1. Introduction

Definitions / Impact. Atrial fibrillation (AF) and sleep apnea-hypopnea syndrome (SAHS)

Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice.1 Accounting for one-third of hospital admissions for cardiac arrhythmias, AF represents an important challenge because it is associated with increased rates of heart failure, thromboembolic events, cerebrovascular accidents, and death.2 The incidence and prevalence of AF increase with age, increasing twofold to threefold between the ages of 60 and 80 years. About 8.8 million people in Europe (2% of the population) and 1 million people in Spain have AF. 3,4 These figures are expected to increase with increases in life expectancy and the progressive aging of the population. In addition to being associated with structural heart disease, AF is also associated with extracardiac factors such as systemic arterial hypertension, diabetes mellitus, obesity, and obstructive sleep apnea-hypopnea syndrome (SAHS), among others.5 In fact, obesity is a well-established risk factor for developing AF, and the risk increases with increases in body mass index.6

SAHS is the most prevalent nocturnal respiratory disorder in our society. It is characterized by repeated episodes of upper respiratory tract obstruction during sleep that lead to a progressive increase in respiratory efforts, intermittent oxygen desaturation, and sleep fragmentation, night after night.7 SAHS should be suspected in any patient who reports intense snoring with observed nocturnal apneas, poor nocturnal rest, and/or excessive daytime sleepiness, especially if the patient is obese or overweight. SAHS has harmful effects on cognitive-behavioral, respiratory, cardiac, metabolic, and inflammatory components of health. Thus, SAHS can lead to worsening quality of life,8 hypertension,9,10 cardiovascular disease,11 cerebrovascular disease,12 and traffic accidents.13 Fortunately, there are effective treatments for SAHS, such as nocturnal administration of continuous positive airway pressure (CPAP). Thus, considering the medical complications of SAHS, its repercussions on social life and work, and its negative impact on the quality of life, this disease is a public health problem, and physicians must therefore identify patients that can benefit from treatment.14 Various studies have shown that the failure to diagnose and treat patients with SAHS results in a twofold to threefold increase in the use of resources.15,16 SAHS is estimated to affect 17% of men and 9% of women 50 to 70 years old. These estimates are clearly higher than those two decades ago and most likely reflect the growing worldwide obesity epidemic17 since obesity is a risk factor for developing SAHS.

2. Concurrence. Risk factors. Common pathophysiological mechanisms

In recent decades, owing to increased obesity/overweight and cardiovascular disease in our society, the prevalences of AF and SAHS have increased. AF and SAHS share risk factors and complex, probably bidirectional, pathophysiological mechanisms; thus, SAHS can lead to AF, but AF can also contribute to the development of SAHS. Epidemiologic studies have identified a significant association between SAHS and AF; patients with SAHS have two to four times greater risk of AF than those without SAHS.18 Moreover, the frequency of cardiac arrhythmias increases as the apnea-hypopnea index, a measure of the severity of SAHS, increases.19 Other studies have found that more than 50% of patients with AF have SAHS.20

Ineffective inspiratory efforts against an occluded upper airway during apnea cause an abrupt decrease in intrathoracic pressure, resulting in an increase in the transmural pressure of the heart, which is also increased by hyperactivation of the sympathetic nervous system. The intermittent low oxygen saturation resulting from repeated apneas are associated with hemodynamic changes in left and right heart function, with progressively abnormal ventricular filling that can favor cardiac dysfunction and is also associated with changes in the structure and function of the atria. SAHS is associated with vascular changes related with the induction of a proinflammatory state and oxidative stress.21 These changes can be partially reversible when the harmful effects of the apneas are eliminated by treatment with CPAP.22

Despite the robust evidence of an association between SAHS and AF, the potential causative role of SAHS in the development of AF remains to be elucidated, since the disorders share risk factors that can confound this association. Experimental studies with animal models suggest that intermittent nocturnal hypoxia and fluctuations in intrathoracic pressure SAHS predispose to AF by electrical and structural remodeling. Different animal models have shown that exposure to increasing degrees of chronic intermittent hypoxia leads to an imbalance in the autonomic system that precipitates electrical changes in the atria that could predispose to the development of AF.23,24 Similarly, murine models have shown that applying fluctuations in intrathoracic pressure that mimic those occurring in SAHS also results in changes in electrical and structural remodeling in the atria that can lead to AF.25

3. Impact of SAHS on AF (progression, recurrence, quality of life).

The prevalence of AF is constantly increasing. Numerous studies have established a correlation between AF and various potentially modifiable risk factors such as obesity, SAHS, hypertension, and sedentary lifestyle. Treating these comorbidities can significantly reduce the negative impact of AF and its rate of recurrence after cardioversion or ablation. Thus, the classical treatment of AF based on cardiac ablation and/or antiarrhythmic drug therapy may not be sufficient. A multidimensional approach combining prevention and optimization of modifiable risk factors for AF is probably necessary to increase the success rate. 26-28

Patients with SAHS also have an increased risk of AF, and nocturnal CPAP reduces this risk. In the first year after electrical cardioversion, the rate of recurrence of AF is 82% in patients with SAHS not treated with CPAP, twice the rate in those correctly treated.29 Moreover, the rate of recurrence of AF in patients who have undergone radiofrequency ablation of the pulmonary veins is higher in those with untreated SAHS than in those without SAHS,30,31 and the rate of recurrence in those with treated SAHS is similar to the rate in those without SAHS. The Outcomes Registry for Better Informed Treatment of AF,32 which included 10132 patients with AF, found that those who had SAHS (18% of all patients) required more admissions to hospital, although the risk of death due to cardiovascular causes and the overall risk of death were similar in patients with and without SAHS. However, patients with SAHS receiving appropriate CPAP treatment were less likely to progress to permanent AF (HR 0.66; 95% CI, 0.46–0.94; p = 0.02). The mechanism through which CPAP reduces the risk of AF recurring remains to be determined, but correcting nocturnal apneas may minimize certain changes in cardiac structure induced by SAHS. On the other hand, CPAP could also mitigate other risk factors (e.g., hypertension) that are common to both SAHS and AF.

4. Benefits of treating SAHS in patients with AF.

Patients with AF and symptoms suggestive of SAHS need to undergo the appropriate diagnostic workup and, if necessary, CPAP treatment for their respiratory disorder to correct apneas to optimize the treatment of AF and especially to reduce its recurrence.33 The American Academy of Sleep Medicine recommends a sleep study to rule out SAHS in patients with AF and compatible symptoms (snoring, observed apneas, poor nocturnal rest, excessive daytime sleepiness).34 For various reasons, however, this recommendation is not vigorously followed in clinical practice. Many specialists managing AF are largely unaware of the high prevalence of concomitant SAHS and clinical suspicion of SAHS in patients with AF is often lower than it should be. Furthermore, the care pathways for referring patients with clinical suspicion are not well standardized in all centers. The current evidence clearly indicates that a multidisciplinary approach is the best way to ensure optimal treatment for AF, with referral to a specialist in sleep medicine for screening for SAHS and nocturnal CPAP treatment when necessary.

To this end, it is crucial to obtain high-quality sleep studies with optimal validity and interpretation to guarantee the correct diagnosis of SAHS. It is equally important to provide individualized management of SAHS. The correct diagnosis and treatment of SAHS by a team of experts in sleep medicine can help guarantee optimal control of AF, preventing recurrence and progression. Finally, appropriately applied nocturnal CPAP benefits patients with SAHS and associated symptoms (poor nocturnal rest, tiredness/fatigue, and daytime sleepiness) by improving sleep quality and overall quality of life.

5. Conclusions

  • The classical treatment of AF based on cardiac ablation and/or antiarrhythmic drugs may be insufficient to ensure optimal management. To increase the success rate of AF treatment, it is best to employ a multidisciplinary approach focusing on multiple dimensions, combining the prevention and optimization of modifiable risk factors, such as SAHS. Left untreated, SAHS can increase the risk of recurrence of AF; fortunately, correcting SAHS with CPAP significantly reduces the risk of recurrence.
  • Patients with AF and symptoms suggestive of SAHS (snoring, observed apneas, poor nocturnal rest, excessive daytime sleepiness) should undergo sleep studies to screen for SAHS. To optimize the treatment of AF and especially to reduce its rate of recurrence, nocturnal respiratory disorders should be treated with nocturnal CPAP to correct apneas.

6. References

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