Ageing of the population, life style and increased survival of patients with cardiovascular diseases has favoured the development of heart failure and made of it a growing epidemiological problem in developed countries. The understanding of the mechanisms of progression of this disease and the recent advances in medical therapy has improved symptoms and prognosis of these patients. However, the degree of disability, the impairment in quality of life and mortality rates of patients with advanced heart failure remain high. Despite appropriate treatment, progressive mechanical and electrical remodeling of the heart may occur, favouring the development of arrhythmias (increasing the risk of sudden death and development of atrial fibrillation) and conduction disturbances that will further complicate the course of this disease and the treatment of these patients.
Up to one third of the patients with systolic heart failure, may present signs of intra-ventricular conduction delay manifested by a broad QRS complex on the electrocardiogram, which is considered a surrogate for electrical dyssynchrony. These ventricular conduction disturbances have proven to be associated to more advanced heart disease and a worse prognosis. They usually take the form of left bundle branch block and produce a dyssynchronous contraction that reduces myocardial efficiency, further impairing systolic and diastolic function and worsening mitral regurgitation
