Atrial fibrillation: the tip of the iceberg

Atrial fibrillation (AF) usually results from profound alterations of the functional properties and structure of the atrial myocardium. For instance, at the cellular level AF is associated with a marked shortening of the action potential (AP) also seen in dilated atria in sinus rhythm. Drastic down-regulation of the I-type Ca2+ current that activates during the plateau phase is one of the main mechanisms responsible for this AP shortening. The down-regulation could be due to a variety of mechanisms including decreased channel expression and alteration of their camp-dependent phosphorylation. There are also alterations of repolarizing currents such as the transient outward potassium current or acetylcholinegated-inward rectifier potassium current. The electrical remodeling of diseased atria is most often associated with severe tissular and cellular alterations including: fibrosis, myocyte dystrophy with myolysis and dedifferentiation, apoptosis and gap junction disorganization. These abnormalities could result from a common and non specific adaptive response to changes in the working conditions of the atrial myocardium. The main goal of research in this field is now to link up the various abnormalities observed during AF and to determine their respective roles in atrial vulnerability to arrhythmia.     

Circulating cytokines: the tip of the iceberg?

Circulating cytokines, particularly TNF alpha, IL-1, IL-6 and IL-8, can be detected during severe infections consecutively to an exacerbate release by activated cells. The presence or absence of cytokines within biological fluids reflects a rather complex balance between enhancing and inhibitory signals acting on producer cells, between production and catabolism, and between their binding to the target cells and the modulation of their receptors on the cell surface. Furthermore, their presence does not necessarily parallel their activity and a possible interplay between the cytokines and their corresponding inhibitors should be considered. On the contrary, the absence of detectable circulating cytokines does not indicate an absence of production by activated cells. We discuss the concept that circulating cytokines represent the tip of the iceberg.     

HIV in Nepal: is it rare or the tip of an iceberg?

Acquired immunodeficiency syndrome (AIDS) has reached alarming proportions in SE Asia. The magnitude of the epidemic is projected to exceed that of sub-Saharan Africa as we enter the 21st century. Nepal has much in common with India geopolitically and socially and the prevalence of HIV is expected to be no different from the rest of SE Asia. However, evidence thus far paints a different picture altogether--a very low prevalence of HlV even in high-risk population groups. This is surprising, particularly since high-risk behaviour is evidenced by a high rate of drug abuse. In addition, other communicable diseases commonly associated with HIV infection, such as tuberculosis and HBV/HCV infection, are common in Nepal and yet still the prevalence of HIV infection in these patients and in the general population is reported to be low. This paper identifies some of these anomalies and attempts to analyse the reasons for this discrepancy. We emphasize the need for extended survey and strict surveillance to avoid an explosion of this dreaded infection.     

Hepatitis A in childhood. The tip of an infectious disease iceberg

The objectives of this study were to analyze the seroepidemiologic prevalence of Hepatitis A Virus (HAV) in children of the city of Resistencia by means of specific antibody detection, relate these data with the socio-sanitary conditions, and discuss vaccine strategies. Two hundred and eighty eight children between 2 and 14 years of age, with a mean of 6.6 years, of both sexes and with no patent liver disease were studied. Blood samples were taken, and the presence of total anti-HAV antibodies was determined. A prevalence of 83.3% was found with no significant differences between sexes. When age groups were compared, antibodies were found in 57.3% of children between 2 and 4 years of age, 90.8% in the 5 to 9 group, and 96.6% in the 10 to 14 group. It was seen that the precarious system of excreta elimination, the lack of potable water in the dwellings, and the absence of sanitary devices, were statistically associated with the high prevalence of HAV infection. In view of the high endemicity found in the first years of life, and considering this disease as a marker of other pathologies with a similar pattern of dissemination, these data may represent the tip of an iceberg holding a broad base of accompanying infections with a high impact in the health of the population. A simultaneous approach towards anti HAV vaccination in young children, and the political decision of improving socio-sanitary conditions and decreasing poverty indexes, should be promptly implemented.     

Hypomagnesemia and proton pump inhibitors: below the tip of the iceberg

Severe magnesium deficiency associated with proton pump inhibitors (PPIs) has been described recently with clinical presentations varying from life-threatening conditions to muscle cramps and paresthesias. Probably milder cases go undetected. We report an asymptomatic case of hypomagnesemia associated with chronic use of PPIs in a 67-year-old woman. She had had symptoms of gastroesophageal reflux disease for several years, which abated partially with PPIs, and denied any other symptoms or medications. Her initial evaluation showed an unexplained hypomagnesemia with a very low magnesium excretion rate in urine. Serum calcium, phosphorus, potassium, and glucose levels and renal function were normal. After PPI withdrawal, serum and urinary magnesium levels normalized.