Asymmetric thickness of the left ventricular wall resulting from asynchronous electric activation: A study in dogs with ventricular pacing and in patients with left bundle branch block

Abstract

Various kinds of abnormal, asynchronous electric activation of the left ventricle (LV) decrease mechanical load in early versus late activated regions of the ventricular wall. Because myocardium usually adapts its mass to changes in workload, we investigated by echocardiography whether regional differences in wall thickness are present in two kinds of asynchronous electric activation of different origin and conduction pathway: epicardial ventricular pacing in dogs and left bundle branch block (LBBB) in patients. In six dogs, 3 months of epicardial LV pacing at physiologic heart rates decreased the thickness of the early activated 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 than the late activated posterior wall. The asymmetry most pronounced was 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 the heart induces redistribution of cardiac mass. This redistribution occurs in hearts, which differ in impulse conduction pathway, disease, and species and is characterized by thinning of early versus late activated myocardium.

The mechanical and metabolic basis of myocardial blood flow heterogeneity

“…They also showed that there was a striking inverse relationship between isovolumetric phase strain and ejection phase strain: those regions shortening early against a relaxed ventricle contributed less to the external work of the heart. Late-activated regions hypertrophy with chronic pacing and earlyactivated region atrophy (77,98).…”

Electrocardiographic markers of left ventricular systolic dysfunction in patients with left bundle branch block

“…It also contributes to functional impairment of myocardium and negatively affects perfusion, haemodynamics, systolic, and diastolic functions [10]. LBBB is usually accompanied by LV dilatation and reduced EF [11][12][13]. The perfusion of the septum is impaired in patients with LBBB even in the absence of coronary artery disease [14,15].…”

Pacing Therapy in Infants and Children with Congenital and Acquired Complete Atrioventricular Block: Optimal Pacing Strategies, Management, and Follow-up

“…Recent studies have demonstrated that pacing from the RV apex may induce left ventricular dyssynchrony (Thambo et al, 2004;Tops et al, 2007;Cheng et al, 2009). It has long been recognized that ventricular dyssynchrony caused by a variety of cardiovascular diseases, including heart failure, ventricular preexcitation, and left bundle branch block mediate ventricular remodelling and subsequently myocardial dysfunction (Prinzen et al, 1995;Kass, 2008;Udink ten Cate et al, 2010a;Udink ten Cate et al, 2010b). Evidence is now emerging that pacing-induced ventricular dyssynchrony disturbs myocardial regional workload and wall stress, which may result in wall motion abnormalities, myocardial perfusion defects, changes in coronary blood flow, increased left ventricular cavity volume, and asymmetrical changes in left ventricular wall thickness (Karpawich, 2004;Kass, 2008;Cheng et al, 2009).…”