Investigating the force-frequency response through high-precision cardiac pacing assessment and its effect on cardiac output in heart failure
D Abraham, J S Singh Mohal, A Arnold, Z WhinnettAbstract
Background
A positive force-frequency response (FFR) describes increased left ventricular contractility with increasing heart rate (HR) which is impaired in patients with heart failure. Determining an individual’s FFR helps identify an optimal HR for rate-responsive pacing. The current echocardiographic method for FFR-guided pacing is time-consuming and impractical. This study investigates Finometry, a technique measuring beat-by-beat systolic blood pressure (SBP), as an alternative for determining optimal HR. Its accuracy and precision will be compared against echocardiographic left ventricular outflow tract velocity time integral (LVOT VTI).
Methods
A baseline HR using dual chamber pacing was set 10bpm above patients’ resting HR. 10 transitions were made from baseline to testing HR, recording continuous SBP and echocardiographic Doppler waves. The change (Δ) in SBP/Cardiac output (CO) was calculated for each HR and the optimal HR producing the largest ΔSBP/CO from baseline was determined using both methods.
Results
Two HFrEF and five HFpEF patients qualified for final analysis. Finometry displayed a parabolic relationship between increasing HR and ΔSBP. Echocardiographic LVOT VTI produced matching or opposite parabolas, with a linear relationship between increasing HR and ΔCO in some patients. In patients with matched parabolas, the average difference between optimal HRs was 5.5bpm. The average SE:Mean ratio around the optimum HR determined using Finometry was 0.2527.
Discussion
Finometry demonstrated good accuracy and moderate precision for identifying optimal heart rates in patients with matched haemodynamic and echocardiographic data. Precision may be improved by increasing the number of pacing transitions, while larger studies are needed to strengthen conclusions regarding accuracy. Discrepancies between methods suggest that echocardiographic assessment using ΔVTI rather than ΔCO may reduce LVOT-related measurement error. Conclusions could not be drawn specifically on HFpEF versus HFrEF due to low power.
Conclusion
Finometry shows potential as a technique for determining optimum HR for pacing in HF patients however, further testing employing larger sample sizes is necessary to draw stronger conclusions.Haemodynamic Pacing ProtocolFor image description, please refer to the figure legend and surrounding text.Effect of increasing HR on ΔSBP/ΔCOFor image description, please refer to the figure legend and surrounding text.