Sleep Apnea's Impact on a Patient's Heart

Though sleep apnea often causes atrial fibrillation, there is a lack of awareness.

Neglecting sleep disorders is easy. They are widely prevalent, and yet poorly diagnosed and an underrated risk factor for many health conditions. Sleep apnea, one of the most common sleep disorders touches 3-7% of the population(1). It increases the risk of high blood pressure, diabetes, and various heart disorders. But the fact that sleep apnea could be a reason behind the heart arrhythmia is often neglected.

Sleep apnea is often divided in to obstructive and central. Obstructive is caused mainly due to obesity, or some changes in the throat, that lead to obstruction of the airway while sleeping. On another hand, central sleep apnea is caused due to poor control of breathing by the brain when a person is sleeping.

Atrial fibrillation (AF) is one of the most common problems of heart rhythm. It is a disorder when the upper chambers of the heart do not beat in a regular fashion, thus affecting the blood flow in the whole of the body. People with atrial fibrillation would often complain about feeling a thumping heart, light-headedness, weakness, nausea, shortness of breath, and chest pain. AF is the cause of more than 750,000 hospitalizations and more than 130 000 deaths in the US each year(2). It also increases the risk of heart-related deaths by two-fold and increases the risk of stroke by five-fold, yet the survey shows that only one-third of Americans are aware of such risks(3,4).

AF has now been recognized as an independent risk factor for stroke, while sleep apnea has been accepted by the scientific community to increase the risk of AF. Professional organizations like the European Society of cardiology already recommend the screening for sleep apnea in all the patients suffering from AF (5).

What causes atrial fibrillation in sleep apnea?

It has been proposed that sleep apnea leads to a remodeling of the heart, chronic systemic inflammation that results in AF(6).

Inflammation, hypoxia and oxidative stress

Repeated episodes of sleep apnea at night cause a decrease in oxygen in blood and increase in the concentration of carbon dioxide. It triggers the so-called chemoreflex leading to increased activity of the sympathetic nervous system, causing an upsurge in heart rate (tachycardia) and blood pressure. Elevation in blood pressure and cardiac rhythm further increases the cardiac load and need for oxygen, hence injuring the heart muscles and conduction system.

After the fit of hypoxia in sleep apnea, there is re-oxygenation, which causes the increased oxidative stress, inflammation, cardiac remodeling.

Substantially negative intrathoracic pressure

Forced inspiration due to the blockage of the respiratory pathway in sleep apnea causes negative pressure in the thoracic cavity, which disturbs the working of heart by creating unwarranted changes in hemodynamics. The heart has to work harder in the phases of low intrathoracic pressure, which leads to hypertrophy of the cardiac muscles. These repeated swings in intrathoracic pressure over an extended period have an adverse effect on working of the heart. This negative intrathoracic pressure has been found to be a potent trigger for AF.

Hyperactivity of the cardiac autonomic nervous system

During our sleep, two important patterns called NREM and REM are repeated. In NREM there is an increase in parasympathetic activity, and slowdown in all the bodily function, metabolism, body temperature and heart rate. Later in night NREM is followed by the REM, which is characterized by increased sympathetic activity and heart rate. That is why people who have a weak heart for some reasons, often suffer from a heart attack in the early morning or first half of the day.

But in those suffering from sleep apnea, this sleep pattern is disturbed, and baseline sympathetic activity is much higher in them. Sympathetic overactivity along with hypoxia in sleep apnea leads to increased cardiac activity, cardiac load, and high blood pressure. This increased neural activity in many cases may serve as the initiator of AF(7).

Treating sleep apnea to reduce to risk of atrial fibrillation

Sleep apnea often remains the underlying cause of refractory AF. Hence the importance of timely diagnosis and treatment of sleep apnea. A person who suffers from sleep apnea would usually have headaches and fatigue in the morning, would often be woken up at night due to the pauses in breathing, and spouse may also complain about loud snoring.

In cases of AF along with sleep apnea, drug therapy would not always be an effective option for the treatment of an obstruction in the respiratory tract and improving the sleep quality. CPAP is the golden standard for the treatment of obstructive sleep apnea. It is also one of the most studied interventions. CPAP therapy has been proven to have a beneficial effect on the cardiac remodeling.

In one of the cohort study by Shukla et al. analyzed the effectiveness of CPAP therapy on the reduction of occurrence of AF. The author found that CPAP was associated with significant reduction in the incidence of AF.  The benefit of CPAP was substantial both in those on medical drug therapy and who underwent ablation for AF. The effect was consistent in various population groups, thus proving the efficacy of CPAP(8).

Autonomic neuromodulation is another emerging therapy for preventing atria fibrillation in those suffering from sleep apnea. While renal nerve denervation (RND) has failed to prove its efficacy in drug-resistant hypertension,but it is showing promise in improving blood pressure and prevention of atrial fibrillation in those suffering from sleep apnea (9).

Considering the high prevalence of atrial fibrillation in the US and its relation to sleep apnea, it is vital to appreciate the significance of sleep apnea in the development of AF. It is essential to adequately treat sleep apnea to improve outcomes in those suffering from atrial fibrillation.

References

Punjabi NM. The Epidemiology of Adult Obstructive Sleep Apnea. Proc Am Thorac Soc. 2008 Feb 15;5(2):136–43.

Atrial Fibrillation Fact Sheet|Data & Statistics|DHDSP|CDC [Internet]. 2017 [cited 2017 Nov 26]. Available from: https://www.cdc.gov/dhdsp/data_statistics/fact_sheets/fs_atrial_fibrillation.htm

AHA. What is Atrial Fibrillation (AFib or AF)? [Internet]. 2017. Available from: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/AboutArrhythmia/What-is-Atrial-Fibrillation-AFib-or-AF_UCM_423748_Article.jsp#.WhrvM1WWbIX

Wolf PA, Abbott RD, Kannel WB. Atrial fibrillation as an independent risk factor for stroke: the Framingham Study. Stroke. 1991 Aug 1;22(8):983–8.

Kirchhof P, Benussi S, Kotecha D, Ahlsson A, Atar D, Casadei B, et al. 2016 ESC Guidelines for the management of atrial fibrillation developed in collaboration with EACTS. Eur Heart J. 2016 Oct 7;37(38):2893–962.

Gottlieb DJ. Sleep Apnea and the Risk of Atrial Fibrillation Recurrence: Structural or Functional Effects? J Am Heart Assoc. 2014 Jan 3;3(1):e000654.

Zhang L, Hou Y, Po SS. Obstructive Sleep Apnoea and Atrial Fibrillation. Arrhythmia Electrophysiol Rev. 2015;4(1):14–8.

Shukla A, Aizer A, Holmes D, Fowler S, Park DS, Bernstein S, et al. Effect of Obstructive Sleep Apnea Treatment on Atrial Fibrillation Recurrence: A Meta-Analysis. JACC Clin Electrophysiol. 2015 Mar 1;1(1–2):41–51.

Jaén-Águila F, Vargas-Hitos JA, Mediavilla-García JD. Implications of Renal Denervation Therapy in Patients with Sleep Apnea. Int J Hypertens [Internet]. 2015 [cited 2017 Nov 26];2015. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4605362/