Cardiovascular radiology. The fibrillatory propensities of contrast agents

Ventricular fibrillation threshold (VFT), the electrical stimulus strength required to fibrillate the heart during the vulnerable period of the cardiac cycle, has been used to evaluate the properties of many arrhythmogenic and antiarrhythmic drugs, and is easily adaptable to determining ventricular vulnerability following coronary arteriography. Using this method, the authors find that there is a large decrease in VFT within seconds following intracoronary arteriography with 1 ml of sodium meglumine diatrizoate. During the first minute, the threshold decreases by an additional 10%, then returns rapidly and completely to control levels. The change in threshold persists much longer than artery-to-sinus transit time, longer than changes in contractility, and somewhat longer than repolarization changes in the surface electrocardiogram. There is a strong dose relation. Injections through impacted catheters or slow injections cause disproportionate decreases in VFT. Ionic solutions of CaCl2 progressively lower VFT, but, when added to sodium meglumine iothalamate solutions, minimize the fibrillatory potential of ionic contrast agents in a complex way. A modified model of myocardial ischemia produced by intracoronary mercury injection is described. With myocardial ischemia, the fibrillation threshold falls, and during coronary arteriography still lower thresholds are seen. The use of VFT measurements is recommended for further evaluation of the fibrillatory potential of contrast media in clinically relevant situations.