A Case-Crossover Analysis of Particulate Air Pollution and Cardiac Arrhythmia in Patients with Implantable Cardioverter Defibrillators

Abstract

We investigated the relationship between air pollution and incidence of cardiac arrhythmia in a study of patients with implantable cardioverter defibrillators (ICDs). Thirty-four patients (ages 15–85 yr, 80% male) with ICDs residing in the Vancouver, Canada, area were included in the analyses, representing all patients attending the 2 ICD clinics in the study region who had recorded at least 1 ICD discharge during the 14 February to 31 December 2000 study period. Air pollutant (PM_2.5, PM₁₀, SO₄²⁻, elemental carbon [EC], organic carbon [OC], O₃, SO₂, NO₂, and CO) concentrations on days for which ICD discharges were observed (“case days”) were compared to concentrations on control days in case-crossover analyses. Control days were selected symmetrically, 7 days before and after each case day. ICD discharges occurring within 72 h of 1 another were grouped and considered as 1 discharge event. Temperature, relative humidity, barometric pressure, rainfall, and wind speed were included simultaneously as covariates. Sensitivity analyses examined the effect of grouping ICD discharges, of including meteorological variables, and of excluding discharges that were considered inappropriate by a cardiologist. As in previous studies, mean concentrations and interquartile ranges of air pollutants in Vancouver were low (e.g., PM_2.5 mean = 8.2 ug/m³). Although in general there were no statistically significant results, there were trends that might indicate associations between pollutants and ICD discharges. Odds ratios (OR) were consistently higher in summer than in winter (e.g., lag 0 per interquartile range increase in EC: 1.09 [0.86–1.37] vs. 0.61 [0.31–1.18]) and, in general, the highest ORs were observed for same-day effects. The one major exception was the observation of high ORs for ozone in winter (e.g., lag 1: 2.27 [0.67–7.66]). While an OR of 1.55 (0.51–4.70) was observed in summer at lag 0 for PM₁₀, no indications of positive associations were observed for PM_2.5 or SO₄²⁻. For indicators of local combustion-source pollution, EC, OC, CO, and SO₂, ORs were elevated at all lags (0–3 days) in summer. In summary, this study provides little evidence that specific components of PM affect risk of cardiac arrhythmias, although power limited the ability of the study to detect small effects.

This study was supported by a grant from the Toxic Substances Research Initiative, a combined program of Health Canada and Environment Canada. Kira Rich's work was supported by a fellowship from the Michael Smith Foundation for Health Research. The authors acknowledge Charles Kerr, MD, and John Yeung, MD, Department of Medicine, University of British Columbia, for their assistance with providing access to patient charts for review and data abstraction, and Rick White, Department of Statistics, University of British Columbia, for assistance in carrying out time-stratified case-crossover analyses. Supported in part by funding from the Michael Smith Foundation for Health Research to the Centre for Health and Environment Research at The University of British Columbia.