Objectives Elevated ozone levels have been associated with cardiovascular morbidity and mortality. We investigated the effects of ozone on heart rate (HR) and repolarisation parameters in potentially susceptible populations.

Methods Between March 2007 and December 2008, 363 ECG recordings including >2000 1 h intervals were measured in 64 individuals with type 2 diabetes or impaired glucose tolerance and in 46 healthy individuals with a potential genetic predisposition on the detoxification pathways from Augsburg, Germany. Associations between 1 h averages of ozone and HR, Bazett-corrected QT-interval (QTc), T-wave amplitude and T-wave complexity were analysed using additive mixed models. A variable indicating season and participants' location during the 1 h ECG recordings (summer and outdoors vs winter or indoors) was used as a potential ozone effect modifier.

Results We observed concurrent and 1–4 h lagged increases in HR of 0.5–0.7% for each 20 μg/m³ increase in ozone. These effects were stronger (1.0–1.2%) when participants were outdoors during the summer. We detected in all participants a concurrent (−1.31%; 95% CI −2.19% to −0.42%) and 1 h lagged (−1.32%; −2.19% to −0.45%) T-wave flattening. Elevated ozone levels were associated with 1 h (2.12%; 0.81 to 3.52) and 2 h lagged (1.89%; 0.55% to 3.26%) increases in T-wave complexity. However, no effects were seen for QTc. Ozone effects were generally more pronounced in individuals with metabolic disorders than a potential genetic predisposition.

Conclusions Changes in repolarisation might contribute to underlying pathophysiological changes associated with the link between elevated ozone levels and reported adverse cardiovascular outcomes.