Background: Cytostatic agents such as anthracyclines may cause changes in the electrophysiologic properties of the heart. We hypothesized that anthracyclines facilitate life-threatening proarrhythmic side effects of cardiovascular and non-cardiovascular repolarization prolonging drugs.
Methods and results: The electrophysiologic effects of chronic administration of doxorubicin (Dox) were studied in ten rabbits, which were treated with Dox twice a week (1.5 mg/kg i.v.). A control group (11 rabbits) was given NaCl solution. Two of ten Dox rabbits died suddenly, the remaining animals showed mild clinical signs of heart failure after a period of six weeks. Echocardiography demonstrated a decrease in ejection fraction (pre treatment: 74 +/- 23% to post treatment: 63 +/- 16% (p <0.05)). In isolated hearts, action potential duration measured by eight simultaneously recorded monophasic action potentials (MAP) was similar in Dox and control hearts. However, in Dox rabbits, administration of the I(Kr)-blocker erythromycin (150-300 microM) led to a significant greater prolongation of the mean MAP duration (63 +/- 21ms vs 29 +/- 12 ms, p <0.05) and the QT interval (100 +/- 32ms vs 58 +/- 17 ms, p <0.05) as compared to control. Moreover, I(Kr)-block led to a more marked increase of dispersion of MAP(90) in the Dox group as compared to control hearts (23 +/- 7ms vs. 9 +/- 4 ms). In the presence of hypokalemia more episodes of early afterdepolarizations and torsade de pointes occurred (p <0.05).
Conclusion: Even during the early phase of chemotherapeutic treatment,before significant QT-prolongation is present,anthracyclines lead to an increased sensitivity to the proarrhythmic potency of I(Kr)-blocking drugs. Thus, anthracycline therapy reduces repolarization reserve and thereby represents a novel contributing factor for the development of life-threatening proarrhythmia.