Short-Term Associations Between Ambient Air Pollution and Arrhythmic Events in Patients With Implanted Cardioverter Defibrillators, 1993–2002

Abstract

SAB4-PD-13 Introduction: To investigate the effect of air pollution on cardiac arrhythmia, we have compiled one of the largest databases of patients with implanted cardioverter defibrillators (ICDs) from 3 electrophysiology clinics for the time period 1993 to 2002. ICDs continuously monitor the heart rate for tachyarrhythmias, emit electrical therapy or shocks to regulate heart rhythm, and record data on each event, including date, time, and type of therapy. Our database includes 884 patients, of whom 518 had 13,108 recorded ventricular fibrillation and ventricular tachycardia events. We previously examined associations between these events and daily air pollution concentrations; results were generally consistent with the null. In the current analysis, we used hourly pollution data to refine our assessment of short-term associations. Methods: We performed case-crossover analyses using conditional logistic regression to examine associations between the hour of tachyarrhythmic events and hourly ambient particle and gas concentrations. This analysis design implicitly controls for time trend, seasonality, and diurnal patterns. “Event-hours” were defined by truncating subjects’ event times to the nearest hour and excluding events occurring within 24 hours of a previous event. “Control-hours” were matched to events by subject, year, calendar month, day of week, and hour of day. We excluded control-hours if a subject experienced an event within the previous 24 hours. After exclusions, we had information on 506 subjects contributing 5193 event-hours and 15,250 control-hours. We used several pollutant metrics in our models with event data, including hourly lags of 0 and 1, as well as 3-, 6-, 12-, and 24-hour moving averages prior to the event. Results: Associations were generally consistent across the different time metrics for both particle and gaseous pollutants. Results were largely consistent with the null, although there was some evidence of associations with nitrate, total carbon, nitric oxide, and total reactive odd nitrogen (NOy). When we restricted our analysis to events that resulted in electrical therapy, these associations persisted, although there was a loss of power. For the most severe outcome group, events that resulted in high-energy shock, several estimated associations were negative. Discussion: In this analysis, use of hourly pollution data allowed for a more refined assessment short-term associations. Our current results are consistent with our previous analyses, although we observed some suggestive associations that need further exploration.