Responses of beagle dogs to acute myocardial ischaemia

22DIASTOLIC CHAMBER STIFFNESS: DIFFERENT EFFECTS OF HYPOXEMIA AND ISCHEMIA. Laura F. -kxler, MD, Carl. S. Apstein, MD, Boston U. and Boston City Hospital, Boston, .ass. .ve have shown that global ischemia (Isch) causes an initial decrease in diastolic chamber stiffness (DCS) due to collapse of the coronary vasculature ("erectile" effect), followed by a progressive increase in DCS due to late ischemic contracture (C). In contrast, hypoxemia (Hypox), i.e., anaerobic coronary flow, causes an acute increase in DCS within 20-120 sec. We reasoned that if the same mechanism causes early hypoxic C and late ischemic C, the effect on DCS of Hypox followed by Isch should be additive. LV DCS was assessed from LV diastolic prescore volume curves and is reported here as the LV vol (ml) at LVEDP=20mmHg (LVvol20): In seven hearts, control LVvol20 was 1.23+0.13. At 5" post-Isch, it increased to 1.57+0.14 (PC ,005) After-return to control (erectile effect of OT34ml) and was then stable over 120". state, 120"of Hypox decreased LVvol20 to 0.8750.1 (P_< ,005) indicating acute hypoxic C. When Isch was superimposed on hearts with hypoxic C, LVvol2C increased to 1.19: 0.01 at 5" post-Isch (P< .005) (erectile effect of 0.32ml) but, in contrast to the initial Isch run, LVvol20 continued to increase to 1.68~0.16 (P< ,005) at 120" postAnother difference between Isch, indicating complete reversal of hypoxic C by Isch. late ischemic C and early hypoxic C is that a single stretch of an intra-LV balloon lysed late ischemic C at 30 min (LVEDP pre-stretch=63+5mmHg; post-stretch=5+lmmHg, P<.OOl) but did not affect early hypoxic C (25~5 vs ?7+mmHg, P=N.S.) These differences suggest different sub-cellular mechanisms-for these increases in DCS. 23 RESPONSES OF BEAGLE DOGS TO ACUTE MYOCARDIAL ISCHAEMIA. C.A. Campbell, M. Meier. Biological Research Laboratories of the Pharmaceuticals Division of Cuba-Geigy Limited, Basle, Switzerland. Beagle dogs are used extensively for pharmacological testing and have a reputation for responding unusually to acute myocardial ischaemia, at least with regard to arrhythmias (1). The arm of this study was to investigate the responses of beagles to brief periods of ischaemia. Chloralose-anaesthetised, open-chest beagles were subjected to 3-min occlusions of the LAD, every 30 min, and the degree of ischaemia assessed from the epicardial ECG recorded from 5 electrodes sutured to the epicardial surface within the expected ischaemic region. In response to occlusion of the LAD, the epicardial ECG can, within the same ischaemic region, change to produce either classical ST-segment elevation, or a form of QRS-T merging whereupon the ST-segment becomes obscured. Using the third occlusion as the control, the epicardial ST-segment elevation, or the form of QRS-T merging is consistent and stable in subsequent occlusions. These parameters of ischaemia are reduced or delayed by metoprolol 0.1-3 mg/kg and by nifedipine 0.16-0.32 mg/kg administered as slow intravenous infusions. Thus, the epicardial ECG of beagles in response to lschaemia and anti-ischaemic drugs is similar to that of other strains of dogs. (1) Marshall, R.J. and Parratt, J.R., J. Physiol., Paris, 1980, fi,699-715

24 X%WiVRB AI3 ~U.,Cl'I311 I,. X+.ZI...,ii'i'AL 3U3,,~LOC,~..LjI~~L i~iii~..IB i.Bariith, Lliagyar. 2nd Lkpartnent oi' i.A.;dicinc and 3eparLwct of Z.:Lnta16c2y, ,"atholo&y, Postgraduate kedical Zchool, audapost, hungary Subendocardial ischemia vas in&c-d on open chest dogs' heart by lull, narrowing + atria1

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contraction and relaxntion , myocardial blood flow/ and /ST segment deviation, the histological-ultrastructural patteriis. The ST segment dev:.ation was c.cccpted as reference-change. Ghen only the subendocardial cLctroda snowed ;jq segment elevation without epicardial ST sz:;ment depression, a slight reduction of subendocardial flow and inhibition of relaxation occur. Lorpbologically, only the mitochondrial electron-density decreased, CV?:I iI1 lor~p, term ischenia. In casts with epicardial ST segment depression significant subendocardial flow reduction and the inhibiton of contraction and relaxation :lere present. After the first 15 minuted without structural changes, "coagula'cion necrosis with contraction bands" in a focal arrangement, mixed with the later dcvzloped "myocardial myocytolysis" occured in the subcndocardial layer, but without further aggravation of the functional pattern. No direct correlation between the functio;lal and structural disorders induced by subendocardial ischemia, as the fxctional abnoP nalities can appear before and without structural changes. On the other hand the developed functional disorders do not show aggravation witil the progress of the structural changes. even not after 6 hours durction.