A recent study by Somers et al in the New England Journal of Medicine estimated that Sleep Disordered Breathing (SDB) affects between 17% and 24% of adults in the USA.
Further research conducted at Stanford University's Chanwell Clinic Institute for Heart and Sleep Disorders has shown that nearly all cardiac patients have underlying Obstructive Sleep Apnoea (OSA) syndrome.
Given these startling figures, those behind the research conclude that sleep medicine can have profound effects on the treatment of cardiac patients and should play a major part in their treatment.
In the study at the Chanwell Clinic, apnoea was defined as the complete cessation of breathing or airflow for more than ten seconds with a drop in Sa02 desaturation by 4% or more. Some 98% of cardiovascular patients were found to have varying degrees of SDB in the form of Upper Airway Resistance (UAR) or OSA.
OSA can adversely affect the treatment outcome for cardiovascular patients, as it induces profound changes in right ventricular function with repetitive oxidative stress to the myocardium and cardiovascular system, increasing the risk of refractory and pulmonary hypertension, acute coronary syndrome, heart failure, stroke, malignant arrhythmia and sudden cardiac death.
OSA also causes insulin resistance, which, if untreated, may cause patients to develop diabetes. Some diabetes specialists now advocate routine sleep testing for diabetics, as many die of cardiovascular complications.
ACTION ON SDB
OSA is the most common form of SDB and many factors – some outside the patient's control – are involved, including genetics, age, obesity and drug intake.
"If parents snore, the chances are their children will develop OSA as they get older," says Antonio Chan, chairman of Chanwell Medical Group, Inc at the Chanwell Clinic. "Ageing is another factor. After age 40, the upper pharyngeal muscles lose their tone and readily collapse, particularly during REM sleep, when there is complete muscle atonia. Increasing weight as one approaches middle age tends to narrow the upper airway muscles and limit airflow to the lungs."
"Alcohol and hypnotics, such as sleeping pills, tend to relax the upper airway muscles, contributing to upper-airway obstruction during sleep. Drinking wine or spirits at night increases snoring and upper-airway resistance," he adds.
With OSA so common, it is surprising that such conditions often remain undiagnosed. Often this is due to a lack of education, as fundamental sleep medicine is not widely taught in medical schools.
It is particularly remarkable that few cardiologists are trained in SDB, given that 80%–90% of cardiovascular diseases result in conditions such as OSA.
Chan says: "Very few cardiologists are aware of this, hence the root causes of cardiovascular disease are not treated, allowing progressive deterioration of patients' health. Medical school curricula must be overhauled."
"Cardiologists must have continuing education in sleep medicine and incorporate this knowledge into their practice. The net result could be better care and quality of life, with an overall reduction in healthcare costs," he adds.
At the Chanwell Clinic, physicians routinely take a sleep history for every visiting patient, examining factors such as the time they go to bed to sleep, how long it takes to fall asleep, whether they or their spouses snore, frequency of urination at night (nocturia) and levels of daytime alertness, indicated by the Epworth Score.
Taking more than 30 minutes to fall sleep indicates a degree of insomnia. Frequent nocturia could also indicate OSA, as the condition induces hypoxemia, increasing blood levels of Atrial Natriuretic Peptide (ANP) and prompting the kidneys to produce more urine. Effective treatment of OSA can normalise blood oxygen and ANP levels, thus lessening the need to urinate.
Chan says: "Sleep history questions add 5–10 minutes to each patient encounter. However, the dividend is very high. A suspicion of OSA could prompt the physician to refer the patient to a sleep specialist for a sleep polysomnogram."
TESTING AND TREATMENT
Most large cities, in the USA at least, have sleep specialists, yet the waiting time for tests can be up to three months, which Chan feels is too long.
"Cardiac patients could deteriorate quickly," he says. "The Mayo Clinic and Yale University investigators have recently shown that OSA increases the risk of stroke and early morning sudden cardiac death by 30%."
Treatments for OSA have developed significantly over the years, starting in 1972 with the radical but effective measure of tracheostomy. In 1981, uvulopalatopharyngoplasty (UVPP) was introduced, although it has a patchy record. UVPP is a major and painful procedure, with a high failure rate.
At the same time, the use of Continuous Positive Airway Pressure (CPAP) devices emerged. It is now a $10bn industry, spawning technological improvements such as breath-by-breath upper airway resistance and usage compliance tracking.
Devices such as C-Flex and Auto Bi-Flex from Respironicsas as well as Resmed's S8 Autoset Spirit have improved the comfort of nasal devices, thus promoting patient compliance. Chan's own research has shown that prompt treatment with CPAP devices reduces pulmonary hypertension and the heart failure rate among patients with OSA and improves their quality of life within 30–60 days, alleviating cardiac enlargement and serious arrhythmia.
Chan can vouch for the effectiveness of CPAP as a long-term, permanent solution to OSA, having used it himself for the last 11 years. Following three car accidents in one year, he was diagnosed with OSA, which often causes daytime drowsiness.
"CPAP is almost always effective in treating OSA, provided the patient is motivated to get well," he says. "Physicians should regularly follow patients and work hand in hand with them to ensure CPAP use compliance. We hold regular CPAP clinics to address any issues the patient may have. We want to make sure that patients with OSA regularly use a CPAP device at night."
CONSTANT PURSUIT OF PROGRESS
Although sleep medicine is not sufficiently considered in the treatment of cardiac patients, research into SDB progresses nonetheless.
Recent developments include assessment of a rate-adaptive pacemaker with an intra-cardiac impedance sensor for monitoring the cardiovascular impact of OSA in a patient with chronic atrial flutter fibrillation, sick sinus syndrome, pulmonary hypertension, diastolic heart failure and severe OSA.
Results suggested that an implanted device, using intracardiac impedance measurements, may help to quantify and monitor the cardiovascular disturbance associated with OSA, and could be particularly powerful if continuous, wireless remote monitoring of cardiovascular disturbance was added in, to facilitate the long-term multidisciplinary management of cardiac disease in outpatients.
Advances in therapy are also being made. Leading pacemaker companies, such as Medtronic, Guidant, St Jude and Biotronik, are examining artificial cardiac pacing as a way of ameliorating the severity of OSA, although much work remains to be done.
For Chan, the most important step will be for cardiologists to learn sleep medicine and retool their practices, possibly along the lines of the Chanwell Clinic model, where the cardiac lab and sleep lab are combined to ensure timely diagnosis and care.
"The net result would be cost-effective care that prevents the deterioration of cardiac diseases," Chan says. "I do believe that most heart attacks, heart failure, strokes and sudden cardiac deaths are preventable through timely diagnosis and treatment for OSA. The number of patients worldwide that would require expensive cardiac pacemaker implants, cardiac surgeries, cardiac transplants and even kidney transplants could fall dramatically. You do the maths – billions of dollars in healthcare costs could be saved."
Whatever the evolutionary path of OSA therapies, the first and most crucial step is to educate clinicians and improve diagnostic rates.