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

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. © 2009 American Heart Association, Inc.