Automatic recognition of abnormal respiratory events during sleep by a pacemaker transthoracic impedance sensor

A number of pacemakers use transthoracic impedance to derive minute ventilation as a sensor for rate adaptation. Transthoracic impedance is also able to track fluctuations in tidal volume occurring in sleep apnea/hypopnea syndromes (SAS). We evaluated the feasibility of a transthoracic impedance-derived pacemaker algorithm for monitoring sleep respiratory disturbances.

Forty-two patients who presented with a conventional indication for DDD pacing or cardiac resynchronization underwent conventional polysomnography 1 month after implantation of a Talent trade mark 3 pacemaker (ELA Medical). The respiratory disturbance index (RDI) stored in the pacemaker memory was compared to the apnea/hypopnea index (AHI) derived from polysomnography. The ability of the pacemaker to identify severe SAS patients (AHI > or = 30) was assessed. A minimal systematic error was observed from a Bland and Altman plot (bias = 0.9 events/hour). The ability of the pacemaker RDI to identify severe SAS patients was determined by analysis of the receiver operator characteristic. A cutoff RDI value of 30.6/hour of recording was found to yield 75% sensitivity, 94% specificity, 75% positive predictive value, and 94% negative predictive value.

The RDI monitoring function appears to be of value in screening pacemaker patients for SAS. Its performance is comparable to existing simple screening techniques. The ability to permanently monitor respiration, in combination with other diagnostic capabilities (such as Holter functions), presents a unique opportunity to monitor the association between arrhythmias and disturbances of breathing during sleep.