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Introduction
Sleep-disordered breathing (SDB) is common in patients with heart failure (HF), 1 2 both in form of obstructive sleep apnoea (OSA) and central sleep apnoea (CSA), and impacts on disease progression and prognosis. 3 4 Adverse effects of SDB in HF are mainly mediated by increased sympathetic nervous system activity, leading to high mortality rates. 5 6 In patients with OSA, the combination of recurrent apnoeas, hypoxia and arousal is accompanied by an increase in chemoreflex-mediated adrenergic activity that also persists during daytime. 7-9 Similarly, in patients with HF and CSA, a further increase in resting sympathetic drive has been demonstrated during apnoea episodes 10 11 leading to adrenergic modulation of chemoreflex and altered ventilatory control. 12 Increased urinary and blood levels of cathecolamines, higher cardiac noradrenaline spillover 13 and impaired muscle sympathetic nerve traffic 5 11 have been demonstrated in patients with HF and SDB and it has been reported that ventilatory therapy reduces sympathetic nervous system activity. 14 15 However, few data are available on the relationship between SDB and cardiac sympathetic innervation, assessed at myocardial level, in patients with HF. In the present study we sought to investigate the prognostic relationship between SDB and cardiac sympathetic innervation, assessed by 123 I-metaiodobenzylguanidine (123 I-MIBG) imaging, in patients affected by systolic HF.
Materials and methods
From April 2010 to April 2014, 94 consecutive patients with systolic HF referring to the HF Unit at Federico II University of Naples, Italy, were included in the analysis. Study inclusion criteria were diagnosis of systolic HF (left ventricular ejection fraction, LVEF <=45%) evaluated by transthoracic echocardiograms in at least two consecutive determinations, stable HF since at least 6 months (New York Heart Association, NYHA I-III), no acute coronary syndrome or acute HF in the 6 months before, no planned revascularisation in the next 6 months, ability to tolerate nocturnal cardiorespiratory monitoring and capability to sign informed consent. At enrolment all patients were on optimised medical therapy for HF. All patients gave written informed consent and local ethic committee approved the protocol.
Study procedures
On the first day patients' medical history and demographic data were collected. A complete clinical examination and transthoracic echocardiography were performed and nocturnal cardiorespiratory monitoring equipment applied. The day after, patients removed the...