Larger Cell Size in Rabbits With Heart Failure Increases Myocardial Conduction Velocity and QRS Duration

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Abstract
Background— Patients with heart failure (HF) have an increased QRS duration, usually attributed to decreased conduction velocity (CV) due to ionic remodeling but which may alternatively result from increased heart size or cellular uncoupling. We investigated the relationship between QRS width, heart size, intercellular coupling, and CV in a rabbit model of moderate HF and in computer simulations. Methods and Results— HF was induced by pressure-volume overload. Heart weight (21.1±0.5 versus 10.2±0.4 g, mean±SEM; P P L ; 79±2 versus 67±4 cm/s; P T ; 43±2 versus 37±2 cm/s; P TM ) was unchanged (25±2 versus 24±1 cm/s; P =NS). Patch-clamp experiments demonstrated that sodium current was unchanged in HF versus control. Immunohistochemical experiments revealed that connexin43 content was reduced in midmyocardium but unchanged in subepicardium. Myocyte dimensions were increased in HF by ≈30%. Simulated strands of mammalian ventricular cells (Luo-Rudy dynamic model) revealed increased θ L and θ T with increased myocyte size; however, increased CV could not compensate for increased strand size of longitudinally coupled cells, and consequently, total activation time was longer. Conclusions— Increased myocyte size combined with the observed expression pattern of connexin43 yields increased θ L and θ T and unchanged θ TM in our nonischemic model of HF. A hypertrophied left ventricle together with insufficiently increased θ L and unaltered θ TM results in a prolonged QRS duration.