Incidence of ventricular fibrillation during coronary arteriography in the rabbit. A comparative study of isotonic ioxaglate and iohexol

The incidence of major ECG changes, particularly ventricular fibrillation, was evaluated in rabbits during prolonged, selective right coronary injection of sodium/meglumine ioxaglate (Hexabrix 160) and iohexol (Omnipaque 140), two isotonic contrast media. The anesthetized animals (n = 12) per test solution) each received 1.5 ml of contrast material, delivered at a rate of 3 ml/minute. Both contrast media caused major ECG changes, which were reversible within seconds after administration. No fibrillation occurred with ioxaglate, but ventricular fibrillation was seen in seven animals given iohexol. There was a significant difference in the incidence of ventricular fibrillation between the contrast media (P less than .01). Both test solutions induced transient, more or less marked bradycardia, but without significant differences. The intracoronary injections produced similar decreases in blood pressure for both contrast agents. Reactive hypertension was observed only in those animals in which an episode of fibrillation occurred with iohexol. The causes underlying these effects are analyzed for both contrast agents.     

Epicardial distribution of ST segment and T wave changes produced by stimulation of intrathoracic ganglia or cardiopulmonary nerves in dogs

Sixty-three ventricular epicardial electrograms were recorded simultaneously in 8 atropinized dogs during stimulation of acutely decentralized intrathoracic autonomic ganglia or cardiopulmonary nerves. Three variables were measured: (1) isochronal maps representing the epicardial activation sequence, (2) maps depicting changes in areas under the QRS complex and T wave (regional inhomogeneity of repolarization), and (3) local and total QT intervals. Neural stimulations did not alter the activation sequence but induced changes in the magnitude and polarity of the ST segments and T waves as well as in QRST areas. Stimulation of the same neural structure in different dogs induced electrical changes with different amplitudes and in different regions of the ventricles, except for the ventral lateral cardiopulmonary nerve which usually affected the dorsal wall of the left ventricle. Greatest changes occurred when the right recurrent, left intermediate medial, left caudal pole, left ventral lateral cardiopulmonary nerves and stellate ganglia were stimulated. Local QT durations either decreased or did not change, whereas total QT duration as measured using a root-mean-square signal did not change, indicating the regional nature of repolarization changes. Taken together, these data indicate that intrathoracic efferent sympathetic neurons can induce regional inhomogeneity of repolarization without prolonging the total QT interval.