LEFT ATRIOVENTRICULAR VALVE DEGENERATION, LEFT-VENTRICULAR DILATION AND RIGHT-VENTRICULAR FAILURE - A POSSIBLE ASSOCIATION WITH PULMONARY-HYPERTENSION AND ETIOLOGY OF ASCITES IN BROILER-CHICKENS

The results presented here are based on a collection of heart necropsy data obtained from a large population of ascitic and normal broiler c hickens raised at low altitude. The hearts were subjected to gross pos tmortem evaluation. Generally, gross changes in the cardiac muscle pre dominantly consisted of various degrees of right and left ventricular enlargement and atrial enlargement, and were observed in all hearts fr om birds that developed ascites and in some apparently normal chickens . These hearts appeared flaccid, had a thin ventricular muscle wall, a nd lacked the normal tone of healthy heart muscle. Ventricular enlarge ment (mostly dilation) and AV valve degeneration (endocardiosis) were observed as early as 7 to 10 days of age and throughout the remaining growth period in broilers with or without ascites. The hearts from 264 ascitic and 255 apparently normal commercial broilers were used for q uantitative analysis, with emphasis on dilatory changes of the ventric uli and detailed evaluation of the atrioventricular (AV) valves. The l esions of the AV apparatus and the degree of dilation of the ventricul i were graded according to a priori established standards, and categor ized as mild, moderate or severe. Severe or moderate dilation of both the right and left ventricle were observed more frequently (P < 0.001) in ascitic birds than in normal birds. Of hearts from apparently norm al birds, 34 and 61% had grossly normal right and left ventricle, resp ectively. Overall, 30% of ascitic birds had a grossly normal left vent ricle, but some degree of right ventricular dilation was found in all ascitic birds. Prominent endocardiosis was a common feature in a major ity of hearts from ascitic birds and in some apparently normal birds. Endocardiosis of the left AV valves was observed considerably more fre quently (P < 0.001) than of right AV valves. Most severe lesions were found on left AV valves, and consisted of nodules or coalescing format ions associated with annulus, valve cusps, chordae tendineae, and some times spread to the mural endocardium in the vicinity of the valve app aratus. Frequently the cusps appeared thickened and rigid, and had rol led edges. Chordae tendineae were frequently thickened, and sometimes ruptured. These severe left AV valve lesions were found most frequentl y (P < 0.001) in the hearts from ascitic birds (52%) in comparison to apparently normal birds (18%). The right AV valve lesions were mainly in the form of small nodules found around the orifice, and less freque ntly seen on the muscular leaflets of the right valve. Only in a few i nstances the nodules were larger, -ranging from 1 to 3 mm in diameter. The severity of gross lesions on the left AV valve were indicative of stenosis and/or insufficiency of the valve apparatus. A hypothesis th at left atrio-ventricular valve degeneration and left ventricular dila tion should be considered as a possible aetiologic association with pu lmonary hypertension, right ventricular failure, and ascites in broile r chickens is presented and discussed.