P.E. VARDAS, E. SIMANTIRAKIS, S.E. SCHIZA
Sleep apnoea syndrome is a serious health problem that according to the National Institute of Health afflicts 18 million Americans. Its incidence is estimated to be 4% in men and 2% in women in a population of middle-aged adults considered to be healthy [1]. Sleep apnoea is divided into two types, obstructive and central. Obstructive sleep apnoea syndrome is defined as repeated episodes of upper airway occlusion during sleep with consequent excessive daytime sleepiness, impaired quality of life, and abnormal car- diopulmonary function. The central type of the syndrome is characterised by simultaneous absence of inspiratory airflow and respiratory movements due to dysfunction of the central respiratory control mechanisms. Patients with sleep apnoea display increased morbidity and mortality, mainly because the syndrome is linked to an increased risk of cardiopulmonary dis- eases [2], and also have an increased risk of being involved in traffic acci- dents [3], as well as a decline in their family, social, and professional lives [4].
Sleep Apnoea Syndrome Therapy
Central Sleep Apnoea
The central type of apnoea is often seen in patients with congestive heart failure (CHF). Its appearance has known to be dependent on the cause and degree of seriousness of CHF, and SAS has been recorded in 40–60% of patients with CHF [5, 6]. Its presence is related to the patients’ prognosis [7]
and the progress of CHF, as it is associated with increased sympathetic nerve activity, higher urinary and plasma norepinephrine concentration, and, pos- sibly, elevated endothelin.
Cardiology Department, University Hospital of Crete, Heraklion, Greece
The haemodynamic improvement of patients with CHF is often associat- ed with a significant reduction of central sleep apnoea. However, in cases where despite therapy of CHF, the patients continue to suffer from central sleep apnoea, more drastic therapy is required. Treatment with theophylline or the nocturnal administration of oxygen has been used, but evaluations show that, although the seriousness of the symptoms may be reduced, the long-term improvement of the patients’ prognosis remains an unknown quo- tient. Continuous positive airway pressure (CPAP) therapy has been found to increase ejection fraction and the transplant-free survival rate [7, 8], but a number of studies have shown that patients with CHF often do not tolerate CPAP therapy, quite apart from the fact that the ventilation device is cum- bersome and constraining for the patient [9, 10]. The efficacy of CPAP in CHF patients with central sleep apnoea may be related to a decrease in the obstructive component accompanying central sleep apnoea or may be due to some direct haemodynamic effects of CPAP.
Recently, cardiac pacing has been investigated as an alternative method of therapy for sleep apnoea. In one well-designed study by Garrigue et al.
[11] in patients with mildly reduced function of the left ventricle who were being paced for conventional indications, atrial pacing at a rate 15 bpm higher than the average nocturnal heart rates significantly reduced episodes of central type sleep apnoea. Certainly, further studies are needed to confirm the findings and to evaluate whether the beneficial result continues over the long-term and whether there is an improvement in the quality of life and prognosis of such patients.
In addition, recently the role of cardiac resynchronisation therapy (CRT) as a therapy for central sleep apnoea and Cheyne–Stokes breathing in patients with CHF was investigated. In these patients it is known that CRT improves the haemodynamic and functional status and reduces mortality. Concerning cen- tral sleep apnoea, it was found that CRT led to a significant decrease in Apnoea Hypopnoea Index (AHI) (19.2 ± 10.3 to 4.6 ± 4.4, P < 0.001) and Pittsburg Sleep Quality Index (PSQI) (10.4 ± 1.6 to 3.9 ± 2.4, P < 0.001) without Cheyne–Stokes respiration and to a significant increase in Sao2min (84 ± 5%
to 89 ± 2%, P < 0.001) [12]. So, CRT led to a clear reduction of central sleep apnoea and to an increased quality of sleep in patients with heart failure and sleep-related breathing disorders. However, further studies are necessary to evaluate the prognostic implications of breathing patterns and their therapy in patients with CHF.
Obstructive Sleep Apnoea
Obstructive apnoea has been associated with numerous cardiopulmonary diseases, particularly arterial hypertension, stroke, cardiac arrhythmias, and
pulmonary hypertension. Our understanding of the nature and pathophysi- ology of the disorder is very limited. Anatomical narrowing of the airway, inversed collapsibility of the airway tissues, disturbance in reflexes that affect upper airway calibre, and pharyngeal muscle function all contribute to upper airway occlusion during sleep [13]. However, there is much data to suggest that obstructive sleep apnoea is a systematic illness rather than a local abnormality, a manifestation of a metabolic syndrome [14]. To date, a variety of types of therapy have been used, including upper airway surgery, weight loss, oral appliances, and nasal CPAP. From 1981, the latter has been considered the therapy of choice and has proved to be highly effective in alleviating symptoms, reducing morbidity and mortality, and improving quality of life [15–17]. However, patient compliance with CPAP is a problem and has been found to range from 65–80% , mainly because of problems with the nasal mask interface, acceptance of treatment, and poor educational pro- grammes before CPAP titration [18, 19]. Thus new therapeutic methods remain the aim of ongoing research. Recently, it was found that increasing and stabilising the cardiac rhythm during sleep by atrial pacing can be help- ful in patients with sleep apnoea [11]. This followed the observation that some patients who had received a pacemaker with atrial overdrive pacing to reduce the incidence of atrial tachyarrhythmias reported a reduction in breathing disorder after the implantation of the pacemaker. In this study, atrial pacing at a rate of 15 bpm higher than the average nocturnal rate led to a reduction not only in episodes of central type apnoea, but also in episodes of obstructive sleep apnoea [11].
Similar results were reported in an earlier small study by Kato et al. [20], which found that after physiological cardiac pacing in three patients with a mixed type of the syndrome, AHI was reduced with the increase in the aver- age heart rate. In such patients, it seems that cardiac pacing, by improving cardiac function and avoiding periodic breathing that may play a role in the pathophysiology of some cases of obstructive sleep apnoea syndrome, could reduce the number of secondary obstructive events. It should be noted, how- ever, that in a more recent study, Pepin et al. [21] stated that they were unable to find beneficial effects of pacing in another, more representative popula- tion with moderate to severe, predominantly obstructive sleep apnoea and mean left ventricular ejection fraction of 64 ± 13% who had been paced for conventional indications.
Furthermore, Luthje et al. [22] found in another study that in patients with normal or impaired left ventricular function, atrial pacing had no effect on the AHI and oxygen desaturation. In another study by our department with a crossover design, we evaluated prospectively the effects of atrial pac- ing after 24 h and 1 month in patients with pure obstructive sleep apnoea syndrome and compared it with the established CPAP therapy [23]. We
found that although CPAP therapy was highly effective, atrial pacing had no effect on the treatment of such patients. From the findings of these studies, it becomes obvious that correctly programmed cardiac pacing may have some place in the therapy of patients with obstructive apnoeic episodes, but fur- ther study is necessary to estimate which subgroups of patients stand to ben- efit.
In conclusion, CPAP therapy, despite the limited compliance, remains the first-line therapy for patients with sleep apnoea syndrome. The role of car- diac pacing in the treatment of such patients still remains obscure and more studies are needed to evaluate whether it could benefit some subgroup or subgroups of patients.
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