Sleep Fragments

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Vital Signs: What is the Arrhythmia?

Contributed by Susheel P. Patil, MD, PhD, Assistant Professor of Medicine, Johns Hopkins School of Medicine, Baltimore, MD


41 year-old African American male with hypertension and schizophrenia presenting with loud snoring and nocturnal choking.

  1. His Epworth Sleepiness Scale score is 13/24.
  2. His body-mass index is 38.1 kg/m2 with an airway Mallampati score 3.
  3. His medications include trazadone, nifedipine, and monthly haloperidol injections.
  4. His baseline EKG shows no evidence of QT prolongation.
  5. Sleep study demonstrated severe obstructive sleep apnea with an RDI of 98.4 events/h.

On physical examination his BMI was 36 kg/m2 and his neck circumference was 42 cm.

What is the EKG abnormality in the fragment below?


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Answer : 2nd degree AV block, Mobitz type I (Wenkebach) during REM sleep


  • This arrhythmia was observed during an obstructive apnea with an oxyhemoglobin desaturation to 76% (see 2 minute view).
  • Bradyarrhythmias are observed in 5-10% of patients with obstructive sleep apnea. The majority of bradyarrhythmias occur during REM sleep.
  • Mechanisms thought to be responsible for bradyarrhythmias during REM sleep and obstructive respiratory events include:
    • Increased parasympathetic tone and decreased sympathetic tone during tonic REM compared to wake and NREM sleep. Phasic REM in contrast is associated with surges in sympathetic activity.
    • Hypoxemia stimulates carotid chemoreceptors leading to increased vagal stimulation and bradycardia.
    • Obstructive events tend to be of longer duration and oxyhemoglobin desaturations are often more severe during REM sleep than NREM sleep.
  • During the patient’s CPAP titration night, no further bradyarrhythmias were observed at the therapeutic CPAP pressure level
    • Elimination of obstructive respiratory events and intermittent hypoxemia are thought to mitigate the increase in vagal tone that predisposes to the development of bradyarrhythmias during sleep.
  • Since patients with severe OSA are predisposed to arrhythmias  during sleep, careful review of the EKG tracing should be performed during sleep study interpretations.


  • Koheler U, Fus E, Grimm W, Pankow W, Schafer H, Stammnitz A, Peter JH. Heart block in patients with obstructive sleep apnea: pathogenetic factors and effects of treatment. Eur Resp. J 1998; 11: 434-439.
  • Becker HF, Bradenburg U, Peter JH, vonWichert P. Reversal of sinus arrest and atrioventricular conduction block in patients with sleep apnea during nasal continuous positive airway pressure. Am J Resp Crit Care Med 1995; 151: 215-218.
  • Guilleminault C, Connolly SJ, Winkle RA. Cardiac arrhythmia and conduction disturbances during sleep in 400 patients with sleep apnea syndrome. Am J Cardiol 1983; 52: 490-494.
  • Verrier RL, Harper RM, Hobson JA. Cardiovascular physiology: Central and autonomic regulation. In: Kryger MH, Roth T, Dement W, editors. Principles and Practice of Sleep Medicine, 4th ed. Philadelphia, PA: W.B. Saunders; 2005. p. 192-202.


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