Higher VPC Frequency Found in Severe Obstructive Sleep Apnea

The National Heart, Lung, and Blood Institute estimates that more than 12 million Americans have sleep apnea; it can occur in anyone, but is most prevalent in overweight males over the age of 40 who snore loudly. In its report, Wake up America: A National Sleep Alert, the National Commission on Sleep Disorders Research estimated that as many as 18 million Americans might have obstructive sleep apnea with an apnea-hypopnea index (AHI) greater than 5.0 events per hour of sleep.

People who have had myocardial infarctions, other heart disease, or hypertension often have frequent VPCs. In these patients, VPCs are associated with a mortality rate about twice that of patients with no heart disease.

-Mari Watanabe, MD, PhD

Regardless of the numbers, many people with obstructive sleep apnea syndrome (OSAS) often go undiagnosed and untreated, even though treatment using either continuous or bilevel positive airway pressure (CPAP or BiPAP) is fairly simple and effective.

Since sleep medicine is a relatively new field that is rapidly evolving, we, as otolaryngologists, are often the first to recognize the signs and symptoms of OSAS and to begin the evaluation of the patient, said Pell Ann Wardrop, MD, Medical Director of the Kentucky Sleep Center in Lexington, who is board-certified in both otolaryngology and sleep medicine (see sidebar, p. 14).

We have an obligation to stay informed about the diverse manifestations of OSAS and the growing evidence supporting its association with various cardiac abnormalities, such as arrhythmias, heart failure and nocturnal cardiac death.

VPCs and OSAS

A recent study, presented at the American Heart Association’s Scientific Session in Chicago in November 2006, analyzed data obtained from 134 patients with coronary heart disease, but without diagnosis of any sleep disorder.

During a two-night polysomnogram (PSG) performed in a sleep medicine lab, researchers studied the frequency of a benign heart arrhythmia, ventricular premature contraction (VPC), during different sleep stages and found that 41% of these patients had severe sleep apnea, but were unaware of it.

The VPCs were especially frequent during rapid eye movement (REM) sleep and their frequency increased with the apnea severity. Patients with an AHI > 15.0 were classified as having severe apnea, whereas those with an AHI ≤ 15.0 were considered to have mild apnea.

The participants’ total sleep time diminished as AHI increased (r² = 0.109, p < 0.001); they spent approximately 60% of their time asleep in stage S2 and 25% in REM stage, regardless of apnea severity. Patients with severe apnea spent more time in S1 compared to patients with mild apnea and, correspondingly, less time in S2, S3/4, and REM, the deeper stages of sleep.

-Pell Ann Wardrop, MD

The absolute VPC count paralleled the amount of time spent in a particular sleep stage. A greater AHI was associated with a greater VPC count (r² = 0.013, p < 0.001) and frequency (r² = 0.049, p < 0.0001). During the three sleep stages of wake, S2, and REM, patients with mild apnea showed no difference in VPC frequency (n = 74, p = 0.19), whereas those with severe apnea had different VPC frequencies over the three sleep stages (n = 50, p = 0.037). In the severe apnea patients, the VPC frequency was significantly greater in REM than in wake (p = 0.011; statistical significance criterion was p < 0.017).

The researchers also found that there is a prolonged period of low oxygen in the dream or REM stage of sleep as compared with other stages. The oxygen desaturation duration per apnea event was longer in REM than in non-REM sleep. Heart rate turbulence, a recently discovered marker for sudden cardiac death, was found to correlate better with the oxygen saturation duration than with AHI values.

The longer oxygen desaturation duration during REM sleep may be the cause of higher VPC frequency during sleep in patients with severe sleep apnea, as well as the propensity for sudden cardiac death during sleep in these patients. This contrasts strikingly with sudden cardiac death in people without OSAS, who more often die in the few hours after waking up.

On the Front Line

As ENTs, we have an advantage over other specialties involved in sleep medicine, as often our findings from the head and neck exam will prompt us to ask questions about OSAS, even if the patient has not volunteered complaints, said Dr. Wardrop.

I begin an evaluation with a history and physical exam that focuses on the risk factors, symptoms, and physical findings frequently seen in patients with sleep disorders, said Dr. Wardrop. I pay particular attention to BMI [body mass index], increased neck size, retrognathia, nasal obstruction, and the collapsibility of the airway.

Since normal healthy adults can have VPCs, there is no ‘typical’ patient who presents with them, said study author Mari Watanabe, MD, PhD, Research Assistant Professor in the Division of Cardiology at Saint Louis University School of Medicine. However, people who have had myocardial infarctions, other heart disease, or hypertension often have frequent VPCs. In these patients, VPCs are associated with a mortality rate about twice that of patients with no heart disease.

A 24-hour Holter ECG would display all the VPCs a patient has in a day, added Dr. Watanabe. If a person has frequent VPCs, they could well show up during a routine office ECG, but if a few minutes of recording do not show anything, a 24-hour ECG would help. According to our study, VPCs seem to be caused by apnea, so VPCs that are more frequent at night may be a sign that a person has OSAS.

Many patients have more than one sleep disorder and I find that a patient questionnaire can be helpful in screening for these, added Dr. Wardrop (see sample form, pp. 13-14). In addition to questions regarding breathing/snoring during sleep, questions about sleep hygiene, alcohol/sedative use, and sleepy driving should be included. A medical history that includes obesity, hypertension, stroke, congestive heart failure, or cardiac arrhythmia suggests the presence of OSAS and the patient should be sent for a PSG.

The natural conclusion of our study would be that once a patient is properly diagnosed, his or her sleep apnea would be treated with a CPAP or BiPAP machine that could help to prevent heart arrhythmia during sleep, Dr. Watanabe said. However, this hypothesis would need to be tested.

Some ENTs are comfortable treating all aspects of sleep disorders and are very qualified to do so, while others may choose to work closely with other sleep medicine colleagues and specialists, said Dr. Wardrop. The decision to refer a patient to a cardiologist would be made based upon the patient’s symptoms while working in conjunction with the patient’s primary care physician. If a serious cardiac abnormality is detected by the otolaryngologist, then referral would naturally occur.

As long as our patients receive excellent care for their sleep disorders, either model works, said Dr. Wardrop.

Certification in Sleep Medicine

The American Board of Otolaryngology (ABOto), in conjunction with the American Boards of Internal Medicine, Pediatrics, and Psychiatry/Neurology, now subcertifies eligible otolaryngologists in Sleep Medicine. Applications are currently being taken for the first examination, which will be given in November 2007. Otolaryngologists interested in becoming subcertified in Sleep Medicine should go to the ABOto Web site (www.aboto.org/sleep_medicine.aspx ) to obtain more information.