Chronic heart failure is a complex clinical syndrome that can result from any structural or functional cardiac or non-cardiac disorder that impairs the ability of the heart to respond to physiological demands for increased cardiac output. Chronic heart failure is characterised by symptoms such as exertional breathlessness and fatigue, and signs of fluid retention as well as signs associated with the underlying cardiac disorder. Patients with chronic heart failure suffer from reduced quality of life and a significantly higher risk of morbidity and mortality.~There is cumulating evidence of a high prevalence of sleep breathing disorders in both patients with acute and chronic heart failure. Most of these reports, however, suffer from important limitations including small sample size, retrospective study design, and/or use of pulse-oximetry or cardio-respiratory polygraphy to screen for sleep disordered breathing rather than full-night polysomnography. Hence, previous studies may have underestimated the full scale of concomitant sleep disordered breathing in patients with chronic heart failure. Furthermore, to the best of our knowledge, there is no report on the incidence of sleep disordered breathing in patients with chronic heart failure.~In this context the presence of sleep disordered breathing in patients with chronic heart failure has important prognostic relevance. Pathophysiological effects of sleep apnea include intermittent hypoxia, sympathetic hyperactivity, systemic inflammation, and sleep fragmentation. These factors may contribute to the worsening of cardiac function and explain the reportedly higher risk of cardiac morbidity and mortality in patients with both chronic heart failure and concomitant sleep disordered breathing. Accordingly, the aims of the present study are three-fold. First, to investigate the prevalence of sleep breathing disorders in patients with stable moderate-to-severe chronic heart failure using the diagnostic gold standard of full-night-polysomnography. Second, to assess the two-year incidence of sleep disordered breathing in patients with chronic heart failure. Third, to identify potential risk factors associated with the presence or absence of sleep disordered breathing in patients with chronic heart failure. The latter will be assessed by using lung function measurements, hemodynamic parameters, and laboratory markers of neurohumoral activation, systemic inflammation, and endothelial function in patients with chronic heart failure.~For this purpose 200 patients with stable moderate-to-severe chronic heart failure will be studied during a 2 year-period. Patients with chronic heart failure will be screened for eligibility during their regular visits at 4 independent heart failure outpatients clinic in Vienna. Eligible patients will undergo full-night-polysomnography, lung function testing, non-invasive hemodynamic monitoring, a six minute-walking-test, and laboratory measurements at 6 months intervals for a total of 2 years (4 visits).
Only few prospective studies systematically investigated the prevalence of sleep disordered breathing in patients with stable chronic heart failure. Furthermore there is no report on the incidence rate of sleep disordered breathing in this population. This is a prospective multi-centre study of sleep-disordered breathing in 200 patients with stable moderate-to-severe chronic heart failure. Eligible patients will undergo overnight full-night polysomnography, lung function testing, laboratory measurements, and hemodynamic recordings. Measurements will be repeated at 6 months interval for a follow-up period of two years irrespective of the presence or absence of sleep disordered breathing. The primary outcome variable for this study is the prevalence of sleep disordered breathing in the study population. Secondary outcome variables include the 2-year incidence rate of sleep disordered breathing, quality of life measurements, exercise capacity, sleep quality, hemodynamic measurements, and laboratory markers of neurohumoral activation, systemic inflammation, and endothelial function in the study population.