Cardiac electrophysiology, arrhythmogenic mechanisms and roentgen contrast media.

Contrast media (CM) affect normal cardiac electrophysiology when injected into the coronary arteries. High-osmolality CM cause more pronounced electrophysiological effects than do low-osmolality CM. Further, both high- and low-osmolality ionic CM have more pronounced effects than the nonionic CM. The CM-induced electrophysiological effects involve regional disturbances of depolarization and repolarization, thereby causing disturbances of impulse conduction as well as dispersion of refractoriness. Recent experimental studies have demonstrated that the addition of sodium or a balanced electrolyte supplement to nonionic CM reduces the risk of ventricular fibrillation (VF), particularly when the CM is injected in a wedged catheter situation. The reduced risk of VF may be due to the small and transient lengthening of repolarization seen in the CM-perfused area of the myocardium. Iodixanol, which is an isotonic nonionic dimer supplemented with NaCl and CaCl(2), is as well tolerated as iohexol during free coronary flow. However, when flow is restricted, such as when CM is injected through a wedged catheter, the risk of VF is less with iodixanol than with iopamidol, iohexol and ioxaglate.