Pacemaker Syndrome in a Patient with DDD Pacemaker for Long QT Syndrome

A patient with long QT syndrome was treated with beta blockers and had a permanent DDD pacemaker implanted. The lower rate was set to 85 beats/min because this provided the best shortening of QT interval at the lowest paced heart rate. The atrioventricular (AV) delay was programmed to 250 msec to allow native AV conduction. Patient returned complaining of symptoms suggestive of pacemaker syndrome. ECG during one of these episodes showed AV sequential pacing. Doppler echocardiography of hepatic vein flow suggested atrial contraction against a closed tricuspid valve. Endocardial electrogram telemetry demonstrated ventriculoatrial (VA) conduction with the retrograde atrial electrogram falling within the atrial refractory period and thus was not sensed. The following atrial stimulus did not capture because of the atrial refractoriness. Ventricular pacing proceeded after the programmed AV delay. Reprogramming the AV delay to 200 msec restored AV synchrony by allowing the atrial stimulus to capture by placing it outside of the refractory period of the atrium. No further symptoms reported during six months of follow-up.     

Maize production, drought and AIDS in Monze District Zambia

The 1992 Southern African drought focused the world's attentionon the precarious food security situation of that region. InMonze District, southern Zambia, in addition to the droughtthere was also a serious epidemic of East Coast fever amongthe cattle, which resulted in the deaths of a large percentageof the district's herd causing further impoverishment amongsome of the district's poorer households. At the same time,AIDS and HIV disease are increasingly making an impact on theproductivity of the district's population, with as many as onein 6.5 households already having experienced illness or a deathdue to AIDS. This paper describes the history of maize in Zambia,the impact of the 1992 drought and of the epidemic of East Coastfever, and the likely impact of AIDS on agriculture in the district.     

EFFECT OF DILTIAZEM ON PORCINE MALIGNANT HYPERPYREXIA INDUCED BY SUXAMETHONIUM AND HALOTHANE

We have studied the ability of the calcium channel antagonistdiltiazem to inhibit and reverse the porcine malignant hyperpyrexia(MH) syndrome. Pretreatment with diltiazem modified an MH response.Treatment with diltiazem was partially effective against a mild(or early) MH response. Diltiazem should not be considered tobe an effective therapeutic agent for MH and should not displacethe use of dantrolene.     

The relationship between failure and design in conventional bridgework from general dental practice

A total of 142 failed bridges constructed in general dental practice were assessed for design factors that might relate to failure. The overall mean age of the bridges at failure was 6.2 years; anterior and complex bridgework had a mean age of about 5 years, compared with 7.5 years for posterior bridges. The lifespan of the bridgework was significantly correlated with the number of retainers but not with the number of units. Bridges with one or two retainers had an average lifespan of just over 7 years, whilst those with three or more retainers had been in service for, on average, only 4 years. The practical difficulties of constructing multi-abutment bridgework could account for this difference. One hundred and ninety-one of the 346 retainers were porcelain bonded to semi non-precious metal crowns, and had a mean lifespan of 3.7 years, whilst those that were gold based lasted at least twice as long. Post crowns as retainers survived on average for 6.2 years.     

The Electrophysiological Substrate of Atrial Fibrillation

The electrophysiological substrate that predisposes the human atrium to sustain alrial fibrillation is incompletely understood. However, abnormalities of atrial size, refractory period and conduction are important precursors to this arrhythmia. The propensity of various disease states, cardio active drugs and the autonomic nervous system to potentiate atrial fibrillation may be explained by changes in these electrophysiological properties.