Abstract :
Objectives: Description of methodological issues in a trial designed to evaluate if a multi-component
intervention aimed at vascular risk factors can prevent dementia. Design, setting and participants: Multi-center,
open, cluster-randomized controlled clinical trial (preDIVA) including 3535 non-demented subjects aged 70-78,
executed in primary practice and coordinated from one academic hospital. General practices are randomized to
standard care or intensive vascular care. Intervention: Vascular care consists of 4-monthly visits to a practice
nurse who monitors all cardiovascular risk factors. Hypertension, hypercholesterolemia, overweight, lack of
physical exercise and diabetes are strictly controlled according to a protocol and treated in a way, tailored to the
characteristics of individual participants. Measurements: Primary outcomes are incident dementia and disability;
secondary outcomes are mortality, vascular events (stroke, myocardial infarction, peripheral vascular disease),
cognitive decline and depression. Results: Between May 2006 and February 2009, 3535 subjects from 115
general practices have been included. The clusters have an average size of 31 (SD 22, range 2-114). 1658 Patients
from 52 practices were randomized to the standard care condition and 1877 patients in 63 practices to the
vascular care condition. Discussion: When designing a cluster-randomized trial, clustering of patient data within
GP practices leads to a loss of power. This should be adjusted for in the power calculation. Since intensive
vascular care will probably lead to a reduction in cardiovascular mortality, the competing risks of mortality and
dementia should be taken into account.
