Records of cardiac arrhythmias detected in patients with implanted cardioverter defibrillators will be linked with measurements of the concentration and constituents of ambient particulate air pollution. Time series methods will be used to assess temporal associations, adjusting for seasonal, weekly, and diurnal patterns, meteorology, and co-pollutants. Characteristics of subjects showing the strongest air pollution associations will be assessed, as well as effect modification by medication and co-morbidities.

ICD patients are followed up clinically every three to six months. The ICD device is interrogated and data are retrieved by non-invasive radio frequency retrieval from the implanted device. Device performance is checked. Detected arrhythmias and therapeutic interventions are listed. For each detected episode, date and time is recorded, along with a short electrogram of the heartbeats immediately before and during the event.

Daily ambient particle mass (PM10 and PM2.5) and particle constituents have been measured in Boston since January 1995. The Massachusetts Department of Environmental Protection has measured concentrations of gaseous pollutants including carbon monoxide, nitrogen dioxide, ozone, and sulfur dioxide. Meteorological factors including temperature, humidity, and barometric pressure have been measured at the National Weather Service station at Logan airport. Meteorologic factors and gaseous co-pollutants will be considered as independent predictors of arrhythmic events, and as confounders of the particulate air pollution associations.