Central Sleep Apnea in Congestive Heart Failure: Prevalence, Mechanisms, Impact, and Therapeutic Options

Shahrokh Javaheri, M.D.

Disclosures

Semin Respir Crit Care Med. 2005;26(1):44-55. 

In This Article

Epidemiology of Heart Failure, and Sleep Apnea in Patients With Heart Failure

Heart failure is a highly prevalent syndrome.[6] It is estimated that ~5 million Americans, ~2% of the population, have heart failure, with an approximate annual incidence of half a million. It is projected that the prevalence of heart failure will continue to rise into the 21st century. Multiple factors contribute to the rising incidence of heart failure. Among these are increased average life and the aging population, improved therapy of ischemic coronary artery disease, and hypertension.

Heart failure with left ventricular systolic dysfunction is a malignant disorder associated with excess mortality. Several factors, such as left ventricular ejection fraction, high plasma norepinephrine level, and New York Heart Class are predictors of excess mortality.

However, depending on age, a considerable number of patients with symptoms of congestive heart failure may have isolated diastolic heart failure. Similar to systolic heart failure, isolated diastolic heart failure is also associated with excessive morbidity and repeated hospitalization.

The economic impact of heart failure is huge. The estimated cost of heart failure in the United States was ~$29 billion for the year 2003.[6] The cost is largely driven by hospitalization for acute decompensation.

Heart failure is a disorder of the elderly. The prevalence of heart failure increases twofold after age 45 years. The age-dependent prevalence of heart failure may have important bearing with sleep-related breathing disorders, which are also highly prevalent among aged population.

Prevalence of sleep-related breathing disorders has been studied most systematically in heart failure due to left ventricular systolic dysfunction. Systematic studies on diastolic heart failure are lacking.

Studies[7,8,9,10,11,12,13,14,15,16,17] of patients with stable heart failure and left ventricular systolic dysfunction (Fig. 1) show that at least 45% have an apnea-hypopnea index of ≥ 10 per hour, and 40 to 80% have an apnea-hypopnea index ≥ 15 per hour. These indices include both central and obstructive sleep apnea.

The largest prospective study[9] involved 81 ambulatory male subjects with stable, treated heart failure. In this study, 92 consecutive eligible subjects who were followed in a cardiology clinic were asked to participate (88% recruitment). Importantly, no information was sought about symptoms or risk factors for sleep apnea. Using an apnea-hypopnea index of ≥ 15 per hour as the threshold, 41 subjects (51% of all patients) had moderate to severe sleep apnea-hypopnea with an average index of 44 ± 19 (1SD [standard deviation]) per hour.

In systolic heart failure both obstructive and central sleep apnea may occur simultaneously, and at times polysomnographic distinction is difficult. Using arbitrary polysomnographic criteria, 5 to 40% of all patients with systolic heart failure have predominantly obstructive sleep apnea, and 30 to 60% have central sleep apnea (Fig. 1). In our prospective study of subjects with systolic heart failure,[9] ~11% had predominantly obstructive sleep apnea-hypopnea, and 40% had predominantly central sleep apnea (Fig. 1).

Prevalence of central and obstructive sleep apnea in patients with heart failure. Black, central sleep apnea (CSA); White, obstructive sleep apnea (OSA).

Subjects with systolic heart failure and obstructive sleep apnea are significantly heavier, snore habitually, and have a higher systemic blood pressure than subjects with central sleep apnea.[9,10,11,12] In contrast, habitual snoring and obesity are not risk factors for central sleep apnea and are commonly absent in this disorder.[9] This makes it difficult to suspect presence of central sleep apnea on clinical grounds. Furthermore, symptoms of sleep apnea and heart failure are overlapping. Sleep interruption, nocturia, nocturnal dyspnea, waking up unrested, and daytime sleepiness are common in heart failure and may be thought to be due to heart failure itself or related to use of medications. Therefore, in the presence of heart failure, sleep apnea in general, and central sleep apnea in particular, remains occult.[7,9] The overlapping of symptoms of heart failure with symptoms of sleep apnea undoubtedly contributes to underdiagnosis of sleep-related breathing disorders in heart failure. However, there are certain laboratory markers for central sleep apnea. These include presence of hypocapnia, atrial fibrillation, ventricular tachycardia, a low left ventricular ejection fraction, a high New York Heart Class (III and IV), and excess premature ventricular beats and couplets.

As already noted, there is a large range in the reported prevalence rates of sleep apnea and also central versus obstructive sleep apnea in the studies of patients with systolic heart failure (Fig. 1).

The major reasons for such differences are (1) the varied definition of hypopnea (the more sensitive the criteria used; e.g., 2% rather than 4% drop in saturation, the more the number of hypopneas); (2) the pattern of recruitment of patients (e.g., consecutive vs referral); (3) the severity of left ventricular systolic dysfunction (the lower the left ventricular ejection fraction, the more chances to see central sleep apnea); (4) the level of PCO2 (the lower the PCO2, the higher the chances to observe central sleep apnea), the New York Heart Class (the higher the class, the more central the sleep apnea); (5) accuracy of classification of disordered breathing events (obstructive vs central); (6) the absolute number or the percent of the obstructive breathing events relative to the total number of the disordered breathing events (to define predominant obstructive vs central sleep apnea); and (7) the number of heart failure patients with obesity enrolled in different studies. Finally, another potential factor that is important is the accuracy of scoring sleep studies both in terms of scoring sleep (which is the denominator of the apnea-hypopnea index) and distinction of various disordered breathing events already noted.

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