Cardiac resynchronization therapy in asymptomatic and mildly symptomatic chronic systolic heart failure: a new era of systolic heart failure management?

T he incidence and prevalence of heart failure syndrome continue to increase, and it therefore remains a significant health problem in developed western countries. It is accompanied by high morbidity and mortality, and significantly affects the burden on health care system as well as the patients’ quality of life. Cardiac resynchronization therapy (CRT) with biventricular stimulation has recently emerged as an adjunctive treatment modality in patients with chronic systolic heart failure and documented electrical and mechanical dyssynchrony. Electrical dyssynchrony may be expressed as atrioventricular, interventricular or intraventricular asynchrony. The latter is associated with the presence of a wide QRS complex (mainly left bundle branch block pattern) and implies that different segments of the left ventricle (LV) do not contract simultaneously, resulting in LV mechanical dyssynchrony. Electromechanical intraventricular asynchrony is associated with diminished stroke volume, susceptibility to mitral regurgitation, impaired LV filling, increased LV wall stress, delayed relaxation time and adverse neurohormonal activation. Biventricular pacing resynchronizes the timing of global LV depolarization and theoretically improves mechanical contractility, with concomitant enhancement of reverse LV remodeling. Many heart failure experts maintain that LV reverse remodeling is achieved due to a therapeutic intervention when ejection fraction (EF) increases by more than 15% and/or the difference between LV end-systolic and end-diastolic volumes increases by more than 10%. The clinical benefit of CRT, especially in terms of mortality and morbidity, has been established in patients with advanced heart failure, who are in functional NYHA class III or IV despite optimal drug treatment. In the majority of recipients, an improvement in heart failure symptoms has been demonstrated by multiple controlled and uncontrolled randomized trials. According to the new guidelines, candidates for CRT include patients with dilated type cardiomyopathy, either ischemic or non-ischemic, EF <35%, QRS width >120 ms, in NYHA class III or IV despite optimal medical therapy (including loop diuretics, bblockers, angiotensin-converting enzyme inhibitors or angiotensin receptor blockers). Despite the undoubted significance of mechanical dyssynchrony, no echocardiographic or magnetic resonance imaging criteria have yet been established in clinical practice. Although CRT is an established treatment modality for patients with advanced systolic heart failure, uncertainty exists Cardiac Resynchronization Therapy in Asymptomatic and Mildly Symptomatic Chronic Systolic Heart Failure: A New Era of Systolic Heart Failure Management?