Editor's Note: Commentary based on Ding N. Prevalence and Risk Factors of Sleep Disordered Breathing in Patients With Rheumatic Valvular Heart Disease. J Clin Sleep Med 2013;9:781-7.

Background

Heart Failure is a major health problem in United States and its prevalence continues to rise with ageing population. Guidelines emphasize intense pharmacologic as well as non-pharmacologic measure to reduce the associated morbidity and mortality. Sleep disordered breathing (SDB) is being increasing recognized as a common association with heart failure, be it reduced or preserved ejection fraction and contributes to adverse outcomes. The pathophysiologic mechanism underlying sleep disorder in heart failure is complex and there is often a flux between the types of sleep apnea (obstructive versus central) as dictated by the clinical course. Studies in heart failure patients evaluating sleep disorder have included minority of patients with primary rheumatic valvular etiology due to its low prevalence in the western world. Henceforth, little is known about the prevalence, characteristics and risk factors associated with sleep disorder in this population.

Methods

Authors studied 260 patients presenting with the diagnosis of rheumatic heart disease, referred for valve surgery and had complete record of full night sleep study. Baseline characteristics, detailed echocardiographic analysis, polysomnography results, functional class analysis using New York Heart Association and the six minute walk were collected.

Results

Patients with biventricular valvular involvement had higher incidence of SDB, predominantly of the central type in comparison to the left sided alone. These patients also had higher numbers of worse NYHA functional class with poor six minute walk and lung to finger circulation time. Among patients with SDB, those with central sleep apnea (CSA) exhibited poor functional class, worse left ventricular ejection fraction and higher arrhythmia burden. Risk factors were more often identified with CSA, and varied depending on the gender and the type of SDB. Decreasing Pao2, increasing age and six minute walk < 300m were identified as the risk factors for entire cohort. Left ventricular dysfunction was not associated with poor outcome in SDB patients.

Conclusion

The study confirms many previously established risk factors associated with SDB in a population which is unique to developing and underdeveloped countries, with valvular heart disease and preserved LV function. Biventricular valvular involvement confers higher heart failure functional class and is associated with increased burden of SDB, particularly CSA. Six minute walk distance < 300 m and PaO2 < 85mm Hg were identified as risk factors associated with SDB in this cohort.

Commentary/Perspective

The study revealed some interesting findings. The most striking fact about the study was higher prevalence of SDB, predominantly of the CSA in these patients with biventricular rheumatic valvular involvement. Historically, the incidence of CSA is higher with worse LV function and higher body mass index (BMI) and the type of SDB tends to shift to obstructive type with improvement in LV function. The incidence of SDB and that of CSA in this study was tied with poor heart failure functional class and 6 minute walk distance, thus implying worse disease, despite a comparably normal LV function and BMI. Several well-described risk factors associated with SDB in patients with LV dysfunction were similarly observed in patients with heart failure of rheumatic valvular etiology. Hypoxia with PaO2 of < 85mm Hg and six minute walk distance of < 300m were identified as new independent risk factors for any type of sleep disorder is not surprising as they invariably imply advanced stage in the disease course. Take home message from this study would be to alert the clinicians to keep a high index of suspicion to screen patients with clinical heart failure for SDB , as there is growing evidence to suggest presence of occult central as well as obstructive sleep apnea in patients with normal BMI as well as preserved LV function.

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References

1. Javaheri S. A mechanism of central sleep apnea in patients with heart failure. N Engl J Med 1999;341:949–954.
2. Javaheri S, Parker TJ, Liming JD, et al. Sleep apnea in 81 ambulatory male patients with stable heart failure: types and their prevalences, consequences, and presentations. Circulation 1998;97:2154–2159.

Keywords: Heart Failure, Morbidity, Prevalence, Sleep Apnea Syndromes, Sleep Wake Disorders

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