Electromechanical Effects of Two Low Osmolality Contrast Media, Ioxaglate and Iohexol, on Isolated Rat Atria

Abstract

This study aimed at investigating the direct effects of two low osmolality radiographic contrast media, iohexol (non-ionic) and ioxaglate (ionic), on transmembrane action potentials, contractile force and refractoriness of isolated rat atrial preparations. Superfused with 10% solution, ioxaglate induced a biphasic mechanical response, initially decreasing and thereafter increasing contractile force. The same concentration of iohexol only increased contractile force. The two contrast media increased the resting membrane potential, action potential amplitude and rate of depolarization to the same extent. Iohexol prolonged repolarization. Both contrast media decreased the effective refractory period. The direct effects of contrast media on myocardial contractility in this study can explain the different haemodynamic effects of iohexol and ioxaglate in vivo. The observed effects on the action potentials in vitro can explain commonly observed ECG changes during coronary arteriography. The changes in depolarization, repolarization and refractoriness are probably related to the arrhythmogenic properties of these contrast media.

The iodinated radiographic contrast medium iohexol mimics the vasodilator effect seen with small increases in extracellular K+ in the isolated rabbit central ear artery

“…No study has, to our knowledge, been conducted on IRCM effects on the membrane potential of vascular smooth muscle. However, Kløw et al (14) and Tande et al (27) have shown that IRCM lower the membrane potential of myocardial cells, supporting our suggestion that IRCM evoke their vasodilator effects by hyperpolarizing smooth muscle. The recent finding by Bøyum and co-workers (4), that iohexol stimulates efflux of K + from monocytes, gives further support to this hypothesis.…”

Addition of Sodium to the Nonionic Contrast Medium Iohexol during Coronary Angiography in Man

“…The short-lasting augmentation of Q R S duration a n d the shift in the Q R S axis by b o t h iohexol preparations in this study are probably d u e t o reduced velocity of intraventricular conduction a n d depolarization (12,23). T h e changes observed in the Q R S axis were on average less than 25° a n d smaller than t h e reported 30 t o 120° axis deviation found with high osmolar contrast media (8,15).…”

“…Disturbances in impulse formation may increase automaticity, but probably more important are the regional changes within the myocardium in impulse conduction and conductivity resulting in re-entry tachyarrhythmias (12,19). Thus, in the isolated myocardium iohexol has been shown to reduce the conductivity and shorten the effective refractory period despite prolonged action potential duration (12,23). …”