The link between obstructive sleep apnea (OSA) and cardiovascular disease is increasing in awareness amongst researchers and clinicians worldwide. Evidence has established that sleep apnea is associated with hypertension, atrial fibrillation (AFib), coronary artery disease, congestive heart failure and stroke. According to the widely cited Wisconsin Sleep Cohort Study published in 1993, 4% of middle-aged men and 2% of middle-aged women (ages 30-60 years) have OSA. An update published in 2013 now suggests that the current prevalence estimates of moderate to severe OSA are 10% among 30–49-year-old men; 17% among 50–70-year-old men; 3% among 30–49-year-old women; and 9% among 50–70 year-old women. These estimated prevalence rates represent substantial increases over the last two decades.¹ Additional medical research will help navigate this developing and compelling association.

It is important for the cardiologist to recognize and embrace the fact that multiple sleep disorders have a direct adverse affect on the cardiovascular system. At present the opportunity and role of the physicians in this convergence are ill defined and warrant an evolutionary team approach consisting of cardiologists and sleep physicians working cooperatively to tackle this health care crisis.

The purpose of this article is to provide educational information for cardiologists and raise awareness about the significance of the convergence between cardiovascular diseases and sleep disorders. I am very enthusiastic to share information of this type with my colleagues and hope to stimulate growing interest in the importance of our role in this dynamic relationship.

As a clinician early on in my private practice experience it become apparent to me that a high percentage of my patients manifested signs and symptoms of sleep apnea. To this end I began referring patients to sleep medicine colleagues for testing and treatment. Many months later when these patients returned for follow-up, I noticed that they were clinically improved and their cardiovascular disease seemed to be more stable. This prompted me to explore the evidence available at the time linking the two disease entities. I then continued to incorporate sleep medicine to a greater degree in my cardiology practice. While there was not an abundant amount of robust information, there was enough to prompt me to pursue more formal training, additional education and board certification in sleep medicine.

Association: Over the past couple of decades, clinical and academic research as well as epidemiological population based studies and trials have clearly established a close association between sleep apnea and cardiovascular diseases of many types. The strongest association involves HTN resulting in the addition of sleep apnea as an identifiable cause in JNC-7 which also concludes that CPAP therapy can also be an effective treatment of HTN. Additional close associations between cardiovascular disease and sleep apnea include arrhythmias such as AFib, CHF, CAD/MI, CVA and Type II Diabetes. If you also consider the increasing prevalence of obesity worldwide, the argument supporting the importance of recognizing sleep apnea and cardiovascular disease being convergent becomes even more compelling. In addition, the risk factors for both disease entities are virtually identical.

Statistical facts about sleep apnea also merit the close attention of the cardiovascular disease specialist:

• 50% of OSA patients are hypertensive²
• An estimated 30% of hypertensive patients also have OSA²
• OSA patients have diminished heart rate variability and increased BP variability²
• Nocturnal arrhythmias have been shown to occur in up to 50% of OSA patients²
• 71% of all patients diagnosed with cardiovascular disease have sleep apnea³
• Studies have reported a 53% prevalence of OSA and CHF⁴
• Obstructive sleep apnea is independently associated with sudden cardiac death, as reported in the August 2013 Journal of the American College of Cardiology⁵

There is also a growing body of evidence that other sleep disorders are associated with cardiovascular disease. Insomnia and Restless Legs Syndrome are both associated with HTN, CAD and/or CHF.^6,7 Additional research is under way to establish stronger associations and evaluate outcomes.

Treatment: The impact of sleep apnea treatment on cardiovascular disease is also quite revealing:

• There is a clear body of evidence showing that there is an association between atrial fibrillation and OSA. In a landmark study in 2004, Gami et al. showed that after adjusting for body mass index, neck circumference, hypertension, and diabetes mellitus, approximately half of patients with AFib were likely to have OSA (adjusted OR 2.19, 95% CI 1.40–3.42).⁸ Treating obstructive sleep apnea improves AFib recurrence after both cardioversion and ablation.⁹
• The data from small studies on CPAP and CHF in patients with obstructive and central sleep apnea reveal benefits in morbidity and mortality with improved LV hemodynamics and LVEF.^10,11 There are ongoing large scale studies evaluating both morbidity and mortality in the USA and Europe utilizing more sophisticated PAP devices.
• OSA is associated with an increased risk for CAD.¹² Treatment has been shown to improve long-term cardiovascular outcomes.¹³
• Adherence to CPAP improves glycemic control in patients with OSA and type 2 diabetes.¹³ CPAP also improves markers of inflammation.¹⁵

Conclusions: As we enter a new paradigm of healthcare delivery in an already evolving healthcare system, we are faced with ever increasing burdens forcing us to balance the needs of our patients with our professional careers. The trend within cardiology practices has led many to opt for employment in large healthcare institutions and away from traditional private practices. This has resulted in a degree of financial stability which comes at a cost of the employee physician's need to exercise a greater degree of efficiencies with concurrent increased pressure on productivity. When considering this coupled with the gradual adoption of the Affordable Care Act, hospitals and their cardiology employees are compelled to address head on the critical problem of inpatient readmissions.

Within cardiology, it is clear that we have made great strides in managing our CHF, arrhythmia and CAD patients but readmission rates especially for CHF and recurrent AFib remain a significant problem. Considering the association between these disorders and sleep apnea, the cardiologist is presented with an interesting opportunity to take a leadership role in identifying patients with sleep apnea, participate in their diagnosis and incorporate our sleep physician colleagues in the sleep apnea management team.

An opportunity also exists in the diagnostic test arena with home sleep testing. There has been tremendous growth in the last several years with many home sleep test monitors available that not only have validation studies compared to the traditional in-lab testing but also data showing that patient outcomes are no different based on how their diagnosis was made.¹⁶ These devices are cost effective and, when appropriately utilized, provide an excellent and easy method for streamlining the diagnostic testing process. So, cardiologists can easily incorporate home sleep testing in their practices.

My response to the issue brought forth by this article, "The Role of the Cardiologist in Sleep Disordered Breathing Management; "Opportunity or Obligation?" is a resounding YES. It is both an opportunity and an obligation for us to accept this as an integral part of our practice to deliver the best care to our patients. A presentation at the European Society of Cardiology, 2012 is titled and concludes, "Sleep Apnea is a major unrecognized cardiovascular risk factor"¹⁷ of which I would concur.

While we clearly need more rigorous clinical and academic data looking at hard endpoints of MACE, the evidence from published studies clearly links the two disease processes in a more compelling manner than with any other subspecialty. We are all keenly aware that heart disease is the number one cause of mortality in men and women. In addition, we need to recognize epidemiological data suggesting that 40 million people in the USA have sleep disorders of which at least 20 million have OSA. In addition, a recent article published by the CDC concludes that one in four deaths from cardiovascular disease is preventable with healthy lifestyle changes and better management of associated co-morbidities of hypertension, diabetes and obesity.18 Needless to say, all these are linked to OSA.

I would suggest that our opportunity and obligation as cardiovascular disease specialists is to become educated in a more thorough manner on sleep disorders and become proactive in screening and performing or referring for diagnostic testing to the board certified sleep physician for management.

Our cardiology training programs should place a greater emphasis on educating cardiology fellows about the associated sleep disorders, testing modalities and treatment options so it becomes ingrained in their scope of care.

Physicians that are aware of the relationship between sleep and cardiovascular disease have a unique opportunity to make a major impact on the future of global health care. They will be able to enhance quality of life, work with the idea of prevention of major diseases and halt the progression of preexisting diseases. The scope of the cardio-sleep relationship is broad and its depths need to be discovered further. Clinical and academic researchers will brave the existing medical community and search for additional life changing discoveries that link sleep and cardiovascular disease to help refine practice guidelines and establish definitive outcomes data. This research must be cultivated and generously supported.

The recognition of the converging specialties of cardiology and sleep medicine is already in place but more dedicated research is required. We simply see the very tip of the iceberg — but it has given us enough vision to know that we need to dive deeper to learn more about the connection and most importantly, to learn how we can utilize the findings to provide efficient, cost-effective and optimal patient care.

Lee A. Surkin, MD, FACC, FASNC, FCCP is triple board certified in cardiovascular disease, nuclear cardiology and sleep medicine. He is also the founder of the American Academy of Cardiovascular Sleep Medicine which is an organization dedicated to supporting research, promoting awareness and providing education about the convergence of cardiovascular disease and sleep disorders. His private practice in Greenville, NC uniquely combines cardiovascular disease prevention and management with sleep medicine and obesity medicine.

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References

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12. Sorajja D., Gami A.S., Somers V.K., Behrenbeck T.R., Garcia-Touchard A., Lopez-Jimenez F.; Independent association between obstructive sleep apnea and subclinical coronary artery disease. Chest 2008; 133:927-933.
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14. Tasali E, Abraham V, Arohnson R, et al. Effective CPAP treatment of obstructive sleep apnea improves glycemic control in type 2 diabetics. Sleep 2013; June 1-5, 2013; Baltimore, MD. Abstract 0344.
15. Baessler A, Nadeem R, Harvey M, et al. Treatment for sleep apnea by continuous positive airway pressure improves levels of inflammatory markers - a meta-analysis. J Inflamm (Lond) 2013;10:13..
16. Berry RB, Hill G, Thompson L, McLaurin V. Portable monitoring and autotitration versus polysomnography for the diagnosis and treatment of sleep apnea. Sleep 2008;31:1423-31.
17. Costas Tsioufis (P.Penteli, Athens, Greece), Sleep apnea is a major unrecognised cardiovascular risk factor. Oral Presentation at ESC Congress 2012
18. http://www.cdc.gov/vitalsigns/HeartDisease-Stroke/

Keywords: Atrial Fibrillation, Coronary Artery Disease, Coronary Disease, Hypertension, Sleep Apnea, Obstructive, Cardiovascular Diseases

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