[Mitral regurgitation in patients with systolic heart failure: more than a bystander].

Limitation of exercise capacity is a hallmark of chronic congestive heart failure (HF), varying directly with the severity of the disease. Muscular fatigue and dyspnea on exertion are the most common symptoms of exercise intolerance; however, their origin is still not fully explained. Heart failure is a multifaceted clinical syndrome characterized by the inability of the heart to generate cardiac output at levels capable of meeting the metabolic needs of the organism associated with metabolic and inflammatory disorders and neurohormonal activation. Several studies have shown that exercise intolerance in patients with chronic HF results from a complex interaction between the pulmonary, cardiovascular, skeletal muscle, hematopoietic, and neurohumoral systems. Mechanisms that could limit exercise capacity include the heart’s inability to sufficiently raise cardiac output during effort, chronic elevated systemic vascular resistance, abnormal peripheral vasodilatatory capacity, and abnormal distribution of blood flow with subsequent tissue hypoperfusion, metabolic dysfunction in skeletal muscles, and impaired pulmonary ventilation capacity, all of which are characteristics of HF. The measurement of respiratory gas exchange during a maximal exercise test, used to obtain peak oxygen consumption, is established as an objective and reproducible method for assessing exercise capacity and prognosis in patients with HF. The 6-min walk test (6MWT) is a simple test that does not require expensive equipment or advanced training for technicians. The patient is asked to walk the longest distance possible on a walking course (eg, a corridor), preferably at least 30 m long, in a set interval of 6 min. Furthermore, due to its wide availability and the safety and ease of implementation, it is being used increasingly as an alternative to cardiopulmonary exercise testing to evaluate the functional capacity of patients with HF. The 6MWT is considered a submaximal exercise that mimics everyday activities and is generally well tolerated by patients. The distance walked during this test is a strong and independent predictor of morbidity and mortality in patients with left ventricular (LV) dysfunction.