Air Pollution and Cardiac Arrhythmias in Patients with Implantable Cardioverter Defibrillators

Abstract

Epidemiological studies have demonstrated associations between short-term increases in outdoor air pollution concentrations and adverse cardiovascular effects, including cardiac mortality and hospitalizations. One possible mechanism behind this association is that air pollution exposure increases the risk of developing a cardiac arrhythmia. To investigate this hypothesis, dates of implantable cardioverter defibrillator (ICD) discharges were abstracted from patient records in patients attending the two ICD clinics in Vancouver, BC, for the years 1997–2000. Daily outdoor air pollutant concentrations and daily meteorological data from the Vancouver region were obtained for the same 4-yr period. Generalized estimating equations were used to assess the association between short-term increases in air pollutant concentrations and ICD discharges while controlling for temporal trends, meteorology, and serial correlation in the data. Air pollution concentrations in the Vancouver region were relatively low from 1997 to 2000, as expected. In the 50 patients who resided within the Vancouver region and who experienced at least 1 ICD discharge during the period of follow-up, no significant associations between increased air pollution concentrations and increased ICD discharges were present. When the patient sample was restricted to the 16 patients who had at least 6 months of follow-up and experienced a rate of at least 2 days with ICD discharges per year, there was a statistically significant association between increased sulfur dioxide (SO₂) concentration and ICD discharge 2 days after the SO₂ increase. When stratified by season, no associations between increased air pollutant concentrations and increased risk of ICD discharge were observed in the summer, although for several pollutants, concentration increases were associated with a decrease in ICD discharges. In the winter, increased SO₂ concentrations again were seen to be associated with increased risk of ICD discharge, at both 2 and 3 days following increases in SO₂ concentrations. These findings provide no compelling evidence that short-term increases in relatively low concentrations of outdoor air pollutants have an adverse effect on individuals at risk of cardiac arrhythmias. The findings regarding SO₂ are difficult to interpret. They may be chance findings. Alternatively, given the very low concentrations of SO₂ that were present in Vancouver, SO₂ may have been serving as a surrogate measure of other environmental or meteorological factors.

We are indebted to Charles Kerr, MD, John Yeung, MD, and their staff, Division of Cardiology, St. Paul's Hospital, and the Department of Medicine, University of British Columbia, Vancouver, Canada, for their assistance in accessing and interpreting their clinic records. This study was supported by a grant from the Toxic Substances Research Initiative, Government of Canada. Kira Rich's work was supported by a fellowship from the Michael Smith Foundation for Health Research.