Effect of chronic toluene exposure on heart rhythm parameters

Toluene is used extensively in various industrial processes, and an increasing number of workers are getting exposed to its vapor. Cardiac abnormalities that have been reported in association with toluene exposure (in toxic doses) are atrioventricular conduction abnormalities, sinus bradycardia, ventricular tachycardia, recurrent myocardial infarction, dilated cardiomyopathy, and coronary vasospasm.

We aimed to investigate the effects of chronic toluene exposure on cardiac rhythm.

In this study, 40 workers in the polishing industry with more than 3 months of exposure to a mixture of organic solvents including toluene and 38 control subjects working in other fields who were matched by age, sex, smoking, habits, and living accommodation were investigated. Twelve-lead surface electrocardiogram and 24-hour Holter recordings were performed to determine QRS duration, PR duration (P and R wave interval on electrocardiograms), P wave dispersion, corrected QT dispersion, and heart rate variability parameters.

The maximum heart rate was significantly lower in the toluene-exposed group compared to the control group (130.5 ± 15.1 vs 138.6 ± 16.0, P = 0.02). Corrected low frequency (cLF) and cLF/corrected high frequency (cHF) were also significantly lower in toluene-exposed group (43.6 ± 7.2 vs 50.7 ± 10.5, P = 0.01 and 1.4 ± 0.4 vs 2.2 ± 1.0, P < 0.01, respectively). Mean cHF, root-mean-square successive difference, and standard deviation of all five-minute NN interval means values were significantly higher in the toluene-exposed group (32.8 ± 8.1 vs 25.4 ± 8.2, P ≤ 0.01; 74.0 ± 46.1 vs 60.3 ± 59.4, P = 0.02; and 149.5 ± 77.0 vs 108.9 ± 43.2, P = 0.01, respectively).

This study implies that chronic toluene exposure disturbs cardiac autonomy, particularly by suppressing sympathetic activity, and parasympathetic suppression also occurs with increased exposure duration. We also demonstrated that chronic toluene exposure was not associated with major cardiac arrhythmias and rhythm conduction system disorders.