Level III, case-control analytic study.

This methods paper outlines the overall design of a community-based multidisciplinary longitudinal study with the intent to stimulate interest and communication from scientists and practitioners studying the role of physical activity in preventive medicine. In adults, lack of regular exercise is a major risk factor in the development of chronic degenerative diseases and is a major contributor to obesity, and now we have evidence that many of our children are not sufficiently active to prevent early symptoms of chronic disease. The lifestyle of our kids (LOOK) study investigates how early physical activity contributes to health and development, utilizing a longitudinal design and a cohort of eight hundred and thirty 7-8-year-old (grade 2) school children followed to age 11-12 years (grade 6), their average family income being very close to that of Australia. We will test two hypotheses, that (a) the quantity and quality of physical activity undertaken by primary school children will influence their psychological and physical health and development; (b) compared with existing practices in primary schools, a physical education program administered by visiting specialists will enhance health and development, and lead to a more positive perception of physical activity. To test the first hypothesis we will monitor all children longitudinally over the 4 years. To test the second we will involve an intervention group of 430 children who receive two 50min physical education classes every week from visiting specialists and a control group of 400 who continue with their usual primary school physical education with their class-room teachers. At the end of grades 2, 4, and 6 we will measure several areas of health and development including blood risk factors for chronic disease, cardiovascular structure and function, physical fitness, psychological characteristics and perceptions of physical activity, bone structure and strength, motor control, body composition, nutritional intake, influence of teachers and family, and academic performance.

The patient was an 83-year-old woman with recurrent syncope caused by profound sinus bradycardia of sick sinus syndrome (Fig 1).A temporary and then permanent VVI pacemaker was implanted (Fig 2).In both tracings, the narrower capture beats (capture beats are always early) are preceded by sinus P waves with left atrial abnormality (LAA). In Fig 1, only 3 P waves are visible, corresponding to sinus bradycardia 28 per minute; another one can be inferred to be hiding within the third QRS complex. The first one distorts the ST segment of the initial broad QRS complex and is conducted with a very long PR interval of 0.72 second. The second one, well beyond the TU wave of the fourth complex, conducts over 0.58 second. The third one is the earliest of the 3 visible ones, peaking just after the onset of ST segment of the sixth QRS; it is too early to be conducted. Both the broader and the narrower QRS complexes are of the left bundle branch block type; the former may be either idioventricular or junctional escapes.In Fig 2 the initial 3 P waves are too early to effect a capture. Then comes the conundrum: the PR intervals progressively decrease while the R-R intervals of the captured beats increase. This is opposite of what happens in Wenckebach conduction, where progressive PR intervals increase by decremental amounts, crowding the QRS complexes together. Here, as the R-R intervals lengthen, the pacemaker spikes reappear in the second half of the trace, producing 2 pseudofusion and (last complex) one fusion beat. This fusion beat is important here be-

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