ASYMMETRIC THICKNESS OF THE LEFT-VENTRICULAR WALL RESULTING FROM ASYNCHRONOUS ELECTRIC ACTIVATION - A STUDY IN DOGS WITH VENTRICULAR PACINGAND IN PATIENTS WITH LEFT-BUNDLE-BRANCH BLOCK

Various kinds of abnormal, asynchronous electric activation of the lef t ventricle (LV) decrease mechanical load in early Versus late activat ed regions of the ventricular wall. Because myocardium usually adapts its mass to changes in work load, we investigated by echocardiography whether regional differences in wall thickness are present in two kind s of asynchronous electric activation of different origin and conducti on pathway: epicardial ventricular pacing in dogs and left bundle bran ch block (LBBB) in patients. In six dogs, 3 months of epicardial LV pa cing at physiologic heart rates decreased the thickness of the early a ctivated anterior wall by 20.5 +/- 8.1% without significantly changing LV cavity area and septal thickness. In a retrospective study of 228 LBBB patients, the early activated septum was significantly thinner th an the late activated posterior wall. The asymmetry most pronounced wa s as large as 10% in 28 patients with LBBB and paradoxic septal motion . No difference in regional wall thickness was present in 154 control patients. In conclusion, chronic asynchronous electric activation in t he heart induces redistribution of cardiac mass. This redistribution o ccurs in hearts, which differ in impulse conduction pathway, disease, and species and is characterized by thinning of early versus late acti vated myocardium.