Far-Field R Wave Oversensing in a Dual Chamber Arrhythmia Management Device: Predisposing Factors and Practical Implications

WERETKA, S., et al. : Far-Field R Wave Oversensing in a Dual Chamber Arrhythmia Management Device: Predisposing Factors and Practical Implications. Initial experience with the Medtronic Jewel 7250, the ICD designed to detect and treat ventricular and supraventricular tachyarrhythmias, is very promising. Its effectiveness, however, depends on sensing performance, which has not yet been systematically examined. The aim of the study was to determine the incidence of, predisposing factors for, and practical implications of far-field R wave oversensing (FFRWOS) in this dual chamber ICD. During a total follow-up of 797 months in 48 patients who had the Jewel 7250, follow-up strip charts, 12-channel Holter recordings and, in particular cases, Holter recordings with intracardiac markers were analyzed for the presence of FFRWOS. FFRWOS was documented in ten (21.3%) patients. Compared to other lead locations, the right atrial appendage lead position was most frequently associated with FFRWOS (  7/27 vs 3/21, P < 0.05  ). Patients with FFRWOS had significantly more treated and nontreated atrial episodes, many of which were judged to have been detected inappropriately. In one case, inappropriate atrial antitachycardia pacing due to R wave oversensing triggered sustained ventricular tachycardia, terminated eventually with a high energy shock. In dual chamber ICDs, FFRWOS may represent a frequent phenomenon possibly leading to serious consequences. For atrial leads, a lateral atrial wall position seems to be preferable. In most cases, FFRWOS can be eliminated by optimization of atrial sensing parameters. Given the possibility of ventricular proarrhythmia with atrial pacing therapy, the capability of ventricular backup defibrillation in respective devices is at least reassuring.     

Demographic models for child survival and implications for health intervention programmes

The child survival strategy in developing countries has beendriven largely by a selective disease control approach, whichfocuses on a few specific and inexpensive technical interventionsdirected toward conditions such as acute dehydrating diarrhoeaand the immunizable diseases. Conceptually, this approach ofdesigning health programmes in poorer developing countries byconsidering diseases one at a time is inadequate, because itfails to take into account the fact that children are typicallyafflicted with multiple disease conditions concurrently as wellas sequentially. Furthermore, this technology-centred approachautomatically eliminates from consideration a range of interventionsfor highly prevalent conditions such as low birth weight, parasiticinfestations, or vitamin A deficiency, which may not be consideredas direct ‘causes’ of death but, in fact, have amajor indirect contribution to mortality by making childrenmore frail. In this paper we develop an analytical model which demonstrateshow multiple disease conditions interact through the mechanismsof competing risks and production of frailty to produce thehigh mortality levels witnessed among children in developingcountries. This model permits an assessment of the demographicimpact of different combinations of disease control interventionson reducing infant mortality. In terms of health policy, theanalytical model demonstrates that there are multiple routesto improving child survival in developing country populations.Important in this context is the evidence that a modest reductionin several risk factors simultaneously - for example by improvinghousehold sanitation and personal hygiene - has the potentialfor producing substantial improvements in infant and child survival.The model does confirm a role for selective primary health care,but the criteria for selecting diseases for intervention shouldrelate not only to their anticipated direct impacts on mortality,but also to their indirect effects on mortality through leavinglarge numbers of afflicted survivors more frail, and thereforeat greater risk of dying of other disease conditions.     

Tuberculous splenomegaly with the hypersplenism syndrome; a case report

A case of tuberculous splenomegaly with leukopenia and anemia followingmiliary tuberculosis has been presented. Splenectomy was required after streptomycin failed to control the cytopenias, progressive emaciation, and splenic infection. However, following what appeared to be six weeks of marked improvement,the patient developed a fulminating tuberculous meningitis and died.

Note: ACKNOWLEDGMENTThe authors are indebted to Dr. Byrd S. Leavell for his suggestions in the preparation of this paper.