodal Pathways

Conduction System in Dual AV Nodal Pathways. Introduction: Although the electrophysiologic criteria for dual atrioventricular nodal pathways are well established, the anatomical substrate is still unclear.
Methods and Results: We examined the hearts from 10 patients who had been studied electrophysiologically prior to cardiac transplantation. All 10 patients were male, aged 22 to 60years. Nine of the 10 patients had dual atrioventricular nodal pathways according to acceptedcriteria. Histologic studies of the atrioventricular conduction system showed normal structureof the atrioventricular node in all 10 hearts, with minor variations within the node in 3 cases, within the penetrating bundle in 3 cases, and within the nonbranching bundle in 3 cases. Theatrial approaches to the atrioventricular node were generally scanty in 6 hearts. The solitarycase that was shown electrophysiologically to lack dual pathways had no obvious difference inthe structure of the nodal area other than sparsity of transitional cells. We were unable tolocate any extranodal atrial tracts as described by other investigators.
Conclusion: The anatomical substrate for conduction over dual pathways may he too subtleto be detected by gross morphologic studies. Since dual pathways were unmasked in allpatients but one during electrophysiologic studies, it may be that the potential for these pathways is ubiquitous.     

Mature liver stages of cloned Plasmodium falciparum share epitopes with proteins from sporozoites and asexual blood stages

The liver merozoites of malaria parasites are of paramount importance, as they initiate the parasite invasion of red blood cells and start the cycle associated with the clinical features of malaria. Investigating liver merozoite antigen is difficult because of the lack of a rodent model of human malaria. In addition, only a low proportion of cells are obtained in vivo, the parasites from Cebus and Aotus monkeys are immature, and in-vitro experiments with liver cells are often confounded by contamination with the natural mosquito flora copurified with the sporozoites used for seeding the liver cultures. In our study, mature liver schizonts were shown to possess many of the antigenic determinants recognized by MoAbs and sera specific for defined sporozoite and blood-stage antigens. We employed an immunofluorescence procedure based on evaluating parasites in cryosections prepared from infected chimpanzee liver. Sufficient numbers of sectioned parasites were evaluated with each antibody to assure the reproducibility of the results, and the fixation procedure used was sufficiently non-destructive to parasite antigens so that clear differences between reactions of specific antibodies and negative controls were observed. Our evidence for sharing of epitopes by liver merozoites and sporozoites or by liver merozoites and asexual blood-stage parasites raises the possibility that immune responses elicited against sporozoites or asexual stage antigens being considered as vaccine candidates may also act against this important, little-studied stage of the parasite.     

INITIAL DEVELOPMENT OF A NEW CULTURE-SPECIFIC SCREEN FOR EMOTIONAL DISTRESS IN OLDERCARIBBEAN PEOPLE

Previous research and our own observations suggested that older Caribbean people might use terms for emotional distress that differed from those found in standard screening instruments. Using a combination of qualitative approaches derived from the ‘new cross-cultural psychiatry’, we have developed a new 13-item culture-specific screen containing items which both overlap and differ from those found in, for example, the Geriatric Depression Scale. Further research is in progress to test the validity of this screen in a large community sample.     

Polymerization Depths of Contemporary Light-Curing Units Using Microhardness

Purpose: This research investigated composite depths of cure using a variety of light‐curing units and exposure protocols. Materials and Methods: Composite (Herculite XRV, shade A2, Kerr, Orange, California) was exposed in opaque compules to conventional quartz tungsten halogen (QTH) units, soft‐start units, high‐intensity QTH and plasma arc (PAC) curing lights, and one argon laser. Cured compules were sonicated to remove uncured composite and were sectioned and polished along the long axis to expose cured composite. Knoop hardness was measured 0.5 mm from the irradiated, top surface and then at 1.0 mm and in 1.0‐mm increments until reliable readings could no longer be obtained. Hardness values were compared by analysis of variance at similar depths within a specific curing‐light classification, using the hardness of the standard 40‐second conventional QTH exposure as comparison (Dunnett's t‐test). Depth of cure was defined as the deepest hardness value found equivalent to that at 0.5‐mm depth for a specific curing light and scenario. Results: Conventional QTH lights provided similar hardness profiles. At 2‐mm depth, use of a different unit or curing tip made no difference in hardness compared with the standard. At this depth, soft‐start (pulse‐delay and step‐cure) methods yielded hardness similar to that of the standard. High‐intensity QTH lights provided similar hardness at 2‐mm depth in 10 seconds to that of the standard 40‐second exposure. Plasma arc exposure for less than 10 seconds produced inferior hardness compared with the standard. A 10‐second PAC and a 5‐second laser exposure gave hardness at 2‐mm depth equivalent to that of the 40‐second standard. Depth of cure for almost all curing scenarios was not greater than 2 mm. CLINICAL SIGNIFICANCE Similar‐type conventional QTH lights with different tip diameter (8 and 12 mm) provide similar composite cure characteristics. Soft‐start techniques provide similar cure profiles to those achieved with conventional QTH technique when used according to manufacturer's recommendations. High‐intensity QTH units and the argon laser can reduce exposure time while providing composite with similar hardness to that of conventional QTH curing. Plasma arc exposure should be at least of 10 seconds duration to provide hardness equivalent to that achieved with conventional 40‐second QTH exposure. Even with consideration of high‐intensity curing units, composite increments should still be no greater than 2 mm to provide homogeneous hardness.     

Pharyngeal diverticula

A series of 73 hypopharyngeal (Zenker's) diverticula is reported and the choice of treatment and technique of excision are discussed. The problems of excision include operation on an infected site with limited access but few patients are unfit for the procedure. Preoperatively the sac should be packed and the oesophagus stented. The side of approach is unimportant as the condition is essentially midline. Cricopharyngeal myotomy appears to reduce the recurrence rate, possibly by improving coordination of pharyngeal contraction and upper oesophageal relaxation. The use of electrocoagulation is not recommended as 20% of patients require repeated general anaesthesia and the procedure fails in 13%. For all but the smallest pouches, excision is the treatment of choice.