Action of a calcium blocking agent (D600) on electrogenesis in the normal heart and the ischaemic heart in the dog
Van Bogaert, A.; De Schepper, J.
Acta Cardiologica 37(3): 183-197
1982
ISSN/ISBN: 0001-5385 PMID: 6289576 Document Number: 196906
Ca blocking agents act mainly on spontaneous supranodal function. The action potentials (AP) of sinus and nodal autonomous tissue are, in fact, chiefly related to the action of Ca2+ ions, whereas those of the ventricular autonomous and myocardial tissue are principally related to Na+ ions. The slow channels are not exclusively Ca conductors; they conduct both Ca and Na. The action of verapamil and its derivative D600 affect the activity of autonomous and ventricular myocardial tissue, and these drugs are capable of altering the direction of the T-wave and the isoelectricity of the ST segment, phenomena which are related to the duration of the action potentials and their distribution in the myocardial space. Apparently, Ca blocking agents reduce the extent of experimental ischemia (ligation of the left anterior descending coronary artery, LAD) and consequently attenuate its ECG presentation. Attenuation was not observed either at low or higher doses of D600, despite a bradycardia, diminution of afterload and reduction in myocardial contractile force. Since the necrotic focus is a permanent source of disturbed electrogenesis, D600 should neutralize an electrical abnormality of ischemic orgin, the drug itself being the cause of a regional redistribution of action potentials throughout the myocardium.