| Abstract
| - Abstract. Study objective - The aim of the study was to investigate the mechanisms behind ECG changes and ventricular arrhythmias during coronary arteriography. Design - Transmembrane action potentials were recorded from isolated heart muscle preparations superfused with contrast media. Conductivity of plasma diluted with contrast media was determined in vitro. Epicardial ECG recordings were made during coronary arteriography. Subjects - Epicardial ECG recordings were made in eight mongrel dogs of either sex, weight 14-22 kg. Atrial appendages were excised from the same dogs and used for heart muscle preparation studies. Measurements and main results - Iohexol and ioxaglate affected the action potentials similarly: resting potential, amplitude, rate of depolarisation, and action potential duration increased; effective refractory period decreased. Both contrast media reduced plasma conductivity. During coronary arteriography both media increased R wave amplitude, depressed ST segment, and prolonged QT time on epicardial ECG. Conclusions - ST segment deviation on ECG reflects hyperpolarisation and increased amplitude of action potential rather than depolarisation consistent with ischaemia. Increased rate of depolarisation and amplitude of action potential together with reduced conductivity after contrast media may explain increased amplitude of QRS voltage on ECG. Observed regional changes in depolarisation, repolarisation, and refractoriness may be important in the genesis of ventricular arrhythmias.
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