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Original Articles

Novel Use of Cardiac Pacemakers in Heart Failure to Dynamically Manipulate the Respiratory System Through Algorithmic Changes in Cardiac Output

Resham Baruah, MBBS, BSc, MRCP; Charlotte H. Manisty, MBBS, MRCP; Alberto Giannoni, MD; Keith Willson, MSc, FIPEM; Yoseph Mebrate, MSc; A. John Baksi, MBBS, BSc, MRCP; Beth Unsworth, BSc; Nearchos Hadjiloizou, MBBS, BSc, MRCP; Richard Sutton, DSc, FRCP; Jamil Mayet, MD, MBA, FRCP and Darrel P. Francis, MA, MD, FRCP

From the International Centre for Circulatory Health (R.B., C.H.M., K.W., Y.M., A.J.B., B.U., N.H., R.S., J.M.), St. Mary’s Hospital and Imperial College, London, United Kingdom; Institute of Clinical Physiology (A.G.), Monasterio Foundation, Pisa, Italy; and Royal Brompton Hospital (K.W.), London, United Kingdom.

Correspondence to Resham Baruah, MBBS, BSc, MRCP, 2nd Floor, International Centre for Circulatory Health, 59-61 North Wharf Road, London W2 1LA, UK. E-mail rb98{at}doctors.org.uk

Received July 12, 2008; accepted January 30, 2009.

Background— Alternation of heart rate between 2 values using a pacemaker generates oscillations in end-tidal CO₂ (et-CO₂). This study examined (a) whether modulating atrioventricular 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.

Methods and Results— We applied pacemaker fluctuations by adjusting heart rate (by 30 bpm) or atrioventricular delay (between optimal and nonoptimal values) or both, with period of 60 s in 19 heart failure patients (age 73±11, EF 29±12%). The changes in cardiac output, by either heart rate or atrioventricular 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 heart rate (14), or by atrioventricular delay (2) or both (3). The square wave produced 191% larger and 250% more sudden changes in blood pressure than the sine wave alternations (22.4±11.7 versus 13.6±4.5 mm Hg, P<0.01 and 19.8±10.0 versus 7.9±3.2 mm Hg over 5 s, P<0.01), but peak-to-trough et-CO₂ elicited was only 45% higher (0.45±0.18 versus0.31±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 blood pressure fluctuations.

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

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