Cardiodynamic Effects of Experimental Bundle-Branch Block in the Dog

• There is disagreement as to whether bundle-branch block causes a delay in con-traction of the homolateral (blocked) ven-tricle. Previous studies in animals and man have produced conflicting results. The major-ity of investigators have found that a delay in electrical activation of one of the ven-tricles, as occurs in bundle-branch block or an extrasystole originating in the contra-lateral ventricle, produces a delayed mechani-cal contraction of the ventricle. Others have concluded that no such electrical-mechanical relationship consistently occurs in man or the experimental animal. Many of the pre-vious studies have used indirect methods for timing the mechanical events of the heart. Recently, however, there have been studies in man- 2 and in the experimental animal" using simultaneous right and left intraven-tricular pressures as a method for deter-mining the onset of isometric contraction of the respective chambers. Previous animal studies have not been performed, to our knowledge, with pressure measurements in the closed-chest animal with chronic bundle-branch block. The present study was under-taken to evaluate further electrical-mechani-cal relationships in the canine heart under these conditions. Methods The experiments were performed on medium-sized mongrel dogs under pentobarbital anesthesia (25 mg./Kg.). Simultaneous right and left cardiac catheterizations were performed by posterior per-cutaneous transthoracic approach using no. 18 thin