Published Online
on March 23, 2009

A more recent version of this article appeared on May 1, 2009

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Original Article

Novel use of cardiac pacemakers in heart failure to dynamically manipulate the respiratory system through algorithmic changes in cardiac output

Resham Baruah^1,4; Charlotte Harriet Manisty¹; Alberto Giannoni²; Keith Willson¹; Yoseph Mebrate³; John Arun Baksi¹; Beth Unsworth¹; Nearchos Hadjiloizou¹; Richard Sutton¹; Jamil Mayet¹ and Darrel Parthipan Francis¹

¹ International Centre for Circulatory Health, St Mary's Hospital and Imperial College, London;
² Institute of Clinical Physiology, Monasterio Foundation, Pisa;
³ St Mary's Hospital and Imperial College; Royal Brompton Hospital, London

⁴ E-mail: rb98{at}doctors.org.uk

Background—Alternation of heart rate (HR) between two values using a pacemaker generates oscillations in end-tidal CO₂ (et-CO₂). This study examined (a) whether modulating AV delay can also do this, and (b) whether more gradual variation of cardiac output can achieve comparable changes in et-CO₂ with less-sudden changes in blood pressure (BP).

Methods and Results—We applied pacemaker fluctuations by adjusting HR (by 30 bpm) or atrioventricular (AV) delay (between optimal and non-optimal values) or both, with period of 60 seconds in 19 heart failure patients (age 73±11, EF 29%±12%). The changes in cardiac output, by either HR or AV delay or both, were made either as a step ("square wave") or more gradually ("sine wave"). We obtained changes in cardiac output sufficient to engender comparable oscillations in et-CO₂ (p=NS) in all 19 patients either by manipulation of HR (14), or by AV delay (2) or both (3). The square wave produced 191 % larger and 250 % more sudden changes in BP than the sine wave alternations (22.4±11.7 versus 13.6±4.5 mmHg, p<0.01 and 19.8±10.0 versus 7.9±3.2 mmHg over 5s, p<0.01), but peak-to-trough et-CO₂ elicited was only 45 % higher (0.45±0.18 versus 0.31±0.13 kPa, p=0.01).

Conclusion—This study shows that cardiac output is the key to dynamically manipulating the respiratory system with pacing sequences. When manipulating respiration by this route, a sine wave pattern may be preferable to a square wave, because it minimizes sudden BP fluctuations.

Key Words: heart failure • hemodynamics • pacemakers • reflex • respiration