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

Abstract

Background: Alternation of heart rate between 2 values using a pacemaker generates oscillations in end-tidal CO(2) (et-CO(2)). 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-CO(2) 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-CO(2) (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-CO(2) elicited was only 45% higher (0.45+/-0.18 versus 0.31+/-0.13 kPa, P=0.01).

Conclusions: 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.

Figures

Figure 1

Protocol for deciding how to alter cardiac output. In each algorithm (HR alone, AV delay alone and both), both square wave and sine wave changes were made in each subject. Changes in cardiac output were deemed “sufficient” if a clear change in end-tidal CO2 and ventilation could be seen following the alternation in cardiac output.

Figure 2

Upper panel: an example of a square wave alternation of heart rate Lower panel: an example of a sine wave alternation with ‘ideal’ sine wave (red) and programmable heart rates (blue) Alternations of AV delay and AV delay and heart rate were made in a similar way

Figure 3

An example of the variables recorded in one subject after four cycles of square wave heart rate manipulation (left panel) and the resultant signal-averaged cycle (right panel). Each individual cycle on the left is represented by a different colour (blue, red, black and green) and the resultant signal-averaged cycle on the right is depicted in red. Square wave changes in cardiac output can be seen to elicit, rapid and sizeable blood pressure oscillations (MAP) and sinusoidal fluctuations in end-tidal CO2 and O2

Figure 4

An example of the variables recorded in one subject after four cycles of sine wave heart rate manipulations (left panel) and the resultant signal-averaged cycle (right panel). Again, each individual cycle on the left is represented by a different colour (blue, red, black and green) and the resultant signal-averaged cycle on the right is depicted in red. The heart rate manipulation resembles a sine wave and the resultant cardiac output change elicits less rapid blood pressure (MAP) changes but nevertheless achieves comparable oscillations in ventilatory gases.

Figure 5

A single alternation of heart rate (preceded by 30 seconds of free breathing without any pacemaker manipulation) demonstrates a rise in heart rate (top panel), is first followed by a rise in end-tidal CO2 (middle panel) and then a rise in ventilation (bottom panel).

Figure 6

Recording from one subject, in whom alternations in cardiac output were establishes, demonstrating sinusoidal manipulations of cardiac output (upper panel) were followed by end-tidal carbon dioxide oscillations (middle panel) and then fluctuations in ventilation (bottom panel).

Figure 7

Comparison of peak-to-trough blood pressure, end-tidal CO2 and ventilation elicited via (i) sine wave alternations and (ii) square wave alternations in all patients

Figure 8

An example of five 60-second averaged ventilatory cycles from one patient of square wave changes of heart rate (upper left) and resultant change in blood pressure with marked upstroke and down-stroke (middle left) and change in end-tidal CO2. Right-hand panel demonstrates sinusoidal heart rate change (upper right) in the same patient and resultant more gradual change in blood pressure (middle right) and comparable oscillation of CO2.