[Influence of spontaneous collaterals on the fibrillation threshold of the heart following acute coronary occlusion].

Fibrillation threshold (FS) were determined in 27 mongrel dogs by direct electrical stimulation of the myocardium by 50 Hz AC impulses of 0.20-0.28 sec during the vulnerable period. The FS is the current which just suffices to produce ventricular fibrillation. Sinus rhythm was restored 10 sec after onset of ventricular fibrillation by defibrillation. Determinations of FS were carried out for each animal repeatedly before and 3 min after acute ligation of the circumflex ramus respectively the descendens ramus of the left coronary artery. Post mortem selective coronary angiography was performed in all cases and the extent of spontaneous collateral vessels was estimated by the rate of retrograde contrast radiography of the ligated coronary artery. The FS fell appreciably following acute ligation of both the circumflex ramus and the sescendens ramus. Beside the size of the ligated area (the circumflex ramus supplies a larger area of the myocardium in the dog than the ramus descendens) the extent of collateral supply was the determining factor for the reductions of the FS: Following coronary ligation of the circumflex ramus the FS fell on the average from 24.0 mA to 4.1 mA if no collateral vessels were detectable; in the animals with well developed collaterals the FS was reduced from 24.8 to only 14.1 mA. After acute occlusion of the descendens ramus the FS fell from 27.9 mA to 11.5 mA in the group with not sufficient collateral supply and from 31.2 mA to only 21.5 mA in the group with well developed collaterals. The comparison of the different decreases of the FS after coronary occlusion clearly shows that the influence of the in size differing ischemic areas on the decrease of the FS is particularly evident if no collateral vessels are existent. If collateral vessels are well developed this difference is not significant. These results demonstrate that the influence of well developed collaterals on the decrease of the FS after coronary occlusion exceeds the dependence on the size of the ischemic area.