CARDIAC chronotropic effects of sleep-disordered breathing in patients with heart failure

It is still not known whether the oscillation in heart rate (HR) induced by sleep-disordered breathing (SDB) in patients with heart failure entails significant chronotropic effects. We hypothesised that since cyclical changes in ventilation and arterial blood gases during SDB affect HR through multiple and complexly interacting mechanisms characterised by large inter-subject variability, chronotropic effects may change from patient to patient. A total of 42 patients with moderate-to-severe chronic heart failure with systolic dysfunction underwent an in-hospital sleep study. Chronotropic effects of SDB were quantified by comparing the distribution of instantaneous HR during SDB with that during periods without SDB (noSDB) within the same night in each patient. Based on distribution changes from noSDB to SDB, 12, nine, 11, and 10 patients showed a significant tachycardic, bradycardic, tachycardic and bradycardic, and neither significant tachycardic nor significant bradycardic effect, respectively. Tachycardic and bradycardic effects were primarily due to an increase in the rate rather than in the magnitude of cyclical HR elevations and reductions, and were more prevalent and severe in patients with dominant obstructive and central events, respectively. The apnea-hypopnea index did not differ between groups. Conversely, the time spent with an oxygen saturation of <90% was greater in the tachycardic and tachycardic-bradycardic groups compared to the bradycardic group. These findings indicate that HR distribution changes induced by SDB can vary from patient to patient revealing four distinct and well-characterised chronotropic effects. These effects are related to the degree of hypoxic burden brought about by SDB and are affected by the type of sleep apnea (central/obstructive).